North Peoria Area Drainage Master Plan - Flood Control District of ...

TABLE OF CONTENTSPreface ....................................................................................................................................................... iiiAcknowledgements ..................................................................................................................................vList of Figures ...........................................................................................................................................viList of Tables .......................................................................................................................................... viiIntroduction ............................................................................................................................................... 1Purpose and Goals .................................................................................................................................... 2Background ................................................................................................................................................ 3Project Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3Land Ownership . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4Land Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4Regional and Local Planning Efforts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4Peoria General Plan . . . . . . . . . . . . . . . . . . . . . . . 5Lake Pleasant/North Peoria Area Plan . . . . . . . . . . . . . . . . . 5Peoria Desert Lands Conservation Master Plan . . . . . . . . . . . . . . 5White Tanks/Grand Avenue Area Plan . . . . . . . . . . . . . . . . . 5Desert Spaces . . . . . . . . . . . . . . . . . . . . . . . . . . 5Desert Spaces-Environmentally Sensitive Development Areas . . . . . . . . . 6Environmental Hazards Identification ................................................................................................. 6Hydrology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6Hydraulics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7Geomorphic Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8Sediment Engineering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8Flood and Erosion Hazard Zones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9Environmental Characteristics ............................................................................................................... 9Biological Resource Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9Cultural Resources Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10Landscape Character and Visual Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11Multiple-Use Opportunities ................................................................................................................. 12Public Involvement ................................................................................................................................ 13Flood Control Management Alternatives Development and Evaluation .................................... 13Flood Control Management Alternatives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13Alternative Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15Public Safety Criterion . . . . . . . . . . . . . . . . . . . . . . 15Social Criterion . . . . . . . . . . . . . . . . . . . . . . . . . 15Environmental Criterion . . . . . . . . . . . . . . . . . . . . . . 16Economic Criterion . . . . . . . . . . . . . . . . . . . . . . . . 17i

NORTH PEORIAAREA DRAINAGE MASTER PLANSummary of Evaluation Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17Preferred Flood Control Management Alternatives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19Compatibility with Other Planning Documents .............................................................................. 19Rules of Development ........................................................................................................................... 21Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21North Peoria Area Drainage Master Plan Elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21Environmental Hazards Identification . . . . . . . . . . . . . . . . . 22Development/Planning Considerations . . . . . . . . . . . . . . . . 23Environment . . . . . . . . . . . . . . . . . . . . . . . . . . 24Biological Resources . . . . . . . . . . . 25Visual Character . . . . . . . . . . . 25Cultural Resources . . . . . . . . . . . 26Multiple-Use Opportunities . . . . . . . . . . . . . . . . . . . . . 26Design Guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27Flood Hazards . . . . . . . . . . . . . . . . . . . . . . . . . 27Erosion Hazards . . . . . . . . . . . . . . . . . . . . . . . . . 27Typical Scope of Work for Detailed Erosion Hazard Analysis . . . . 28Technical Analysis Work Plan . . . . . . . . . 28Final Product . . . . . . . . . . . . 31Earthen Dams (Stock Tanks) . . . . . . . . . . . . . . . . . . . . 32Retention/Detention Facilities . . . . . . . . . . . . . . . . . . . . 32Standard Retention Practice . . . . . . . . . 32In-stream, In-Line Detention Basins . . . . . . . . 32In-stream, Off-line Retention Basin . . . . . . . . 33Floodplain Encroachment . . . . . . . . . . . . . . . . . . . . . 34Low Impact Structural Alternative . . . . . . . . . . . . . . . . . . 35Channelization . . . . . . . . . . . . . . . . . . . . . . . . . 35Roadway Crossing Drainage Structures . . . . . . . . . . . . . . . . 36At-Grade Crossings . . . . . . . . . . . 36Culverts . . . . . . . . . . . . . 37Bridges . . . . . . . . . . . . . 38Utility Crossings . . . . . . . . . . . . . . . . . . . . . . . . 39Aesthetic Design Guidelines . . . . . . . . . . . . . . . . . . . . 39Structural Erosion Protection Measures . . . . . . . 39Channels . . . . . . . . . . . . . 39Drainage Structures . . . . . . . . . . . 40Maintenance Plan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40Maintenance Plan ................................................................................................................................... 40Considerations for Existing Structures in Flood Hazard Areas ..................................................... 40General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40Glossary .................................................................................................................................................... 42References ................................................................................................................................................ 44ii

PREFACEAt the request of the City of Peoria, the FloodControl District of Maricopa County (District),under the authority of Arizona Revised StatutesTitle 48, Chapter 21, initiated the NorthPeoria Area Drainage Master Plan (North PeoriaADMP). The North Peoria ADMP is aregional approach to watershed management.The District prefers a regional approachto watershed and floodplain managementbecause it enables the District to develop floodcontrol strategies that are both sustainable andsensitive to the environment. This approachworks to minimize the public cost of protectingcitizens from flooding that may resultfrom private and public development’s cumulativeeffect on drainage characteristics. TheNorth Peoria ADMP provides a uniform andcoordinated approach to watershed management.A multi-faceted approach will ensurethat present and future residents are protectedfrom the damaging effects of flooding.Within non-urbanized/rural watersheds naturalenvironmental hazards associated withrunoff from storm events exist. Without sufficientplanning and management, natural hazardsare compounded as development occurswithin a watershed. In order to protect privateand public property, natural occurringenvironmental hazards and hazards createdby urbanization are identified. Environmentalhazards associated with storm runoff are categorizedinto flood hazards and erosion hazards.As part of the North Peoria ADMP,approximately 36 linear miles of new floodplaindelineation and 54 miles of erosion hazardzone delineation was conducted.The North Peoria ADMP provides a regionalapproach to flood control management.Development of flood control managementalternatives and policies that form the foundationof the plan takes into account engineering,environmental, landscape, social, andeconomic considerations. Watershed managementalternatives are developed to mitigate/minimize the effect of urbanization on stormwaterrunoff and conveyance while recognizingthe values of the community and theopportunity to protect the unique characteristicsof the region. The primary purpose forflood control management alternative developmentand evaluation is to develop a rangeof plans that provide public safety from floodand erosion hazards, determine the cost andbenefits of each alternative, qualitativelydetermine impacts of the alternative on identifiedenvironmental resources, and select a preferredmanagement plan.The North Peoria ADMP study area encompassesapproximately 73 square miles withinunincorporated Maricopa County and theCity of Peoria. Numerous watersheds drainthe area to the Agua Fria River. Major watercoursesdraining to the Agua Fria River areMorgan City Wash, nine unnamed washes,Caterpillar Tank Wash, and Twin Buttes Wash.Approximately 66 linear miles of watercoursesare considered in the development ofthe North Peoria ADMP.iiiFlood control management alternatives developedand evaluated for the North PeoriaADMP are categorized into two groups,watercourse management alternatives andstormwater storage alternatives. Watercoursemanagement alternatives evaluated include anon-structural, a partial structural, a lowimpact structural, a full structural, and a noaction. Stormwater storage alternatives evaluatedinclude the standard practice of retainingthe volume of flow from the 100-year, 2-hourevent, in-stream, in-line detention alternativeand an in-stream, off-line retention alternativeDescriptions of the five z management alternativesevaluated are:The full structural alternative is based on currentfederal, state and local floodplain managementregulations that allow encroachmentinto the floodway fringe. The full structuralalternative typically requires at a minimum,structural stabilization of wash side slopes forthe entire reach.

ACKNOWLEDGEMENTSThe success of developing this document isattributed to the many individuals who contributedtheir professional expertise andshared belief that with appropriate planning,public safety and quality of life can be maintainedfor the citizens of Maricopa County andthe City of Peoria. Our sincere appreciation isextended to the following governmental bodies,agencies, individuals, and consultants fortheir help and perspective while developingthe North Peoria Area Drainage Master Plan:0$5,&23$&2817

LIST OF TABLESTable 1: Regional and Local Planning Documents. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4Table 2: Watercourses Evaluated . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17Table 3: Summary of Evaluation Results Watercourse Management Alternatives. . . . . . . . . . . . 18Table 4: Summary of Evaluation Results Stormwater Storage Based Alternatives . . . . . . . . . . . 19Table 5: Summary of Regional and Local Planning Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20vii

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INTRODUCTIONThe natural physical character of the NorthPeoria Area Drainage Master Plan study areais unique to north central Maricopa County,the City of Peoria, and the Phoenix metropolitanarea. The area is characterized by diverselandforms, sinuous washes that dissect theterrain, and varied plant communities. Thearea is also rich in wildlife, and historical andcultural resources. The natural topographyand vegetation types associated with topographyoffer a scenic quality that is unparalleledanywhere else in the valley. The natural physicalcharacter also includes flood prone areasand associated erosion hazards which arepublic safety concerns.7ZLQ%XWWHVDue to impending development pressures innorth Peoria, the Flood Control District ofMaricopa County (District) in cooperationwith the City of Peoria and under the authorityof Arizona Revised Statutes (ARS) Title 48,Chapter 21, initiated the North Peoria AreaDrainage Master Plan (North Peoria ADMP).The North Peoria ADMP is a regionalapproach to watershed management. TheDistrict prefers a regional approach to watershedand floodplain management because itenables the District to develop flood controlstrategies that are both sustainable and sensitiveto the environment. This approach worksto minimize the public cost of protecting citizensfrom flooding that may result from privateand public development’s cumulativeeffect on drainage characteristics. The NorthPeoria ADMP provides a uniform and coordinatedapproach to watershed management. Amulti-faceted approach will ensure thatpresent and future residents are protectedfrom the damaging effects of flooding.The District contracted with Stantec ConsultingInc. (Stantec) to develop the North PeoriaADMP. Stantec assembled a qualified teamconsisting of hydrologists, engineers, environmentalengineers, archeologists, landscapearchitects, and planners to assist in the developmentand evaluations of flood control managementalternatives. The team worked withDistrict and City of Peoria personnel in thepreparation of the ADMP.The North PeoriaADMPstudy areaencompassesapproximately73 square mileswithin unincorporatedMaricopaCounty and theCity of Peoria.Numerouswatershedsdrain the areato the AguaFria River.Major watercoursesdrainingto the Agua0RUJDQ&LW\:DVKFria River are Morgan City Wash, nineunnamed washes, Caterpillar Tank Wash andTwin Buttes Wash. Approximately 66 linearmiles of watercourses are considered in thedevelopment of the North Peoria ADMP. Thestudy area does not include the Agua FriaRiver and associated 100-year floodplain. Thelocation of the study area relative to City ofPeoria, City of Phoenix, and Maricopa Countyboundaries is displayed on Figure 1.Development of the North Peoria ADMPincludes, public coordination, survey and1

NORTH PEORIAAREA DRAINAGE MASTER PLANmapping, hydraulics, hydrology, sedimentationand geomorphic evaluations, environmentaland visual resources overviews,identification of flood hazards, identificationof erosion hazards, historical character evaluation,multi-use recreational opportunities, policiesto help guide development andformulation of flood control managementalternatives. Detail descriptions of evaluationand overviews are contained in the North PeoriaArea Drainage Master Plan, Technical DataNotebook, and attachments to the TechnicalData Notebook. The following reports weredeveloped as part of the North Peoria ADMP:• North Peoria Area Drainage Master Plan,Flood Insurance Technical Data NotebookStandards Affecting Stormwater Drainage• Attachment 11 Floodplain/Erosion HazardMaps10City of PeoriaStudy Area8560Figure 1Vicinity Map17MetroPhoenix106087• North Peoria Area Drainage Master Plan,Technical Data Notebook88Maricopa County boundary• Attachment 1Hydrology and Hydrau-• Attachment 2licsFiled Survey ReportPURPOSE AND GOALS• Attachment 3 Sedimentation Engineeringand Geomorphic Evaluation TechnicalMemorandums• Attachment 4 Landscape Character andVisual Assessment Report• Attachment 5 Multi-Use OpportunitiesAssessment Report• Attachment 6 Plant Communities andBiological Resources• Attachment 7 Historic CharacterAssessment Report• Attachment 8 Cultural ResourcesAssessment Report• Attachment 9 Environmental RegulatoryRecords Review• Attachment 10 Investigation of ExistingOrdinances, Policies, Regulations andWithin the next 25 years, the City of Peoriaand Maricopa County north of BeardsleyRoad to Lake Pleasant will be developed withnew homes, shopping, and employmentopportunities to serve a population nearing200,000 people. These residents and businesseswill expect protection from naturalhazards (such as flooding and erosion hazards)that complements the natural environmentand scenic beauty of their community.To meet these expectations a comprehensiveregional approach to watershed and floodcontrol management is developed. The purposeof the North Peoria ADMP is to identifyflooding and drainage patterns and recommendsustainable strategies that will protectthe public from flooding and erosion hazards.The North Peoria ADMP presents aholistic management approach in that watershedmanagement solutions take into accountenvironmental, landscape, social and economicconsiderations. Flood control managementalternatives are developed to mitigate/2

minimize the effect of urbanization on stormwaterrunoff and conveyance while recognizingthe values of the community and theopportunity to protect the unique characteristicsof the region. A holistic approach insuresthat public’s safety and quality of life is maintained.Goals of the North Peoria ADMP are:• Identify flood and erosion hazards alongmajor watercourses.• Develop policies and strategies to protectresidents from flood and erosion hazards.• Preserve the natural flood control functionof the existing washes and channels.• Incorporate public and private interests,issues, and concerns.• Minimize future expenditures of publicfunds for flood control and emergencymanagement.• Consider environmental and landscapecharacteristics of the watershed in thedevelopment of watershed managementalternatives.• Minimize disturbance of existing floodplainand floodway ecosystem and habitats.• Consider multiple-use activities for floodplainareas.BACKGROUNDPROJECT AREAThe North Peoria ADMP study area encompassesapproximately 73 square miles withinunincorporated Maricopa County and theCity of Peoria. The study area is divided intofour planning areas based on physical characteristicsand/or geographic location of eachplanning area. The four planning areas are theMorgan City Area, Big Spring Area, East TerraceArea, and the Twin Buttes Area. TheHieroglyphic Mountains, located within theMorgan City Area, Big Spring Area, and thenorthern portion of the Twin Buttes Area arecharacterized by peak, ridge, wash, and valleylandforms. Terrain slopes within the HieroglyphicMountains range from less than 10percent to greater than 25 percent. Rock outcropand rock fragments typify soil constituentswithin the Hieroglyphic Mountains.Within the Morgan City Area and Big SpringArea, washes are typically incised in rock orwell-cemented alluvial material. The East Terracearea located east of the Agua Fria Riverand the southern portion of the Twin ButtesArea have landforms characterized with terrainslopes of less than 10 percent and areunderlain typically by alluvial material. Sinuousnatural channels that are cut into alluvialmaterial characterize washes in the East TerraceArea and in the southern portion of theTwin Buttes Area. With the exception of thelower reach of Morgan City Wash, washesdraining the study area watersheds areephemeral. Springs deliver water to the lowerreach of Morgan City Wash providing flowyear around. Figure 2 displays major watercoursesthat drain from the study area to theAgua Fria River, specific planning areas delineatedby unique physical characteristics, andphotographs of some of the physical characteristicof the area.One of the unique characteristics of the area isthe contrast in terrain from the planes and flatlands of the valley to the varied landforms ofthe Hieroglyphic Mountains. Figure 3, TerrainSlope Map, is a graphic representation ofterrain slope in the area. Terrain slope is oftenused by communities and agencies to definesignificant areas of preservation or areaswhere special development considerationsmust be met. Maricopa County encouragespreservation of, and applies development considerationsfor significant mountainous areaswith terrain slopes of greater than 15 percentwhere as the City of Peoria applies specialdevelopment considerations for areas withterrain slopes of greater than 10 percent.3

