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<br />was 372,000 ac ft. with a weighted average of 288 mg/l
<br />TDS, while that of the Salt River was 533,000 ac ft.
<br />with 591 mg!l TDS (Arizona Water Commiaslon Files;
<br />Water Resources Data for Arizona; Hubbard, person.
<br />allntervlew). The project ia presently pumping 252
<br />wells. Over the 10-year period ending In 1970 they
<br />pumped an average of 400,000 ac ft per year while the
<br />depth to water In selected wells dropped an average of
<br />13 feet per year (Arizona Water Commission files). In
<br />1970 the U.S. Geological Survey estimated that a safe
<br />groundwater yield for the Salt River Project area ia
<br />300,000 ac ft per year, including that pumped by
<br />others within the Salt River Project boundaries.
<br />
<br />It ia estimated that by 1980 Salt River Project
<br />obligations will be 766,000 ac ft for agriculture,
<br />190,000 for municipal and Industrial,. and 239,000 (20
<br />percent) transportation and storage losses. With a
<br />continued supply of 850,000 acre feet of surface water
<br />and curtailed pumping of 200,000 acre feet, minimum
<br />balance to meet this obligation would be 150,000 acre
<br />feet of Central Arizona Project water.
<br />
<br />Tbe salinity In tbe active wells ranges from
<br />around 800 to 2,897 mg/l TDS with an average of 980
<br />mg!l (Hubbard, personal Interview). Since Central
<br />Arizona Project water ia supposed to replace
<br />groundwater on a one to one basia, the highest salt
<br />content wells could be eliminated to bring thia average
<br />down to somewhere near the present 775 mg/I of the
<br />Colorado River at Parker Dam. However, for
<br />the purposes of thia report, an average groundwater
<br />quality of 980 mg/l TDS ia used.
<br />
<br />If we assume a continued supply of 850,000 ac ft of
<br />surface water and curtailed pumping of 275,000 ac ft,
<br />an allotment of 75,000 ac ft of Central Arizona Project
<br />water would meet the minimum balance needed to fill
<br />Salt River Project obligations. The project water
<br />
<br />before addition of Central Arizona Project water
<br />would. then have an average salinity of around 600
<br />mg!l ToS which would be Increased only slightly by
<br />the addition of Central Arizona Project water and its
<br />present level, and only another 40 mg/l when the
<br />Central Arizona Project reaches 1400 mg/l (Table
<br />3-82). If the Salt River Project were aliotted the
<br />150,000 ac ft of Central Arizona Project water they
<br />have requested, the salinity of the blend would be
<br />slightly lower initially and only 26 mg/l higher when
<br />Centrat Arizona Project water reaches 1400 mg/l
<br />(Table 3-83). Thia ia because of the trade off of
<br />groundwater for Central Arizona Project water. Since
<br />thia is the case, crop declinations are figured on the
<br />basia of the higher allotment.
<br />
<br />The soils of the general area served by the Salt
<br />River Project irrigation system are assigned to
<br />drainage groups in Table 3.84. This breakdown was
<br />made from a general soils map of Maricopa County and
<br />Salt River Indian Reservation prepared by the U.S.
<br />Soil Conservation Service (General Soil Map, Marico-
<br />pa County, Arizona). The proportions of different
<br />soils claSses as shown here are used for both the Salt
<br />River Valley Water Users Association and areas of
<br />supplemental irrigation service. Of the total 165,942
<br />acres assumed for the model, 184,225 acres are
<br />allocated to single cropping purposes while 31,717
<br />acres are assigned to double cropping possibilities.
<br />
<br />The crops selected for the Salt River Project are
<br />listed in Table 3-85. In addition, the table also shows
<br />the rotation sequence of double cropping alternatives,
<br />Wheat, barley, sorghum, lettuce, and to lesser extent
<br />onions, are the dominant crops in the double cropping
<br />rotation for this area.
<br />
<br />Table 3.66 contains the data used to derive base
<br />yield figures for the area. These data were then
<br />compared to the effective values of soil saturation
<br />extract conductivities for the three drainage classes as
<br />
<br />
<br />Table 8-8~. Effects of i"""ea.ing salinitll of Centrol Arizona Project water when it is blended into the Salt River
<br />Project water (assuming an allotment of 75,000 ac It of Centrol Arizona Project water).
<br />
<br /> 1,200,000 ao ft
<br />850,000 aeft 275,000 aeft l.t25,OOO ac..ft 75,000 aoft Blended Central
<br />Salt and Verde Groundwater Salt River Central Arizona Arlzol\a Project
<br />Rivers Watera TDS(mg/l) Project Water Project Water and Salt River
<br />TDS (mgf1) TDS (mg/l) TDS (mg/l) Project
<br /> TDS (mg/1)
<br />467b 980c 592 775d 604
<br />467 980 592 900 612
<br />467 980 592 1000 618
<br />467 980 592 1100 624
<br />467 980 592 1200 630
<br />467 980 592 1300 637
<br />467 980 592 1400 643
<br />
<br />8Nine-year average flow (1964-1972) of 905,000 acre feet less 5.6 percent to the Roosevelt Water Conservation District,
<br />leaves 854,000 acre.feet surface water.
<br />
<br />bThe 9-year average flow of the Verde River below Bartlett Dam was 372,000 acre-feet with an average of 288 mg/l TDS,
<br />while that of the Salt River below Stewart Mountain Dam was 533,000 acre-feet with an average of 591 mg/l TDS.
<br />
<br />e Average salinity of active Salt River Project wells. Figure supplied by the Salt River Project Office. TDS of individual
<br />wells ranges from 200 to 3000 mg/l Volwnetric average varies according to whieh wells are being pumped.
<br />
<br />dPresent salinity of Colorado River water of the Central Arizona Proj~ct diversion point above Parker Dam.
<br />
<br />180
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