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
Prado Dam
Main purpose is
flood control
Water conservation
is additional
beneficial use
Prado
Dam
Prado Basin
Area = 11,500 acres
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
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
Sediment
-
deficient high flows change sediment
characteristics below Prado Dam
─
Cause armoring and coarsening
Percolation reduced
Percolation Impacts
Changes in Sediment
Characteristics
SAR at
Imperial
SAR at
Five Coves
SAR at
Weir Canyon
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
Prado Basin
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
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
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
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