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I I I I I I I I I I I I I I I I I I I I -7- planted in frequently inundated low areas below bridges and drop structures to help dissipate residual en ergy. Capacity improvements were accomplished at roadway crossings without replacing existing bridges or culverts, resulting in significant savings, At Broadway, the capacity of the existing bridge was increased by channel improvements and the addition of three 10- by 10-foot reinforced concrete box culverts. The use of precast concrete box culverts enabled timely completion of this portion of the project with less disruption to traffic, At South Sherman Street, an existing 12-foot-high by 18-foot- wide concrete box culvert was improved by adding two Il-foot-high by IS-foot-wide cast-in-place concrete boxes. The existing debris-strewn channel beneath the U.S. 285 bridge was made more efficient by installation of a concrete-lined channel and concrete slope paving. The channel improvements between Broadway and Clarkson Streets were completed in 1987 at a cost of $3 million. Channel Improvements in Downtown Englewood In November 1988 construction was completed on the fInal portion of flood control improvements in downtown Englewood, The focal point of the downtown project is an on-stream lake created by a self- modulating, 8.5-foot-high by 42-foot-wide fabridam located at the inlet of the box culvert. The water- inflated fabridam adjusts itself for normal fluctuations in creek flow to maintain a stable lake water surface during non-flood periods, When a major flow occurs, the fabridam will automatically deflate, enabling the concrete-lined lake to function as an efficient flood channeL Controls for the fabridam are housed in a nearby subsurface pump station, These controls include an emergency siphon system whereby the water inside the dam would be automatically evacuated in the event of a power failure during a major flood. Thus, emergency flood capacity is provided without the presence of an operator. Storm flows were routed through the lake by detailed hydrologic modeling techniques to determine proper inflation and deflation rates for the fabridam. A computer program was written to perform the routing of the various flood events through the lake, Elevation settings for proposed sensors or probes to activate dam inflation/deflation were chosen by trial and then run through the computer simulation, Optimum operational probe settings were obtained after a number of iterations. during this analysis it was determined that sediment flushing could be achieved by lowering of the dam as flood flows increased over a predetermined level. A location at the crest of a drop structure just upstream of Broadway was chosen as the best site for an adjustable remote probe to sense this flow