LAND OWNERSHIPNORTH PEORIAAREA DRAINAGE MASTER PLANThere are four primary entities with land ownershipin the area: the United States FederalGovernment, Arizona State Trust Lands, MaricopaCounty, and private interests. The percentof land owned by each entity is 35%Federal, 32% State Trust, less than 1% County,and 31% private. Figure 4 displays the distributionof land ownership in the study area.Currently the study area is predominatelyundeveloped, however to identify futuretrends in stormwater runoff and conveyance,the City of Peoria’s Land Use Plan developedas part of the city’s General Plan is utilized inthe development of the North Peoria ADMP.Figure 5, Future Conditions Constraints;depicts land use designations, floodplains,and areas of impending development in thestudy area.LAND USEPlanning documents developed by communitieshave a land use element that provides aframework for defining future developmentpatterns. The Land Use element helps guidefuture growth, revitalization and preservationefforts in the community. An understandingof future or anticipated land use is key to thedevelopment of an area drainage master plan.Urbanization of an area typically alters existingrainfall runoff relationships that ultimatelycould result in flooding impacts to thecommunity.REGIONAL AND LOCAL PLANNING EFFORTSThere are a number of planning documentsthat have been developed by county and cityagencies to provide direction and guidance inregards to development and future land usewithin the North Peoria ADMP study area.Planning documents reviewed as part of thedata collection are listed in Table 1. A briefsummary of the purpose of the document andrelevance to the North Peoria ADMP is providedin the following sections.Table 1Regional and Local Planning DocumentsAgencyCity of PeoriaDocumentGeneral PlanLake Pleasant/North Peoria Area PlanPeoria Desert Lands Conservation MasterPlanRiver Master PlanTrails Master PlanFlood Control District of Maricopa CountyMaricopa CountyAgua Fria Watercourse Master PlanComprehensive Plan-Maricopa CountyEye To The Future, 2020White Tank/Grand Avenue Area SpecificPlanMaricopa County Association ofGovernmentsDesert SpacesDesert Spaces-Environmentally SensitiveDevelopment Areas4

Peoria General PlanThe Peoria General Plan is the fundamentalplanning document for the City of Peoria toguide growth and development within theCity and its planning areas. The plan wasupdated to include increased planning effortsmandated by Growing Smarter and GrowingSmarter Plus legislative statutes. The GeneralPlan adopted by Peoria’s voters went intoeffect June 15, 2001. Land Use, Recreation andOpen Space, Safety, and EnvironmentalResources elements of the plan provide policylevel guidance for development that aredirectly applicable to the North Peoria ADMP.The General Plan recognizes the unique characterand natural resources of the northernhalf of the city which includes the North PeoriaADMP study area and provides guidanceso that there is a balance between facilitatingdevelopment without endangering the protectionof the natural resources in the area.Lake Pleasant/North Peoria Area PlanThe Lake Pleasant/North Peoria Area Plan,completed by the City of Peoria in Novemberof 1999, provides guidelines to assist in thepreservation and enhancement of the environmental,recreational and aesthetic values ofthe Lake Pleasant Area while allowing forcontrolled development that is sensitive to thegoals of the plan and the natural environment.The Plan recognizes the assets of the uniquephysical characteristics, flood hazard, biologicaland visual resources, as well as existingdevelopment constraints within the area. Theeastern portion of the Morgan City Area lieswithin the Lake Pleasant/North Peoria Planboundaries.Peoria Desert Lands Conservation MasterPlan5The major goal of the Peoria Desert LandsConservation Plan, completed in August of1999 is to “Maintain the vitality of the uniqueSonoran Desert environment by providinghigh quality passive and active open spaceareas, while encouraging development that issustainable and supportive of the environment”.To meet the intent of the goal, recommendedpolicies that prescribe a course ofaction are provided to help guide development.In addition to recommended policies,sensitive land areas identified for potentialpreservation or conservation are presented.Sensitive land areas referred to as drainagecorridors include, Morgan City Wash in theMorgan City Area, Unnamed Washes 1, 2, and3, and their major tributaries in the Big SpringArea, and Twin Buttes Wash in the TwinButtes Area.White Tanks/Grand Avenue Area PlanAdopted in 1997, the Comprehensive Plan-Maricopa County Eye to the Future 2020,requires that County-area plans be updated toensure consistency with the ComprehensivePlan. The White Tanks/Grand Avenue AreaPlan adopted December 6, 2000 is an updateof the White Tank/Agua Fria Policy andDevelopment Guide and the Grand AvenueCorridor Area Land Use Plan. The plan recognizesthe scenic beauty in the northern portionof the North Peoria ADMP study area andencourages preservation while recognizingproperty rights of landowners to develop theirproperty.Desert SpacesIn 1995, the Maricopa Association of Governments(MAG) adopted the Desert Spaces plan.Desert Spaces is a regional open space managementplan designed to guide the membersof MAG in protecting open space while allowingfor future community growth and development.The intent of the plan is to preserve,protect, and enhance significant natural andcultural resources. Natural resources includeupland landforms, rivers and washes, andwildlife habitat. The plan also presents aregional network of trails that when implementedwould allow the public to enjoy thediversity of open space that the plan presents.Mountainous areas designated for openspace preservation includes the HieroglyphicMountains. Approximately half of the NorthPeoria ADMP study area is located in theHieroglyphic Mountains.

NORTH PEORIAAREA DRAINAGE MASTER PLANDesert Spaces-Environmentally SensitiveDevelopment AreasThe Environmentally Sensitive DevelopmentAreas (ESDA) Plan adopted by MAG in Juneof 2000, presents policies and design guidelinesfor areas identified in the Desert SpacesPlan as “Retention Area”. The purpose of thedesign guidelines is to provide guidance forboth the public and private sectors for developmentprojects within Environmentally SensitiveDevelopment Areas. EnvironmentallySensitive Areas presented in the Plan includethe northern portion of the North PeoriaADMP study area north of the Central ArizonaProject Canal.ENVIRONMENTAL HAZARDSIDENTIFICATIONWithin non-urbanized/rural watersheds naturalenvironmental hazards associated withrunoff from storm events exist. Without sufficientplanning and management, natural hazardsare compounded as development occurswithin a watershed. In order to protect privateand public property, naturally occurringenvironmental hazards and hazards createdby urbanization need to be identified. Environmentalhazards associated with storm runoffcan be categorized into flood hazards anderosion hazards. Under the authority of ARS48-3605, the Arizona Department of WaterResources (ADWR) has established criteriaand standards for determining flood and erosionhazard areas. The North Peoria ADMPconsiders hydrology, hydraulics and geomorphicevaluations, sediment engineering andcriteria established by ADWR in the identificationof flood and erosion hazards.HYDROLOGY,PSRXQGPHQW$UHD8SVWUHDPRI6WRFN7UDFNHydrologic analysis evaluates rainfall-runoffrelationships for a given area (watershed)where the volume and rate of runoff is estimatedat specific locations. An understandingof the hydrology of an area, both in existingand future watershed conditions is key indetermining flood hazards and in identifyingpotential impacts to watercourses drainingthe watershed due to urbanization. Theresults of hydrologic analyses conducted aspart of the North Peoria ADMP are used for:• Delineation of 100-year floodplain atselected locations.• Sedimentation engineering and geomorphicanalyses.• Hydraulic evaluation of flood controlmanagement alternatives.• Hydraulic evaluation of stormwater storagealternatives.Approximately 126 watersheds were delineatedwithin the study area to determine rainfallrunoff relationships for the 2-, 5-, 10-, 25-,50-, and 100-year frequency storm events forboth existing and future conditions. Figure 6depicts watersheds evaluated for the NorthPeoria ADMP.6

HYDRAULICS8QQDPHG:DVK%LJ6SULQJHydraulic analyses are conducted to determinethe physical characteristics of a watercourseduring a rainfall-runoff event.Hydraulic computer models facilitate the analysisand are developed to determine extent offlooding, water surface elevations, depth offlow, and velocity of flow for a runoff event.Models are developed for existing naturalconditions and to evaluate different flood controlmanagement alternatives. Results ofmodels developed to evaluate flood controlmanagement alternatives are compared to theresults from models that evaluate existingconditions to assess the impacts of an alternativeon a watercourse.Computer models utilized for the North PeoriaADMP were developed as part of theADMP or are models from effective FederalEmergency Management Agency (FEMA)100-year floodplain delineation. Hydraulicmodels were developed for Unnamed Washes1, 2, and 3 that drain the Big Spring Area to theAgua Fria River. Existing models developedfor the FEMA 100-year floodplain delineationare used as the bases for hydraulic modelingof flood control management alternativesdeveloped for the Twin Buttes Area.Floodplain delineation conducted as part ofthe North Peoria ADMP were performed utilizingdetail and approximate method floodplainhydraulics. Detail hydraulics requiresthe development of a computer model thatdefines 100-year floodplain and floodwaylimits. Approximate method hydraulic utilizesan equation referred to as Manning’sequation to define 100-year floodplain limits.1DWXUDO*UDGH&RQWUROZLWKLQ8QQDPHG:DVK7

NORTH PEORIAAREA DRAINAGE MASTER PLANGEOMORPHIC EVALUATIONGeomorphologyis the study oflandforms, thephysical processesthat formsthe land surfaceand the changesthat take place inthe evolution ofthe landform.Geomorphicevaluations conductedfor theNorth PeoriaADMP focusedon watercourse8QQDPHG:DVK&DQ\RQ5HDFK landforms andlateral stability ofa watercourse.Geomorphic evaluations conducted are basedon field observations, aerial photographs(both historic and recent), historical channelposition, stream longitudinal profile andallowable velocity guidelines. The results ofthe evaluation documents physical changes tothe watercourse that have occurred over timeand suggest the types of changes that can beexpected in the future.In general, historical and field evidence suggeststhat the floodplains of the watercoursesin the study area, where not incised in bedrock,are subject to lateral erosion. Thestreams in the study area flow within shallowcanyons comprised of Middle to Late Pleistocenealluvium or bedrock. Within recentgeologic time, the streams appear to havemigrated over the entire canyon bottom, graduallywidening the canyons through lateralerosion. The highest erosion hazards occur onthese canyon bottoms and at the margins ofthe older surfaces that form the canyon walls.The results of the geomorphic evaluation indicatethere is a potential for lateral migration inthe study watercourses and thus a potentialpublic safety hazard. Results of the evaluationsare used to develop erosion hazardzones.6FRXU+ROH8QQDPHG:DVKSEDIMENT ENGINEERINGThe primary objective of the sediment engineeringanalysis for the North Peoria ADMP isto estimate the existing and future sedimentyield, with emphasis on sediment depositionand maintenance requirements upstream ofthe Central Arizona Project (CAP) canal drainagecrossings, and sediment storage for futureregional retention/detention facilities.Sediment yield is the amount of solid materialtransported past a given point in a stream system,or alternately, the amount of materialdeposited in an enclosed basin. Sedimentyield includes particles small enough to becarried in suspension by the flowing water(suspended load) and particles moved alongthe bottom of a channel by rolling, sliding, orbouncing (bed load). When flow velocities arereduced, sediment carried by a stream isdeposited. Flow velocities can be reduced bynatural or manmade changes in channel slopeor channel geometry, or by impoundment inflood control basins. Sediment yield is a majorconcern for public officials in charge of maintainingthe effectiveness of flood control structuresbecause sedimentation behind dams orin floodways reduces the volume of waterthat can be stored or transported through thesystem. A reduction in effective storage volumeincreases the likelihood of a spillover inlarger runoff events, increasing the chances ofinjuries, damage to the structure itself, propertydamage downstream and possible loss ofhuman life.8

FLOOD AND EROSION HAZARD ZONESWith the exception of the East Terrace Area100-year floodplains and erosion hazardzones where delineated for watercourses withdrainage areas of approximately one squaremile. In the East Terrace Area, due to soil conditions,rainfall runoff relations were higherthan in the rest of the study areas, thereforefloodplains were delineated for watercourseswith drainage areas of less than a square mile.Floodplains and erosion hazard zones developedas part of the North Peoria ADMP, andfloodplains previously delineated by otherstudies are displayed on Figure 7, Figure 8,Figure 9, and Figure 10.ENVIRONMENTAL CHARACTERISTICS%DQN6ORXJKLQJZLWKLQ(URVLRQ+D]DUG=RQHFloodplain delineation and erosion hazardzones form the basis for the identification ofpotential public safety hazards associatedwith natural processes that form the physicalcharacteristics of watercourses within thestudy area. Floodplains based on a 100-yearpeak discharge and erosion hazards zonedelineation were conducted for watercoursesin the Morgan City Area, Big Springs Area,and the Twin Buttes Area, whereas only floodplaindelineation was conducted for the EastTerrace Area.Environmental overviews were conducted todefine the ecological/biological resources, cultural/historicalresources, regulatory hazardouswaste sites, and visual resources of thearea. The overviews are based on availableexisting information and data collected duringreconnaissance level field visits. Results of theoverviews are then utilized in the formulationand evaluation of flood control managementalternatives.BIOLOGICAL RESOURCE OVERVIEW7ULDQJOH/HDI%XUVDJH)RRWKLOOV9HJHWDWLRQ&RPPXQLW\(URVLRQDW6WRFN7DQN'DPThe focus of the biological resources overviewwas to describe and map vegetation communitiesto the association level, identify thepotential occurrence of sensitive, threatened,and endangered species and assess sensitiveor special status habitats within the projectarea. Mapping of vegetation communitiesand assessment of sensitive or special statushabitats were based on low intensity field surveys.Threatened, endangered, and sensitivespecies that potentially occur in the planningarea were determined by consulting the specieslist from the U.S. Fish and Wildlife Servicefor Maricopa County, and through a search of9

