Powerline Plan and Environ. Assessment Jan. 2013 - Flood Control ...

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Powerline Flood Retarding Structure Pinal County, AZ Draft Supplemental Watershed Plan and Environmental Assessment vee-shaped incised drainages that carve into them. The drainages create finger-like patterns overlaying the flat surface of the ground plane. During the Site Analysis verification site visit, a significant amount of water was observed in the low flow areas within the reservoirs upstream of the dams from a storm event. The dams and associated reservoirs and low flow channels have altered the historic drainage pattern in a way that allows pooling to occur immediately upstream of the dams. This altered drainage pattern created an ideal environment for the formation of a unique mesquite bosque ecosystem immediately upstream of the dams. Careful consideration should be given to future development of land and resource goals and objectives, as well as desired recreation and open space functions to preserve this unique ecosystem to the extent feasible as part of a larger regional habitat corridor. The preservation of the mesquite bosque should also be considered for its potential to serve as an open space amenity and attraction. The significant stand of trees should be considered vegetation of high scenic quality. The upstream portion of the watershed to the east of the PVR dams is primarily alluvial desert. Land use is predominantly undeveloped land with some urban development occurring along the study area fringes north and west of the PVR dams. In these areas, land use includes agriculture, industrial, and low density housing. The landscape on the upstream side of the dams is unusual for its native Sonoran Desert scrubland context due to the lushness provided by the mesquite bosques and pooling in the low flow reservoirs. The visually dominant dams adjacent to the mesquite bosques constitute another key component of the landscape character. According to the Sponsor’s descriptions of methods for providing flood protection for use in scenery and recreation resource assessments of context sensitivity, the structural method employed in this context can be described as a “semi-hard structural method.” While the primary objectives of the Sponsor’s Policy for Landscape and Aesthetic Treatment of Flood Control Facilities are the preservation of natural landscapes and protection of local community character, flood protection methods vary in their relative ability to complement or enhance the visual character of the landscape setting and achieve context sensitivity. The panoramic views provided from the tops of the embankments to the surrounding mountains are spectacular. Sponsor’s policy is to not allow public access onto the dams. However, where possible, views to the Superstition Mountains and Tonto National Forest to the northeast, views to the Usery and Goldmine Mountains to the northwest, and views to the San Tan and distant mountains to the south should be preserved and focused. The view sheds as described in this section may be important to traditional (cultural) landscapes. Consultation with appropriate tribes for proposed project input on traditional cultural properties has been initiated. USDA- NRCS Page 4-15 January 2013 Kimley-Horn and Associates, Inc.
Powerline Flood Retarding Structure Pinal County, AZ Draft Supplemental Watershed Plan and Environmental Assessment 5.0 ALTERNATIVES 5.1 GENERAL The Powerline FRS is one of three earthen flood retarding structures (Vineyard Road FRS and Rittenhouse FRS are the other two) located east of the Central Arizona Project (CAP) canal. The three structures were originally designed by the NRCS to operate as an integrated system as the principal spillways at Powerline FRS and Vineyard Road FRS both discharge into a common channel – the Powerline Floodway. The Rittenhouse FRS principal spillway discharges into the Vineyard Road FRS flood pool. The result is that all three principal spillways eventually flow into the Powerline Floodway. The “Powerline, Vineyard Road, and Rittenhouse FRSs Rehabilitation or Replacement Project” (Project) was initiated to formulate alternatives to mitigate identified dam safety deficiencies at the three dams. One of the objectives in the formulation of alternatives for the three dams was to maintain the integrated operational relationship of the three dams (or alternatives) to discharge to the Powerline Floodway. This Supplemental Watershed Plan and Environmental Assessment (Plan/EA) presents the alternatives evaluated and preferred alternative for Powerline FRS. The Powerline FRS is a structural plan element of the Apache Junction-Gilbert Watershed Work Plan. A separate Supplemental Watershed Plan/EA has been prepared for the Vineyard Road FRS and Rittenhouse FRS as these two dams are structural elements of the Williams-Chandler Watershed Work Plan. This section describes the development and formulation of planning alternatives for the Powerline, Vineyard Road, and Rittenhouse Flood Retarding Structures Rehabilitation or Replacement Project. The formulation of alternatives was developed to meet Sponsor (District) goals and to mitigate or eliminate identified inadequacies associated with the structures. The primary project goal as defined by the District is to develop an implementable project designed to maintain or improve upon the level of flood protection currently being provided by the PVR FRSs and associated features for the new PVR Project life of 100-years. The Project must meet both District and NRCS requirements for flood protection and must meet District, NRCS and Arizona Department of Water Resources requirements for dam safety. A secondary project goal is to feasibly minimize the future project “footprint”, the overall land area encompassed by the future flood control features and flood conveyance and flood impoundment land areas, and to identify other potential land uses and activities that are compatible with the safe and proper function, operation and maintenance of the future PVR Project and associated features. 5.2 FORMULATION PROCESS PRELIMINARY ALTERNATIVES The District, NRCS, and Consulting team held three preferred alternatives selection workshops. These workshops were held on December 8, 2010, April 26, 2011, and April 19, 2012. The purpose of the workshops was to discuss and screen the formulated alternatives and measures. The results of the workshop meetings are summarized in the memorandums for those workshops. Several of the alternatives and measures were screened and determined by the workshop attendees (consisting of the District, NRCS, Arizona State Land Department, and other stakeholder representatives) to be unreasonable because the alternatives were not technically feasible, estimated costs were too excessive compared to other alternatives, an alternative was incorporated or USDA- NRCS Page 5-1 January 2013 Kimley-Horn and Associates, Inc.
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Powerline Flood Retarding Structure
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Signal Butte Rd Meridian Rd Ironwoo
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POWERLINE FRS TYPICAL SECTION
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Ironwood Rd Gantzel Rd Mountain Vie
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Figure 22 Figure 21 - Conceptual Mu
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