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<br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />e <br />e <br />e <br />e <br />. <br />. <br />. <br />. <br />. <br />e <br />. <br />. <br />'. <br />. <br />. <br />. <br />,e <br />'. <br />Ie <br />'. <br />I. <br />. <br />I. <br />Ie <br />i. <br />:. <br />I: <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br /> <br />Bosley Wash Drainage Master Plan Phase I: Watershed Floodplain Delineation <br />_ ai'l!pIl'i -;,"~'~''''W&'''\V'i''''1@''''W''''~~_'';:\Gi~Z'~?;''''Z;: ;,,- ,""!ii:;:, "">,', <br />~ ~ ;~~::~~it~~'].'~~~-5wi_:~~":;t:0,'5Ctb/"$;"j;,,*;~,-",;.t.>'~;,p;-- <br /> <br />5.2.6 Other Channels and Facilities <br /> <br />The Henchy Waste and other tributaries to Bosley Wash were beyond the scope of this study and <br />were not modeled in detail in this study, <br /> <br />5,2,7 Culverts <br /> <br />Culverts were modeled as either projecting end sections, with headwalls or as a siphon, <br /> <br /> <br />depending on their physical geometry, It was assumed that all culverts and channels were free of <br /> <br />silt and debris, This condition was deemed appropriate due to regular maintenance by GJDD, <br /> <br /> <br />Typical maintenance includes cleaning culverts and channels of debris and sedimentation, as <br /> <br />well as proper control of vegetation in the ditches through processes such as controlled burns, <br /> <br />Minor debris may exist, but it was assumed that during the peak flow events that most of the <br /> <br />sediment would be mobilized and not be deposited until the falling limb of the hydrograph <br /> <br />occurred, <br /> <br />5,3 Hydraulic Analysis <br /> <br />The hydraulic analysis performed during this study established the water surface profile for a <br /> <br />number of runoff events. A summary of the computed water surfaces at select locations within <br /> <br />the watershed for various storms is presented in Table 7 and a graphic representation of the water <br /> <br />surface profiles are presented as Figures 6,1 though 6.4, <br /> <br />5.4 Floodway <br /> <br />A floodway was identified based on allowable encroachment into the 100-year floodplain, <br /> <br />Floodway widths were calculated using the encroachment feature in HEC,RAS, The floodway <br /> <br /> <br />was based on approximately equal reduction in conveyance on both sides of the floodplain that <br /> <br />would result in a total increase of not more than 1,0 feet in the water surface profile, Because of <br /> <br />the unique character of this watershed, the flooding is generally coincident with the Channel <br /> <br />banks, Results of these calculations are presented in Table 8. <br /> <br />~R'~: ~ -~~~~f{r;:}\:~,\~:'fE,-_\) <br /> <br />~ <br /> <br />lilt <br /> <br />,y""''''''''- <br />,!- >. <br />.-, '-.' <br />~~";&~~~i'-;;;"'"\ . <br /> <br />.'Z',:;;, <br />~ <br /> <br />Page 21 <br />