NORTH PEORIAAREA DRAINAGE MASTER PLANthe heritage database at the Arizona Gameand Fish Department.Twelve plant associations were identifiedwithin the project area. Several of the associationshave large numbers of plant species incommon, such that the associations differ onlyin respect to the relative proportions of eachspecies. The location and distribution of plantcommunities are displayed on Figure 11.0RUJDQ&LW\:DVK5LSDULDQ*DOOHU\)RUHVWTwo special statusspecies, SonoranDeserttortoise and lowlandleopardfrog, are knownto occur withinthe planningarea. The distributionof lowlandleopardfrogs is restrictedto the lower limitsof MorganCity Wash andthe Agua FriaRiver drainage,while Sonoran Desert tortoise probably occurthroughout most of the planning area. Additionally,southwestern willow flycatchers andlesser-long nosed bats may not occur withinthe area at present, but suitable and sufficienthabitat exists to support individuals of bothspecies. Additional species might becomelisted as threatened or endangered by the federalgovernment before development is initiatedin the area (e.g., yellow-billed cuckoo).Surveys for species that are currently listed orthat may become listed as threatened orendangered, and possibly consultations withthe U.S. Fish and Wildlife Service, will be necessaryto minimize or avoid developmentimpacts to these species. At present, there areno critical habitat designations for any specieswithin the planning area.9HOYHW0HVTXLWH9HJHWDWLRQ&RPPXQLW\The only sensitive and biologically uniquehabitat within the planning area is the aquaticarea and the accompanying riparian galleryforest that occur along the lower reaches ofMorgan City Wash. This habitat extends fromthe confluence with the Agua Fria Riverupstream to above the springs that deliverwater to the wash. The riparian gallery forestis well developed and mature throughout thisarea. The stream supports numerous speciesof wetland plants and aquatic species includingnative fish such as longfin dace (Agosiachrysogaster) and lowland leopard frogs.CULTURAL RESOURCES OVERVIEWCultural Resources is a very broad term. Forthe purposes of the North Peoria ADMP, werefer to cultural resources within the contextof preservation. A cultural resource includesprehistoric, historic, architectural, and traditionalcultural sites. These sites are consideredimportant, because they representlocations and data that can inform us aboutcultures and cultural change through time.Cultural resourcelaws are designedto afford protectionto significantsites so that importantcultural andhistorical informationis not lost.&XOWXUDO5HVRXUFH6LWHProtection canoccur by simplyprotecting sites, or by professionally excavat-10

ing them before they are destroyed in order togather relevant information.The Cultural Resources Overview is based ona literature review of existing archeologicaldatabases. The overview describes the locationand significance of known culturalresources. Of the 46,720 acres within thestudy area approximately 7,703 acres havebeen previously surveyed. This computes toapproximately 17 percent coverage of theproject area, with 83 percent of the project areanot surveyed. A total of 239 surveys wereaccomplished within the project area, ofwhich 325 archaeological sites were observed,with 278 of those prehistoric, 35 of those historic,and 12 of those multi-component sites.Figure 12 displays the location of archeologicalsites in the project area determined fromthe overview.LANDSCAPE CHARACTER AND VISUALRESOURCESLandscape Characterand VisualResources Assessmentevaluationsare conducted aspart of the NorthPeoria ADMP forthe purpose to:• Assess the scenicqualities/attractivenessof the existingnatural and culturalfeatures.6SULQJ)ORZHUV• Assess the existing visual conditions orscenic integrity.• Identify existing major viewing points andlandmarks with the intent that they befocal points for possible flood controlmanagement alternatives.• Develop landscape character themes(including existing, future, and historic)that could be incorporated into the designof flood control management alternatives.• To aid in the development of landscapedesign guidelines that will achieve thedesired character theme(s) as they applyto possible flood control managementalternatives.Visual resources are defined by the scenicquality/attractiveness of the natural and culturalfeatures of an area. Loosely defined scenicattractiveness rates the inherentattractiveness of a landscape on a scale of (A)distinctive, common, (B) typical, or (C) indistinctive.Landforms such as mountain peaksand ridges, plains, valleys, and washes aretaken into consideration along with the presenceof water in defining scenic attractiveness.Criteria published in the Landscape CharacterTypes of the National Forest in Arizona andNew Mexico by the USDA Forest Service(1989) were utilized to rate scenic attractiveness.Figure 13 displays scenic attractivenessclassifications for the study area.8SSHU0RUJDQ&LW\:DVK:DWHUVKHGLandscape character units for the study areaare defined utilizing criteria per the LandscapeAesthetics Handbook #701 publishedby the USDA Forest Services (1995). Landscapecharacter is the “particular attributes,qualities and traits of a landscape that give animage and make it identifiable or unique”. Inthe project area landscape character units arebased on tectonic provinces, vegetation typesand existing land use. Within the project areasix existing landscape character units were11

NORTH PEORIAAREA DRAINAGE MASTER PLANidentified: Mountain Lands, Slopes, Plains,Commercial Use, Rural Subdivisions, andRiparian Gallery Forest.study area) of the City, additional landscapedretention areas within Planned Area Developments,water recharge areas, open space buffersadjacent to Lake Pleasant Regional Park,the Agua Fria and New River recreation corridorsand New River Dam retention area beused to meet its open space goals of providing10 acres of open space per 1000 population.7ZLQ%XWWHV:DVKMULTIPLE-USE OPPORTUNITIESMultiple-use opportunities are opportunitiesidentified to meet local community needs forrecreation, open space, protection andenhancement of natural landscape and localcommunity character as related to proposedflood control management alternatives. Existingand proposed recreational facilities, managementplans and trails plans are inventoriedon a regional and local level so that the extentto which flood control management alternativescould be used to enhance and connectthese resources can be identified. Regionalpassive recreational resources (existing andplanned) adjacent to the study area include,Lake Pleasant, Hells Canyon Wilderness Area,Castle Hot Springs, and linear park/openspace networks (City of Peoria’s Rivers MasterPlan (January 1999)) that connect with a trailsystem proposed in the City of Peoria TrailsMaster Plan along the Agua Fria River. Figure14 displays the recreational regional context ofthe area. Existing local recreational resourcesare characterized by the privately owned CanyonRaceway, Pleasant Valley Airport, andopen space land use proposed in the City ofPeoria’s General Plan. The City of Peoria’sGeneral Plan recommends that the environmentallysensitive areas in the northern region(includes portions of the North Peoria ADMPAs an element of the North Peoria ADMP, anassessment of opportunities and limitationsfor integrating multiple-use recreational featuresinto preferred flood control managementalternatives was conducted. Opportunitiesidentified are primarily located along MorganCity Wash in the Morgan City Area, UnnamedWashes 1, 2 and 3 in the Big Spring Area, andCaterpillar Wash and Twin Buttes Wash in theTwin Buttes Area. The location of multiple–use recreational facilities along these washcorridors are primarily limited to the 100-yearfloodplain and/or erosion hazard zone andpossible detention/retention facilities, locatedwithin a wash, that may be constructed bydevelopers. Figure 15 displays potential washcorridor trail systems for the north PeoriaADMP area.7\SLFDO9HJHWDWLRQ$ORQJ%DQNV12

PUBLIC INVOLVEMENTAn integral part of the preparation of theNorth Peoria ADMP was public and communityparticipation. Ninety-eight percent of theproperty in the study area is held by federal,state and private interest with the majority ofthe private interest (approximately 31% of thearea) held by a few individuals or partnershipsthat are planning on developing theirproperty. Typically, private lands are undevelopedand owners are absentee owners. Thenature and distribution of land ownershipdoes not lend itself to a typical public involvementprocess of conducting a series of publicinformation meetings. A public outreach programconsisting of questionnaires, newsletters,individual meetings with landownersand federal, state and local agencies and apublic meeting was initiated to obtain publicand community participation.3XEOLF:RUNVKRSLandowners in the area were notified of thedevelopment, goals, and progress of the planthrough individual mailings of newsletters,questionnaires, and public announcements inlocal newspapers. A public workshop washeld to present data collection results, policydevelopment, alternative stormwater managementapproaches developed for the plan andto obtain comments and suggestions from participants.Throughout the term of the project, individualmeetings were held with engineers and/orplanners representing the interests of ongoingdevelopment projects. Development projectswithin the plan area include Lake PleasantVistas, Saddleback Heights, White PeaksRanch, Lake Pleasant Heights, Lakeland Village,Upco, and the groundwater rechargeproject conducted by the Central ArizonaProject.FLOOD CONTROL MANAGEMENTALTERNATIVES DEVELOPMENT ANDEVALUATIONThe North Peoria ADMP provides a regionalapproach to flood control management.Development of flood control managementalternatives and policies that forms the foundationof the plan takes into account engineering,environmental, landscape, social andeconomic considerations. Watershed managementalternatives are developed to mitigate/minimize the effect of urbanization on stormwaterrunoff and conveyance while recognizingthe values of the community and theopportunity to protect the unique characteristicsof the region. Flood control managementalternatives are evaluated on how well eachalternative meets the goals of the North PeoriaADMP. The primary purpose for flood controlmanagement alternative development andevaluation is to develop a range of plans thatprovides public safety from flood and erosionhazards, determine the cost and benefits ofeach alternative, qualitatively determineimpacts of the alternative on identified environmentalresources and to select a preferredmanagement plan.FLOOD CONTROL MANAGEMENTALTERNATIVESFlood control management alternatives developedand evaluated for the North PeoriaADMP are categorized into two groups:watercourse management. Alternatives andstormwater storage alternatives. Watercoursemanagement alternatives evaluated includeda non-structural, a partial structural, a low13

NORTH PEORIAAREA DRAINAGE MASTER PLANimpact structural, a full structural, and a noaction. The full structural alternative is basedon current federal, state, and local floodplainmanagement regulations that allow encroachmentinto the floodway fringe. The full structuralalternative typically requires, at aminimum, the structural stabilization of washside slopes for the entire reach. The partialstructural alternative also is based on currentfloodplain management regulations, howeverthe partial structural solution is applied atonly specific locations along the watercourse.The low impact structural alternative allowsfor development activity to occur within theerosion hazard zone as long as the activitydoes not significantly alter the natural formand function of the watercourse. The nonstructuralalternative defines a corridor thatallows the watercourse to function naturally.The no action (do nothing) alternative providesflood control management based on currentfederal, state and local floodplainmanagement regulations that allowsencroachment into the floodway fringe. Typically,under current regulations encroachmentsinto the floodway fringe are allowed ona piece-meal fashion without taking into considerationthe effect of the encroachment orcollective encroachments on the entire watercourse.Typical sections of watercourse-basedalternatives are depicted in Figure 16, Figure17, Figure 18, and Figure 19. Stormwater storagealternatives evaluated include the standardpractice of retaining the volume of flowfrom the 100-year, 2-hour event, in-stream, inlinedetention alternative and an in-stream,off-line retention alternative. Perspectives ofthe in-line detention alternative and the offlineretention alternative are presented as Figure20 and Figure 21.14The evaluation/application of an alternativefor a given watercourse is based on physicaland data constraints. Physical constraintsinclude land use, topography, the location,and distribution of rock outcrop, and characteristicsof the floodplain (i.e. floodway limitscoincidental with floodplain limits). Data constraintsare the availability of hydraulic models.Hydraulic evaluations of watercoursebasedalternatives are developed for watercoursesin which detail hydraulic models weredeveloped as part of the study or availablefrom previous studies. The full structuralalternative is applied only to watercourses inthe Twin Buttes area below the CAP canal.The partial structural alternative is evaluatedfor the three unnamed washes that drain theBig Spring Area to the Agua Fria River. Thelow impact structural alternative is evaluatedfor all watercourses in which erosion hazardzones have been delineated as part of thisstudy. The non-structural alternative and theno action alternative are evaluated for allwatercourses in which hydraulic models wereavailable.Both Maricopa County and the City of Peoriarequire retention/detention (stormwater storagefacilities) for all new developments. Thegoal of this requirement is to reduce/minimizethe impacts of the increased runoff dueto development in the watershed. Ideally, thisis accomplished by controlling the post-developmentrunoff such that it is equivalent inmagnitude, duration, and temporal distributionto the pre-development conditions. Toachieve this goal, both Maricopa County andthe City of Peoria use the 100-year, 2-hourstorm as the design event for sizing retention/detention facilities.Traditionally, retention has been accomplishedby storing the 100-year, 2-hour runoff volumein below grade basins. These basins typicallyare drained by percolation into the soil and/ora small outlet structure connected to a watercourseoften via an extensive storm drain system.The effectiveness of this type of facility,both economically and hydraulically, is afunction of the soil and terrain characteristics.Shallow soils with low permeability ratesand/or soils that occur on steep slopes are notconducive to this particular application.Fifty percent of the North Peoria ADMPproject area have soils types that are characterizedby moderate to moderately slow permeability;low to very low available watercapacity and shallow depth to bed rock or

hard pan, typically less than two feet. Additionally,these soils typically occur on steepslopes. The steep terrain associated with thesesoils combined with the shallow depth to bedrockresults in physical conditions that are notsuitable to the traditional technique for providingretention. As a result, the retention/detention requirement for development siteswith these characteristics has, in the past,often been waived; however, the presence ofsuch physical characteristics does not meanthat alternative methods of retention/detentionshouldn’t be investigated or required.Therefore, two alternative methods for reducingor decreasing the effects of increased runoffdue to development are evaluated for thisstudy area. These methods are in-stream, offlineretention and in-stream, in-line detention.ALTERNATIVE EVALUATIONFlood control management alternatives areevaluated on how well each alternative meetsthe goals of the North Peoria ADMP. The evaluationsof the alternatives are based onweighted elements of four criteria. The criteriaare Public Safety, Social Impacts, EnvironmentalImpacts, and Economic Impacts. Aweighting factor was developed by the steeringcommittee that represents the “relativeimportance” of each element in the evaluationprocess. The weighting factors were measuredon a scale of 1 to 10, where a factor of 10represented highest importance. Weighingfactors of 10, 3, 6, and 4 were used for PublicSafety, Social Impacts, EnvironmentalImpacts, and Economic Impacts, respectively.Each criterion is made up of several elementsthat are individually rated. A rating system isused to measure the effectiveness of eachalternative at meeting the elements of each criterion.The rating system ranges from 1 to 5.A value of 1 represents a “very low” rating atmeeting the criteria element, a value of 2 representsa “low” rating, a value of 3 representsa “moderate” rating, a value of 4 represents a“high” rating, and a value of 5 represents a“very high” rating. Rated values for each elementare averaged to obtain an average valuefor the criterion. The average rating value is15then multiplied by the appropriate weightingfactor to obtain a score for the criterion. Scoresdetermined from the four criterion are thenadded together to obtain an overall score forthe alternative.Public Safety CriterionThe public safety criterion is based on evaluatingthe threat for loss of human life, possibledamage to structures and property andimpacts to water quality resulting from implementationof a given alternative. This criterionis an indicator of how well the proposedalternative will succeed in reducing or eliminatinglife threatening, or potentially lifethreatening, flood and erosion related hazards,as well as reducing the potential forflood and erosion related damage to publicand private properties. The evaluation of thepublic safety criterion is based on the effectivenessof each alternative in satisfying thetwo elements of the Public Safety Criterion.The two elements are Protect Life and Propertyand Water Quality.Protect Life and Property. Historically, societyhas experienced loss of life and property dueto flooding and erosion that is associated witha stormwater runoff event. This element ratesthe function of the alternative to keep the publicout of harms way during a 100-year stormevent while minimizing potential downstreamimpacts to life, property and structures.Water Quality. Federal guidelines mandatethat communities develop Best ManagementPractices (BMPs) to promote water quality.This element accounts for the impacts of analternative on water quality.Social CriterionThe evaluation of the social impact criterion isbased on the effectiveness of each alternativein satisfying the elements of CommunityAcceptance, Multiple-use Opportunities, andCompatibility with Other Plans.Community Acceptance. This element accountsfor the input received from the public involve-

