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<br />001671 <br /> <br />Operation Plan for the Proposed Long Hollow Reservoir-Preliminary Draft, March 17, 2004 <br /> <br />the confluence of Long Hollow and the La Plata River, and 4 miles upstream of the Colorado- <br />New Mexico state line (Figure 1 ). <br /> <br />The maximum reservoir pool volume would be 5,432 AF. The maximum pool elevation would <br />be 6,310 feet above sea level and will have a surface area of approximately 160 acres., <br /> <br />LHR would be operated by the La Plata Water Conservancy District (LPWCD) according to this <br />plan and in cooperation with the Colorado Office of the State Engineer, as outlined in a <br />Memorandum of Agreement currently being prepared. <br /> <br />3.0 LA PLATA RIVER HYDROLOGY <br /> <br />3.1 La Plata River Flow Characteristics <br /> <br />Hydrographs of gauge flow during the 14-year period of 1989 through 2002 at the La Plata River <br />at Hesperus (Hesperus gauge) and La Plata River at New Mexico State Line (State Line gauge) <br />are shown in Figures 2a and 3a, respectively. These hydrographs show that La Plata River flows <br />at the Hesperus and State Line gauges are derived predominantly from spring snowmelt and <br />rainfall during wet monsoonal periods. Average daily flows for the 85-year period .of record <br />measured at the Hesperus gauge show the La Plata River flow characteristic.s. The river rises <br />sharply when the snowpack melts in April and then falls quickly in the early summer. <br />Monsoonal rains occur in late July and August, increasing river flows (see Figure 4). In <br />Colorado, groundwater inflows that provide stream base flows to the La Plata River are limited <br />between the Hesperus and State Line gauges. Most irrigation return flows accrue to the La Plata <br />River below Cherry Creek. Base flows in most La Plata River tributaries are minor. Some base <br />flows occur in Hay Gulch and Cherry Creek and occur above Cherry cree1:.- Long Hollow is <br />supplied primarily from groundwater inflows that result from irrigation on Red Mesa. These <br />return flows provide a steady source of supply to Long Hollow and its tributaries. , <br /> <br />Mean daily discharges between 0 and 100 cfs for these two gauges were plotted for the 14-year <br />study period between 1989-2002 (see Figures 2b and 3b). These hydrographs show the low-flow <br /> <br />991-077.000 <br />March 2004 <br /> <br />Wright Water Engineers, Inc. <br /> <br />Page 2 <br />