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<br />B) Hydraulics <br />The hydraulics for the Big Dry Creek Channel were <br />determined by utilizing the "HEC-2 Water Surface Profiles" <br />computer program, a modification of a computer program <br />developed in the Hydrological Engineering Center of the Corps <br />of Engineers. This program computes and plots the water <br />surface profile for drainage channels of any cross section <br />for either subcritical or supercritical flow conditions. The <br />effects of various hydraulic structures such as bridges, <br />culverts, weirs, embankments and dams may be considered in <br />the computation. The principal use of the program is for <br />determining channel flow profiles for various frequency floods <br />for both natural and modified conditions. The latter may <br />include channel improvements, levees, floodways, dams, etc. <br /> <br />The computational procedure is similar to Method 1, <br /> <br /> <br />"Backwater Curves in River Channels" in the Engineering <br /> <br /> <br />Manual 1110-2-1409 of the U. S. Army Corps of Engineers. This <br /> <br /> <br />method applies Bernoulli's theorem for the total energy at <br /> <br /> <br />each cross section and Manning's formula for the friction <br /> <br /> <br />head loss between cross sections. In this program the <br /> <br /> <br />average friction slope for a reach between two cross sections <br /> <br /> <br />is determined in terms of the average of the conveyances at <br /> <br />the two ends of the reach. The critical water surface elevation <br /> <br /> <br />corresponding to the minimum specific energy is computed by <br />using an iterative process. <br /> <br />-40- <br />