NORTH PEORIAAREA DRAINAGE MASTER PLANment process. There is a nationwide trendtowards promoting non-structural approachesand ecosystem preservation, as witnessed bythe removal of flood control structures inmany parts of the country. Federal agenciessuch as the U.S. Army Corps of Engineers andthe U.S. Bureau of Reclamation have, in recentyears, significantly changed their focus fromhard engineering solutions to include nonstructuralalternatives, preservation of naturalhydrologic functions, and ecosystem restoration.The specific input from the publicinvolvement process was that the preservationof watercourses and their associated habitat ismore important than maximizing developableland by destroying the natural hydrologic processes,which results from encroaching intowatercourses.Multiple-use Opportunities. This element is anindicator of the multiple-use opportunities ofan alternative. Examples of such usesincluded passive and active recreation, trails,and open space. The effectiveness of the criterionis based on the extent of multi-use opportunitiesthat result from implementing a givenalternative.Compatibility with Other Existing Plans. Thiselement is an indicator of the compatibility ofa proposed alternative with planning policiescited in other existing planning documents.Planning documents reviewed are, ComprehensivePlan-Maricopa County’s Eye to theFuture 2020 (1997), and White Tank/GrandAvenue Area Plan (December 6, 2000); MAG’sDesert Spaces Plan (1995) and ESDA (June2000); and the City of Peoria’s General Plan(June 2001), Desert Lands Conservation MasterPlan (Auusst 1999), Lake Pleasant/NorthPeoria Area Plan (November 1999) and TrailsMaster Plan (January 1999).Environmental CriterionThe evaluation of the Environmental Criterionis based on the effectiveness of each alternativein satisfying the three elements of EnvironmentalImpacts, Visual Resources andAesthetic Compatibility, and Impacts on CulturalResources.16Environmental Impacts. This element consists oftwo sub elements: complexity of environmentalpermitting and impacts on biologicalresources. Complexity of Environmental Permittingfocuses on the acquisition of the U.S.Army Corps of Engineers 404 Permits and 401Water Quality Certifications. The alternativesare measured based on the potential for needinga 404 Permit, the level of 404 Permitrequired (Nationwide vs. Individual), and thelevel of mitigation necessary to gain federalapproval to construct the alternative. To evaluatethis element, it is assumed that alternativeswith structural features will causedisturbance to the land within the Waters ofthe United States. The more extensive thestructural features, the lower the rating. As anexample, constructing a wide, rectangular,concrete channel would place fill within theWaters of the United States, require an Individual404 Permit and 401 Water Quality Certification,and require extensive mitigationmeasures to replace the relatively high-valuehabitat and vegetation associated with theundisturbed desert riparian wash. Impacts onbiological resources accounts for the potentialimpact on biological resources by the proposedalternatives and how well the proposedmanagement alternative will succeed in preservingor restoring the natural riparian environmentfound along the study watercourses.The most important indicator of this is theability of a given alternative to preserve wildlifehabitat or minimize disruption to existinghabitat.Visual Resource and Aesthetic Compatibility.This element evaluates the relative degree ofcontrast between the various components ofthe alternatives and their setting in the landscape.Visual contrast is based on spatialdominance, visual compatibility, color, line,and form.Impact on Cultural Resources. This elementaccounts for the potential impact on culturalresources by a given alternative. It is also anindicator of how well the alternatives will succeedin preserving cultural resources.

Economic CriterionThe evaluation of the economic criterion isbased on the effectiveness of each alternativein satisfying two elements: ImplementationCost and Maintenance Cost.Implementation Cost. This element representsthe estimated cost of the proposed alternativeto the public, either through increased developmentcosts passed on to future residents ofthe area who will directly benefit from theimprovements (local public) or the costs to thegeneral public. The cost for a structural alternativeconsiders the cost of the structuralimprovements necessary to implement theproposed alternative (a positive cost), thevalue of land that is reclaimed from the floodplain/erosionhazard zone by the structuralimprovements (a negative cost, i.e., benefit).Added together, these costs represent the totalnet cost of the alternative. The effectiveness ofa given alternative is measured by using thetotal net cost. The lower the net cost thehigher the rating for the Economic Criterion.Maintenance Cost. This element accounts forthe potential maintenance costs associatedwith the structural components of an alternative.It has been assumed that such costs areproportional to the length of bank protectionproposed for a given alternative. The greaterthe bank protection length, the higher thepotential maintenance cost and the lower therating.SUMMARY OF EVALUATION RESULTSFlood control management alternatives weredeveloped for watercourses in the MorganCity Area, Big Spring Area, and Twin Buttesarea. Table 2 lists the watercourse evaluatedwithin the specific planning areas. The watercourseswithin a planning area have similarphysical and hydraulic characteristics andtherefore are evaluated collectively. Results ofthe evaluation are applied to all watercoursesin a specific planning area. Scoring results, forwatercourse management alternatives, forplanning areas are listed in Table 3.Stormwater storage flood control managementalternatives were developed and evaluatedfor the Big Spring Area with the intentthat the results are applied to other planningareas that have characteristics such that thestandard practice of retaining the 100-year, 2-Table 2Watercourses EvaluatedPlanning AreaMorgan CityWatercourseMorgan City WashBig Spring Unnamed Wash 1Unnamed Wash 2Unnamed Wash 3Twin ButtesCaterpillar Tank WashTwin Buttes WashEast Garambullo WashWest Garambullo WashWhite Peak WashWest Fork of White Peak Wash17

NORTH PEORIAAREA DRAINAGE MASTER PLANTable 3Summary of Evaluation Results Watercourse Management AlternativesPlanningAreaEvaluationCriteriaWeightingFactorNon-Structural Low ImpactStructuralPartial Structural Full Structural Do NothingRating Score Rating Score Rating Score Rating Score Rating Score1 2 3 4 5 6 7 8 9 10 11 12 13Morgan City Public Safety 10 8 80 8.3 83 NA NA NA NA 6 60Social 3 11 33 9.8 29.4 NA NA NA NA 7.5 22.5Environmental 6 14 84 10.8 64.8 NA NA NNA NA 5 30Economic 4 6 24 6.6 26.4 NA NA NA NA 2 8Total Score = 221 203.6 120.5Big Spring Public Safety 10 8 80 8.3 83 7.5 75 NA NA 6 60Social 3 10 30 9.8 29.4 9 27 NA NA 7 21Environmental 6 15 90 10.8 64.8 7.8 46.8 NA NA 5 30Economic 4 6 24 6.6 26.4 4.4 17.6 NA NA 2 8Total Score = 224 203.6 166.4 119Twin Buttes Public Safety 10 7.9 79 8.3 83 NA NA 6.7 67 6 60Social 3 10.9 32.7 9.8 29.4 NA NA 7.2 21.6 7 21Environmental 6 14.5 87 10.8 64.8 NA NA 4.6 27.6 5 30Economic 4 6 24 6.6 26.4 NA NA 4 16 2 8Total Score = 222.7 203.6 132.2 11918

Table 4Summary of Evaluation Results Stormwater Storage Based AlternativesPlanningAreaEvaluationCriteriaWeightingFactorIn-Stream, Off-LineRetentionIn-Stream, In-LineDetentionRating Score Rating Score1 2 3 4 5 6 7Big Spring Public Safety 10 7 68 6 64Social 3 11 34 10 31Environmental 6 10 60 9 53Economic 4 6 24 6 24Total Score = 186 172hour event is not practical. Scoring results forthe stormwater storage are listed in Table 4.PREFERRED FLOOD CONTROL MANAGEMENTALTERNATIVESThe preferred watercourse-based flood controlmanagement alternative is the non-structuralalternative. The non-structuralalternative defines a corridor that allows thewatercourse to function naturally and isdefined by the 100-year floodplain, erosionhazard zone and a buffer if applicablebetween human activity and a wash corridor.The plan recognizes that there may be situationsin which development activities may berequired or desired within the erosion hazardzone, for this situation the plan presents a lowimpact structural alternative. Channelizationis not a preferred flood control managementalternative; however, the plan also recognizesthat there may be situations in which channelizationmay be required. The preferred stormwaterstorage alternative is the standardpractice of retaining the volume from the 100-year, 2-hour rainfall event, however this practicemay not be practical for certain portions ofthe study area. The standard retention practicesif implemented within an entire watershedwould have negative impacts in regardsto sustaining native vegetation along watercourses.The plan offers two stormwaterreduction alternatives to the standard practice.The stormwater storage alternatives are basedon reducing post-development peak dischargesto pre-development magnitudes. Thealternatives are referred to as the in-stream,off-line retention alternative and in-stream, inlinedetention alternative. The in-stream, offlineretention is the preferred alternative of thetwo.COMPATIBILITY WITH OTHERPLANNING DOCUMENTSComponents of preferred flood control managementalternatives are compared to componentsof environmental resources, safety, andopen space elements of other planning documentsto ensure that there is consistencybetween the intent of the North Peoria ADMPand the intent of other planning documents.Table 5 lists the themes of objectives and policiesfrom the North Peoria ADMP and otherapplicable planning documents that have similargoals.19

NORTH PEORIAAREA DRAINAGE MASTER PLANTable 5Summary of Regional and Local Planning ObjectivesPlanning Document Objective PoliciesDiscourage Development within 100-yearfloodplain in Environmentally Sensitive AreasDisrourage Development withinErosion Hazard ZonesEncourage the Use of Non-Structural FloodControl Management Techniques Where ApplicablePromote the Design of Flood Control Structures thatare Sensitive to the Natural EnvironmentManage Increases in Stormwater Runoffdue to UrbanizationChanges to Natural Drainage Patterns Should beAvoided in Environmentally Sensitive Land AreasAppropriate Structures Should beDesigned for Roadway Cross DrainageRecognition/Preservation of Unique LandformsDesignation of Environmentally Sensitive AreasRecommend Development Guidelines that areSensitive to the Natural EnvironmentPreserve and Protect Habitat Areas and Areasof Vegetative SignificancePreserve and Protect Historical andArchaeological ResourcesRecognize Multiple-Use RecreationalOpportunities within an Open Space NetworkEstablish Buffer Between Human Activities andEnvironmentally Sensitive AreasRecommend that Special Development Guidelinesfor Area with Terrain Slopes Greater than 10%(City of Peoria) or 15% (Maricopa County).City of Peoria’s General Plan (June2001)Lake Pleasant/North Peoria AreaPlan (November 1999)X X X X X X X X X X XX X X X X X X X X X X XPeoria Desert Lands ConvervationX X X X X X X X XMaster Plan (August 1999)Desert Spaces (1995) X X X X X X X X X X X XWhite Tank Grand Avenue Area SpecificPlan (December 6, 2000)North Peoria Area Drainage MasterPlan (2001)X X X X X XX X X X X X X X X X X X X X X20

INTRODUCTIONRULES OF DEVELOPMENTCommunities develop drainage ordinances,policies, and standards with the intent to mitigate/minimizeflooding impacts due tourbanization of a watershed. The purpose ofthese regulations is to minimize the occurrenceof losses, hazards, and conditionsadversely affecting the public health, safety,and general welfare that might result fromflooding caused by the surface runoff of rainfall.Potential rainfall runoff relation impactsto a watershed due to urbanization are:• Decrease of stormwater infiltration capacitywithin a watershed due to urbanizationincreases peak discharge from awatershed unless measures are undertakento reduce post development peakdischarges.• An increase of peak discharge, frequency,and runoff volume due to urbanization ina watershed increases the potential forerosion and sedimentation within watercourses.• An increase in erosion potential can resultin loss of property and riparian habitat.• Due to an increase in peak discharge,existing drainage structures downstreamof newly urbanized areas will be undersized.• Increase in peak discharge increases theamount of property within a floodplain.Existing structures within or adjacent tothe predevelopment floodplain are at riskof a greater flood impact.• Disruption of natural flow paths can disruptthe natural system equilibrium andinduce bank erosion and long-term degradationof the channel bed.• An increase in bank erosion and long-termchannel bed degradation can result in theneed of grade control structures and bankstabilization.• Increased erosion and deposition willresult in greater costs for future structures,higher potential damage and likelihood offailure of existing structures, andincreased maintenance cost.• Increased deposition results in loss ofchannel capacity and increased flood levels.NORTH PEORIA AREA DRAINAGE MASTERPLAN ELEMENTSThe North Peoria ADMP is one of the manytools that have been developed to guidegrowth and development in the study area sothat impacts of urbanization on the environmentare minimized. The focus of the NorthPeoria ADMP is on flood and erosion controlmanagement; however, the plan takes intoconsideration the impacts of different floodcontrol management alternatives on environmental,cultural, and visual resources andlooks at multi-use opportunities. The intent ofthis plan is to work in conjunction with otherplanning documents and ordinances developedby the City of Peoria and MaricopaCounty. The plan is to be used by policy makersin the City of Peoria and Maricopa County,future residents, and developers when makingdecisions concerning development in thearea.Implementation of and guidance provided bythe plan is based on a set of managementgoals, objectives, and policies for each of thefour elements of the plan. The elements areEnvironmental Hazard Identification, Developmentand Planning Considerations, Environmental,and Multiple-Use Opportunities.The following definitions of goal, objective,and policy area are offered as a guide for theusers of the plan.21Goal:A statement that describes in generalterms a desired future condition.

