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<br />HYDROLOGY <br /> <br />(PREVIOUS STUDIES) <br /> <br />EXISTING STRUCTURES <br /> <br />The two previous Corps studies addressed the problem of <br />hydrological storm peak attenuation due to storage <br />structures along the river in somewhat different manners. <br /> <br />The 1973 Corps study recognized two hydrological structures; <br />the Milton Seaman Reservoir, constructed in 1947 by the City <br />of Greeley for municipal water supply, and the Halligan <br />Reservoir, built in 1910 for irrigation water storage. The <br />1973 Corps study concluded that nl2ither structure had any <br />significant effect on subsequent discharge records, and no <br />adjustment was made to the discharge data by the Corps. <br /> <br />The 1981 Corps study included the Worster, also known as the <br />Eaton Reservoir, as well as the previously mentioned <br />structures. This study concluded that Worster and Seaman had <br />little effect on discharge data, but that the Halligan <br />Reservoir provided significant attenuation effects <br />downstream. Therefore, data gathered before its completion <br />in 1910 was not used in their final discharge probability <br />analysis. In addition, the 1981 Corps study concluded that <br />the effects of the numerous small irrigation ditches and <br />reservoirs in the basin had little or no effect on the <br />consistency of gaging records. <br /> <br />DISCHARGE PROBABILITY <br /> <br />Both previous Corps studies ana.lyzed discharge data at two <br />gaging stations along the river, <br /> <br />At the Bluffline <br /> <br />The gage located at the blufflin.e \vhere the Cache La Poudre <br />River leaves the mountains records the discharge from the <br />mountainous region of the basin. Continuous records from <br />this station are available beginning in 1882. Floods in 1891 <br />and 1904 destroyed the station, but estimates of their <br />magnitude based on historical sources (ref 3) were used for <br />the 1973 Corps analysis. The flood of 1891 was estimated to <br />be 21,000 cfs, and that of 1904 was estimated to be 25,000 <br />cfs. <br /> <br />The 1973 Corps study evaluated 89 years of data using <br />Beard's analytical method (log-Pearson Type III), shaping <br />the curve with a generalized skew coefficiE!nt of +1.0, and <br /> <br />Page 3 <br />