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I I I I I I I I I I I I I I I I I I I TABLE 2 .H........._._._...................... ........................................ ...................................... ........................................ ......................."............... ........................................ ...HYJ).........:g....O......u...O......O.....J..c........... ... . ... .... ::: .: ::' :~ :;.: -.".-:'.: :::.;::..'::': :.-::.:{{ ...................................,.... ........................,...-.......... ......................................... ...................p..o. ..INT........ ............................ ........... .. ............. ............ . .. ............. :::::::::::::::::::;:::--:-:- :'.:;':;;:;:::::::::::::::::;:::::: .................................... "' . ........................ ......."................. ................................... ...............-................... .................................... .................................... .................................... .....nkAlNA'GSu. ..............-..................... ............,....................... ................................... .~~Q?;~;) GI G2 G3 G4 G5 G6 G7 5628 mi2 DELTA GAGE BELOW UNCOMPAHGRE RIVER BELOW ROUBIDEAU CR BELOW.ESCALANTE CR BELOW DOMINGUEZ CR GAGE AT WHITEW A TER (BELOW EAST CR) CONFLUENCE WITH COLORADO RIVER a 6760 mi2 6998 mi2 a b b b 7274 mF 7532 mF 7928 mF a 8010 mi2. b Sources of Drainage Areas a Determined from published information and USGS gage values b Determined from upstream USGS gage information combined with planimetering · FEMA published value at confluence (7870 mi2) was found to be unverifiable based on the USGS gage value at a location approximately 9 miles upstream Only one problem was encountered during the drainage area determinations. The drainage area published by FEMA for the mouth of the Gunnison River in the Delta County FIS (7870 me) was found to be lower than the value at the USGS gage location approximately 9 miles upstream at Whitewater. The value at the gage location (7928 mi2) was used as a base value and planimetering downstream to the confluence provided the confluence value for this report (8010 mi2). The FEMA value was assumed to be in error. Figure 4 shows the study reach and each of the hydrologic analysis points listed in Table 2. 2.5 Flood Characteristics Major flooding in the Gunnisori River basin has been primarily the result of rapid snowmelt beginning as early as late April. Snowmelt flooding can continue into early July. Flooding can also occur from rainfall on snowmelt in late winter or early spring. Due to the small areal extent and limited duration of thunderstorms, they do not typically constitute a major flood threat on streams as large as the Gunnison or Uncompahgre Rivers. They do, however pose a problem for some of the smaller tributaries in the Gunnison River basin. Snowmelt. flooding is characterized by moderate peak flows, large volume of runoff, long duration, and diurnal fluctuation of flow. Flooding from general rainfall alone, though uncommon on the Gunnison River, is characterized by high peak flows and moderate duration 6