NORTH PEORIAAREA DRAINAGE MASTER PLANObjective: A statement that describes a specificcondition to be attained.Policy:A course of action or rule of conductto be used to achieve the goalsand objectives of the plan.The plan area for the North Peoria ADMP lieswithin two jurisdictional areas, MaricopaCounty and the City of Peoria. The specificguidance that is offered by each of the governmentalbodies within their adopted planningprograms vary depending on their needs andtheir vision for managing growth. The goalsobjectives and policies developed for theNorth Peoria ADMP are applicable to bothjurisdictions; however, reference is made toother planning documents that offer developmentguidance. The user of this documentshould also take into consideration specificgoals, objectives and policies developed forthe area by both jurisdictions.North Peoria ADMP elements, goals andaccompanying objectives and policies that aresimilar or the same as guidance/direction providedin adopted planning documents, and/or ordinances are presented or repeated forthis plan because they are instrumental to theimplementation and maintenance of the preferredflood control management alternativesof the plan.Environmental Hazards IdentificationWithin non-urbanized/rural watersheds naturalenvironmental hazards associated withrunoff from storm events exist. Without sufficientplanning and management, natural hazardsare compounded as development occurswithin a watershed. In order to protect privateand public property and the health andgeneral welfare of the public, naturally occurringenvironmental hazards and hazards createdby development need to be identified.Environmental hazards associated with stormrunoff can be categorized into natural floodhazards, erosion hazards, sediment depositionhazards, and flood hazards associated withdevelopment.22The following environmental hazard identificationGoals, Objectives, and Policies seek toadvance the intent of Federal, State, County,and City of Peoria guidelines for the treatmentof identified environmental hazards.Goal EH1 - Identify environmental hazards associatedwith stormwater runoff.Objective EH.1.1Identify special flood hazard zones per theguidelines of FEMA and the District.Policy EH.1.1.1Require all development to use at leastthe regulatory 100-year floodplaindelineation identified by FEMA and/or the District and associated 100-yearpeak discharges in their planning anddesign efforts.Policy EH.1.1.2Require all development to delineateflood hazards zones for areas not coveredby delineation conducted byFEMA or the District.Objective EH1.2Identify potential flood hazards associatedwith existing man-made structures withinthe planning area. Possible examples ofman-made structures include, but are notlimited to, stock tanks, drainage crossingsat roadways and canals, levees, bridges,and retention basins.Policy EH1.2.1Evaluate the structural integrity andpossible failure of existing earthendams along watercourses. (Earthendams have been identified in the BigSpring, East Terrace, and Twin Buttesplanning areas.)Policy EH1.2.2Evaluate ponding limits upstream of awatercourse crossing of roadways andcanals.

Objective EH1.3Identify erosion hazard zones associatedwith watercourses.Policy EH1.3.1Require all new development to usethe erosion hazard zone identified bythe District in their planning anddesign efforts.Policy EH1.3.2Require all new development to delineateerosion hazard zones for areas notcovered by delineation’s conducted bythe District.Objective EH1.4Identify stream reaches that have experiencedhistorical and/or recent long-termdegradation or aggradation.Policy EH1.4.1Require all new development to takeinto account the effect of aggradationand degradation on drainage facilities(such as retention/detention, off-line/in-line facilities). Drainage facilitiesconstructed in the watercourse shallstrive to maintain the watercourse sedimentcontinuity.Development/Planning ConsiderationsThe following Development/Planning Goal,Objectives, and Policies provide guidance tominimize potential impacts to a watersheddue to development.Goal DP1 - Establish area-specific Design andPlanning Standards to promote development thatacknowledges environmental hazards associatedwith stormwater runoff, preserves the naturalintegrity and function of watercourses within awatershed and minimizes the potential to increasethe magnitude of the hazards due to urbanization.Objective DP1.1Discourage development in 100-yearfloodplain and associated erosion hazardsetbacks.Policy DP1.1.1Encourage non-structural flood controltechniques over typical structuralflood control techniques.Policy DP1.1.2Where structural control measures aredeemed necessary, encourage the useof low impact structural flood controltechniques. Low impact structuralmeasures shall not adversely affect thestability of a watercourse or adverselyalter flooding and erosion conditionson adjacent property. Low impactstructural alternatives shall complementthe visual integrity of the area.Policy DP1.1.3Development in, or modification of,the floodplain is discouraged. Shouldthere be a need to modify the floodplain,the modifications shall result inminimum disruption of the naturalsediment transport capacity of thechannel and floodplain.Objective DP1.2Encourage design and planning effortsthat mitigate potential disruptions to thepredevelopment function of a watersheddue to development.Policy DP1.2.1Discourage changes to natural drainagepatterns in rural and low-densityresidential land use areas.Policy DP1.2.2In areas where the non-structural alternativeis applied, preserve vegetationon and adjacent to the channel banks,and in the floodplain in order to maintainthe stability of existing channelbanks and minimize the potential forlateral channel movement.Policy DP1.2.3Design roadway alignments in such amanner that runoff collected by the23

NORTH PEORIAAREA DRAINAGE MASTER PLANroadway is conveyed to its historicwatercourse.Policy DP1.2.4Design roadway watercourse crossingssuch that the alignment of theroadway is perpendicular to thewatercourse alignment and at locationswhere the floodplain and erosionhazard limits are narrow.Policy DP1.2.5Discourage roadway crossing ofwatercourses at locations where thewatercourse is braided.Policy DP1.2.6Provide access roads to culvert orbridge roadway crossing of watercoursesto facilitate access by maintenancevehicles.Policy DP1.2.7Culvert/bridge crossings shall minimizedisruption to the natural channelform and function.Policy DP1.2.8Design culvert crossings to account forpotential clogging due to the accumulationof sediment and debris.Policy DP1.2.9Design drainage crossings to minimizedownstream scour, minimize the riskof erosion of roadway approaches, andmaintain sediment continuity up tothe bank full discharge.Policy DP1.2.10At-grade roadway crossings of watercoursesshould only be considered forwatercourses that are characterized byshallow flow conditions. At-graderoadway crossings in rural and lowdensityresidential land use areas areacceptable (specific design criteriasuch as allowable depth of flow overthe roadway will need to be met) withagency approval.24Policy DP1.2.11The standard practice for retaining thevolume of runoff from the 100-year, 2-hour storm event should be employedunless it is demonstrated not to bepracticable. The standard retentionpractice is encouraged for commercial,business park/industrial and highdensityresidential land use areas. Anacceptable alternative to the standardpractice is a facility that reduces postdevelopmentpeak discharges to predevelopmentmagnitudes.Policy DP1.2.12Encourage the use of in-stream, in-linedetention or in-stream, off-line retentionwhere it can be demonstratedthrough engineering analyses thatinfiltration rates, and/or topographydoes not merit incorporating stormwaterretention facilities, and wherereducing post-development peak dischargesand runoff volumes to predevelopmentconditions can beachieved. These stormwater storagefacilities inherently to not have waterquality benefits for managing pollutantsin stormwater. Stormwater qualitybest management practices willneed to be employed in the watershedwithin or upstream of the receivingfacility. Typically, the first flush from arunoff event will need to be retainedand treated.Policy DP1.2.13Prohibit use of irrigation canals as anoutfall for stormwater runoff.EnvironmentThe project area for North Peoria ADMPoffers a unique biological resource, aestheticcharacter, and is rich in natural and culturalresources. The plan offers guidelines forfuture development in a comprehensive mannerthat strives to identify and integrate environmentalfeatures such as the existingbiology, visual resources, watersheds anddrainage patterns and cultural resources for

the purpose of watershed and watercoursemanagement.Biological ResourcesGoal BR1 - Preserve sensitive habitats within theNorth Peoria ADMP Peoria project area.Objective BR1.1The reach of perennial flow for MorganCity Wash and Agua Fria River and theadjacent riparian habitats should be protectedfrom future development in orderto maintain the ecological integrity andintact condition of these habitats.Policy BR1.1.1Encourage that developers contact theArizona Game and Fish Departmentfor specific development design considerationsfor areas adjacent to theperennial flow reach for Morgan CityWash and the Agua Fria River locatedin the Morgan City Area.Objective BR1.2Riparian vegetation habitats should bepreserved along major washes in the MorganCity, Big Spring, East Terrace, andTwin Buttes areas to enhance bank stability,to decrease lateral erosion, and tomaintain the existing sediment balance ofstreams.Policy BR1.2.1Recommend that vegetation and anadjacent buffer zone be preservedalong major washes.Desert Lands Conservation Master Plan(August 1999), and the Lake Pleasant/NorthPeoria Area Plan (November 1999).Visual CharacterGoal VC1 - Maintain the existing visual character(natural, historic) of the region.Objective VC1.1Minimize the visual impact of stormwaterstorage facilities.Policy VC1.4.1Encourage that stormwater storagefacilities be designed to appear in conformancewith the natural contoursand alignment of the terrain.Objective VC1.2Encourage maintenance of the naturalwash side-slope texture and color in areasof disturbance.Policy VC1.2.1Where constructed, flood control facilitiesand side-slope stabilization measuresshould match the adjacentterrain in color and texture.Objective VC1.3Minimize the number of wash crossings inorder to prevent disrupting views up ordown the wash. Minimize impacts toplant and animal habitats, and avoid disturbingthe existing sediment balance,decrease the need for public maintenanceand minimize scour and deposition.Other applicable policies and guidelines forpreservation of sensitive habitats, buffer areasadjacent to riparianriparian corridors, preservationof significant stands of representativeplant communities and revegetation of disturbedareas are presented in the ComprehensivePlan-Maricopa County Eye to the Future2020 (1997), and the ESDA (June 2000) forareas within Maricopa County. For areaswithin the City of Peoria, applicable policiesand guidelines are presented in the City ofPeoria’s General Plan (June 2001), Peoria25Policy VC1.3.1Where utility, trails, or roadway crossingsare necessary, cross perpendicularto wash, at the narrowest point and/orat the point of least vegetation disturbance.Policy VC1.3.2Replant disturbed areas using existingnative plant species types and densitiesthat are consistent with existingconditions.

NORTH PEORIAAREA DRAINAGE MASTER PLANOther applicable policies and guidelines forpreservation of landform visual resources arepresented in the Comprehensive Plan-MaricopaCounty Eye to the Future 2020 (1997),Maricopa County’s Zoning Ordinance (HillsideDevelopment Standards (August 1993))and the ESDA (June 2000) for areas withinMaricopa County. For areas within the City ofPeoria, applicable policies and guidelines arepresented in the City of Peoria’s General Plan(June 2001), Peoria Desert Lands ConservationMaster Plan (August 1999), Lake Pleasant/North Peoria Area Plan (November 1999),Zoning Ordinance (September 1995 (HillsideDevelopment Overlay District)).Cultural ResourcesOur cultural resources inform us of prehistoricand historic cultures and cultural changethrough time. Both Maricopa County and theCity of Peoria recognize the importance of culturalresources and have adopted conservationand preservation policies that strive toprotect our cultural resources. Applicable policiesand guidelines for the identification, protectionand conservation of cultural resourcesare presented in the City of Peoria’s GeneralPlan (June 2001), Comprehensive Plan-MaricopaCounty Eye to the Future 2020 (1997),and Maricopa County’s Desert Spaces Plan(1995).Multiple-Use OpportunitiesAs an element of the North Peoria ADMP, anassessment of opportunities and limitationsfor integrating multiple-use recreational featuresinto preferred flood control managementalternatives was conducted.26Opportunities identified are primarily locatedalong Morgan City Wash in the Morgan CityArea, Unnamed Washes 1, 2, and 3 in the BigSpring Area, and Caterpillar Wash and TwinButtes Wash in the Twin Buttes Area. Thelocation of multiple–use recreational facilities(identified as part of this study) along thesewash corridors are primarily limited to the100-year floodplain and/or erosion hazardzone and possible detention/retention facilities,located within a wash, that may be constructedby developers. Multiple-useopportunities constraints are the physicaldimensions of the 100-year floodplain anderosion hazard zone and steep terrain. Washcorridors in the Morgan City Wash Area, BigSpring Area, and the Twin Buttes Area abovethe CAP canal are typified by incised channels,steep banks, narrow floodway limits thatare coincidental with floodplain limits (minimumdevelopment potential with floodplain)and erosion hazard zones that are not significantlydifferent than the 100-year floodplainlimits. Twin Buttes below the CAP Canal ischaracterized by a wider floodplain and erosionhazard zone than the reach above theCAP. Given the 100-year floodplain and erosionhazard zone dimensions and steep terrainconstraints multiple-use opportunitiesassociated with flood control managementalternatives are primarily limited to trails andopen space located within a wash corridor(the wider the floodplain/erosion hazardzone the greater the opportunity). Multiple-Use opportunities could be enhanced by planningrecreational facilities located outside ofthe wash corridor that connect to potentialtrail systems/open space areas within andadjacent to a watercourse.Planning efforts for multiple-use recreationalfacilities in the North Peoria ADMP shallinclude where merited the incorporation ofguidelines and standards developed for theCity of Peoria and Maricopa County in variousplanning documents that include, the Cityof Peoria’s Trails Master Plan (January 1999)and River Master Plan (January 1999), theFlood Control Districts Agua Fria WatercourseMaster Plan (2001), Maricopa County’s, Highway74 Scenic Corridor Overlay Zoning OrdinanceXXII-F-1, (August 1993) and, MaricopaCounty’s Parks and Recreation Department,Proposed Maricopa County Regional TrailSystem (on going).The following general goals are offered asopportunities to meet local community needsfor recreation and open space. Specific objectivesand policies are not developed as part of

the North Peoria ADMP. Users of the NorthPeoria ADMP should consult with the appropriatejurisdiction concerning specific planningelements, design criteria, and standardsfor multiple-use recreational needs. Discussionconcerning opportunities and constraintsfor multiple-use recreation, identified as partof the North Peoria ADMP, is located in NorthPeoria ADMP, Technical Data Notebook,Attachment 5, Multi-Use OpportunitiesAssessment Report.Goal RR1 - Promote continuous trails and vistas ofscenic areas along accessible washes.Goal RR2 - Promote connectivity between possiblewash corridor trail systems and to development,area destinations, and other shared-use recreationalfacilities.Flood HazardsAccording to ARS 48-3609A and under theauthority outlined in ARS 48-3605A floodplaindelineations shall be conducted on allwatercourses with drainage areas more than¼ of a square mile or having a 100-year estimatedflow rate of more than 500 cfs. Floodplaindelineations shall be conducted inconformance with State Standard 2-96 guidelines,guidelines presented in MaricopaCounty Drainage Design Manual Volume II-Hydraulics and guidelines presented in theCity of Peoria Infrastructure DevelopmentGuidelines.Erosion HazardsGoal RR3 - Protect the integrity of washes whileproviding opportunities for recreation and theenjoyment of the natural environment and scenicareas.DESIGN GUIDELINESThe following design/planning guidelines arepresented to aid designers and planners intheir efforts. The guidelines are in part fromand in addition to guidelines and criteria presentedin Maricopa County Drainage DesignManual Volume II-Hydraulics, State Standardsdeveloped by the Arizona Departmentof Water Resources and the City of PeoriaInfrastructure Development Guidelines.8QQDPHG:DVK27([DPSOHRID6WUXFWXUDO%DQN3URWHFWLRQ0HDVXUH'HVLJQHGWR0LQLPL]H/DWHUDO&KDQQHO0LJUDWLRQIn addition to establishing 100-year floodplainlimits, erosion hazard zone delineations shallbe conducted on all watercourses with drainageareas more than ¼ of a square mile or havea 100-year estimated flow rate of more than500 cfs. Erosion hazard delineation shall beconducted at a minimum in conformance withState Standard for Watercourse System SedimentationBalance (State Standard 5-96)guidelines. Depending on the level of detailneeded, State Standard 5-96 presents three levelsof evaluation. Level I evaluation assumesthat the results of the evaluation will be moreconservative than results from a Level II or IIIevaluation. This assumption may be generallytrue, but may not be valid in areas of potentialchannel avulsion or lateral migration. Level IIand Level III evaluations are technically morerigorous and the results may or may not indicatereduced erosion hazard zones relative tothe results of a Level I evaluation. Caution

