Cache Creek Flood Study
Yolo County and City of Woodland
Northern California
The scope of this 20 miles study, from Capay Dam to Interstate 5 in the proximity
of Sacramento, California, was to perform hydrologic and hydraulic analysis of
Cache Creek and to compute the 100-, and 500-year flood profiles and floodplain
and floodway along Cache Creek. The photo on the left shows Cache Creek flowing over
Capay dam at the upstream limit of the flood study. The unique feature of this
study was the modeling of the breakout flows from Cache Creek channel as a
result of the failure of the non-certified levees along both banks of the channel
in accordance with FEMA's Guidelines and Specifications. Four (4) levee failure
scenarios were used. Another important feature of this study was the hydraulic
modeling of the extensive gravel mining areas located in the lower reaches of Cache
Creek. Digital Terrain Model (DTM) of Cache Creek floodplain was used to perform the
hydraulic analysis using HEC-2 model. Hydrologic analysis was performed in
coordination with Sacramento District using calibrated HEC-1 model. Flood
maps for Cache Creek were prepared on hard copy and in digital format.
The scope of the hydraulic analysis was to use the breakout flows from
Cache Creek channel and from levees failure scenarios to determine the
100-year shallow flooding in the City of Woodland, located
approximately 20 miles northwest of Sacramento. The principal
of hydraulic balance, using HEC-2 model, was used to compute the
depths of flow across the City of Woodland and to determine
the remaining flow toward the Yolo-By-Pass. This complex study
required the retrieval of all available data and information and
extensive site investigation and coordination, particularly to
identify levee locations and non-returning split flow breakout areas.
