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®Bellecci & Associates January 22,2013 VIA E-MAIL Mr.William Harris,ASLA Principal Harris Design Re: Bernal Park Phase 2 Bernal Avenue Drainage Channel Options Revision 2 Dear Bill, We are writing to summarize the on-going concerns and improvement options for the Bernal Avenue drainage channel along the north edge of Bernal Park Phase 2 project;and the related flooding impacts on the Bernal Park Phase 2 improvements. Drainage Conditions and Impacts The Bernal Avenue open ditch along the southside of Bernal Avenue is identified in the"Summary of Hydrologic and Hydraulic Analysis"by Balance Hydrologics,dated Sept 25,2006 as follows: "The existing open ditch along the southside of Bernal Avenue is not adequate to convey the predicted 15-year discharge from the Fairgrounds property." The report shows two drainage areas tributary to Bernal Avenue open ditch: "Fairgrounds West"and "Fairgrounds East"drainage, These drainage areas extend from the County Fairgrounds across Bernal Avenue via two culverts into the existing open ditch. When the Bernal Avenue open ditch overflows,it discharges overland to the south across the open field towards the"Fairgrounds Channel"(aka"Farmer's ditch"). In the future this Bernal drainage channel overflow would discharge towards the new Bernal Park Phase 2 soccer fields adjacent to Bernal Avenue. During our concept design phase in 2009-2010,we prepared 5-7 drainage exhibits as alternatives to solve the flood control issues. Some of these potential solutions studied are described below as optional services for Bellecci: Optional Service#1-Redirect"Fairgrounds West Drainage"into Oak Woodland Area City and Harris Design may elect to extend"Fairgrounds West Drainage"culvert from Bernal Avenue into the engineered Oak Woodland drainage basins and low flow channel. The existing culvert conveys 46 cfs(15-yr storm), per the September 2006 drainage report. Redirecting"Fairgrounds West Drainage"into the Oak Woodland would reduce the flow in the Bernal Avenue open ditch. Listed below is the scope of work for this task: 1. Prepare hydrology/hydraulic calculations for pipe extension into Oak woodland 2. Revise pond calculations for Fairgrounds West Drainage discharge 3. Design drainage channel within Oak Woodland 4. Prepare details for pipe extension (environmental permitting not included) In addition to the measures above, Bernal Park soccer fields would need additional protections from the"Fairgrounds East Drainage"culvert overflow. Optional Service#2-Redirect"Fairgrounds East Drainage"into Oak Woodland Area City and Harris Design may elect to extend the larger culvert from Bernal Avenue into the Oak Woodland drainage basins and low flow channel. The culvert is identified in the September 2006 report as"Fairgrounds East Drainage"and conveys approximately 120 cfs(15-yr storm). Listed below is the scope of work: 1. Prepare hydrology/hydraulic calculations for pipe extension into Oak woodland 2. Revise pond calculations for Fairgrounds West Drainage discharge 3. Design flood control channel within Oak Woodland 4. Prepare details for pipe extension(environmental permitting not included) CONCORD PLEASANTON 2290 Diamond Blvd. Suite 100 6601 Koll Center Parkway,Suite 240 Concord,CA 94520-5744 Pleasanton,CA 94566-3127 Civil Engineering Land Surveying Tel. 925.685.4569 Tel. 925.681.4885