NORTH PEORIAAREA DRAINAGE MASTER PLANshould be used in interpreting and applyingthe results of a Level I evaluation. Watercoursescharacterized with wide geologicfloodplains, multiple or braided channels,highly erosive banks, poorly vegetated banks,and potential for channel avulsions should beevaluated at a higher level than Level I.Areas located within the recommended erosionhazard zones developed as part of theNorth Peoria ADMP may be subject toincreased risks to public safety that warrantspecific development restrictions. Given thelevel of detail used to develop the recommendederosion hazard zones the developer/landowner is given the option of completing amore detailed erosion hazard zone evaluation.A typical scope of work for such an analysis islisted below:• Sediment Yield Analysis• Sediment Gradation AnalysisSpecific tasks likely to be conducted with eachof these analyses are outlined below.Technical Analysis Work PlanTask 1 – Hydraulics AnalysisHydraulic Data – HEC-RAS Models. Hydraulicdata will be obtained from modeling preparedfor the effective FEMA Flood Insurance Studiesor new modeling prepared for this study.Specific tasks include the following:• Convert HEC-2 to HEC-RAS Format. Inaddition to simple translation of the fileformat from line-based HEC-2 input towindow-based HEC-RAS input, the inputfiles will be screened for consistent channelbank stationing, extraneous GR points,and ineffective flow areas.([DPSOHRI8QGHU'HVLJQHG6WUXFWXUDO%DQN3URWHFWLRQTypical Scope of Work for Detailed ErosionHazard AnalysisChannel stability, or the potential for lateralmigration, will be evaluated using the followingtypes of analyses:• Interpretation of Geologic Surfaces• Historical Analyses• Field Analyses• Geomorphic Analyses• Hydraulic and Empirical Analyses• Sediment Transport Modeling• Plot Cross Sections. Cross section plotsshowing existing condition 2-, 10-, and100-year water surface elevations will beprepared. If the future conditions flowrates change significantly from existingcondition flow rates, then water surfaceelevations and channel geometry will alsobe plotted for future conditions. Ineffectiveflow areas in cross sections will alsobe documented.• Prepare Plots of Hydraulic Data from HEC-RAS. Plots of top width, hydraulic depth,flow cross section area, maximum flowdepth, mean channel velocity, and otherdata, as needed, will be prepared. At minimum,data from the 100-year event willbe plotted. Additional plots for the 10-year event may be made to estimate conditionsfor the dominant discharge.• Define Channel Subreaches. Plots of HEC-RAS data will be used to define characteristichydraulic reaches based on uniformflow sections, erosion prone sections (narrowwidth, high velocity), choke sections28

(short, constricted reaches), backwater sectionsupstream of choke sections, longitudinalprofile, and potential grade controls.To eliminate potential data scatterbetween cross sections that may masktrends, running averages of hydraulic datawill also be examined to help definereaches. Reach definition will be coordinatedwith results of geomorphic analysesdescribed below.Sediment Gradations. Sediment data for thechannel bed and banks will be collected foruse in hydraulic and geomorphic analyses.Specific tasks include the following:• Sediment Sampling. Samples of bed sedimentsfrom representative locations atapproximately one-mile incrementsthroughout the study reach will beobtained for sieve analysis. In addition,surficial sediment size data will be estimatedusing pebble counts. Bank sedimentdata will be collected from detaileddescriptions and photographic records.These supplemental bed and bank sedimentdata will be collected at cross sectionsspaced approximately 1,000 feetapart throughout the study reach. Allsampling locations will be noted on adetailed exhibit.• Sediment Analysis. Sediment gradationsshowing D90, D84.1, D50, D15.9, and D10will be prepared for each sediment sample.Sediment gradations will be reviewedto verify that reach definitions are supported,and to quantify reach-averagedsediment gradation data. Bed, bank, andoverbank sediment characteristics will becompared and quantified. Armoredreaches will be identified. Size gradationfor HEC-6 model input will be quantifiedfor each subreach. Ranges of size gradationwill be defined so that various scenariosof sediment transport analyses can beconstructed to identify zones of potentialaggradation or degradation, for use insensitivity analyses of HEC-6 modeling.Sediment Yield. Sediment supply to the studyreach will be evaluated to quantify sedimentsources outside the study limits. Specific tasksinclude the following:• Regional Sediment Yield Estimates. Sedimentyield information will be compiledand analyzed from published reports,regional data, and site specific analysis.Regionalized estimates of sediment yieldwill be made for the 2-, 10-, and 100-yearevents. Rough estimates of sediment yieldwill made using pre- and post-developmentconditions.• HEC-6 Modeling. Sediment yield estimateswill be used as HEC-6 inflow boundaryconditions, and will also be used to assesslong-term impacts due to sediment accumulationsin ponding areas or other backwaterareas.HEC-6 Modeling. HEC-6 models of existingand future (alternative) conditions will be preparedto estimate trends in scour and depositionin the study reach. The primary goal ofthe HEC-6 modeling is single event simulationof general sedimentation trends of aggradationor degradation, as reflected in a net sedimentdeficit or surplus. The HEC-6 modelwill be used to assess sediment transport andrelated channel stability for the 10-year, dominantchannel forming discharge, 100-yearflood discharge, and possibly an extreme catastrophicdischarge event. Specific tasksinclude the following:• Base Condition Modeling. HEC-6 modelsfor existing conditions will be prepared,defined as the conditions indicated by theDistrict’s topographic mapping.• Alternatives Modeling. Base conditionHEC-6 models will be modified, as appropriate,as alternatives are evaluated and asfloodplain encroachment alternatives areconsidered.Model development will be based on hydraulicgeometry, with appropriate adjustments,29

NORTH PEORIAAREA DRAINAGE MASTER PLANfrom the HEC-RAS models, sediment yieldestimates, and size gradations as previouslydiscussed, and on the in-flow hydrographs.Initial model development and verificationwill be prepared for a test reach. Upon satisfactoryverification of the proposed modelingtechnique, HEC-6 models will be developed ina similar manner for the other study reaches.• Measure historical channel characteristics(width, sinuosity, etc.).• Plot and compare historical longitudinalprofiles.• Catalogue types of human impacts, plotlocations.Task 2 – Lateral Stability AssessmentInterpretation of Geologic Surfaces. Geologicdata will be used to identify and map recentgeomorphic surfaces near the stream. The ageand position of these surfaces will be used toconstrain the rate of lateral and vertical movementover recent geologic time. Specific tasksinclude the following:• Interpret aerial photographs.• Select soil test pit locations.• Describe soil profiles in soil test pits.• Describe surficial soil characteristics.• Inspect surfaces in field.• Prepare geomorphic mapping.Historical Analyses. Historical data will beused to identify historical patterns of channelbehavior, historical impacts on the stream byhumans, and past rates of lateral and verticalchannel change. Historical data will be usedto set the context for interpretation of existingconditions and prediction of future channelresponse. Specific tasks include the following:• Collect historical maps and topography.• Collect historical aerial and ground photographs.• Digitize historical channel position.• Determine rates and types of channelchange from digitized channel plots.• Prepare time line of watershed and channelchanges.Field Analyses. Field data will be collected toidentify areas of channel instability, quantifychannel and bank characteristics, and documentexisting channel conditions. Specifictasks include the following:• Select index cross section spacing andlocations.• Measure channel characteristics at indexcross sections.• Measure bank characteristics at indexcross sections.• Document existing conditions with photographsand notes.• Perform boulder counts for channel bedsediments.• Describe soil pits excavated in the channelbottom.• Collect sediment samples from the channelbottom for sieve analysis.Geomorphic Analysis. A geomorphic descriptionof the stream characteristics will be preparedto identify appropriate types ofhydraulic and empirical analyses, identifyexisting channel processes, and to predicttrends in future channel behavior. Specifictasks include the following:• Describe regional geologic history.30

• Collect hydrologic data - peak dischargerates, flow duration curve, mean andmonthly flow rates, annual flood series,flood history, climatic data, etc.• Measure channel planform characteristics– channel pattern, meander features, pooland riffle spacing, width, slope, periodicityof narrow and wide reaches.• Identify evidence of paleofloods.• Identify stream analogs on adjacent watersheds.• Evaluate tributary characteristics – drainagearea, slope, sediment type, sedimentyield, flow rates, location of confluence.• Assess impacts of tributaries and tributarysediment load on main channel morphology.• Apply applicable methodologies from theDistrict Piedmont Flood Hazard AssessmentManual (Draft, August 1998) to identifysurface ages and stability.• Perform stream classification.• Define stream reaches.Hydraulic and Empirical Analyses. Engineeringanalyses based on hydraulic data obtainedfrom a HEC-RAS model of the study reachwill be performed to assess the potential forbank erosion and scour. These analyses willbe used to determine whether a stream is stable,whether it is likely to experience bank erosionand/or scour, and what amount of lateralerosion is likely to occur. Where hydraulicdata are required, the computations will bebased on 2-, 10-, and 100-year reach-averagedhydraulic data. Specific tasks include the following:• Revision of HEC-RAS model as describedabove.• Define stream reaches using hydraulicdata and physical stream characteristics.• Determine reach-averaged hydraulic data.• Compute allowable velocity.• Compute scour depths (general, local, andlong-term).• Compute armoring potential & depth toarmor.• Compute equilibrium slope.• Compute reach sediment continuity relationships.• Apply lane relation to stream reaches.• Apply regime equations to stream reaches.• Apply hydraulic geometry relationships tostream reaches.• Apply empirical channel geometry relationshipsto stream reaches.• Apply appropriate regional lateral stabilityprediction methodologies – these mayinclude the AMAFCA Prudent Line,ADWR State Standard 5-96, King County(WA) methodology, Rosgen bank assessmenttechniques, etc.Impacts Analysis. The proposed developmentwill be modeled to assess the potential downstreamand upstream impacts, using the sameprocedures and methodologies listed above.Final ProductThe final product for these tasks will include amap showing the recommended erosion hazardzone boundaries and a final report. Thefinal report will include the following:• Discussion of assumptions and limitationsof methodologies.31

NORTH PEORIAAREA DRAINAGE MASTER PLAN• Discussion of how the results of the variousanalyses were combined with the sedimenttransport modeling results, sandand gravel mining impact assessmentanalysis, and were translated into the erosionhazard zone(s).• Recommendation for future updates ofhazard zone boundaries.• Recommendation for long-term monitoring.• Recommendations for how to modify theerosion hazard boundaries and/or underwhat conditions development can occurwithin the boundaries.Earthen Dams (Stock Tanks)There are a number of stock tanks in the NorthPeoria ADMP study area. Stock tanks typicallyconsist of a non-engineered earthen damof varying height placed across a watercourseto impound stormwater runoff. Vegetationtypically lines the impoundment area. Shoulddownstream areas become urbanized theseearthen dams would present a hazard. TheADWR Dam Safety Section, has legal jurisdictionover dams (embankments) which exceedcertain height and storage limits. ADWRdefines a jurisdictional dam as “either 25 feetor more in height or stores more than 50 acrefeet.If it is less than six feet in height regardlessof the storage capacity or does not storemore than 15-acre-feet regardless of height, itis not jurisdictional”. However even though astructure may not be considered jurisdictionalall dams (embankments) in an urban environmentare considered as having high hazardpotential.The structural integrity and safety of existingstock tanks shall be evaluated to access downstreamimpacts to existing or proposed developmentdue to a dam break. Criteria for thedesign and evaluation of dams can be foundin the book entitled “Design of Small Dams”,third edition (1987, Bureau of Reclamation). Aprofessional engineer registered under thelaws of Arizona, and having proficiency in32civil engineering as related to dam technology,shall conduct evaluation and/or designof an earthen structure.Retention/Detention FacilitiesAll detention/retention facilities incorporatedwithin new developments will be designed toretain the peak flow and volume of runofffrom the 100-year, 2-hour duration stormevent. In the special case when a detentiononly facility is allowed, the requirement toretain the 100-year 2-hour runoff volume maybe waived; however, the post-developmentpeak discharge leaving the site can not exceedpredevelopment conditions. In addition to the100-year event, the effects of more frequentevents (2- and 10- year events) of using adetention only facility must be determined.Standard Retention PracticeGuidelines for the standard practice of retainingthe volume of runoff from the 100-year, 2-hour event can be found in “Drainage Regulationsfor Maricopa County, Maricopa CountyDrainage Design Manual Volume II-Hydraulicsand City of Peoria Infrastructure DevelopmentGuidelines.In-stream, In-Line Detention BasinsIn-stream, in-line detention basins are stormwaterpeak reduction facilities, which could beemployed with authorization, from thereviewing agency, instead of the standardpractices of retaining the volume of runofffrom the 100-year, 2-hour event. The detentionfacility is typically located in a watercourseand functions only to reduce postdevelopment peak discharges. The facilitytypically consists of an encroachment into the100-year floodplain (possibly at a roadwaycrossing), an outlet structure sized to conveyrunoff from frequent events such that the naturalform and function of the watercourse isnot disturbed (sediment transport capabilitiesare maintained), and to impound runoff sufficiently,so that there enough storage providedto reduce peak discharges. The followingguidelines/consideration should beaddressed in the design of such a facility:

• Basin Outlet (Culvert). The basin outletstructure should be sized to convey the100-year existing (pre-development) conditionpeak discharge without disruptingthe sediment transport capabilities of thechannel for the 2-year and 10-year events.If the basin is to be located at a roadwaycrossing (collector and arterial roadways),then at a minimum, the 100-year future(post-development) condition water surfaceelevation must not be more than 0.5feet above the minimum roadway elevationand flow from the 50-year future conditionevent must not overflow theroadway. Other design guidelines for culvertssuch as sediment deposition, scourholes and long-term degradation mustalso be considered and these guidelinesare presented in subsequent sections.• Basin Volume. The storage volume that isrequired to satisfy the discharge requirementsstated above must consider thepotential loss of storage due to sedimentdeposition. Sediment deposition couldpotentially impact the hydraulic operationof the basin ultimately effecting the maximumwater surface elevation. The storagevolume must also be checked in conjunctionwith the embankment height inregard to the jurisdictional classification.Structures that meet jurisdictional damclassification requirements must bedesigned in conformance with ADWRrequirements, and the design must beapproved by ADWR. Jurisdictional classificationis discussed previously in theearthen dam guideline section.• Drain Time. The basin must be drainedwithin 36 hours after the end of the designstorm.• Downstream Impacts. Hydrologic modelingshall be done to determine if thedetainment of runoff or the increased runoffdue to development worsens existingconditions. Modeling of multiple stormfrequencies (at a minimum 2-, 10-, and100-year events) may be required.33In-stream, in-line detention basins should notbe considered for areas that are characterizedby wide flood plains, significant conveyancein the overbank area or multiple channels.The opportunity to enhance stormwater qualityis minimal for an in-stream, in-line detentionbasin and is not recommended forwatersheds in which the land use is high densityor because of the land use, the percent ofimpervious cover is greatly increased unless,stormwater quality concerns have beenaddressed within the watershed draining tothe site.In-stream, Off-line Retention BasinIn-stream, off-line retention basins are stormwaterstorage basins that could be employed,with authorization from the reviewing agency,instead of the standard retention practice. Instream,off-line retention basins function toreduce post development peak discharge andvolume to pre-development values. Majorelements of the facility are channelization andgrade control structures to control the hydraulicsof the flow; inlet works (typically a weir)to direct flow to the basin, low level outlet todrain the basin and a basin of sufficient volumeto reduce peak discharges. The followingguidelines/consideration should beaddressed in the design of such a facility:• Modeling Software. The current recommendedmodeling software is the Corps ofEngineers HEC-RAS v3.0 using theunsteady flow module.• Flow Regime. The flow regime in the watercourseat the lateral weir structure shouldbe subcritical. This may require the channelizationand/or construction of gradecontrol structures. Design guidelines forchannelization must also be consideredand those guidelines are presented in followingsections.• Grade Control Structures. Grade controlstructures or drop structures may berequired to control flow in the naturalchannel to subcritical flow conditions.

