As a big Pacific storm was slated to drench northern California, the U.S. Bureau of Reclamation announced today it will increase water releases to the American River below Nimbus Dam on Dec. 15 at 9 a.m. from 15,000 cubic feet per second to reach 35,000 cfs by 1 p.m.
This is the largest increase in releases in one day in many years, at least since 2011. Peggy Manza of Reclamation said the purpose of the increased releases was for “storage management/flood control.”
Shane Hunt, public affairs officer for Reclamation’s mid Pacific region. said increased releases are based on “changing conditions and are necessary to maintain space in Folsom Reservoir for projected Sierra runoff.” Current storage in the reservoir is around 158 percent of its 15-year average for December.
“Should inflows continue at current levels or increase, additional releases may be required,” said Hunt. “We haven’t made a final decision when other flow changes will be made and when the high flows will go down. The updated foreceast and real time conditions will dictate when we make another operational change.”
He advised, “People recreating in or along the lower American River downstream of Folsom Dam to the confluence of the American and Sacramento rivers can expect river levels to increase and should take appropriate safety precautions. Some inundation along the American River’s recreational trails and at Discovery Park are expected.”
This release occurs at a critical time for struggling fall-run Chinook salmon and steelhead on the American. The salmon run is near its end as fish spawn in the river or have already spawned. The winter run of steelhead, listed as an endangered species, is starting to move into the river.
Bureau biologists believe that overall, the flows will be beneficial to salmon and steelhead.
“The releases will help clean up algae growth and gravel in the river,” said Hunt. “Given the timing, most of the fall Chinooks have already laid their eggs and we don’t think we will see a significant number of new redds because most of the fish have already spawned. As for the steelhead, they haven’t started spawning yet.”
“There may be some minor effect to some of the existing salmon redds from gravel mobilization, but we don’t think it will be a big effect,” said Hunt.
Due to the high river flows, Discovery, Howe Avenue, Watt Avenue and Gristmill Parks, Campus Commons Golf Course, William Pond Recreation Area and the American River Parkway multi-use trail at mile 20 will be closed Thursday-Sunday.
Midnight Reservoir Elevation and Flows for Folsom may be found at Reclamation’s Central Valley Operations Office website at https://www.usbr.gov/mp/cvo/vungvari/wtr_rpt.pdf. Current American River conditions may be found at the Department of Water Resources’ California Data Exchange Center website at http://cdec.water.ca.gov/river/americanStages.html.