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<br />I <br /> <br />Page Eight <br />Battlement nese' Development Storm Drainage and Flood Plain Study <br /> <br />I <br />I <br /> <br />analyses of detention facilities and its application has been <br />computerized for rapid, highly accurate calculations. <br /> <br />I <br /> <br />A comparison of Tables I and III indicate that a close <br />comparison is obtained between the SCS method utilizing a <br />curve number of 70 and the Colorado Unit Fydrograph Procedure <br />utilizing an infiltration rate of 0.50 inches per hour. Table IV <br />tabulates this comparison: <br /> <br />TABLE IV <br /> <br />I <br /> <br />I <br />I <br />I <br />I <br /> <br />Return <br />Frequency <br /> <br />Runoff Obtained By <br />SCS Method With <br />N = 70 <br /> <br />Runoff Obtained By <br />Colorado Unit Hydro- <br />graph Procedure With <br />Infiltration = .5" Hour <br /> <br />2 year <br /> <br />35 cfs <br /> <br />51 cfs <br /> <br />10 year <br /> <br />196 cfs <br /> <br />173 cfs <br /> <br />100 year <br /> <br />655 cfs <br /> <br />77 3 cfs <br /> <br />I <br /> <br />Based upon the comparison of results from design procedures, <br />field analyses of the volume of runoff which appears to have <br />been handled historically by channels, and experience with similar <br />drainage basins, the Colorado Unit Hydrograph Procedure utilizing <br />a basic infiltration rate of 0.50 inches per hour and a pervious area <br />retention depth of 0.50 inches has been selected for analysis of <br />the major drainageway facilities for the P.U.D. analyses. <br /> <br />I <br />I <br /> <br />As future, individual areas are platted and local storm <br />sewer systems are designed, the rational formula may be utilized <br />with proper recognition of runoff coefficients for the degree of <br />development encountered. <br /> <br />IV. Physical Aspects of site <br /> <br />I <br /> <br />The drainage patterns characteristic of a majority of <br />the site present some unusual drainage considerations. Investi- <br />gation of the topo map reveals that there are no well-defined <br />drainage\~ays bet\~een ~lonument Gulch and Battlement Creek. What <br />appear to be drainage courses in one area may eventually revert <br />to a small irrigation ditch or fade out altoaether. Not until <br />the escarpments- near the Colorado River are ~pproached do well <br />defined channels appear. Careful analyses of the tributary <br /> <br />I <br /> <br />I <br />I <br />I <br />I <br />