NORTH PEORIAAREA DRAINAGE MASTER PLANThe armored length of the structureshould be sufficient to eliminate developmentof a scour hole downstream of thestructure.• Lateral Weir. The lateral weir must besized such that the remaining peak flowand total runoff volume is equivalent toexisting conditions for the design storm.The weir crest elevation must be sufficientlyhigh enough to eliminate potentialbackwater conditions caused by the pondedwater in the basin that would reducethe efficiency of the weir. The potential forscour at the downstream toe of the weirmust be addressed. Sediment depositionwithin the channel at the toe of the weircould significantly alter the hydraulicoperation of the weir and thus the basin.Sediment deposition at the toe of the weirmust be regularly removed.• Drain Time. The basin must be drainedwithin 36 hours after the end of the designstorm. To accomplish this, it may be necessaryto provide a small bleed-off culvert.For this situation, the minimum practicalculvert size should be used. Designguidelines for culverts must also be consideredand those guidelines are presentedin subsequent sections.• Basin Volume. The storage volume that isrequired must consider the potential lossof storage due to sediment deposition.Sediment deposition could potentiallyimpact the hydraulic operation of thebasin ultimately effecting the maximumwater surface elevation. The storage volumemust also be checked in conjunctionwith the embankment height in regard tothe jurisdictional classification. Structuresthat meet jurisdictional dam classificationrequirements must be designed in conformancewith ADWR requirements, andthe design must be approved by ADWR.Jurisdictional classification is discussedpreviously in the earthen dam guidelinesection.• Downstream Impacts. Hydrologic modelingshall be done to determine if thedetainment of runoff or the increased runoffdue to development worsens existingconditions. Modeling of multiple stormfrequencies may be required.• An in-stream, off-line retention basin reducespeak discharge in a watercourse by capturingflow near the peak of thehydrograph and therefore offers minimalopportunities for enhancement of stormwaterquality. Stormwater qualityenhancement deals with managing flow atthe beginning of the ascending limb of ahydrograph. Stormwater quality concernsand best management practices shall beaddressed/employed upstream of thefacility.Floodplain EncroachmentFor most reaches of the major watercourses inthe North Peoria ADMP study area, the floodplainand floodway are coincident due to thechannel and floodplain geometry in the deep,narrow canyons, and the floodway modelingtechniques used for the floodplain delineationstudies. Therefore, in reaches where thefloodway and floodplain are coincident, it isunlikely that any floodplain encroachmentwill occur. The majority of the wider floodwayfringe areas in the study area occur on CaterpillarTank Wash, Twin Buttes Wash, and theTwin Buttes Wash tributaries.Where floodway fringe areas exist in theNorth Peoria ADMP study area, floodplainencroachment should be avoided exceptwhere it meets the low-impact criteria definedbelow. Encroachment that exceeds the lowimpactcriteria should be allowed only whereit can be demonstrated that no long-term orshort-term off-site impacts to channel stabilityoccur, the encroachment is adequately protectedfrom erosion and flooding, and a longtermmaintenance and inspection program isadopted.34

Low Impact Structural AlternativeFor the purposes of the North Peoria ADMP, a“low-impact” development alternative isdefined as any activity within the floodwayfringe or erosion hazard zone that does notsignificantly alter the natural form and functionof the watercourse. The following standardsare proposed to quantify the definitionof “low impact”:• Minimal velocity increases.• The average 10-year velocity in thechannel or overbank should not change(± 0.0 fps).• The average 100-year velocity in thechannel or overbank should not change(increase or decrease) by more than 10percent or one-foot per second (fps),whichever is less.• Minimal water surface elevation increase.• The 10-year water surface elevationshould not change (± 0.0 ft.).• The 100-year water surface elevationshould not increase or decrease by morethan 0.1-foot.• Minimal disturbance of the main channel.• No decrease in the bankfull width of themain channel.• No excavation or deepening of the streambedin the main channel.• No removal of bank vegetation. Wherebank vegetation is temporarily disturbedby construction, it should bereplaced, monitored for health, and irrigatedif required to assure its survival.• No relocation of the low-flow channelwithin the floodplain.• No offsite impacts.35• No erosion, sedimentation, or floodimpacts to adjacent properties withoutwritten permission of affected propertyowners.• Engineering and geomorphic analysisrequired to demonstrate no long-term,short-term, or 100-year off-site impacts.• Preservation of natural landscape characterand habitat within the floodplain.Alternatives that exceed the standards listedabove are not considered low-impact alternatives.Such alternatives may be acceptablemethods of mitigating flood and erosion hazards,if properly engineered.Examples of and design guidelines for a lowimpactstructural alternative are provided inthe North Peoria ADMP, Technical Data Notebook,Attachment 3, Sedimentation Engineeringand Geomorphic Evaluation TechnicalMemorandums, Chapter 5.ChannelizationChannelization is defined as construction ofan engineered channel with bank protectionand grade control structures. Channelizationis generally known to have the followingimpacts on channel stability:• Velocity. Channelization generallyincreases channel velocities. Velocity isexponentially related to sediment transportrate and erosion potential.• Depth. Channelization can increase theflow depth by eliminating the floodplainarea available for conveyance. Increaseddepths result in greater scour depths andhigher velocities.• Discharge. Channelization eliminates thearea available for storage of floodwaterson the floodplain, resulting in decreasedattenuation and increased peak dischargesdownstream. Increased peak dischargesare directly related to increased sedimenttransport rates and erosion.

NORTH PEORIAAREA DRAINAGE MASTER PLAN• Design Standard. Engineered flood controlchannels are typically designed to a 100-year standard. Therefore, damage mayoccur to development adjacent to a 100-year channel (or to the channelizationitself) if flow rates greater than the 100-year event occur. If design dischargeschange due to watershed changes or revisionsto hydrologic modeling standards,retrofit solutions are required to maintainthe same standard of protection.• Design Life. Engineered structures have alimited design life, and require regularmaintenance and inspection, and eventualreplacement.only where it can be demonstrated that nolong-term or short-term off-site impacts tochannel stability occur, that downstreamreaches are adequately protected from erosionand flooding, and a long-term maintenanceand inspection program is adopted. Wherestructural flood control measures are necessary,the design and installation of such structuresshould compliment the environmentand be accomplished with the least disturbanceto the natural setting. Design guidelinesand standards for structural flood controlimprovements are provided in the MaricopaCounty Drainage Design Manual Volume II,Hydraulics and the City of Peoria InfrastructureDevelopment Guidelines.• Equilibrium Slope. Because of the increasein discharge, velocity, and depth, the stableslope is generally flatter than the existingchannel slope, which will cause longtermscour and require grade control toprevent undercutting of bank protection.• Habitat. Channelization typically eliminatesmost of the natural floodplain andstream bank habitat, and requires mitigationmeasures.• Sediment Supply. Bank erosion is animportant source of sediment supply forthe streams in the study area. Constructionof bank protection eliminates thissource of sediment, increasing the likelihoodof erosion of adjacent and downstreamreaches.• Downstream Impacts. Excessive instabilityshould be expected at the outlet of a channelizedreach due to the changes in velocity,sediment supply, and discharge.Depending on the channel geometry, theexpected response can range from lateralerosion and scour to sediment depositionand overbank flooding.Channelization, a structural flood controlmeasure, is not recommended as a developmentalternative in the North Peoria ADMPstudy area. Channelization should be allowedRoadway Crossing Drainage StructuresAt-Grade Crossings“At-grade crossings” typically have only minimalor localized impacts on channel stability.More commonly, the streams impact the atgradecrossing, rather than vice versa. Flowover the at-grade crossing can cause erosion ofthe pavement and subgrade, deposition ofsediment in the road section, and disruptionof traffic flow. Channel stability impacts commonlyobserved near “at-grade crossings”include the following including recommendationsfor mitigation:([DPSOHRIDQ´$W*UDGH&URVVLQJµ• A scour hole often forms on the downstreamside of an “at-grade crossing” dueto acceleration of flow over the hydraulicallysmooth pavement surface andincreased turbulence as flow transitions36

ack at the natural channel bed. In mostcases, formation of a scour hole doesn’timpact stream reaches located far from the“at-grade crossing”, however the developmentof a scour hole could undermine the“at-grade crossing”, leading to failure ofthe facility. Upstream and downstreamcut off walls shall be designed for at gradecrossings.• An “at-grade crossing” of a watercoursereach which is experiencing degradationwill ultimately function as a grade controlstructure. Until equilibrium is achieved,down stream degradation will continueincreasing the drop immediately downstreamof the “at-grade crossing”. Longterm degradation shall be considered indetermining the depth of cut off walls.If the “at-grade crossing” is constructed at anelevation slightly above the natural channelbed, deposition will occur upstream of thecrossing. Deposition leads to expansion of thefloodplain, and may increase the risk of avulsionsand accelerate formation of the downstreamscour hole. The minimum elevation ofan “at-grade crossing” shall not be higherthan the existing channel invert.stream properties. The impacts of undersizedculverts on channel stability include the followingincluding recommendations for mitigation:• Sediment Deposition. Much of the stream’ssediment load will be deposited in theheadwater pool at the culvert inlet. Thevolume of sediment deposited depends onthe culvert capacity relative to the discharge,the duration of the ponding condition,the geometry of the ponding area,and the size of the sediment in transport.Sediment deposition decreases channel(and culvert) capacity, increases the potentialfor overbank flooding and avulsions,and requires maintenance to restore naturalconditions. Culvert rise (height) at aminimum should be as high as the averagemain channel bank height. In theevent of width and height limitations dueto natural conditions, the structure doesnot convey the design event, increasingthe height dimension or providing reliefculvert structures in the overbank areasshould be considered before increasing thewidth. Culverts that do not obstruct themain channel will have less frequentimpacts on channel stability.“At-grade crossing” is not a recommendedwatercourse/roadway crossing in the City ofPeoria.CulvertsThe design of culvert structures takes intoconsideration public safety, long term functionand maintenance, and impacts to the naturalchannel form and function. Typically, theimpact of culvert crossings on a watercoursesystem is primarily a function of their size inrelationship to design discharge, natural channeland floodplain morphology, cloggingpotential, sediment transport capacity andscour potential.Undersized (relative to natural channel andfloodplain geometry) culverts and culvertsthat create headwater ponding can have detrimentalimpacts to both upstream and down37• Floodplain Encroachment. A culvert is aform of floodplain encroachment, with thesame types of encroachment impactsdescribed in the floodplain encroachmentdiscussion above.• Scour Hole. A scour hole may form at theculvert outlet due to accelerated velocitythrough the culvert, discharge of sediment-deprivedwater, and turbulence atthe culvert/natural channel interface.Design of culvert structures shall includean evaluation of the scour potential at theoutlet of the structure and provisions forchannel protection at the outlet shall beprovided.• Long-term Degradation. Where a significantpercentage of the sediment load isdeposited upstream of a culvert due to

