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The data presented in Table 7-6 show that PET exceeded estimated precipitation by about • <br />three inches. Actual evapotranspiration (AET) can be determined once the hydrologic <br />balance for Hubberson Culch has beers quantified using the equation: <br />R=P- PET - 5 <br />where: <br />R = Runoff <br />P = Precipitation <br />PET = Potential evapotranspiration <br />5 = Storage <br />Hubberson Culch discharged about 3.67 x 107 ft' of water during the study period at the <br />USCS flume (USGS Station 09244464). The Hubberson Culch watershed has an area of about <br />22.96 x 107 ft~; therefore, 41.56 x 107 ft' of water fell on the watershed (using a <br />precipitation value of 1.81 feet from Table 7-6). Similarly, potential evapotranspiration <br />for the watershed was 47.30 x 107 ft' (using a PET value of 2.06 from Table 7-6). <br />Therefore, the annual water balance for this period was: <br />R=P-PET-S <br />3.67 x 107 ft' _ (41.56 x 107 ft') - (47.30 x 107 ft') - S • <br />5 = -9.41 x 107 ft' <br />The negative storage value is due to PET being larger than precipitation and indicates <br />that there was little or no ground water recharge during this period. Actual <br />evapotranspiration can be estimated using the equation: <br />AET=P- R <br />AET = (41.56 x 107 ft') - (3.67 x 107 ft') <br />AET = 37.89 x 107 ft' <br />Dividing by the Hubberson Culch watershed area of 22.96 x 107 ft~, AET is about 1.65 feet, <br />or 19.8 inches. <br />As the data above indicate, evapotranspiration significantly reduces the amount of <br />precipitation available for runoff or ground water recharge. It should be noted that the <br />calculations above represent general approximations of alluvial system conditions in the <br />Seneca II-W area. <br />• <br />Aquifer Characteristics. Until recently, little data concerning site-specific aquifer <br />28 <br />