DSOD Gives Sweetwater Dam a Downstream Hazard Rating of "Extremely High"
In her latest article "Dozens of California Dams Need Repair as El Niño Winter Draws Closer", CalMatters' Rachel Beck writes:
|
The California Department of Water Resources issues an annual report from its Division of Safety of Dams (DSOD) department. The most recent report was compiled in September 2025 and this is what it tells us about our Sweetwater Dam.
Sweetwater Dam is the last dam on the image above and listed as 2020-0/CA00775. It is owned by Sweetwater Authority.
The dam is 112 feet high from the downstream toe of the dam to the dam crest. The crest length from one abutment to the other is 700 feet.
The reservoir capacity or maximum amount of water that the dam can impound is 27,689 acre-feet of water.
It is listed as CERTIFIED meaning the certified status is "Jurisdictional sized dams that may safely impound water to the elevation specified on the Certificate of Approval."
The condition is assessed as FAIR, with the following definition.
No existing dam safety deficiencies are recognized for normal operating conditions. Rare or extreme hydrologic and/or seismic events may result in a dam safety deficiency. Risk may be in the range to take further action. Note: Rare or extreme event is defined by the regulatory agency based on their minimum applicable state or federal criteria.
Other Circumstances:
• Lack of maintenance requires attention to prevent developing safety concerns.
• Maintenance conditions may exist that require remedial action greater than routine work and/or secondary studies or investigations.
• Interim or permanent risk reduction measures may be under consideration
Sweetwater Dam is a GRAV (Gravity-type) dam and at this time has no restrictions.
"The Division of Safety of Dams may direct or order an owner to operate the reservoir to a specified water surface elevation level that is lower than the maximum storage level. In addition, owners may self-impose a restriction as a result of an owner-initiated study that identifies a dam safety issue. Reservoir restrictions are typically imposed for deficiencies of the dam, spillway, low-level outlet, or other appurtenances with respect to dam safety."
The Final Initial Study/Mitigated Negative Declaration states that "The South Spillway discharges water downstream through three orifices that pass through the body of the dam. However, the concrete structure is deteriorating and is in need of repair."
As of yet, Sweetwater Authority has delayed that project. You may read about the identified objectives of the project in section 1.4 of the Final Initial Study. According to Voice of San Diego, the southern spillway repair is estimated to cost about $24 million.
The last PMF analysis for Sweetwater Dam was conducted in 1981 by the DSOD. PMF stands for Probable Maximum Precipitation or "the greatest amount of precipitation for a given duration that is physically possible over a given size storm area at a particular geographical location during a certain time of the year." Think El Niño of 2026 or the Great Flood of 1916.
As for the Downstream Hazard for the Sweetwater Dam, it is classified as EXTREMELY HIGH. The potential downstream impacts to life and property? A Sweetwater Dam failure would be "Expected to cause considerable loss of human life or would result in an inundation area with a population of 1,000 or more."
Supervisor Paloma Aguirre held an Emergency Preparedness Community Meeting this week to "Prepare for El Niño". The local fire stations have been providing sandbags for flooding.
I think that we may have bigger fish to fry. If this year's El Niño is as big as expected—and our PMF exceeds the forecasts—we could be going for one heck of a ride.
If you're curious what the flooding would look like if the dam failed, you should read "The Great Flood of 1916" and the diary as researched by Steve Schoenherr.
Comments