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I I I I I I I I I I I I I I I I I I I 18 North Dry Gulch from Harlan Street to Pierce Street JEheets 17, 18) In this reach, the channel of North Dry Gulch appears only briefly enough to make it apparent that, at one time, a natural waterway did exist. The gulch has been replaced by culverts, usually about 36" in size, and has been filled so that the drainage patterns are very obscure. The predicted flooding is quite wide and relatively shallow. The flood plain contains nUmerous residential, commercial, and light industrial buildings, some of which could be extensively damaged. There are no specific or unique obstructions to the drainage patterns in the reach; the main characteristic is that of an obscured channel over which the flood must flow between buildings and along streets. the gulch may have reached or crossed the present alignment of Colfax between Balsam and Yarrow, but the construction of Colfax and the associated development have forced the flow to divide in this area. The flow which proceeds to the south of Colfax has been named Colfax Gulch for the purpose of discussion in this report. North Dry Gulch is regarded as that flow which stays north of Colfax Avenue. Because Colfax Avenue causes a division of flow, the computa- tion of the magnitude of flooding on each side of the street is extremely difficult. Extensive flooding of Colfax between Pierce and Lamar Streets has occurred in recent storms. The flooded area along Colfax illustrates that substantial disruption of traffic flow will occur in addition to damage to the structures. The flooding which reaches North Dry Gulch at Dover Street is composed of two distinct flows. The first is that generated by natural runoff in the basin above Dover, which consists of very low density residences with numerous small drainage courses and streets without curbs and gutters. It is anticipated that full development of this basin may include higher density resi- dences, improved street grading, and correction of the numerous small drainage problems. As a result, an increase in this por- tion of the flow is anticipated in the future. The second flow reaching Dover Street is that diverted out of Dry Gulch at Colfax and Garrison. This flow proceeds easterly on Colfax and results in a relatively large initial flow at the upstream end of the study. North Dry Gulch from Pierce Street to Dover Street (Sheets l5, 16, 1 7) Between Pierce Street and Dover Street, the upstream end of the North Dry Gulch analysis, the flood course is very difficult to define. One short length of channel is visible between Wadsworth and Vance, which indicates the historic existence of a channel between Colfax and l6th Avenue. It appears likely that