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<br />....., <br />~t::~, <br /> <br />CHAPTER II <br /> <br />~ <br />CJl <br />UI <br />C"'J <br /> <br />GRAND VALLEY RIVER BUDGET <br /> <br />Unaccounted Flow <br /> <br />The salt inputs and outputs can be adjusted in light of the water <br /> <br />budget's unaccounted .flow. The unaccounted flow is defined as the amount <br /> <br />that the inflows exceed the outflows. Due to measurement and modeling <br /> <br />errors, the total water inflow does not balance the total water outflows. <br /> <br />The unaccounted flow .significant.ly affects the salt pickup estimates, because <br /> <br />the flow discrepancy essentially adds or subtracts water without any associ- <br /> <br />ated salt, ~licitly assuming that all the measurement and .model error lies <br /> <br />in precipitation or consumptive use, but not in streamflow measurement nor <br /> <br />ground water inflows and outflows. <br /> <br />Observing the annual unaccounted flow for the State Line budget (see <br /> <br />;.::.:.--:: <br />"~'.' <br />..."" <br /> <br />Tables 4 and 5, and Figure 3), it can be seen that the unaccounted flow is <br /> <br />aignificantly large, varies greatly from one year to the next, and is usually <br /> <br />positive (i.e., inflows exceeding outflows). For the period of study, the <br /> <br />unaccounted flow averaged a positive 51,700 acre-feet per year, which is a <br /> <br />little more than 1% of the mean annual flow of 4,202,000 acre-feet per year <br /> <br />at the State Line gage. The annual unaccounted flow varied from a positive <br /> <br />5.3% to a negative .2.9% of the mean annual flow at the State Line. <br /> <br />The largest source of error in the budget undoubtly lies in the stream- <br /> <br />flow measurememts. The three major gaging stations, the Colorado River near <br /> <br />Cameo and near the State Line, and the Gunnison River near Grand Junction, <br /> <br />are all rated as "good" by the USGS, which means that about 95 percent of the <br /> <br />daily discharge measurements are within 10 percent of the actual flow. This <br /> <br />does not, however, necessarily imply a 10 percent error in the annual flow <br /> <br />";.', <br /> <br />because the daily errors should average out somewhat over a year. <br /> <br />II-10 <br />