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<br />' ie <br />hibit I V for the <br />th <br />f <br />i <br />t <br />t <br />i <br />fr <br />S <br />E <br />Th <br />NOA A <br />l <br />h <br />i <br />h <br />t <br /> x <br />ows <br />or var <br />ous s <br />orms a <br />var <br />ous <br />equenc <br />s. <br />ee <br />e <br />t <br />as s <br />e <br />so <br />ye <br />s <br />' isohyets for the State of Colorado. Isohyets are lines of the same rainfall intensity; also sometimes <br />100 <br />f <br />l <br />d <br />h <br />d f <br />i <br />f <br />h <br />S <br /> ora <br />o, t <br />e <br />rom the <br />sohyets <br />or t <br />e <br />tate o <br />Co <br />referred to as isopluvials. As can be deducte <br />~' year storm over a 24 hour duration has a rainfall intensity of 3.0 inches. Instead, the input has been <br /> increased to 3.5 inches as a safety precaution as requested by the Department ofMines and Geology. <br />' <br /> The IDF Curves are used to generate the hydrographs and as can be observed from the IDF curves <br />' that the intensity of the rainfall is high during the first 45 to 60 minutes and rapidly tapers off as the <br /> storm duration diminishes. <br /> <br /> IDF curves are based on the following input data: <br />' 100 year storm-24 hours I = 3.5 inches <br /> 100 year storm-6 hours I = 2.4 inches <br />' 2 year storm-24 hours I = 1.6 inches <br /> 2 year storm-6 hours I = I. l inches <br />1 <br /> HYDROLOGIC SOIL GROUPS <br /> <br /> The Soil Conservation Service of the United States Government was instrumental in classifying the <br /> soil into four groups and aze identified by the letters A, B, C & D. <br />' The characteristics of the soil that are associated with each of the soil group are as fo{lows: <br />' Group A: Deep sand; deep loess; aggregated silts. <br />Group Ei Shallow loess; sandy loam. <br />Group C: Clay loams; shallow sandy loam; soils low in organic content; soils usually <br />' high in clay. <br />Group D: Soils that swell significantly when wet; heavy plastic clays; certain saline <br />' soils. <br />The SCS soil group has been identified by the Fremont County Soil Survey prepared by the Soil <br />' Conservation Service and by performing several infiltration tests to establish the infiltration rate of <br />the soil. Attached to this study are three Soil Survey Maps of Fremont County of the area under <br />consideration. E.~dtibit V is a copy of the description ofthe predominant soils found in the drainage <br />basin. PAGE 4 <br />