Santa Cruz, CA
831.421.9291
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  Portland, OR
503.227.5979
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Arroyo Grande Creek Channel Flood Mitigation

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Client: Coastal San Luis RCD, County of San Luis Obispo

In 1959 the lower three miles of the mainstem Arroyo Grande Creek were converted to a trapezoidal flood control channel to reduce flood risk to high value farm land. Sedimentation, vigorous riparian growth and changes in the watershed due to urbanization have altered the flood control channel to the point where it provides very little in the way of flood protection. In addition, environmental regulations that protect sensitive species have limited the ability of the County to perform channel maintenance work. In 2001 a high intensity storm event caused levee failure, resulting in millions of dollars in damage to adjacent farmland and residential properties. In response, the Coastal San Luis Resource Conservation District commissioned Waterways staff, in conjunction with SH+G, to evaluate potential alternatives to improve flood protection along this reach of Arroyo Grande Creek. Identified alternatives included levee raising, environmentally appropriate vegetation and sediment management, and erosion control and flood detention projects in the upper watershed to reduce sedimentation in the flood control reach.

ag-levyHabitat enhancement elements were also recommended to provide mitigation for project impacts. The alternatives were evaluated using a HEC-RAS model to determine the level of flood protection afforded each alternative and their respective costs of implementation. Following selection of a preferred alternative, Waterways has worked with SWCA on the regulatory permitting and environmental review phase of the project. Our role involves preparation of the 30% engineering design for the levee raise and habitat improvement measures, preparation of the Waterways Management Plan, to be included as an appendix to the EIR, and assistance with preparation of regulatory permitting documents, including the Biological Assessment for steelhead and California red-legged frog.

Project Menu

Central California Project Portfolio
Aptos Creek Watershed Assessment and Enhancement Plan
Attiyeh Ranch Conservation Easement
Camp Pico Blanco Fish Ladder and Dam Retrofit
City of Santa Cruz Watershed Management Plan
Corralitos Creek Bank Stabilization
Eureka Canyon Bridge Replacement and Fish Passage Improvements @ Koinonia Conference Center
Fall Creek Fish Ladder
Geyer Quarry Restoration Plan
Mitchell Creek Dam Removals & Fish Passage Improvements
North Monterey County High School Nature Area Design Project
Pajaro River Care Project
Potrero Hills Wetland Mitigation
Quail Hollow Bridge Replacement and Channel Restoration
Salmonid Enhancment Plan for the San Lorenzo River
San Lorenzo River Monitoring
Soquel Creek Floodplain Restoration
Sycamore Creek Bank Stabilization
Valencia Creek Fish Ladder
Watsonville Sloughs Landfill Site Restoration near Ramsay Park
Watsonville Sloughs Manabe Property Wetland Restoration
Watsonville Trails Master Plan
West Valley College Stream and Wetland Enhancement and Riparian Trail Plan
Zayante Area Sediment Source Reduction Plan
Northern Cal-Nevada Project Portfolio
Big Meadow Creek Watershed Assessment
Blackwood Creek Stream Restoration
Cold Creek/ High Meadow Ecosystem Restoration
Coldstream Floodplain Enhancement Project
Edgewood Creek Watershed Assessment, Enhancement Plan, & Restoration
Hat Creek Restoration
Hope Valley Meadow Restoration
Independence Lake Log Cribwall and Fish Barrier Design
Kunzler Ranch Gravel Extraction
Perazzo Meadows Geomorphic Assessment
Russian River Projects
Sonoma County Fish Passage Projects
St. Helena Comprehensive Flood Protection Plan
Trout Creek Restoration
Upper Carson River Watershed Assessment
Pacific Northwest Project Portfolio
Batwater Station Floodplain Enhancement Project
Clackamas County Water Environment Services Action Planning & Geomorphic Monitoring
Dairy Creek- Sturgeon Lake Restoration
East Valley Mine Wetland Mitigation Project
Fox Creek Restoration Plan
Gales Creek Restoration Planning
Gooseneck Creek Restoration
Half Mile Lane Mitigation Bank
Hillsboro Landfill Wetlands Outfall Channel and No-Rise Documentation
Jackson Creek Restoration Plan
Lower Clatskanie Floodplain Restoration
Lower Cottonwood Creek Points of Diversion Modification Projects
Mill Creek Side Channel Restoration
Milton Creek Large Wood Enhancement Project
Murtaugh Creek Fish Passage
North Fork Deep Creek Habitat Enhancement Project
Rinearson Creek Natural Area Restoration
Salmon and Cox Creek Fish Barrier Improvement Project
Scappoose Bay Restoration Plan
South Fork Necanicum Fish Passage Improvement Project
Southern California Project Portfolio
Arroyo Grande Creek Channel Flood Mitigation
Circle G Ranch Fish Passage Improvement
Gobernador Creek Bridge Replacement and Fish Passage Improvements - Widdoes Residence
Morro Fish Review
Pismo Creek Fish Passage Project
Rodriguez Fish Passage Project
Tally Ho Channel Assessment