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. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bosley Wash Drainage Master Plan f.'.'.'..,. L Phase 2: Alterna~ive Drainage Facility Evaluation channel. These reaches have a limited local impact to properties immediately adjacent to the channel. Additionally, there are 'a number of areas within the Bosley Wash Watershed where uncontrolled overflows from an' undersized channel flow away from the channel and don't return as they might in a traditional floodplain. These areas represent a significant area of flooding in the Watershed. In many ofthese cases, the uncontrolled overflows flow down gradient away from the channel and cause flooding unrelated to the water surfaces in the main channel. Since the overflows are no longer impacted by downstream tailwater, they generally flow straight downhill and are often flowing fast, but are fairly shallow. The uncontrolled overflows create a significant nuisance, and can cause considerable cleanup effort, but do not often cause major structural damage to flooded properties. A further consequence of these uncontrolled overflows is that some areas not ordinarily subject to flooding are now impacted. While some of these properties are subjected to only the shallow overland flow, others are impacted when the water eventually reaches a low point and begins to pond until it can be drained by the available drainage facilities in that area. These areas are often flooded at a much deeper level and may experience more significant flood damage. 2.1.1 Hwy 6IUnion Pacific Railroad Channel Flow in the channel along the Union Pacific Railroad (UPRR) occasionally exceeds the capacity of the channel. In these cases, water spreads out to the north until water in the channel recedes sufficiently to drain these flooded areas (see Figure 2). This problem is very localized and has a limited impact on flooding within the Bosley Wash basin. 2.1.2 Stub Ditch The drainage channel along Stub Ditch represents an area of uncontrolled overflows. Along much of the channel, the capacities are not adequate to convey all of the inflows. The flow eventually overtops the southern bank of the drainage channel, overtops Stub Ditch road, and flows downhill to the south. The overflows collect again in the ditch along the Government Highline Canal. For portions of the western reaches of the Ditch, L1LF~\:~:2:;'->~~~'~,~~~,;:;12~:,;'~E~)1:::T:i:~~==z1iill:=:~~~-~..~~~~.~_~~____ ~"~,.~~---::;:~.__ :~L" .~, ;;..~~,v. , ;,;:;~:~.I.i:~l!.fi,c. ..'..". J:..'" / -' ';' :. " ;.. ~ ~<i;.1~:4<:j}:~~~~,'. Page 3 /"'"--...., ~ @'1