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110" 108" 108" IC= 0,.. <br />I t <br />`''�` •••,k�.> NEBRASKA <br />E i <br />WYOMING <br />-- -- Ev <br />Northwest • ,l R„ <br />r Region <br />r✓a Rir <br />PIP - <br />UTAH • ��4Ua• R,i. � • L <br />• •� KANSAS <br />M.— <br />• aar • ••'Y • • an . <br />l 1. •i' .� COLORADO <br />• Mountain Plains L4 <br />Region Region <br />x m R,..r <br />�e • Rio Grande` <br />`,a• legion „"a.0' an Luis e • <br />c; Tailin Dam <br />seethwest • a <br />Region. <br />ARIZONA t • OKLAHOMA <br />I <br />• I ; NEW MEXICO -- -- -- -- -- -- -- <br />. <br />I C • I TEXAS <br />e u 0 so loo MLLES <br />0 50 100 KILOMETERS <br />EXPLANATION <br />• Str—flow g.ging station <br />Continental Divide <br />s Hydralogierogional lb—da,i- <br />Figure 1: Colorado Hydrologic Regional Boundaries <br />Hence, the 100 -year and 500 -year flood magnitudes for the San Luis Basin were computed using the regression equations <br />for the Plains Region and Southwest Region (Table 16). <br />Table 16: Colorado Regional Regression Equations for Peak Streamflow <br />Hydrologic <br />Qioo (cfs) <br />Qsoo (Cf S) <br />Region <br />Plains <br />151 <br />242 <br />Southwest <br />583 <br />1,118 <br />Comparison of the peak streamflow values presented in Table 16 to the peak flows presented in Table 15 reveals that, <br />except for the combination of the RMUH and Kult, results from the rainfall runoff model for the 100 -year and 500 -year are <br />within the range that could be expected when compared to similar drainage basins in the adjacent hydrologic regions in <br />Colorado. However, it should be noted that San Luis is less than 50 miles from the Northern Mountain flood region (Region <br />5) of New Mexico, and review of the envelope curve for Region 5 indicates the region has been subjected to extreme runoff <br />events in the past that may not be reflected when evaluating flood frequencies against the regional regression equations. <br />The various model results presented above represent the band of uncertainty in the flood frequency analysis. The Clark UH <br />with the SCS Curve Number loss method produces the lowest peak runoff rates and, when considered with respect to the <br />New Mexico Region 5 envelope curve, may under estimate the flood frequencies. Conversely, while the combination of <br />RMUH and K„ It produce results that exceed what is expected when compared to the Colorado regional regression <br />equations, when considered with respect to the Region 5 envelope curve, this combination of parameters may simply <br />represent the upper uncertainty band. <br />\\BIL-FS\BIL-projects\26\21099-01\95Rpts\San Luis Flood Hydrology Study_R2.docx Page 8 of 10 <br />