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<br />I, <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />D, WATER SURFACE PROFILE DETERMINATION <br /> <br />The starting water surface elevations at the downstream end of Kinney Creek, Fonder Draw, North <br />Pinery and South Pinery are based on water surface elevationsforthe 10-yearfrequency storm occurring along <br />Cherry Creek. The starting water surface elevations were taken from the "Cherry Creek Corridor - Reservoir to <br />Scott Road Major Drainageway FHAD Study" (Reference 4), The starting water surface elevations for the <br />tributaries at their junctions were calculated based upon the energy method within HEC-RAS, <br /> <br />Water surface profiles at dams/embankments and at roadway crossings were computed assuming <br />embankments are stable for all flood events, even if there was a reasonable expectation of embankment failure <br />during such events, This method produces a conservative estimate of upstream water surface elevations, The <br />computation of dam breach floodplains downstream of embankments was not included in the scope of this <br />project <br /> <br />Water surface profiles were determined using the HEC-RAS program with a sub-critical profile <br />assumption, For some channel reaches, the HEC-RAS analysis, if allowed, would result in supercritical flow <br />regimes and associated lower water surface elevations, However, given the general tendency of stormwater <br />flows in natural channels to gravitate towards sub-critical flow conditions (through naturally occurring hydraulic <br />jumps and other unmodeled energy losses), all supercritical flow regimes were modeled and reported with <br />critical depth elevations, <br /> <br />E. SHALLOW FLOODINGIINEFFECTIVE FLOW AREAS <br /> <br />Several study reaches included ineffective flow areas (Le., ponding of backwater in a shallow depression <br />adjacent to the main channel) and areas where flows are spatially varied and did not reflect the main channel <br />flood profile (Le., on the downstream side of embankments where overflows occur), <br /> <br />For areas of shallow flooding that are not connected to the main channel flood profile, estimated <br />floodplain boundaries were delineated based upon a separate hydraulic analysis utilizing normal depth <br />.~ <br />calculations and by following the flow paths using the 2' contours until such flows return to the main floodplain. <br />Boundaries of ineffective flow areas are delineated based upon a level water surface at the same elevation as <br /> <br />IV.Z <br /> <br />the main channel water surface at an estimated interface location, Average flood depths associated with each <br />shallow flooding area are noted on the drawings, <br /> <br />" <br /> <br />F, SPLIT FLOW AREAS <br /> <br />i <br /> <br />At several locations along Kinney Creek, Fonder Draw, and North Pinery Creek, flood flows will be <br />diverted away from the main channel due to undersized culverts and channel sections. The diverted flows will <br />inundate areas away from the main floodplains and eventually return to the main channel at downstream <br />locations. These areas are shown as shallow flooding areas on the plan and profile sheets, <br /> <br />The amounts of split flows were estimated using the lateral weir split flow computation option within <br />HEC-RAS models. Lateral weirs were defined at locations where the channel and overbank capacities were <br />exceeded, <br />