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<br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br /> <br />Bosley Wash Drainage Master Plan <br />i .' ~','~---'^'^ .-..,... -, . ,. f~-"'-- ". <br />t ~ - ,____.;. <br /> <br /> <br />Phase 2: Alternative Drainage Facility Evaluation <br /> <br />2.3 Inadvertent Storage <br /> <br />Inadvertent storage represents a major source of flooding within the Bosley Wash <br />Watershed. This storage is generally associated with ponding behind culverts that lack <br />capacity to convey the full flow reaching the structure. The water is stored behind the <br />culvert and eventually drains after the inflow flood peak has subsided. This affect, when <br />properly anticipated and designed, can be a very effective way of managing flood flows. <br />However, when the storage is inadvertent, there is often a negative impact, as the ponded <br />area is not confined to dedicated areas. Such is the case within the Bosley Wash <br />Watershed. <br /> <br />In spite of the adverse impac~s that may result from inadvertent storage, there is often a <br />significant benefit. The storage of water, in combination with the limiting culvert <br />capacities, tends to reduce the flow rate downstream. This, in turn, reduces the <br />downstream flood hazard as the channels and culverts are better able to handle the lower <br />flow rates without overtopping. <br /> <br />2.3.1 Upstream of 1-70 <br /> <br />The area upstream of 1-70, near 34 Road extended, is a typical example of inadvertent <br />storage. In this area, water ponds to a significant depth as a result of the limiting capacity <br />of the 1-70 culvert. The culvert, an 8-foot x 6-foot box culvert, is capable of handling <br />about 470 cfs. The inflow from the tributary watershed is approximately 1700 cfs. In <br />order to limit discharges through the culvert to 470 c:fs, approximately 45 acre-feet (AP) <br />of water must be stored. <br /> <br />This area is ideal for inadvertent storage. There are few structures and a limited amount <br />of flood damage associated with ponding. Equally important, there is a dramatic decrease <br />in the downstream discharge, which benefits the entire Watershed below this structure. <br /> <br />2.3.2 G Road <br /> <br />The small culvert beneath G Road creates a large area of inadvertent storage (see Figure <br />5). Approximately 75 AF of water are stored at this location. The resulting area of <br />inundation includes a number of structures in the vicinity of G Road and the Government <br /> <br />EZ2~:' '~j;~-?~~i~"~:;~~!-~,{t-~:~':_~~'~~:':::2SS~' -~"-'-; ~'~ ~ ~:.~ ~-" ._n"'-... "- <br /> <br />[,:{!'1~.1 <br />Y ';: .~~ <br />"':" f~'~~~I~'~~~2~~(': <br /> <br /> <br />Page 6 <br /> <br />1'--,,\ <br /> <br />~~ <br /> <br />@'1 <br />