Walnut Creek Channel Improvement Project, Contra Costa County, California. Hydraulic Model Investigation.

摘要

Tests were conducted on a 1:25-scale model of the existing covered channels in the city of Walnut Creek where Las Trampas Creek and San Ramon Creek join to form Walnut Creek. The purpose of the model investigation was to determine the capabity of the existing flood-control channel system and methods for increasing the capacity and improving the flow characteristics in the channels. The model reproduced approximately 818 ft of Walnut Creek, 2,264 ft of San Ramon Creek, and 1,492 ft of Las Trampas Creek, and was constructed so that the slopes of the channels could be adjusted to reproduce various energy gradients that would result from roughness values different than those anticipated. The slopes of the model were initially adjusted to produce an energy gradient resulting from a Manning's roughness factor n of 0.012 in the prototype. The maximum discharge capacities were determined to be as follows: Las Trampas Creek, 11,000 cfs (100-year frequency flow); San Ramon Creek, 17,400 cfs (2,200 cfs more than the 100-year frequency flow); Walnut Creek conduit, 24,000 cfs. A soffit installed on the bottom of the T-beams on the roof of Walnut Creek increased its capacity to 27,500 cfs.