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1 <br />1 <br />1 <br /> <br />ii <br />1 <br /> <br />TABLE 2 <br />GUNNISON' RIVER HYDROLOGIC ANALYSIS POINTS <br />HYDROLOGIC <br />POINT LOCATION 'DRAINAGE <br />'AREA (DA.) D.A: <br />SOURCE <br />G1 DELTA GAGE 5628 miZ a <br />G2 BELOW UNCOMPAHGRE RIVER 6760 miZ a <br />G3 BELOW ROUBIDEAU CR 6998 miZ b <br />G4 BELOW ESCALANTE CR 7274 miZ b <br />GS BELOW DOMINGUEZ CR 7532 miZ b <br />G6 GAGE AT WHITEWATER (BELOW EAST CR) 7928 miZ a <br />G7 CONFLUENCE WITH COLORADO RIVER 8010 miZ* b <br />' Sowces of Drainage Areas <br />a Determined from published information and USGS gage values <br />b Determined from upstream USGS gage information combined with planimetering <br />* FEMA published value at confluence (7870 miZ) was found to be unverifiable based on the USGS gage value at a location approximately 9 <br />miles upstream <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br />Only one problem was encountered during the drainage area determinations. The drainage area <br />published by FEMA for the mouth of the Gunnison River in the Delta County FIS (7870 miZ) <br />was found to be lower than the value at the USGS gage location approximately 9 miles upstream <br />at Whitewater. The value at the gage location (7928 mil) was used as a base value and <br />planimetering downstream to the confluence provided the confluence value for this report (8010 <br />mi2). The FEMA value was assumed to be in error. <br />Figure 4 shows the study reach and each of the hydrologic analysis points listed in Table 2. <br />2.5 Flood Characteristics <br />Major flooding in the Gunnison River basin has been primarily the result of rapid snowmelt <br />beginning as early as late April. Snowmelt flooding can continue into early July. Flooding can <br />also occur from rainfall on snowmelt in late winter or early spring. Due to the small areal extent <br />and limited duration of thunderstorms, they do not typically constitute a major flood threat on <br />streams as large as the Gunnison or Uncompahgre Rivers. They do, however pose a problem for <br />some of the smaller tributaries in the Gunnison River basin. <br />Snowmelt flooding is characterized by moderate peak flows, large volume of runoff, long <br />duration, and diurnal fluctuation of flow. Flooding from general rainfall alone, though <br />uncommon on the Gunnison River, is characterized by high peak flows and moderate duration <br />6 <br /> <br />