ZONE 7 FLOOD CONTROL CHANNELS PHASE 1 (10 SITES) PL 84-99 PROJECT

THE ZONE 7 FLOOD CONTROL CHANNELS PHASE 1 (10 SITES) PL 84- 99 PROJECT IS AN ONE TIME REPAIR PROPOSED BY USACE TO REPAIR STORM DAMAGED TO FLOOD CONTROL CHANNELS IN ALAMEDA COUNTY. DAMAGES CONSISTED OF EROSION AND BANK FAILURES DURING A SERIES OF ATMOSPHERIC RIVERS BETWEEN DECEMBER 2022 AND MARCH 2023. REPAIRS CONSIST OF TEN (10) SITES ALONG ARROYO MOCHO AND ALAMO CANAL, INCLUDING G-6, G-7, G-8, G-9, G-10, G-13, G-14, F-11, F-12, AND F-13.THE EXISTING FLOOD CONTROL CHANNELS TYPICALLY HAVE EARTHEN SLOPES PREVIOUSLY CONSTRUCTED TO GRADES OF 2H:1V, WITH CHANNEL HEIGHTS RANGING FROM 15-30 FEET. THE DAMAGED SITES VARY IN SIZES. REPAIRS TO DAMAGED SITES WILL RESTORE THE SLOPES TO ORIGINAL GRADE PRIOR TO THE STORM DAMAGES. EARTHWORK WILL START WITH EXCAVATION OF THE DAMAGED AREA, REMOVING DISTURBED SOIL AND VEGETATION WITHIN THE AREA. REPAIRS WILL CONSIST OF PLACING ROCK SLOPE PROTECTION (RSP) AT THE WATERSIDE SLOPE TOE, PLACING SOIL-FILLED RSP UP TO THE 10-YEAR WATER SURFACE ELEVATION, AND RESTORING THE UPPER PORTION OF THE SLOPE WITH COMPACTED BACKFILL. AFTER THE REMAINING SLOPE IS BACKFILLED AND COMPACTED ABOVE THE STONE PROTECTION, EROSION CONTROL MATTING WILL BE INSTALLED AND HYDROSEEDED.