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• 2.05.3(4) Ponds. Imyoundments and Diversions (continued) <br />2.~,gleville Gulch <br />a) Peak Flows and Flood Plain Calculations <br />[n this section, the peak flow calculations for Engleville Gulch are shown and data is <br />presented on the gulch Flood plains in order to determine the safety of structures in the <br />permit area. <br />The SEDCAD program for surface hydrology was used to predict peak flows for the <br />Engleville Gulch watershed. Exhibit BB shows the entire watershed and the various <br />junctions and branches that were used for input to the program. As can be seen from <br />Exhibit BB, Junction 3 is at the low point of the disturbed area near the sediment <br />pond. The peak flow at this junction will be used as the design flow for the permit <br />area. <br />The local SCS office in Trinidad was asked to determine the soil types and runoff <br />• curve numbers for the Engleville Gulch watershed. As is seen in the attached letter, <br />they determined that the hydrologic soil group is a D group and the curve number for <br />brush vegetation is 77 while pinon-juniper is 80. Since brush vegetation is stated to be <br />dominant, an average curve number for the watershed is determined to be 78. <br />The SEDCAD run for the 100 year-24 hour storm is also enclosed in this section. A <br />rainfall of 4.2 inches for this event was determined from SCS TR-55. <br />The printout shows a peak flow of 1559 cfs. <br />-2- <br />• Revised for permit renewal 11/17/95 <br />