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Calculations of Conveyance Losses on the North Platte, <br />South Platte and Platte Rivers in Nebraska <br />Background <br />All water flowing in the North Platte, South Platte, and Platte Rivers above Grand Island is or <br />soon will be tracked using a water accounting program called Platte Water Accounting Program <br />(PWAP). Conveyance losses (CL) for the months of May to September for the North Platte and <br />Platte Rivers for use in the PWAP program have existed for a number of years. The CL values <br />from the Nebraska — Wyoming state line to Lake McConaughy are established in the North <br />Platte River Decree. This study makes recommendations for all new values for the winter values <br />for the reaches above Lake McConaughy, and for all months for the South Platte River in <br />Nebraska and the North Platte and Platte River below Kingsley Dam. The values developed for <br />the South Platte River should be considered as provisional because, as explained below, at the <br />present time the data needed to make an accurate assessment are not available. Values for the <br />North Platte and Platte Rivers will also be updated as new (including new gages) and better data <br />become available. <br />PWAP is a computer program designed to do a daily accounting for natural flow, storage, and <br />environmental account water at specific gage locations. Inputs to PWAP include daily average <br />flow values from stream gages, diversions, and canals and an estimated conveyance loss value <br />based on monthly average estimates. A mass - balance computation is completed by PWAP for <br />each stream reach and the residual value is distributed to the natural flow, storage, and /or <br />environmental account water. The residual exists because of the inability to accurately measure <br />or estimate the input data with a precision of one cubic foot of water per second (cfs) and the fact <br />that variables such as direct precipitation, unmeasured tributaries, seepage and bank storage are <br />unaccounted for. Under the best conditions, gage values may be off by as much as 10% due to <br />the shifting conditions of the streambed and during the winter, ice cover will adversely affect the <br />quality of data from the stream gages. Also, the CL value is based on the historical monthly <br />average. On any given day, the actual amount of CL may be greater or less than the value used <br />in PWAP. For the most part, the daily variation in CL will even out over the month. <br />North Platte and Platte Rivers <br />River Geography <br />The following reaches are used in PWAP. Each reach represents apprAxi1nat�ly e day of_ <br />travel time for river flows. <br />• • Wyoming — Nebraska Stateline to Minatare <br />• Minatare to Bridgeport <br />