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<br />model design points an: de.~igned with the prefix "DP" and routing elements an: designated with
<br />thcprefix "RT").
<br />
<br />ImoerviousArea
<br />Land use a,sumptions for existing and future ba,in conditions were determined using a
<br />combination of zoning maps. City/Counly Comprehensive Plan(s), aerial photogmphs,
<br />transportation planes), and other related land use documents. Land use density and
<br />corresponding curve numbers werc determined in accordance with the City/County Drainage
<br />Criteria Manual (refer to explanation in Section III, Impervious Area). Figure 6 depicts the
<br />proposed land usedistribU!ion assumed in the hydrologic modeling. Previouslypresentedas
<br />Table 4 are the percent of imperviousness assigned for each of the land use categories presented
<br />on Figure 6. Tables 7 and 9 summarize the calculated SCS curve numbers (CN) for both the
<br />cxisting and future conditions for the MonUm<:ntCreek basin. Table 8 presents the percent
<br />impervious calculations for the traffic zones used in the future condition curve number
<br />detennination.
<br />
<br />Desi~nRainfall
<br />The City/County DrainagE Criteria Mun(il)l identifies a number of procedures to be used
<br />in dcveloping storm rainfall for input into hydrologic models. The criteria manual stipulates that
<br />two stOml durations (2-hour and 24-hour) be checked to deTermine the critical design storm (the
<br />storm producing the greatest peak discharge) aod recommends that the SCS Type nA
<br />
<br />distribution be use<! :0 represenT the 14.hour rainfall pattern. Rainfall ucpths shuwn !Il th<-
<br />criTeria manual are based on National OCE<.lMgraphic and Atmospheric Administration (NOAA)
<br />Atla.f2. Areal adjustmcnls representing reductions in point rainfall depths to be applied to large
<br />watershcd area arcnol discussed in the critcria manual.
<br />Based on thereslllts of initial hydmlogic mndeling and inputreceivcd at the technical
<br />review meetings. several modifiC<ltion~ were made to the procedures identified in the drainage
<br />criteria manual. The 24-hour stonn was determined to be the critical design storm for the large
<br />watershed area associated with Monument Creek: therefore. results pertaining to the 2-hour
<br />stoffil are not shown. Similarly, the SCS Type II distribution was determined to consistently
<br />produceg~aterpeakdischarges(byasmuchas40percentlthantheTypeIlAdistribmion.
<br />Point rainfall depth~ (2.03 inche.\ for the IO-year storm and 4.32 inches for the loo-year
<br />storm) developed within the guidelines of the drainage criteria manual were arcally adjusted
<br />based on two different approache~, The fir;t approach consisted of multiplying the point rainfall
<br />depths by a reduction factor published in !Iydrometeorological Report No. 51 (Hydromet 51).
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