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 (6,237 acres) with the Arizona State Land Department (ASLD), which includes the FRSs, flood pool areas, Powerline Floodway, and maintenance access roads. This SNA includes the project limits and extends to the TNW via the Powerline Floodway, the East Maricopa Floodway (EMF) and Gila River. 6.5.2. Lost Dutchman Heights On June 29, 2010, the Corps determined that the 7,700-acre Lost Dutchman Heights (LDH) project (Corps file No. SPL-2008-00674-SDM) and the ephemeral washes within the project area did not have a significant nexus to the TNW (Gila River) and issued an Approved Jurisdictional Delineation that stated there are not waters of the U.S. within the project area. That project and the current PVR project overlap and much of the information in the LDH submittal is also applicable to the PVR project. 6.5.3. Purpose of Significant Nexus Analysis The purpose of the significant nexus analysis was to assess the flow characteristics and functions of the tributaries within the project area to determine if they significantly affect the chemical, physical, and biological integrity of the TNW. For each of the following situations, a significant nexus exists if the tributary has more than a speculative or insubstantial effect on the chemical, physical and/or biological integrity of the TNW. Considerations when evaluating significant nexus include, but are not limited to the volume, duration, and frequency of the flow of water in the tributary and its proximity to the TNW, and the functions performed by the tributary. It is not appropriate to determine significant nexus based solely on any specific threshold of distance (e.g. between a tributary and the TNW). 6.5.4. Conclusion of Significant Nexus Analysis The low frequency of flow events in combination with the peak discharges volumes from the project area ranging from approximately 80 to 150 cfs, the likelihood of flow from the project area reaching the TNW is low. Therefore, the project waters have a low capacity to carry pollutants or flood waters to the TNW, or to reduce the amount of pollutants or flood waters reaching a TNW. Furthermore, the project waters have a low capacity to transfer nutrients and organic carbon that support downstream food webs. The combined peak discharge from the project area (244 cfs) is insignificant in comparison to peak discharge in the TNW (75,883 cfs), and represents 0.3% of the peak flow in the TNW. Therefore, no significant nexus exists with regard to physical and chemical integrity. The project area provides no habitat for aquatic organisms in the downstream TNW, though ponding areas may provide habitat for several invertebrate species. The only listed species overlap is for the Sonoran desert tortoise which could use ephemeral washes and the adjacent uplands as dispersal habitat. The potential for the project area to contribute biologically to the TNW downstream is unlikely and inconsequential. Furthermore, the project waters have a low capacity to transfer nutrients and organic carbon that support downstream food webs. Therefore, no significant nexus exists with regard to biological integrity. The waters analyzed do not significantly affect the chemical, physical, and biological integrity of the downstream TNW and therefor appear not to be jurisdictional waters of the U.S. The SNA was submitted to the Corps for concurrence in June 2012. The Corps has submitted the SNA package to the U.S Environmental Protection Agency in January 2013. As of the date of this report concurrence has not been received. USDA- NRCS January 2013 Kimley-Horn and Associates, Inc. Page 51
Powerline Flood Retarding Structure Pinal County, AZ Draft Supplemental Watershed Plan and Environmental Assessment 7. REFERENCES AMEC Earth & Environmental, Inc. “Powerline, Vineyard Road and Rittenhouse Flood Retarding Structures Rehabilitation or Replacement Project - Final Initial Subsidence and Earth Fissure Report.” August, 2010. AMEC Earth & Environmental, Inc. “Powerline, Vineyard Road and Rittenhouse Flood Retarding Structures Rehabilitation or Replacement Project - Final Geotechnical Summary and Analysis Report.” August 2010. AMEC Earth & Environmental, Inc. “Powerline, Vineyard Road and Rittenhouse Flood Retarding Structures Rehabilitation or Replacement Project - Final Filter Alternatives Memorandum.” May 2012 AMEC Earth & Environmental, Inc. “Powerline, Vineyard Road and Rittenhouse Flood Retarding Structures Rehabilitation or Replacement Project - Final Earth Fissure Risk Zoning Memorandum.” May 2012 Arizona Department of Water Resources. “Arizona Administrative Code, Title 12, Chapter 15, Article 12 – Dam Safety Procedures.” June 2000. Arizona State Land Department. “Desert Drive Area Study Existing Conditions Hydrology.” Prepared by JE Fuller Hydrology and Geomorphology, Inc. December, 2007. Arizona State Land Department. “Desert Drive Area Study Existing Conditions Inundation and Sedimentation Analysis for PVR Structures.” Prepared by JE Fuller Hydrology and Geomorphology, Inc. April, 2008. EPG, Inc. “Powerline, Vineyard Road and Rittenhouse Flood Retarding Structures Rehabilitation or Replacement Project - Site Analysis Report.” February, 2010. Flood Control District of Maricopa County. “Preliminary Design Report – Site Evaluation of Interim Dam Safety Measure, Powerline Flood Retarding Structure.” Prepared by AMEC Earth & Environmental, Inc., July 2009. Flood Control District of Maricopa County. “Structures Assessment Program – Phase I Alternatives Analysis Report: Cave Buttes Dam, Powerline FRS, Vineyard Road FRS, Rittenhouse FRS.” Prepared by Kimley-Horn and Associates, Inc. February, 2001. Flood Control District of Maricopa County. “Structures Assessment Program – Phase I Final Failure Modes and Effects Analysis Report: Cave Buttes Dam, Powerline FRS, Vineyard Road FRS, Rittenhouse FRS, Spook Hill FRS, Signal Butte FRS, Apache Junction FRS.” Prepared by Kimley-Horn and Associates, Inc. July, 2002. Flood Control District of Maricopa County. “Powerline, Vineyard and Rittenhouse Flood Retarding Structures Emergency Action Plan.” Prepared by J.E. Fuller, Inc., 2006. USDA- NRCS January 2013 Kimley-Horn and Associates, Inc. Page 52
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DRAFT SUPPLEMENTAL WATERSHED PLAN A
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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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Exhibit A-2 - Emergency Spillway Di
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Price Price Price Dobson Alma Schoo
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Powerline Plan and Environ. Assessment Jan. 2013 - Flood Control ...

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