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I I I I I I I I I I I I I I I I I I I Jefferson County as well as certain Hydro-Triad, Ltd. analytical procedures and computer programs. Subsequent to the initial data gathering and field reconnaissance work to establish basin boundaries and existing storm drainage features, the study area was divided into 104 separate sub-basins within the 13 major drainageway areas totaling 36.3 main channel miles and 1.0 miles of special shallow flooding evaluation. The physical parameters, i.e., area, length, slope, percent imperviousness of each sub-basin for the future development conditions, were then defined and the design storm hydrographs developed for the 10 and 100 year recurrence interval storms. The design storms werp defined based upon data presented in the Rainfall/Runoff Information report, which were compared to the isopluvial ~aps presented in the Urban Storm Drainage Criteria Manual. The design rainfall values were checked against recently compiled U.S.G.S. data. The combining of the hydrographs and channel routing (Muskingum method) through the basins was accomplished by a computer program which produced the resultant hydrograrhs at the various design points. Routing of the flood hydrographs through the various ponds or reservoirs on the north branc!] of McIntyre Gulch and at the detention areas created by the various road embankments was performed by a reservoir routing program using the Modified Puls method (Reference 6). These data were then used to define future basin development flood plains for the 10 and 100 year floods along the major drain- ageways by performing a backwater analysis throughout the channel reaches. The channel sections used in the backwater analysis were digitized from CHAPTER II GENERAL STUDY AREA DESCRIPTION aerial photographs. A. Study Area The area for the Green Mountain Major Drainageway Planning Study comprises portions of four major drainage basins; McIntyre Gulch, Lakewood Gulch, Lena Gulch, and Bear Creek. The various channels in these basins drain the major portion of Green Mountain. The General Location Map, (Figure I) shows the study area and the major basins. The basin location and boundaries are shown in Figure 3. The 11 drainageways have been assigned letter des- ignations from A to L in a counterclockwise direction around Green Mountain. Drainage from the east side of Green Mountain is tributary to McIntyre Gulch. The McIntyre Gulch portion of the study area contains 2.45 square miles (see Table I). The basin is comprised of Drainageways A, B, C, and D totaling 9.13 stream miles of flood hazard delineation. Drainageways A and B make up the South Branch of McIntyre Gulch and Drainageways C and D make up the Center Branch and North Branch, respectively. The flood hazards for the reaches of McIntyre Gulch below the limits of the Green Mountain study area were previously delineated in Flood Hazard Area Delineation, McIntyre Gulch (Reference 9). The McIntyre Gulch basin and hydrological feature descriptions were set forth in Project Reuse (Reference 4). Since the study area contains only portions of the basins defined by Project Reuse, a direct comparison cann~t be made. However, no significant c~Jnges to the boundaries or the description have resulted from the Green Mountain study. The storm drainage problems in the McIntyre Gulch basin as discussed in Drainage and Geological Hazards, Planning Area 12, (Reference 18) were reviewed as part of the basic input data for this study. 2