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

More documents

Recommendations

Info

Powerline Flood Retarding Structure Pinal County, AZ Draft Supplemental Watershed Plan and Environmental Assessment to an approximately 8-foot-deep by 10-foot-wide channel. The channel is unlined and there is an approximately 5-foot-high earthen embankment on the west side of the channel. The diversion channel extends from the school properties to Baseline Road, crossing under U.S. Highway 60 through two 6-foot-high by 10-foot-wide concrete box culverts and crossing under Baseline Road through three 4-foot-diameter corrugated metal pipes. The channel flows along the east side of the Apache Creek Golf Course between U.S. Highway 60 and Baseline Road. The channel within this area appears to be engineered and ranges from approximately 10 to 20 feet in width and 5 to 15 feet in depth. The banks typically have slope ratios of 1H:1V to 1.5H:1V. In general, the bank on the east side of the channel is higher than the bank on the west side of the channel, and the bank on the east side of the channel is cut by a number of erosion gullies. An exhibit of the Powerline North Diversion Channel is provided in Appendix C as Figure C-8. 2.3.6 POWERLINE FLOODWAY Outflow from the Powerline, Vineyard Road and Rittenhouse FRSs eventually flow into the Powerline Floodway. The Floodway is approximately 8.5 miles in length, extending from the principal outlet of Powerline FRS to the East Maricopa Floodway (EMF) near the northwest corner of the Williams Gateway Airport. The Powerline Floodway carries flows from the principal spillways of both Powerline FRS and Vineyard Road FRS to the EMF. 2.4 INADEQUACIES OF STRUCTURE The Arizona Department of Water Resources (ADWR) conducts inspections of jurisdictional dams throughout the state. Powerline and Vineyard Road FRSs were inspected on January 30, 2012 and Rittenhouse was inspected on January 31, 2012. ADWR issued a Notice of Safety Deficiency letter for Powerline FRS. The following items were listed as Safety Deficiencies for Powerline FRS: • Foundation Concerns • Questionable Adequacy of Central Filter ADWR identified one maintenance action item for the Powerline FRS. ADWR noted that the action item as removing rodent burrowing on the structure in a timely manner. ADWR has reviewed the size and hazard potential classifications for the dam. The classification has not changed from intermediate size and high hazard potential. 2.4.1 FOUNDATION CONCERNS In May 2007, an earth fissure was identified in close proximity to the downstream toe of the dam. In light of the proximity of this earth fissure to the Powerline embankment, and the presence of other documented earth fissures in the general vicinity of the dam, ADWR continues to classify Powerline FRS as being in an “unsafe, non-emergency, elevated risk” condition. As such, the Powerline FRS is one of ADWR’s highest priority unsafe dams in the state. On February 28, 2011, ADWR approved the District’s permit application for the interim mitigation of fissure risk. USDA- NRCS Page 2-4 January 2013 Kimley-Horn and Associates, Inc.
Powerline Flood Retarding Structure Pinal County, AZ Draft Supplemental Watershed Plan and Environmental Assessment 2.4.2 QUESTIONABLE ADEQUACY OF CENTRAL FILTER In a May 8, 2008 ADWR Inspection Report for the Powerline FRS, it was noted that during a recent geotechnical investigation that involved excavation of a shallow trench that exposed the upper portion of the central filter, there were similarities between the filter materials and the compacted embankment soils. Photo-documentation of this condition is presented in Appendix E of the report entitled “Earth Fissure/Ground Subsidence Instrumentation Installation Report and Monitoring Plan” (AMEC 2007). Noted similarities included “soil stiffness that supported vertical trench walls and cracking that extended into the central filter material.” ADWR notes that this observation is contrary to the standard of practice for granular filter design wherein the filter should be free-flowing and self-healing. The April 13, 2012 ADWR inspection letter noted that it was ADWR’s understanding that the adequacy of the filter will be further investigated during the overall rehabilitation design. 2.4.3 UPDATED HYDROLOGIC/HYDRAULIC INVESTIGATIONS Updated hydrologic/hydraulics (H/H) investigations and studies were conducted during the planning study for the Powerline FRS. These studies evaluated the operational response of the structure and principal and auxiliary spillways for existing land use and future land use conditions for multi-frequency events (2-yr through 500-yr). The investigations completed a probable maximum precipitation/probable maximum flood (PMP/PMF) study to determine a planning level recommendation for the PVR structures for the inflow design flood (IDF). The results indicate that the 6-hr PMF is the more conservative over the 24-hr and 72-hr events. The study recommended a reduction of the planning PMP/PMF to approximate an anticipated reduction of the PMP should a future site specific PMP study be conducted for the three PVR watersheds. The updated H/H evaluations also conducted NRCS SITES modeling for the three dams to determine the principal spillway hydrograph (PSH), stability design hydrograph (SDH), and the integrity or freeboard hydrograph (FBH). The SITES study included an allowable stress evaluation of the earth lined spillways and a breach analyses. The results for Powerline FRS indicates that: • Overtopping of the dam crest during the existing and future conditions 6-hour PMP, • Existing conditions principal spillway hydrograph draw down is longer than 10 days (14.4 days), • Future conditions principal spillway hydrograph draw down is longer than 10 days (14.8 days), • Auxiliary spillway erodes during the existing and future conditions stability design hydrograph, and • Auxiliary spillway breaches during the existing and future conditions freeboard design hydrograph. USDA- NRCS Page 2-5 January 2013 Kimley-Horn and Associates, Inc.
Page 1 and 2: DRAFT SUPPLEMENTAL WATERSHED PLAN A
Page 3 and 4: Powerline Flood Retarding Structure
Page 15: Powerline Flood Retarding Structure
Page 67 and 68:
Powerline Flood Retarding Structure
Page 69 and 70:
Page 71 and 72:
Page 73 and 74:
Page 75 and 76:
Page 77 and 78:
Page 79 and 80:
Page 81 and 82:
Page 83 and 84:
Page 85 and 86:
Page 87 and 88:
Page 89 and 90:
Signal Butte Rd Meridian Rd Ironwoo
Page 91:
POWERLINE FRS TYPICAL SECTION
Page 95 and 96:
Ironwood Rd Gantzel Rd Mountain Vie
Page 97 and 98:
Figure 22 Figure 21 - Conceptual Mu
Page 99 and 100:
K:\PHX_WaterResources\91131019\CADD
Page 101 and 102:
K:\PHX_WaterResources\91131019\CADD
Page 103 and 104:
Exhibit A-2 - Emergency Spillway Di
Page 105 and 106:
Price Price Price Dobson Alma Schoo
Page 107 and 108:
Page 109 and 110:
Page 111 and 112:
Page 113 and 114:
Page 115 and 116:
Page 117 and 118:
Page 119 and 120:
Page 121 and 122:
Page 123 and 124:
Page 125 and 126:
Page 127 and 128:
Page 129 and 130:
Page 131 and 132:
Page 133 and 134:
Page 135 and 136:
Page 137 and 138:
Page 139 and 140:
Page 141 and 142:
Page 143 and 144:
Page 145 and 146:
Page 147 and 148:
Page 149 and 150:
Page 151 and 152:
Page 153 and 154:
Page 155 and 156:
Page 157 and 158:
Page 159 and 160:
Page 161 and 162:
Page 163 and 164:
Page 165 and 166:
Page 167 and 168:
Page 169 and 170:
Powerline, Vineyard Road and Ritten
Page 171:
show all

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

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?