Nov 17 2011

Gradient Facility on the Sacramento River

The Glenn Colusa Irrigation District (GCID) Gradient Facility (GF) is located on the Sacramento River west of Chico California, upstream from Hamilton City.

Panoramic view d-s through GF 072203

The GF is part of The Fish Screen Improvement Project completed in 2000.  The primary purpose of the GF is to increase upstream water surface elevation by approximately 3 feet.  The GF is designed with the general characteristics of a natural riffle.  Structurally, the GF consists of three sheet pile cutoff walls and rock riprap revetment along the channel bed and banks.  An outline of the main structure is shown below;


Some stats on the GF:

  • 1,000 ft long
  • 50 ft wide thalweg channel
  • 200 ft wide low flow channel
  • 0.003 longitudinal slope
  • 12 fish depressions
  • 60 ft wide fish depressions
  • 150 ft long fish depressions
  • 2,000 ft long east and west bank revetment


Before going into more detail about the structure and its design, some background on the project is needed to better understand everything involved.  Some of this information is taken from articles written 10-15 years ago, so keep that in mind while reading.

The Sacramento is the largest river in California, and is the lifeblood for one of the most fertile agricultural areas in the world.  GCID supplies water through a 65 mile long main canal and a system of 430 miles of laterals to more than 141,000 acres of farmland and 20,000 acres of wildlife refugees in Glenn and Colusa Counties.  Irrigation water is vital in the dry summer months to GCID farmers.

The amount of water GCID can pump has been reduced during certain times of the year by a 1991 court order intended to reduce juvenile salmon losses.  Juvenile salmon, including the endangered winter-run Chinook, were being injured, some fatally, on the pumping station’s fish screens.  These rotary drum screens, installed by the California Department of Fish and Game in 1972, were designed to keep fish from being pumped into the main irrigation channel.

Project ARea

The population of the winter-run Chinook salmon in the Sacramento River has declined dramatically in the past three decades, from a spawning run high of 117,800 fish in 1969 to a low of 191 fish in  1991.  Jim Smith from the U.S. Fish and Wildlife Service says:

“The winter-run Chinook salmon will disappear without help.  GCID has the largest diversion along the river and any solution developed there will be a major step toward protecting and restoring salmon on the Sacramento River.”

Changes in the river during the past 25 years reduced the effectiveness of the fish screens.  Floods in 1970 caused the cutoff of a bend in the river one-half mile downstream from the GCID pumping station, which is located on a side channel of the Sacramento River that forms Montgomery Island.  The cutoff shortened the river by 1.5 miles over the next two decades and decreased the water level by three feet at the GCID intake channel.  The lower water level resulted in higher water velocities through the fish screens when GCID operates near full capacity, pumping up to 3,000 cubic feet of water per second.  The higher water velocities can pin small fish against the screens instead of allowing them to continue back to the main river channel.

The GF is based on a concept that replicates natural riffles on the Sacramento River.  With a combination of quarried stone and sheet pile placed underwater across the river the riverbed would be reconfigured to provide flow conditions that allow fish and boat passage.  The GF would raise the water level of the river, thus reducing the water velocity through the fish screens and the impacts on juvenile salmon.

More to come…

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