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<br />3.2 Flow Duration <br /> <br /> <br />The flow duration curve for the Uncompahgre Rivl'lr at tile project site was developed in order to <br /> <br /> <br />estimate average annual sediment transport conditions and to provide an additional procedure to estimate <br /> <br /> <br />"dominant" or "channel forming" discharges. <br /> <br /> <br />The flow duration curve for the Uncompahgre River at the project site was developed utilizing USGS <br /> <br /> <br />daily flow values for the Uncompahgre HiveI' below Ouray (Gage # 9146000). the Uncompahgre River near <br /> <br /> <br />Ridgway (Gage # 9146200) and the Urcompahgre River at Colona (Gage # 9147500). The Uncompahgre <br /> <br /> <br />River below Ouray gage was located just upstrean1 of the project area. Unfortunately, this gage was only <br /> <br /> <br />active from 1914 to 1929. During this same period, the Uncompahgre at Colona gage was ac:tive. A gage <br /> <br /> <br />closer to Ouray. the Uncompahgre near Ridgway. has been active since 1958 and more closely reflects <br /> <br /> <br />conditions at the project site. To transfer the larger record for the Uncompahgre near Ridgway to the project <br /> <br /> <br />site. a ratio for the average annual flow at Colona to the average annual flow below Ouray for 1914 to 1929 <br /> <br /> <br />was determined. Then, for the common period of record prior to completion of the Ridgway Dam, 1959 to <br /> <br /> <br />1986. a ratio of the average annual floVl at Colona ;lnd near Ridgway were determined. These ratios were <br /> <br /> <br />0.51 and 0.66 for below Ouray at Colorla and for near Ridgway at Colona, respectively. These ratios were <br /> <br /> <br />combined to yield an estimate of the below Ouray to near Hidgway average annual flows. The resulting ratio <br /> <br /> <br />utilized was 0.80. A flow duration curve for Ouray was then developed by multiplying the near Ftidgway daily <br /> <br /> <br />flow data by the 0.80 factor. A discretized flow dur;;1tion curve is provided in Table 3.2. <br /> <br />3.3 Hydrographs <br />In order to determine the sediment transport conditions during peak events on the Uncompahgre River <br />through the project area. hydrographs were estimated for tile 2- and 1 DO-year events. These hydrographs <br />represent snowmelt runoff and therefore are of long duration. The near Ridgway daily flows were reviewed <br />to select two measured hydrographs to adjust to develop the project area hydrographs for the 2- and 100- <br />year. In these hydrographs. not only the peak but the volume are important. Therefore. both parameters were <br />used in the selection process. The average annual flow was utilized to provide a checK on the volume. The <br /> <br />2-year hydrograph was approximated by the near Ridgway hydrograph for 1980. <br /> <br />3.4 <br />