USACE prepares for large-volume snowmelt at Isabella Lake

U.S. Army Corps of Engineers Sacramento District
Published May 9, 2023
Updated: May 9, 2023

Due to record-high snowpack over the winter, the USACE Sacramento District is preparing for above-average inflows to and outflows from USACE-managed reservoirs throughout California’s Central Valley, including Isabella Lake.

The district expects Isabella Lake to exceed gross pool of 568,000 acre-feet this summer, which will cause the dam’s service spillway to release water for the first time since 1983. Based on the rate and timing of snowmelt, this spill could last several weeks, beginning sometime between late May and mid-June.

There is no expectation that water levels will reach the top of the new labyrinth weir or spill into the emergency spillway. The emergency spillway is designed to be used in a 4,000-year flood situation, meaning that in any given year there is a 1 in 4,000 chance of such an event. Current snowmelt projections are far below this level and are not expected to get there.  

The district has received approval to implement a plan to fill Isabella Lake to capacity this year following the substantial completion of Phase 2 of the Isabella Dam Safety Modification Project, but execution of the fill plan will be adjusted to accommodate this year’s record snowpack.

In accordance with the Isabella Dam Water Control Manual, the district is coordinating with downstream water users for controlled water releases expected to be near, at, or above designated channel capacity levels. USACE water managers are also coordinating with the California Department of Water Resources to determine areas of greatest flood risk.

Extended high-volume releases are likely necessary to minimize flood damages associated with this year’s historic snowpack. The district is working with DWR and other local partners to assess and communicate any potential impacts to Bakersfield and the Tulare Basin.

Previous years’ releases from the service spillway have impacted State Route 178, including delays and closures. The California Department of Transportation (CalTrans) monitors road conditions and advises the public of closures on their website,

While the service spillway is in use, entering Isabella Lake in the general area of the main dam, or the Kern River anywhere downstream of the dam, is extremely dangerous. Those recreating near the lake are strongly advised to stay informed of current conditions and heed any warnings from U.S. Forest Service rangers and Kern County Sheriff personnel.

Members of the public can stay aware of developing situations by closely monitoring communication from local authorities and are encouraged to take steps to prepare for an emergency.

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Jeremy Croft

Release no. 23-019