Inundation Area '06 New Year's Flood in the Laguna-Mark West Drainage

Project Chief: Lorraine Flint

The Laguna de Santa Rosa, located in Sonoma County, California, flows into Mark West Creek, which drains into the Russian River. The Laguna-Mark West drainage is the largest drainage contributing to the Russian River, encompassing approximately 21% of the total Russian River basin. Runoff from precipitation in headwater areas enters fast-flowing creeks that transport water and sediment downstream into a network of flood control channels designed to reduce flooding in the Santa Rosa urban area. The Sonoma County Water Agency (SCWA) and the San Francisco District office of the U.S. Army Corps of Engineers (CORPS) have identified several issues associated with sedimentation in the lower reaches of the Laguna de Santa Rosa and Mark West Creek in Sonoma County. Most predominantly, increased upland erosion and sediment delivery from the eastern side of the watershed to the lower Laguna channel has the potential to significantly increase aggradation and thereby decrease the flood storage capability of the lower basin and limit its function as a wetland (http://www.lagunadesantarosa.org).

On December 31, 2005 and January 1, 2006, the lower Laguna-Mark West drainage system experienced flooding with peak flows of over 6500 cfs at USGS streamflow gage 11465750 (LAGUNA DE SANTA ROSA C NR SEBASTOPOL CA), a location that experiences median flows of less than 500 cfs. This caused overbanking at many channel locations for several periods of time between December 12 and January 6. The timely characterization of the inundation extent and floodplain deposition for this drainage will provide an upper boundary to the floodplain sedimentation in support of current studies evaluating flow and sedimentation conditions on floodplains.

The objectives of this study are to measure and map the inundation extent of the New Year's flood WY2006 on the Laguna de Santa Rosa and lower Mark West Creek, analyze the precipitation intensities and amounts for the region to establish the conditions under which this floodplain deposition occurred, and develop a deposition potential map of the area for this precipitation event.

Contact Information

Lorraine Flint
Office phone: 916-278-3000

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