So Simple, So Important: the Fremont Weir

Doesn't look like much but mightily important for flood protection

Doesn’t look like much but mightily important for flood protection

The Fremont Weir does not impress.  It is about 1.5 miles long (looking like this all along the way).  The Sacramento River is about 100 yards to the left of this photo.  On the day this was taken in March the River was bucolic and lazy.  Nothing suggested that it could swell to the point of overflowing and overtop the Fremont Weir. Yet, during a major storm event this unassuming weir diverts up to 80% of the Sacramento River flows thus protecting City of Sacramento, West Sacramento, and Davis from flooding.  The water flows into the Yolo Bypass.  The I-80 and I-5 causeways allow traffic to continue to move and the water can fill the 59,000 acre bypass to fill from levee to levee and sending it around the estuary to the Bay just above Rio Vista.

Several plans are taking a look at the bypass system and suggesting changes:

  • Central Valley Flood Protection Plan : the regional plan for Sacramento/North Delta is looking at changes to the Yolo Bypass.
  • Bay Delta Conservation Plan : the Yolo Bypass Fisheries Enhancement Planning Team is recommending changes to the Fremont Weir and Yolo Bypass to make them more fish friendly.
  • USBR/DWR Yolo Bypass Implementation Plan: currently in a scoping period until April 4, 2013, the USBR is inviting comment on their proposed plan to meet the requirements under the 2009 Biological Opinion to improve fish passage and habitat for endangered salmon and sturgeon.

We are fortunate that in the early 20th century, after a series of mega-storms, planners had the foresight to create these managed floodplains to deal with flood waters.  Now they give us the opportunity to explore changing their management to recreate the ecological functions that the levee system destroyed.  They already provide agricultural and waterfowl value, now they may also be a lifeline for fish.




Nigiri Project 2013

The experiments to test how well salmon fry will thrive on “surrogate wetlands” (a.k.a. rice fields) is in middle of year two.  The test pods were expanded from 5 acres to 10 2-acre ponds at Knaggs Ranch.  Each of the fields, now ponds, has one of three treatments: fallow with weeds, rice stubble and stomped rice (stubble rolled into soil, twice).  In addition, there are cages within the first pond with all three treatments and the telemetry to track fish behavior using technology like that in Fastrak.

Equipment in pond tracks what type of land treatment the fish prefer: rice stubble, weeds or stomped rice.

Equipment in pond tracks what type of land treatment the fish prefer: rice stubble, weeds or stomped rice.

Another experiment is comparing the success rate of fish that spend time on the floodplain getting fat for 4-6 weeks before swimming to sea, versus going directly into the Toe Drain or into the Sacramento River.  These experiments are coordinated by a Science Team led by Jacob Katz with California Trout.  Scientists from Department of Water Resources, UC Davis Watershed Science Center, National Marine Fisheries Service, CA Department of Fish and Wildlife and US Bureau of Reclamation all collaborate to design the experiments and manage the projects in the field.

The farm manager, John Brennan, is an active partner– especially in solving problems such water supply and field designs. At the beginning of February there was a concern about possible breaks in the field checks.  The good weather relieved those pressures but created other concerns.

The warm weather raised concerns about salmon tolerance for temperature. The sunshine also provided the conditions for the algae bloom that feeds the bugs that feed the fish.  The food is so abundant that the fish are growing at twice the rate of last year, reaching sizes at 3 weeks that were measured after 6 weeks in 2012.

Pilot 2 – Growth 22 days (1)

The floodplains also give the fish space to hang out with few predators while the ocean conditions change to be more salmon friendly.  In another few weeks the Science Team will measure, count and release the fish in to the Toe Drain to swim out to sea. Their report will be available sometime this summer.