Model Study of the Confluence of San Juan Creek and Trabuco Creek, Orange County, California; Hydraulic Model Investigation.
1997
McVan, Darla C.
Tests were conducted on a 1:36-scale physical model of San Juan and Trabuco Creeks to determine the adequacy of the proposed channel improvements, and to determine the effects of the proposed railroad bridge piers on the channel. The model reproduced approximately 5,200 ft (1,585 m) of San Juan Creek, 100 ft (30 m) upstream of the San Diego Freeway with approximately 2,900 ft (884 m) downstream of the confluence (sta 150+00 to 98+00) with Trabuco Creek and 5,100 ft (1,550 m) of Trabuco Creek (station 51+00 to its confluence with San Juan Creek). Flow conditions were observed in both San Juan and Trabuco Creeks for various flow combinations including the design discharges, various unbalanced discharges, and balanced discharges. Later the fixed-bed channel invert was replaced with cohesionless material (fine pea-size gravel) to obtain scour patterns associated with a 24-hour storm hydrograph and 50 percent of peak flow for a 24-hour duration. Because very little scour occurred with the pea-gravel bed, a test was conducted with a 50 percent peak flow for a 24-hour duration using a sand and gravel bed. The model tests revealed that the proposed design with certain modifications would effectively contain design flow conditions in the San Juan Creek channel improvement project. However, due to the magnitude of water velocities in both creeks during the design flows, protection is needed to prevent erosion of the channel beds. A paved or rock-lined channel would provide bed stability; however, the model indicated that a rock-lined channel would increase the boundary roughness and cause overtopping of the banks.
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