RES 09268 - Laserfiche WebLink

Storm Water: Figure V -1 conceptually illustrates the proposed public Staples Ranch storm water system. Each of the development sites and the park sites would be graded so that storm drainage will flow towards the Stoneridge Drive /Auto Mall Place alignment. Each site will be required to meet the Alameda County Clean Water Program's C.3 requirements for storm water treatment, generally by filtering all storm water runoff through vegetated swales and other landscaped areas on site, prior to releasing it into the public storm drainage system in the road alignment. Treated storm water will then flow through 42" pipes within the alignment to the storm water flow control basin that will be integrated into the 5+ acre Neighborhood Park site. There, the water will be metered out through a drainage weir system, so that it mimics the Staples Ranch pre development storm water runoff hydrograph, into a 72" storm drain pipe that will continue west along Stoneridge Drive, connecting with the existing 72" outfall into the Arroyo Mocho located in the southwestern corner of Staples Ranch. Because of the relatively flat topography and a low area in the northwestern portion of the Staples Ranch site, much of the site needs to be filled in order for sewer and storm water lines to flow in the correct direction. The mounds of excavation material stockpiled on the Staples Ranch site are sufficient for this purpose, as well as creating a landscaped berm along the I -580 frontage for the Continuing Care Community site. No substantial import or export of fill material is anticipated. Flood Control: While the 2004 Arroyo Mocho Realignment project created adequate capacity to carry the 100 year flood event in the channel adjacent to Staples Ranch, the arroyos upstream of the Staples Ranch site are currently under capacity and predicted to overtop and send flood waters over El Charro Road and through the northern portion of the Staples Ranch site. However, flood protection improvements are planned to be constructed by Livermore as part of the El Charro Specific Plan, and as outlined in the 2007 Cost Sharing Agreement, which would remove Staples Ranch and much of the El Charro Specific Plan from the 100 year flood zone without impacting constrained stream channels downstream in Pleasanton. These improvements include a North Overbank Barrier and South Detention/Conveyance Facility along the Arroyo las Positas channel in Livermore. Livermore recently filed for a Conditional Letter of Map Revision (CLOMR) and is anticipated to construct the improvements and then file a Letter of Map Revision with the Federal Emergency Management Agency (FEMA) that would remove these areas from the flood zone. If Livermore has not succeeded in executing the CLOMR and removing the Staples Ranch site from the flood zone prior to Staples Ranch development, the Cost Sharing Agreement states that ACSPA will construct the planned Livermore flood protection improvements. Stoneridge Drive Specific Plan Amendment/Staples Ranch Draft October, 2008 54 i L