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|Title:||Walnut Creek Flood-control Project, Contra Costa County, California : hydraulic model investigation|
|Authors:||United States. Army. Corps of Engineers. Sacramento District.|
Davis, W. Glenn.
San Ramon Creek
Contra Costa County, California
|Publisher:||Hydraulics Laboratory (U.S.)|
Engineer Research and Development Center (U.S.)
|Series/Report no.:||Technical report (U.S. Army Engineer Waterways Experiment Station) ; HL- 87-14.|
Abstract: Tests were conducted on a 1:25-scale model of the Walnut Creek channel to determine the adequacy of proposed channel improvements for the Walnut Creek channel, the San Ramon Bypass Channel, and their junction. The model reproduced approximately 1,084 ft of the San Ramon Bypass Channel, 730 ft of the Walnut Creek channel upstream from the junction, with topography reproduced upstream from the entrance to the revised channel, and 640 ft of the existing Walnut Creek channel downstream from the junction. The model was constructed so that the slopes of the channels could be adjusted to reproduce various energy gradients equivalent to those resulting from different prototype Manning' s η roughness factors. The slopes of the model were initially adjusted to produce an energy gradient resulting from a Manning's η roughness factor of 0.012 in the prototype. Unsatisfactory flow conditions were observed in the Walnut Creek channel upstream from the junction due to entrance conditions into the high-velocity channel. A wall was installed which bridged the access ramp and provided satisfactory flow conditions in the portion of Walnut Creek upstream from the junction. Flow exceeded the wall heights at several points downstream from the San Ramon-Walnut Creek junction for both design flows with their maximum concurrent flows. A 40-ft-long divider extension installed at the junction greatly improved flow conditions in the channel downstream and eliminated overtopping of the channel walls. The slopes of the high-velocity channel were adjusted to reproduce the energy gradient resulting from a Manning's η roughness factor of 0.014 in the prototype. For both design flow conditions, overtopping of the wall heights was observed in the Walnut Creek channel. The width of the San Ramon Bypass Channel was reduced by 1 ft to 23 ft just upstream of the junction and the channel alignment was improved at the junction; the slope of the Walnut Creek channel was increased to 0.005 ft/ft downstream from the junction with this slope maintained in the San Ramon Bypass Channel upstream from the junction to sta 584+98; and the slope of the Walnut Creek channel upstream from the junction was increased to 0.0185 ft/ft extending to sta 584+50. These modifications provided satisfactory flow conditions for both design flows in the high- velocity channels. However, by steepening the slopes in the Walnut Creek channel, the upstream elevation of the channel invert was increased 1.5 ft, which increased the upstream pool elevation to an undesirable level. When flow through the access ramp was blocked, channel efficiency was increased and a satisfactory pool elevation was achieved with the design flow in Walnut Creek.
|Appears in Collections:||Technical Report|