Sediment Management in Prado Sediment Management in Prado Basin and Lower Santa Ana River Basin and Lower Santa Ana River

Greg Woodside, P.G., C.HgExecutive Director of Planning & Natural Resources

September 20, 2011

Prado DamPrado Dam

Main purpose is flood control

Water conservation is additional beneficial use

Prado Dam

Prado BasinArea = 11,500 acres

Water/Sediment MechanicsWater/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

Impacts of Prado Basin Impacts of Prado Basin SedimentationSedimentation

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

Sediment-deficient high flows change sediment characteristics below Prado Dam─ Cause armoring and coarsening

Percolation reduced

Percolation ImpactsPercolation Impacts

Changes in Sediment Changes in Sediment CharacteristicsCharacteristics

SAR at SAR at ImperialImperial

SAR at SAR at Five CovesFive Coves

SAR at SAR at Weir CanyonWeir Canyon

Proposed SolutionProposed 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

Prado Basin

Sediment Management Demonstration Project LayoutSediment Management Demonstration Project Layout

Dredging─ Hydraulic dredge

Pump sediments to temporary storage area

Slurry pump sediments to re-entrain in SAR below Prado Dam

Project OutreachProject 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

Near-Term & Near-Term & Long-TermLong-Term

Near-Term─ Prado Basin Demonstration Project

Test in fieldCollect data to measure benefits, assess potential

impacts

Long-Term─ Corps’ Prado Basin Feasibility Study─ Implementation of project(s) from FS