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Atmospheric River swells reservoirs and puts pressure on sanitation collection systems

Jan 17, 2019

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LINK TO California Nevada River Forecast Center Interactive Map 

 

The atmospheric river that swept into Sonoma County this week sent reservoirs levels rising in the two main water supply reservoirs that theSonoma County Water Agency (Sonoma Water) manages, but the heavy rainfall also put pressure on the wastewater collection system in the Sonoma Valley.

 

Between 2-2.5” of rainfall was measured over a 24-hour period in the Sonoma Valley, which contributed to several sanitary sewer overflows, a situation that occurs when a sewer pipeline’s capacity is exceeded due to high inflow of storm water into a pipeline intended only for wastewater. The overflows occurred at the following locations: Vailletti at Casa Bella (2); Highway 12 at Agua Caliente Creek; Rancho Vista Trailer Park at Rancho Drive. It is estimated that less than 50,000 gallons of wastewater overflowed during the four spills. Maintenance crews were on the scene throughout the night and the overflows were stopped at 2 a.m. on Thursday, January 17. Crews were also on scene later in the morning to perform cleanups and monitor flows.

 

Flows into the Sonoma Valley wastewater treatment plant were measured at 20 million gallons per day at 7 p.m. Wednesday night, which is about 10 times greater than flows during dry weather. The increased flows are attributed to inflow and infiltration, which allows groundwater and storm water to enter leaky sewer pipelines, manhole covers and private sewer laterals. The Sonoma Valley County Sanitation District (District) is investing in several projects to reduce inflow and infiltration into its collection system.

 

This summer, the District has plans for a $6-million project to replace 1.8 miles of pipeline along Highway 12. Over the next several years, the District will continue to replace aging pipelines. In addition, the District is implementing a sewer lateral inspection and repair program aimed at reducing inflow from private sewer laterals and illegal connections to the sewer system. Since 1994, the District has completed approximately 9.7 miles of major capacity and structural improvement projects at a cost of $14.9 million.

 

Sonoma Water’s two water supply reservoirs benefitted from the storm, with Lake Mendocino filling to the 72,000 acre-foot level, and rising into the flood control pool for the first time this season. When the reservoir reaches 68,000 acre feet, the US Army Corps of Engineers (Army Corps) then controls the dam operations for flood control purposes. But under a new program being tested this year, the Army Corps will allow Sonoma Water to store an additional 11,650 acre feet of water (3.8 billion gallons) in the flood pool, relying on modern weather prediction technology that can forecast incoming storms and provide the Army Corps with the flexibility to release water in advance of the next storm.

 

Lake Sonoma, the larger of the two reservoirs, saw storage swell to 227,000 acre feet, an increase of 15,000 acre feet over a 24-hour period. Between the two reservoirs, the storm brought an increased storage of 20,000 acre feet, or roughly 6.5 billion gallons of water. 

 

CURRENT INFORMATIONabout Sonoma Water’s water supply levels can be found at: www.sonomawater.org/current-water-supply-levels

 

Lake Sonoma and Mendocino water levels

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