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<br />Table 2. Peak Discharges Along Pawnee Creek Main Channel Under Existing Conditions <br /> <br />1!!::Y.lllir <br />_J cfs) <br />1517 <br />1517 <br />---- <br />2945 <br />--- <br />'Upstream CR. 31 }264 <br />* Split flows cause reduced discharge in the main channel <br /> <br />Location <br /> <br />, <br />. <br /> <br />iO-Year l!l.O.::Yw <br />(cfs) (cfs) <br />2026 2226 <br />2026 2226 <br />5434 6645 <br />6729 8611 <br /> <br />'Mouth (South Platte River I OO-Year Floodplain) <br />'Upstream HWY 6 <br />'Upstream CR. 33 <br /> <br />lhdraulics <br /> <br />The hydraulic analysis for this report was completed using the U.S. Army Corps of Engineers HEC-2 <br />computer prograrn, Version 4.6.2. Existing HEC-2 models from previous studies were used as a basis <br />for the hydraulic analysis and modified to study the proposed improvements in more detail. The <br />source of the base HEC-2 models for Pawnee Creek is the 1992 SCS Report. The base models for <br />Pawnee Creek Overflow, within the City of Sterling, carne from the 1983 LeaflRCI Report. Flow <br />measurements taken by the CWCB from high water marks during the :i 997 flood were used to help <br />calibrate and refine the hydraulic model. Flow characteristics for proposed future improvements were <br />modeled using HEC-2 in conjunction with weir overflow equations. <br /> <br />Hydraulic analysis was made to det,ermine the carrying ca.pacity of Pawnee Creek itself and to help <br />define where and how much out-of~channel flow occurs. Significant diversion of flows occurs at <br />several locations. Overflow spills out of the main channel occur near CR. 29 and 3 t, and along the <br />HWY 6IRailroad embankments. <br /> <br />Alkrnative Improvements <br /> <br />Based on a review of the existing reports and discussions with the proje,;t sponsors ancllocal citizens, <br />six alternative improvement projects were selected for furth(:r study. A mnceptual design of all of the <br />proposed projects was completed in sufficient detail to det(:rmine relativ,e construction quantities, cost <br />estimates, and expected benefits. Approximate locations of the altematives are shown on Figure 4. <br />Each Alternative, with the exception of the "No Action" Altemative, pmtects varying lengths of the <br />area surrounding the lower portions of Pawnee Creek, and the Pavmee Creek overflow. The <br />alternatives studied are as follows: <br /> <br />Alternative No.1: "No Action" Altemative. This alternativt: would not result in any construction of <br />flood prevention improvements. In 'the event of future floods, high damage to cropland, fann houses, <br />residential homes in the City of Sterling, commercial buildings, roads and railroads would very likely <br />occur. Over $10 million in damagt: occurred from the 1997 flood, in the lower reaches of Pawnee <br />Creek. This alternative was not acceptable to the City of Sterling, Logan County and the m~iority of <br />Citizens. <br /> <br />[-7 <br />