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