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I I I I I I I I I I I I I I I I I I I 16 The flooding is affected to a certain degree by the Rocky Moun- tain Ditch which has a side spillway at the point where it crosses the gulch. All flow in the ditch exceeding the spillway crest is discharged into Dry Gulch. Observations have been made of such spills occurring during floods, due to the ditch conveying storm runoff from northern drainage basins. It is estimated that the magnitude of the spill is negligible in comparison to flood flows in Dry Gulch, and its effect has not been computed. Dry Gulch from Garrison Street to Miller Street (Sheets 5, 6) Between Garrison and Kipling Streets, the Dry Gulch channel is completely filled and developed. A small amount of flow is carried through storm sewers, leaving the majority of the runoff to flow overland between buildings. The development along the reach is predominantly commercial, with several light industrial facilities. Flooding is extensive in this area, and numerous large structures are flooded. The area experiences frequent flooding from minor rainstorms. The intersection of Colfax and Garrison is one of the most com- plicated and pivotal in the analysis. Dry Gulch crosses Colfax from northwest to southeast at Garrison, and the channel is com- pletely filled upstream of the intersection. The majority of the runoff reaching Colfax and Garrison is carried as overland flow, except for that which is conveyed in an undocumented storm sewer which ranges in size from a 48" pipe at the upstream end to an 11.6' x 2.5' box culvert at the downstream end. The fact that the culvert is relatively ineffective is illustrated by the flooding at this intersection on several occasions each year. The surface flow reaching the intersection must pond up until it crosses the crown of Colfax. Since the street slopes continually eastward, a significant flow proceeds east along Colfax. This flow leaves the Dry Gulch channel and flows to Dover Street where it enters the North Dry Gulch basin. This "diversion" results in a decrease in flood flows in Dry Gulch and an increase in flood flows on North Dry Gulch. The channel between Kipling and Miller Street at 15th Place is well defined, but is subject to flooding due to inadequate culvert crossings at Kipling Street and 15th Place. Flooding occurs at several homes facing 16th Avenue between Miller and Lee Streets. The flooding between Garrison and Iris Streets is predicted to cause the most extensive monetary loss in the Dry Gulch basin. The anticipated flood flows will reach depths of two to three feet and velocities of seven feet per second. These conditions are sufficient to result in severe property damage as well as potential loss of life. Dry Gulch from Miller Street to SilTll!ls Street (Sheets 3, 4, 5) The defined Dry Gulch channel terminates at 15th Place and Miller Street. Prior to the development in the area, it is believed