Floodflow characteristics of Honcut Creek at State Highway 70 bridges near Live Oak, California

Open-File Report 81-1010



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State Highway 70 crosses Honcut Creek about 3.2 miles upstream from its confluence with the Feather River, by three bridges separated by short approach embankments. The California Department of Transportation is planning to replace or widen these bridges; this report evaluates flow characteristics of the existing and proposed crossings. Agricultural improvements on the flood plain and low levees affect the magnitufe and distribution of flow to the bridges. Water-surface elevations of Honcut Creek are affected by levees on the flood plain, a natural channel constriction about 3,000 feet downstream from the bridges, and by high water levels on the Feather River. The average recurrence interval for overbank flow is less than 2 years. A flood with an average recurrence interval of 50 years would be about 19,000 cubic feet per second. For flows of 20,000 cubic feet per second on Honcut Creek, and with present bridge conditions, backwater caused by the bridge is about 0.4 foot. If the left-bank bridge is eliminated, backwater would increase to 0.5 foot. The bridges and approach embankments occupy about 66 percent of the channel. The average velocity of flow at the bridge ranges from 1 to 3.2 feet per second. For present channel and bridge conditions, overbank flows are distributed among the three bridges in a proportion of about 10, 40, and 50 percent for flows between 2,850 and 8,480 cubic feet per second. (USGS)

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Floodflow characteristics of Honcut Creek at State Highway 70 bridges near Live Oak, California
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Open-File Report
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U.S. Geological Survey,
vii, 39 p., ill., map ;28 cm.