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<br />I <br />il <br />I <br />I <br />I <br />I <br />'I <br />I <br />]1 <br />il <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />-5- <br /> <br />the tailwater conditions for the structure. Then iterative backwater and overflow weir spill calculations <br />were performed upstream of the constriction structure to analyze the spatially varied flow conditions <br />at the side channel spillway. As a result of the hydraulic refmements, it was determined that the <br />spillway would only operate at flows greater than the 20-year flood of 2,900 cfs, Approximately 940 <br />cfs of the totallOO-year peak flow of 4,400 cfs would spill into the storage facility, Storage capacity <br />at 100-year flood level is 85 acre-feet. Water contained within the storage area drains to the northwest <br />corner where it is discharged by gravity via a 36-inch reinforced concrete pipeline, A flap gate at the <br />outlet end of the pipe prevents creek flows from backing into the storage area, <br /> <br />A concrete maintenance path, which also serves as a recreational trail, was designed along the crest <br />of the overflow spillway as a means of providing a fixed control of the spillway crest width and <br />elevation. Hydraulic analyses conducted for various inflows at the spillway resulted in the conclusion <br />that the 4: I grassed slope would withstand velocities for the full range of design flows with minimal <br />erosion, due to the shallow flow depths over the long spillway, <br /> <br />Construction of the off-channel storage facility was completed between Aprill983 and October 1984 <br />at a cost of$1.7 million, To date all systems have performed well and the athletic fields have remained <br />dry and stable under repetitive use. <br /> <br />Channel Improvements Between Broadway and Clarkson Street <br />Prior to the project, the existing Little Dry Creek channel had a constricted waterway with steep banks <br />and limited capacity. Channel widening options were limited due to building encroachment along the <br />channel corridor. To increase channel capacity, cantilever retaining walls were designed for many <br />applications, However, where nearby buildings or structures prevented standard construction <br />methods, retaining waIls comprised of drilled caissons with structural concrete facings were designed, <br />All channel waIls are constructed with buff-colored concrete with a special textured surface pattern <br />and a sandblasted fmish, <br />