A sweet spot for farms and fish on a floodplain

By Richard Howitt and Josué Medellín-Azuara

One of California’s greatest environmental success stories has been the partnership between Sacramento Valley rice growers and wildlife managers to support wintering waterfowl. Farmers have shown they can make good money in the off-season by flooding their harvested fields to grow ducks and geese — attracting fee-paying hunters.

Now, research underway in the Yolo Bypass suggests they can grow salmon, too.

Recent studies indicate the bypass would make a fabulous salmon nursery at relatively little cost to Yolo County’s farming.

Experiments at the Knaggs Ranch rice farm — funded by a consortium of private landowners, conservation groups and government agencies — show juvenile Chinook salmon growing at phenomenal rates, requiring flooding for less than two months in winter and early spring. Test fish in the field had better survival rates and fattened faster than those left to mature in the Sacramento River, earning them the name “floodplain fatties.”

When growers flood their fields of decomposing rice stalks they unwittingly generate lots of fish (and duck) food, namely zooplankton. Indeed, preliminary results indicate that young salmon grow better on rice fields than on unfarmed floodplains.

Seasonal flooding of farmland does reduce the growing season and crop yields. But if it increases salmon growth and populations, farmers in the bypass can be compensated — just as they are now for flood control easements, which also lower land rents.

A recent report found that the costs of sharing the bypass with fish probably would be relatively small. The UC Davis study, commissioned by Yolo County, found a “sweet spot” for flooding that gives fish enough growth time without greatly cutting into crop yields and farm profits.

Fields would be drained by late March, causing a yearly loss of roughly $1.5 million, or less than 1 percent of the total value added for Yolo County’s economy ($212 million in 2009). Extending inundations much further into spring would be a lose-lose proposition: too costly for farmers and too risky for salmon. (As the season progresses, the shallow floodwater becomes too warm for them to survive.)

This flooding scenario is consistent with one state officials are seriously considering — and presumably will pay for — as part of the Bay Delta Conservation Plan. It calls for flooding no more than 6,000 cubic feet per second for 30 to 45 days in the winter. The bypass would be inundated for fish only in years when flooding in the river plain occurs naturally — which, historically, is about half of the time.

Levees in the Central Valley have all but eliminated the seasonal wetlands that served as food-rich rearing grounds for young salmon. Now, operators and contractors of the state and federal water supply systems are looking to increase seasonal flooding on riverside farms to help struggling fish populations. They are obligated under the federal Endangered Species Act to help offset losses of Central Valley Chinook salmon caused by operations of the giant water export pumps in the Delta. Paying farmers to grow salmon would be one way to restore populations.

Results of the recent cost analysis and the ongoing salmon-rearing experiment suggest that farmers in the Yolo Bypass can look forward to profitably farming for fish, as well as for flood control, ducks and crops.

— Richard Howitt is a professor emeritus of agricultural and resource economics with the UC Davis Center for Watershed Sciences, a partner in the Knaggs Ranch experiments. Josué Medellín-Azuara is a center researcher who specializes in economic modeling of water systems.

Special to The Enterprise

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