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 6.1.4 REGIONAL WATER MANAGEMENT PLANS Alternative 1 – No Action. Alternative 1 would provide continued flood protection up to the 100- year event for downstream canals particularly the Central Arizona Project (CAP) canal, a large water supply from the Colorado River to central Arizona. The canal would continue to be vulnerable to breach failure the FRS or overtopping of the structure for storm events approaching the PMF. Alternative 2 - Decommissioning. Alternative 2 would direct storm flows to the Vineyard Road FRS and thus provide continued flood protection up to the 100-year event. The CAP canal would be vulnerable flood events greater than the 100-year. The PMF is not required for Alternative 2. 6.1.5 FLOODPLAIN MANAGEMENT Alternative 1 – No Action. This alternative would have a long-term adverse direct by potentially exposing the downstream floodplain to flooding risks from overtopping flood events or discharges through the auxiliary spillways above the 100-year event. However, Alternative 1 would provide continued flood protection up to the 100-year event for the downstream floodplain. The Federal Emergency Management Agency (FEMA) floodzone Zone A designations could be removed from the floodplain maps. Alternative 2 - Decommissioning. Alternative 2 would direct storm flows to the Vineyard Road FRS and thus provide continued flood protection up to the 100-year event for downstream floodplain. The Federal Emergency Management Agency (FEMA) floodzone Zone A designations could be removed from the floodplain maps. 6.1.6 THREATENED AND ENDANGERED SPECIES Alternative 1 – No Action. This alternative will have no direct effect on special status fish or wildlife or their habitats. Alternative 2 – Decommissioning. A qualified biologist determined that federally threatened and endangered species or critical habitat would not be potentially impacted by this alternative since suitable habitat for these species is not present in the project area. Suitable habitat is present for the Tucson shovel-nosed snake (Chionactis occipitalis klauberi) and dispersal habitat is present for the Sonoran desert tortoise (Gopherus agassizii). These are candidate species for the U.S. Fish and Wildlife Service (USFWS) and may become listed in the future and warrant additional assessment. Survey protocol for the Tucson shovel-nosed snake has not been published by the USFWS. Prior to construction the status of the Tucson shovel-nosed snake on the USFWS threatened, endangered, proposed, and candidate list will be re-verified (i.e. status changed from candidate to threatened) and coordination with the USFWS will be undertaken to determine if a survey protocol has been established and/or if a survey is required. If this species is observed construction will cease until measures can be taken to ensure the preservation of the snake and/or its habitat. Desert tortoise has the potential to occur within the project area. Prior to start of construction, the project area will be canvassed for tortoises and, if any tortoises are discovered, Arizona Game and USDA- NRCS Page 6-2 January 2013 Kimley-Horn and Associates, Inc.
Powerline Flood Retarding Structure Pinal County, AZ Draft Supplemental Watershed Plan and Environmental Assessment Fish Department (AGFD) Guidelines for Handling Sonoran Desert Tortoises Encountered on Development Projects (Revised October 23, 2007) will be followed. Additionally, the project contains suitable habitat for the western burrowing owl (Athene cunicularia hypugaea) which is protected under the Migratory Bird Treaty Act. Prior to start of construction, a survey for burrowing owls will be required in the disturbance area following the AGFD protocol (January 2009). As a result of the actions described above, there will be no effect on federally threatened and endangered species or their critical habitat due to implementation of this alternative. The abovementioned mitigation measures will be utilized to minimize impacts to special status species. 6.1.7 VEGETATIVE COMMUNITIES The biotic community within the study area is identified as the Arizona Lower Colorado River Valley, Sonoran Desert Scrub community. Vegetation is found throughout the FRSs and study area and consists primarily of woody shrubs and herbaceous growth. Alternative 1 – No Action. This alternative has no effect on vegetation communities and allows the continued presence of the mesquite bosque upstream of the dam. Alternative 2 – Decommissioning. The acres of existing mesquite bosque vegetation that may be directly affected by construction activities have been quantified (approximately 120 acres). The mitigation may include planting tall-pot mesquite trees (approximately 60 acres) and salvage of some mature mesquite trees and transplanting in designated areas (e.g., along Powerline Channel and potential mitigation area at north end of Vineyard Road FRS). The Sponsor and NRCS will coordinate with ASLD regarding trees along the existing low flow channel along the Powerline FRS. The costs of mesquite bosque mitigation have been included in the alternative cost estimate. Clearing and excavation of the channel includes an access O&M road on either side of the channel. Disturbed areas will be hydroseeded following construction. Removal of the existing dam embankment and stabilization of the dam site will impact the existing mesquite bosque. Mitigation measures would be implemented to reduce short term and long term impacts. The Alternative 2 channel would have a short-term direct effect on the vegetation community by removal of the predominant vegetation type – desert brush. 6.1.8 FISH AND WILDLIFE The arroyos upstream of the dam is normally dry except during heavy rainfall events and do not support fish populations. This local desert environment is home to several species of birds, reptiles, and mammals that use scrub desert habitat. Alternative 1 – No Action. This alternative will have no direct effect on fish or wildlife or their habitats. Alternative 2 – Decommissioning. Wildlife species present in the study area could have a shortterm direct effect by Alternative 2. Vegetation would be removed from areas along and adjacent to the new channel.Wildlife would also be disturbed by construction activities and would likely move away from the construction area. This wildlife effect would be short-term during construction. Wildlife would likely move back into the construction area as soon as construction is completed. USDA- NRCS Page 6-3 January 2013 Kimley-Horn and Associates, Inc.
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Powerline Plan and Environ. Assessment Jan. 2013 - Flood Control ...

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