NORTH PEORIAAREA DRAINAGE MASTER PLANheadwater ponding, discharge of clearwater may result in degradation downstreamuntil the channel slope adjusts tothe new sediment supply. Culverts shallbe designed so that the disruptions to thenatural sediment transport capabilities ofthe wash are minimized.BridgesBridges that span the floodplain typicallyhave no measurable impact on channel stability,as evidenced by the channel conditionsobserved at the Beardsley Canal flumes overCaterpillar Tank Wash and Twin Buttes Washwithin the North Peoria ADMP study area.Bridges with narrow openings are functionallylike a culvert, and have the impacts onchannel stability described above.([DPSOHRI+HDGZDOO&RQVWUXFWHGRI1DWLYH0DWHULDOOversized (relative to natural channel andfloodplain geometry) culverts structures,which increase the width of the natural channelin order to minimize the height or depth ofponding, can also have detrimental impacts toboth upstream and down stream properties.The impacts of oversized culverts on channelstability include the following:• Long-term Aggradation. Increasing thenatural width of a channel to accommodatea culvert structure would change thesediment transport capacity of the channel.During frequent events or eventslesser than the design capacity of the culvertstructure sediment would be depositedin the section of channel that has beenwidened. Accumulation of sedimentwould decease both the capacity of thechannel and the capacity of the structureultimately resulting in flooding impacts toadjacent properties. Culvert span (width)should be as wide as the main channel(top of left bank to top of right bank)where channels are well defined. Culvertsthat do not obstruct the main channel willhave less frequent impacts on channel stabilitythan culverts that block the mainchannel.38([DPSOHRID%ULGJH6WUXFWXUH&ORJJHGZLWK6HGLPHQWBased on theirlikely impactson channelstability, thefollowingguidelines forroadwaycrossingdesign are recommendedfor watercourses in the NorthPeoria ADMP study area:• Bridges are preferable to culverts. Bridgestypically have less impact on channel stabilitythan culverts due to the wider openingand decreased likelihood of headwaterponding.• Bridge span (width) at a minimum shouldbe as wide as the channel or floodway limits,preferably as wide as the floodplain orerosion hazard zone where channels arewell defined. Bridges that do not obstructthe main channel will have less frequentimpacts on channel stability than culvertsthat block the main channel.• Where braided or multiple channels exist,relief structures outside of the main channelshould be provided to maintain overbankflow paths, preserve overbankconveyance, and prevent floodplain sedimentation;instead of widening one of themultiple channels to provide conveyanceof the design event at one location.• Bridge crossings should be regularlymaintained and inspected to identifypotential problems and impacts to channel

stability, and to assure structure performance.• The need for erosion protection should beevaluated at all bridge crossings of watercourses.Utility CrossingsUtility crossings, if properly constructed, haveno inherent impact on channel stability sincethey are typically buried beneath the channelor extended overhead. Direct impacts onchannel stability can occur during utility constructiondue to disturbance of bank andfloodplain vegetation. Where vegetation isremoved, the underlying soils are more vulnerableto erosion and scour. If floods occurbefore the vegetation is reestablished, erosionof the construction alignment may occur andinitiate erosion of adjacent channel reaches.The following guidelines for utility constructionin the floodplain and erosion hazard zoneare recommended:• Bank and floodplain vegetation removedor damaged during construction shouldbe replaced immediately. Irrigation,inspection, and maintenance may berequired to assure survival of the replacementvegetation.• Underground utilities should be buriedbelow the 100-year general scour depth inthe main channel plus the long-term scourdepth. Utility lines have been damageddue to exposure by long-term scour onnumerous streams in Arizona.• Where the potential for lateral movementexists, underground utilities should beburied at the same depth in the overbankareas or erosion hazard zone as in themain channel, to prevent exposure aftermovement of the main channel.• Support structures for overhead utilitiesshould not be located within the floodplainor erosion hazard zone. Where thelength of the span requires that support39structures be constructed within the floodplainor erosion hazard zone, the structuresshould be designed using the 100-year general scour plus long-term scour inthe main channel burial depth. No structuresshould be placed in the main channel.Aesthetic Design GuidelinesAesthetic guidelines are developed as a tool tobe used by planners and designers to incorporateaesthetic quality into their design that issensitive and consistent with the natural environment.As part of the North Peoria ADMP,landscape character themes are developedthat could be incorporated into the design offlood control management alternatives. Specificthemes developed are a Mountain Themewith a Mining Theme Overlay, and a PlainsTheme with a Native American or RanchingTheme Overlay. Design guidelines and examplesare present in the North Peoria ADMP,Technical Data Notebook, Attachment 4,Landscape Character and Visual AssessmentReport. The following general design guidelinesare offered:Structural Erosion Protection MeasuresStructural erosion protection measures canconsist of a variety of engineered materials.Most common types of engineered materialsused in Maricopa County are rock filled wirebaskets (gabion mattress, Reno Mattress),gunite and soil cement. Structural erosionprotection measures could be aestheticallyenhanced by designing them to blend in color,texture and form with the surrounding environmentand desired landscape charactertheme. Treatments include selection of materialto provide the desired color and texture,artificially coloring material, and treatment offreshly excavated native material with Eoniteor a similar aging product.ChannelsChannel alignments and side slopes should beconsistent with natural channels in the area.Alignments should be sinuous and side slopesshould vary in the angle of slope.

Drainage StructuresNORTH PEORIAAREA DRAINAGE MASTER PLANLandscape character themes could be incorporatedinto the design of bridge and culvertheadwalls. Figure 22 and Figure 23 depictsome possible landscape character themes thatcould be incorporated into a roadway drainagestructure.MAINTENANCE PLANA maintenance plan shall be developed for allstructural type improvements. The plan willdocument required maintenance to beprovided by the owner/owners of structuraltype drainage improvements. The plan shallinclude the following discussions asapplicable:• Type of facility.• Owner of facility.• Required maintenance activity.• Vegetation maintenance.• Bank protection maintenance.• Grade control maintenance.• Removal of debris and sediment fromstructures.• Required permits for maintenance activity.• Required inspection/monitoring activity.• Schedule for inspection and monitoringactivity.• Required agency notification.MAINTENANCE PLANThe North Peoria ADMP presents watercourseand stormwater storage flood controlmanagement alternatives. For this plan to besuccessful, a monitoring and maintenanceplan is required that address the overall nonstructuralgoals as well as the specific elementsof potential structural and low-impactstructural measures. The maintenance planestablishes monitoring and maintenance criteriaand inspection time frames that should be40implemented to sustain the goals of the plan.The maintenance plan is presented in theNorth Peoria ADMP Technical Data Notebook.CONSIDERATIONS FOR EXISTINGSTRUCTURES IN FLOOD HAZARDAREASGENERALWithin the North Peoria ADMP study area,one permanent residential structure was identifiedwithin a flood and erosion hazard zone.The structure is located within UnincorporatedMaricopa County, approximately 0.6miles north of Happy Valley Road along 115thAvenue alignment in the Twin Buttes Washfloodway. Flood Insurance Study work maps[Flood Insurance Study for Caterpillar Tankand Twin Buttes Washes From Agua FriaRiver to CAP Canal Maricopa County, Arizona,(Flood Control District of MaricopaCounty, 1991)] indicate that the structure wasbuilt prior to the original floodplain delineationof Twin Buttes Wash.As part of the North Peoria ADMP, channelimprovements that would mitigate impacts tothe alignment of 115th Avenue and to the residentialstructure from a 100-year runoff eventwere evaluated. Improvements evaluatedconsist of a channel, side slope protection consistingof rock-filled wire-tied baskets and an11 cell 10-foot by 4-foot concrete box culvert.The cost estimate for construction of the channelimprovements (not including land costs) isestimated at $1,299,137.Currently Maricopa County has no capitalimprovement plans to provide roadway/channel improvements along the 115th alignmentbetween Happy Valley and JomaxRoads. City of Peoria personal related thatshould the City of Peoria annex the area, anyimprovements would be funded through animprovement district. There are plans being

developed for the Estrella Roadway, whichwill cross the alignment of 115th Avenue, andTwin Buttes Wash approximately 1000 feetdownstream of the subject structure, howeverthere are no improvements proposed thatwould mitigate flooding to the structure or tothe alignment of 115th Avenue.OPTIONSUnder current Maricopa County floodplainregulations the existing structure could not berebuilt if, due to flooding, fire, or some othercatastrophic event, the structure suffereddamages of greater than 50 percent of itsappraised value. In addition, the current orfuture owners could not obtain building permitsfor new structures. A possible option toaddress the problem is to recommend theproperty be considered for a voluntary acquisitionor on-site relocation program managedby the District. If the home qualifies for theprogram, the homeowner would have theoption of selling their parcel to the Districtand having the structure removed from thesite so that the land could return to its naturalor near natural state or, if there are areas of theparcel outside the floodway and erosion hazardzone, and the homeowner wishes to movetheir home, the homeowner would have theoption of relocating the residence on-site, butoutside the high hazard areas.41

NORTH PEORIAAREA DRAINAGE MASTER PLANGLOSSARY100-year stormA rainfall event that has a 1% chance of occurringor being exceeded in any given year.aggradationA rise in the channel bottom elevation due toan accumulation of sediment over time.avulsionAn avulsion occurs when a watercourse channelmigrates laterally to another positionwithin the natural floodplain. Lateral channelmigration and head cutting are contributingelements to the avulsion process.braidedA braided watercourse is one flowing in severaldividing and reuniting channels resemblingthe stands of a braid. Avulsion andlateral migration processes contribute to thedevelopment of a braided watercourse.erosionThe group of processes whereby rock and/orsediment deposits are loosened and/or dissolvedand removed from their original locations.existing conditionsPhysical conditions within a watershed orwatercourse at the time of evaluation.100-year floodplainA special flood hazard zone that is defined bythe area along a wash that gets wet and carrieswater during a 100-year flood. Criterion todefine the 100-year floodplain is establishedby the FEMA.floodwayThe floodway is that portion of the floodplainreserved by FEMA for the conveyance offloodwaters during a 100-year flood. Buildingsand/or structures that would obstructflow are not allowed within the floodwayboundaries.channelThe deepest portion of a watercourse throughwhich the majority of runoff is conveyed.Braided watercourses will have multiplechannels.computer modelsComputer models developed as part of thisstudy are developed to model hydrologic andhydraulic conditions. The models simulate astorm event (such as the 100-year storm) andestimates how much runoff will be generatedfrom a given area (hydrology) and how deepand fast the runoff will move (hydraulics)within a watercourse draining the given area.degradationA deepening of a channel over time or in a singlestorm event due to erosion processes.ephemeral watercourseA watercourse or potion of a watercourse thatflows only in direct response to rainfall.floodway fringeThe floodway fringe is the portion of the 100-year floodplain located adjacent too and outsideof the FEMA 100-year floodway. UnderFEMA regulations development within thefloodway fringe is permissible providing certaincriteria are met.floodplain encroachmentFloodplain encroachment is defined by developmentactivity that occurs within the floodwayfringe. The collective impact of thedevelopment activity can not increase the 100-year water surface elevation over FEMA 100-year floodway water surface elevations.Floodway water surface elevations are up toone foot higher than floodplain elevations.future conditionsFor this study future condition is the proposedphysical condition of the watershed based onthe City of Peoria’s General Plan.42

gabion mattressA gabion mattress is a structural form of erosionprotection. A gabion mattress consists ofwire baskets filled with rock.geomorphologyThe study of landforms and the physical processesthat form the land surface.guniteA structural bank/channel stabilization measureconsisting of cement, sand and water.soil cementA type of structural channel stabilizationconsisting of cement and native materials.watercourseFor the purpose of this study a watercourse isdefined as a natural drainage way defined bythe 100-year floodplain limits and the erosionhazard zone.hydraulicsFor purpose of this study, hydraulics is howstormwater moves through a watercourse.Through hydraulic evaluations, depth, velocity,width and energy of stormwater flowwithin a watercourse are estimated.hydrologyFor the purpose of this study, hydrology is theestimation of the magnitude of runoff from arainfall event within a given watershed. Typicallyrunoff is that portion of rainfall that doesnot instormwaterfiltrate into the soil.lateral channel migrationThe horizontal movement of a channel withinthe natural floodplain by erosive processesdefines lateral channel migration.paleofloodA flood event at a given time in the geologicpast.riparianperennial flowWatercourses or a portion of watercoursesthat flow year around.scourErosion due to the mechanical process ofwater removing earthen material from a channelbottom or banks.sedimentationThe natural process of flowing waters depositingsoil, sand, gravel, cobbles and boulderswithin a channel and associated natural floodplain.43

NORTH PEORIAAREA DRAINAGE MASTER PLANREFERENCESArizona Department of Water Resources, Engineering Division, Flood Management Section,September 1996, State Standard for Watercourse System Sediment Balance (SS 5-96).Arizona Department of Water Resources, Engineering Division, Flood Management Section, July1996, Requirements for Floodplain and Floodway Delineation in Riverine Environments (SS 2-96).Arizona Revised Statues Title 48, Chapter 21Bureau of Reclamation, 1987, Design of Small Dams.City of Peoria, Arizona, approved July 6, 1993 Zoning Ordinance, City of Peoria, Arizona.City of Peoria, September 1995, Hillside Development Overlay District Zoning and Ordinance.City of Peoria, Arizona, August 1, 1998, Infrastructure Development Guidelines, Interim.City of Peoria, August 1999, Peoria Desert Lands Conservation Master Plan.City of Peoria, January 1999, River Master Plan.City of Peoria, January 1999, Trails Master Plan, prepared for the City of Peoria.City of Peoria, November 1999, Lake Pleasant/North Peoria Area Plan.City of Peoria, June 15, 2001, General Plan.Flood Control District of Maricopa County, August 1998, Piedmont Flood Hazard Assessment Manual.Flood Control District of Maricopa County, 1991, Flood Insurance Study for Caterpillar Tank andTwin Buttes Washes, from Agua Fria to CAP Canal, Maricopa County, ArizonaFlood Control District of Maricopa County, 2001, Agua Fria Watercourse Master Plan.Flood Control District of Maricopa County, March 2002, North Peoria Area Drainage Master Plan,Technical Data Notebook.Maricopa Association of Governments, 1995, Desert Spaces Plan.Maricopa Association of Governments, June 2000, Desert Spaces - Environmentally Sensitive DevelopmentAreas.Maricopa County, August 21, 1993, Highway 74 Scenic Corridor Overlay (Zoning Ordinance XXII-F-1).44

Maricopa County, August 21, 1993, Hillside Development Standards (Zoning Ordinance Article XX-II-A).Maricopa County, Arizona, 1996 Drainage Design Manual for Maricopa County, Volume 2,Hydraulics.Maricopa County, Arizona, 1997, Comprehensive Plan-Maricopa County, Eye to the Future 2020.Maricopa County, Arizona, December 6, 2000, White Tank/Grand Avenue Area Plan.Maricopa County Parks and Recreation Department, On-Going, Proposed Maricopa CountyRegional Trail System.USDA Forest Service, 1989, Landscape Character Types of the National Forest in Arizona and NewMexico.USDA Forest Service, 1995, Landscape Aesthetics Handbook #701.45

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100-year W.S. ElevationBufferFEMA 100-year FloodwayFEMA 100-year FloodplainErosion Hazard ZoneBufferBackfill & RevegetationRevegetated Slope100-year W.S ElevationBackfillBuried Back ProtectionLow Flow ChannelCut BankOffset Bank Protection(Buried rock trench option)100-year Floodway100-year FloodplainArea Removed fromErosion Hazard ZoneErosion Hazard ZoneArea Removed fromErosion Hazard Zone

100-year W.S. ElevationBufferFEMA 100-year FloodwayFEMA 100-year FloodplainErosion Hazard ZoneArea Removed from 100-year FloodplainMaintenance RoadBank ProtectionArea Removed from Erosion Hazard Zone100-year W.S. ElevationArea Removed from100-year Floodplain typ.Area Removed from Erosion Hazard ZoneFEMA 100-year FloodwayFEMA 100-year FloodplainErosion Hazard ZoneMaintenance Road typ.Bank ProtectionArea Removed fromErosion Hazard Zone

NORTH PEORIA AREA DRAINAGE MASTER PLANFIGURE 20IN-STREAM, IN-LINE DETENTION

NORTH PEORIA AREA DRAINAGE MASTER PLANFIGURE 21IN-STREAM, OFF-LINE RETENTION

100-year W.S. ElevationFEMA 100-year FloodplainFEMA 100-year Floodway100-year W.S. ElevationFEMA 100-year FloodplainFEMA 100-year Floodway