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<br />This reduction factor varies with watershed area. The resulting areal]y adjusted rainfall depth
<br />(1.42 inches for the lO-year storm and 3.02 inche~ for the IOO-year storm) was applied uniformly
<br />over the Monument Creek basin, The areal reduction factor published in Hydromet 51 was
<br />,elected instead of an altemate reduction factor identified ill ~OAA Atlas 2 because the
<br />Hydromet 51 factor compares more favorably with recent extreme sumn events in the region.
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<br />The second approach used to adjust point rainfall depths in the large MonumemCreek
<br />basin area consists of the development of an elliptical rainfall pattern. This approach. which is
<br />documented in Hydrometeorological Repon No. 52 (Hydromet 52), attempts to repre~ent an
<br />elliptical storm cell with maximum rainfall depths in a central core and decreasing depths in
<br />locations further removed from the core. Arcal adjustrnenl.'; factors published in Hydrornet5l
<br />were multiplied by the point (core area) rainfall depths to represent reductions in storm depth in
<br />prngressively larger ellipseslocilted funher away from the core.
<br />Suggested orientations for the axis of the elliptical distribution are given for different
<br />parts of the United States within Hydromet 52. The orientation for this region of the United
<br />States is a range of azimuths from approximately 1800102600. Using the range of suggested
<br />orientations and the areas for each isohyetal,the rainfall distribu!ion was placed over Ihe basin in
<br />such a manner that as many complete isohyetals as possible are contained within the basin. This
<br />position would produce me greatest amounl of rainfall over the basin. Figure 7 shows the
<br />location of the isohyetal1ines used for the precipitation distribution for the Hydrornet 52
<br />approach.
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<br />Hvdrolol!icModclin~
<br />The hydrologic model consists of 259 sub-basins, ranging in size from IIU acres to 200
<br />:lCres. linked by drainagewaysor "reaches". Hydrographs are accumulated at design points along
<br />the major drainages. A hydrologic flow chan was developed and is shown in Figures 8 through
<br />13. Both the existing and fUlure devclopment condition hydrologic models are based on the
<br />currenl configuration of Monumem Creek and the tribula!)' drainage channels. During the
<br />alternatIVe evaluation process, the hydrologic mode; wiU bt: moJifio:'; to 'enIXI P'VI'U"w
<br />changedchannelconditionsandpossiblysomedelentiollstomge.
<br />The hydrologic mood for lhe basin is based upon the USGS tupographic quadrangles for
<br />the basin supplemented with the Facility lnvento!)' Management System (FIMS) topographic
<br />mapping provided by the Cily of Colorado Springs Department of Utilities, Ihsin ~lreas, lengths.
<br />slopes. and flow patterns were determined from these maps.
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<br />IY.12
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