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<br />1053 <br /> <br />WATER TABLE FLUCTUATIONS AND TOTAL GROUND WATER STORAGE <br /> <br />In order to determine fluctuations of the water table and to estimate <br />the amount of ground water in storage, six cross sections were selected in the <br />system, and biweekly depth to water measurements at wells on or near the cross <br />sections were made during the irrigation seasons of 1969 and 1970. Locations <br />of the cross sections are shown on Plate 1. <br /> <br />Plates 2-5 for 1969 and Plates 6-9 for 1970 show the details of the <br />cross sections and the ground water table on April 1, July I, September 1 and <br />November 1. All available information was used in constructing the Plates. Bed <br />rock elevations were determined from U.S.G.S. borings and measurements of in- <br />dividual wells. Levels were run by members of the Colorado Water Conservation <br />Board staff to determine elevations of outstanding surface features. The re- <br />sults are, in general, as one would expect. The water table was low on April 1 <br />due to seepage from the aquifer to the river during the non-irrigation season. <br />The water table on July I and September 1 was high after several months of large <br />surface diversions and consequent aquifer recharge. On November 1 the water <br />table was slightly higher during 1970 than 1969 because surface diversions were <br />larger and well pumpage was less. <br /> <br />The effect of pumping on the river during 1969 is particularly ap- <br />parent in the cross section through the company-owned wells shown on Plate 5. <br />On April 1 the slight slope of the water table away from the river indicates <br />small, if any, recharge from the river to the ground water reservoir. On July 1 <br />both the river and the water table were high, and the slight slope shows small <br />recharge from the river. After pumping the company-owned wells during August <br />(see Table 2) the water table on September I was low with a steep slope away <br />from the river. This indicates that a substantial amount of river water is <br />replacing the ground water pumped. If this were not the case, the slope of the <br />water table would be nearly horizontal. On November 1 the water table had re- <br />covered. The same effect is evident during 1970 on Plate 9. <br /> <br />Estimates of the total ground water in storage under the system <br />during the 1969 and 1970 irrigation seasonS were made from the cross sections <br />for each of the dates and are shown below: <br /> <br />1969 - April I 35,580 ac-ft <br /> July I 39,260 ac-ft <br /> September I 39,810 ac-ft <br /> November I 39,350 ac-ft <br />1970 - April 1 37,720 ac-ft <br /> July I 41,050 ac-ft <br /> September 1 40,240 ac-ft <br /> November 1 39,670 ac-ft <br /> <br />These figures confirm the general trend as previously discussed and show that <br />more water was in storage during 1970 than 1969; A comparison of these esti- <br />mates with the results of water budget computations is made in the next section <br />of this report. <br /> <br />- 13 - <br />