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<br />Flooding along the South Platte River ln Morgan County normally <br />occurs from May through September with the most frequent flooding <br />occurring during June. Annual peak discharges, however, have been <br />recorded from February through October. Floods in Morgan County <br />normally occur under non-ice affected conditions. Ice jams, <br />however, are possible even though their historical frequency of <br />occurrence is rare. <br /> <br />Floodwaters on the South Platte River in Morgan County can result <br />from intense localized rainfall or general rains, either of which <br />may be augmented by snowmelt. The intense rainstorm floods result <br />from intense rainfall over areas of relatively small aerial extent. <br />These storms can produce extremely rapid concentrations of <br />floodwaters and ensuant rapid rises in stream levels. Because of <br />the lack of warning time prior to streams attaining flood stages, <br />this type of storm can produce floods which are extremely <br />hazardous. This type of flood produces high peak discharge on <br />tributaries in the general vicinity of the rainstorm. The <br />di scharge, however, at tenuates rapidly on the South Plat te River <br />downstream from the contributing tributaries due to valley storage <br />of the floodwater. <br /> <br />The general rains torm floods result from rainfall over areas of <br />large aerial extent. Rainfall from this type of storm may occur <br />over several days. Because of this time duration, the affected <br />streams rise relatively slow; sometimes over a period of several <br />days. The duration of the flood period also is sometimes of <br />considerable length. Because of the large aerial extent of <br />rainfall, more tributaries contribute to the peak discharge on the <br />South Platte River. This results in increasing discharge <br />progressively downstream over a considerable length of the South <br />Platte River. However, downstream from the contributing <br />tributaries, the effects of valley storage cause flood discharge <br />attenuation. <br /> <br />Erosive effects can be considerable in the event of any flood <br />regardless of its origin. Floods resulting from intense rainstorms <br />typically create severe erosion damages in a short period of time <br />due to the relatively large peak discharge and high velocity of the <br />floodwater. Erosion damages from snowmelt or general rainstorm <br />floods usually result from prolonged exposure of the floodwater <br />because of the long duration typical of these floods. <br /> <br />A lOa-year flood or a SOO-year flood on the South Platte River in <br />Morgan County would result in the inundation of and subsequent <br />damage to primarily agricultural properties and associated <br />developments as well as public utilities and public roadways. Deep <br />floodwater flowing at high velocity and carrying floating debris <br />would create conditions hazardous to persons and vehicles <br />attempting to cross flooded areas. In general, floodwater 3 or <br />more feet deep and flowing at a velocity of 3 or more feet per <br /> <br />8 <br />