Basin and Lower Santa Ana River

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