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I I I I I I I I I I I I I I I I I I I - Bear Creek at Idledale. (Sheets 2 and 3) Tt>e lOa-year discharge is quite large and flood depths on the developed overbank are expected to range from 4 to 6 feet. Therefore, the flooding hazards are high. Because of depths and steep slopes at the edge of the floodplain, no floodway was delineated for this reach. - Sawmill Gulch. (Sheets 12 tt>rough 14) - Bear Creek at Morrison. (Sheets 4 through 6) Data from a previous study made by the Army Corps of Engineer (Reference 4) was used for the floodplain delineation. Within Morri- son corporate limits, the floodway delineated for the Morrison Flood Insurance Study (Reference 5) in accordance with the FEMA criteria was adopted. Outside the corpo~ate limits, the criteria adopted by Jefferson County permits very little encroachment on the floodplain because flow depths are over 2 feet even in areas where the floodplain is wide. Also, development with~n the floodplain of this reach would be the cause of greater flooding in the community. The very steep slope of the streambed and the deeply incised valley results in a narrow floodplain and, therefore, no floodway was delineated. Some limited flooding might occur at the Grapevine Road crossing at the upstream end of the reach where the culvert is under- sized. A portion of the discharge at this location might cause sheetflow down Grapevine Road. - Tu~key Creek at Tiny Town. (Sheets 15 through 17) - Mount Vernon Creek. (Sheets 7 through 11) Data from a study made by the Army Corps of Engineers (Reference 4) was used to delineate the floodplain for the lower reach of the study. Within Morrison corporate limits the floodway delineated for the Morrison Flood Insurance Study (Reference 5) in accordance with FEMA criteria was adopted. At the downstream end of tt>e reach, Mount Vernon Creek is not contained within its banks and flooding will occur on the highly developed overbanks. Upstream, the valley is deeply incised and the lOa-year discharge will be contained within a rela- tively narrow area. No development has encroached onto the floodplain in this area and the two major crossings (Red Rocks Access Roads) can handle the flow without overtopping. No floodway has been delineated for this reach because the adopted criteria does not allow for a substantial encroachment. Upstream of its confluence with Parmalee Gulch, Turkey Creek has a relatively mild slope and a wide floodplain, The only major existing development in the floodplain is the tourist attraction of "Tiny Town" whict> includes small stvuctures and a model railroad with a few bridges whose sizes would not significantly affect the floodplain. Some encroachment is possible in a few areas east of Highway 8 and on a portion of the overbank a~ea where depths are relatively shallow. At the downstream end of the study where Highway 8 crosses the stream, overtopping of the structure will occur and some shallow flooding is expected down Highway 285 until the topography or a. local drainage structure allows this portion of the discharge to go back into the channel. - Turkey Creek U/S Bear Creek Reservoir. (Sheets 18 through 21) This portion of Turkey Creek has a steep slope and the topography indicates that the main channel has meandered in the past. No signi- ficant development has yet taken place in the floodplain. Very little encroachment is possible on most of the reach. At the downstream end of the study, a 2000 feet long 8'x8' reinforced concrete box culvert carries a portion of the flow under the Highway 285 and Soda Lakes Road interchange. The culvert was designed for a 50-year discharge of 1100 cfs. Hand calculations show that the culvert would carry appro~ imately 1300 cfs during a laO-year flood and that the remainder of the discharge would flow overland along Highway 285, under the Soda Lakes Road overpass, and eventually back into the original channel near Bear Creek Reservoir. This overland flow was modeled accordingly. -8-