SU0014674 - Laserfiche WebLink

Home Browse Search

MOUNTAIN HOUSE NEIGHBORHOOD"F"PROJECT INITIAL STUDY Road Crossings. The existing culverts(three 36-inch culverts)under Byron Road are currently inadequate. Flooding occurs frequently at this location. As part of the overall storm water improvements for the project, these culverts would be replaced by three 84-inch culverts. Internal Storm Drainage Lines. At buildout, the Mountain House project would be drained by an extensive system of underground drainage pipes and major trunk lines. These trunk lines would discharge into Mountain House Creek or into planned water quality basins. The main trunk lines would be located within Mountain House Parkway, De Anza Boulevard, Central Parkway, Byron Road, and Marina Boulevard. Water Quality Basins. A series of six water quality basins are planned for the community at ultimate buildout. These basins are intended to capture the first flush of runoff from the development. The idea is that pollutants settle out or are filtered by wetland vegetation. The precise design elements of these basins have not been specifically addressed other than a statement that the sizing would be completed as per the Municipal California Storm Water Best Management Practices(BMP) Manual. No data have been reviewed that explains water residence times or settlement efficiencies. In some instances, water in these basins would need to be pumped from the basin into either Mountain House Creek or the Old River channel. Neighborhood "F" Drainage Plans The fust phase of the project, Neighborhood"F", would include completion of a portion of the Master Drainage Plan elements and installation of some interim flood control measures. The following discussion summarizes these improvements and their implications to the project and flood control in general. Figure 3 indicates which features would be constructed as part of the Neighborhood"F" development. Mountain House Creek. The Neighborhood"F"drainage plan calls for improvements to Mountain House Creek upstream(south)of Byron Road. These improvements include amendments to the farm crossings;retrofitting Irrigation Dam 1 with a new spillway;raising a portion of an existing berm along the south Mountain House Creek bank; and installing an additional 84-inch culvert under Byron Road to help relieve the constant flooding at this location. North of Byron Road, several significant features would be added. All runoff from the urbanized sections of Neighborhood"F"would be conveyed under Byron Road by a series of 84-inch culverts. These culverts would discharge into a channel that parallels the existing creek alignment. Storm water flows would then either flow into the Mountain House Creek channel or flow overland and collect behind the levee. Flows reaching the creek channel would then travel northerly. A short portion of the Creek has very minimal capacity. Thus, a diversion channel would be constructed that would cavy creek overflows. This diversion channel would eventually discharge into the portion of the Mountain House Creek channel that could accommodate its flow. An interim water quality basin is proposed at the downstream end of Mountain House Creek northeast of Byron Road. This basin is intended to accept the "first flush" of runoff during a storm event prior to discharge to Mountain House Creek and ultimately Old river. The basin can catch pollutants and heavy metals in runoff. Diversion berms would be constructed north of Byron Road to contain and direct overland flow of storm water away from the proposed wastewater treatment plant site and into the Mountain House Creek corridor. Flows would then proceed downstream to the Dredger Cut and Old River. The Master Drainage Plan calls for the removal of the existing 48-inch culvert, enlargement of C:VOBS13JUN AL MMYTINALINMAL=Y-PAMDOC(MAW) 93 V.J. HYDROLOGY AND WATER QUALITY