1. Sediment Management in Prado Basin and Lower Santa Ana River Greg Woodside, P.G., C.Hg Executive Director of Planning & Natural Resources September 20, 2011

3. Prado Dam Main purpose is flood control Water conservation is additional beneficial use Prado Dam Prado Basin Area = 11,500 acres

4. Water/Sediment Mechanics Sediment laden water enters Prado Basin Velocity of water slows and sediment settles out in Prado Basin Water released through Prado Dam is sediment deficient ─>95% sediment trap efficiency estimated by Warrick & Rubin (2007) for Prado Dam

5. Impacts of Prado Basin Sedimentation Prado Basin ─Water conservation reduced  25,000 af lost below elev. 505 since 1941 ─Sedimentation threatens infrastructure ─Impacts to endangered species habitat Lower Santa Ana River ─Scouring threatens infrastructure  SAR channel has incised between 5 and 15 feet from Prado Dam to Weir Canyon with localized incision exceeding 15 feet ─Channel incising harms riparian habitat ─Beach replenishment reduced ─Marine ecosystems starved of sediment ─Riverbed armoring & coarsening reduces percolation rate

6. Sediment-deficient high flows change sediment characteristics below Prado Dam ─Cause armoring and coarsening Percolation reduced Percolation Impacts

7. Changes in Sediment Characteristics SAR at Imperial Five Coves SAR at Weir Canyon

8. Proposed Solution Perform demonstration project to remove sediment from Prado Basin and place it below Prado Dam Demonstrate feasibility of re-establishing natural sediment transport regime Allow high flows released from Prado Dam to redistribute sediment down river Use results from demo project to assess feasibility of long-term sediment management solution

9. Prado Basin

12. Sediment Management Demonstration Project Layout Dredging ─Hydraulic dredge Pump sediments to temporary storage area Slurry pump sediments to re- entrain in SAR below Prado Dam

13. Project Outreach U.S. Army Corps of Engineers U.S. Fish and Wildlife Service CA Department of Fish and Game CA State Parks Regional Water Quality Control Board Flood control districts OC Coastkeeper / Inland Empire Waterkeeper Santa Ana Watershed Project Authority Local cities

14. Near-Term & Long-Term Near-Term ─Prado Basin Demonstration Project  Test in field  Collect data to measure benefits, assess potential impacts Long-Term ─Corps’ Prado Basin Feasibility Study ─Implementation of project(s) from FS