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<br />L. Lang <br />February 17, 1987 <br />Page 3 <br /> <br />indicate lower water surfaces by less tl1iln one tenth of a foot <br />throughout the study reach. These results 'imply that the <br />rE!l at i vely small wi dth of the zone exami ned (approximately four <br />percent of the total floodplain width) limits its potential <br />effecti veness for 1 oweri ng flood e 1 evat.i ons. <br /> <br />Summary pri ntouts of all of the HEC-2 runs are i ncl uded in the Appendi x. <br />Section 9 is located at the upstream face of the bridges; Water surfaces <br />at this location may be compared against th,= design low chords of the <br />bridges, indicated in the following table. <br /> <br />Brid[e No.:- <br /> <br />1 (north) <br />3 <br />4 <br />5 (south) <br /> <br />L.ow Chord <br /> <br />3714.!i <br />3716.!i <br />3714.! <br />3714.3 <br /> <br />It should be noted that the one dimensiona.1 nature of the HEC-2 program <br />1 imits the abil ity of the model to accurate.ly portr.ay the compl ex fl ow <br />patterns that would occur in a wide floodplain such as at Crook. For <br />instance, a uniform water surface is indicated by the model at each cross <br />section, whereas in rl~ality numerous var.lations in water surface could <br />exist, reflecting zones of flow ",hich may be partiany or fully <br />hydraul ically disconnected. The model may allow flow to transfer laterally <br />across a sect.ion in an unrealistic manner. A number of these limitations <br />are evident in the hydraulic model of the South Platte River at Crook. <br />HowevE~r, the model does provi de general results t.hat are sui tabl e for <br />assessing the impacts of the proposed 1 !,vee system, just as it was <br />considered suitable for assessing the impacts. of various bridge <br />alternati ves for the Department of Hi ghways. <br /> <br />Please call if you have any questions regarding t.he hydraul'ic analysis that <br />was performed for the proposed levee improvements at Crook. We look <br />forward to proceeding with the preparation of construction plans for this <br />proj e!~t. <br /> <br />Very truly yours, <br /> <br />MUL.LER ENGI~PANY' <br /> <br />ct~~~liman~ P.E. <br /> <br />Sr. Project Engineer <br /> <br />INC. <br /> <br />JTW:lf <br />