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<br />II <br />II <br />~I <br />II <br />11 <br />,II <br />II <br />II <br />II <br />II <br />II <br />II <br />II <br />II <br />II <br />II <br />II <br />II <br />I] <br /> <br />ASSUi~pnONS <br />The fOllowing assumptions were ~ade as guides in conducting the hy- <br />draulic analysis: <br />Blackmer Lake: Starting IOO-year flood elevation at the Lake as <br />taken from the aforementioned Little Dry Creek report is based on the <br />conditions existing in May 1974. It is beyond the scope of the present <br />study to determine if there have been any changes in the spillway and <br />outlet capacities, or the reservoir capacity/depth relationship which <br />might have significantly changed the starting 100-year flood elevation. <br />!:lliLhl ine Canal: Highline Canal was assumed not to intercept 100-year <br />flood runoff even though, at the point where Blackmer Gulch Tributary <br />intersects with the canal, the downstream canal bank is approximately 4.5 <br />feet higher than the upstream canal bank. It was further assumed that <br />the flood waters would overtop the downstream canal bank directly across <br />from the point where the water first crosses the canal, <br />Unnamed Dike at.Sta._l..o_+ 00: This small dike was evidently recently <br />constructed as a temporary crossing of the gulCh to provide acCf:SS to the <br />land north of the end of Fairfax Street. The dike has no provision for <br />overtopping, nor is there any outlet. At the time the aerial photo~]raphy <br />was completed, no water had accumulated behind the dike; however, storm <br />runoff since the mapping was completed has partially eroded a channel <br />through the dike. It was assumed that the erosion would proceed unchecked <br />and that the dike would not present a significant obstruction to major <br />flood fl ows. <br /> <br />Unnamed Dikes at Sta. 41 + 50 and Sta. 51 + 00: These two dikes <br />were considered to be of a more permanent nature than the dike at Sta. <br />30 + 00. As such, flood waters were assumed to flow over the dikes with- <br />out significant erosion of the gulch thalweg. It was further assumed <br />that the ponds formed by the dikes are of insignificant size to warrant <br />storage routing. <br />Holly Street: Construction of the Holly Street improvements added <br />culvert capacity as well as raising the level of the street approximately <br />five feet. Hydraulic calculations were completed based on the constructed <br />improvements. Topography upstream of Holly Street was known to have been <br />altered during the course of the construction. The changes in the topo- <br />graphy upstream of the street crossing are not shown on the drawings, nor <br />were they taken into account in the computer analysis. <br /> <br />- 4- <br />