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H. Compact Call Issues <br />As stated before, the primary goal of the proposed reservoir is to re- regulate the flows in the South <br />Platte River to reduce the potential that GASP members would be forced to curtail diversions to <br />comply with the South Platte River Compact. The South Platte River Compact between the States of <br />Colorado and Nebraska was adopted in 1921 to remove all causes of present and future controversy <br />between the two states. The compact states that "between the first day of April and fifteenth day of <br />October of each year, Colorado shall not permit diversions from the Lower Section of the river, to <br />supply Colorado appropriations having adjudicated dates of priority subsequent to the fourteenth day <br />of June, 1897, to an extent that will diminish the flow of the river at the Interstate Station (Julesburg <br />Gage), on any day, below a mean flow of 120 cubic feet of water per second of time ". <br />The primary purpose of the proposed reservoir will be to augment flows in the South Platte River at <br />times when the flow decreases below 120 cfs due to water use in Colorado. This will allow GASP <br />members to continue their diversions under the terms of the compact. Figure 3 is a summary of the <br />number of days that flows recorded at the Julesburg gaging station were below 120 cfs for the past 30 <br />years. The number of days that the flows dropped below 120 cfs were identified regardless of cause. <br />Depending on the release capacity of the reservoir, there will be a specific range of flow that the <br />reservoir could effectively supplement compact flows. Table 4 is a summary of the estimated <br />reservoir operations for augmenting flows above 70 cfs and the resulting reduction in the compact <br />deficit. <br />I. F000dplain Issues <br />A reconnaissance level floodplain analysis for the South Platte River was performed for the <br />feasibility portion of the GASP Reservoir near the town of Sedgwick. A FEMA floodplain <br />delineation was not available and it was felt that a backwater analysis was not justifiable at this point <br />in the project. An estimate of a water surface elevation through the use of Manning's Equation was <br />used to provide an approximation relative to the reservoir <br />A representative cross - section was constructed using the USGS 7.5' quad of the area. The quad was <br />based on a 10' contour interval which made defining the low -flow channel and the overbank areas <br />not possible. Channel slope in this reach of the South Platte River is relatively constant and a value <br />of 0.00114 ft/ft was used in the calculations. A Manning's n -value of 0.04 was used for the cross - <br />section. <br />• <br />13 <br />