By
Sandra J. Owen-Joyce and C. K. Bell
In a water budget for the regional aquifer, if no change occurs in the volume of water in storage, inflow equals outflow and the system is in steady state or equilibrium. Under transient or nonequilibrium conditions, inflow and outflow are not in balance and the difference is made up by a change in storage. In the upper Verde River area, no appreciable declines in water levels in wells have occurred. There are no significant changes between the water-level contours mapped by Twenter and Metzger (1963) and Levings and Mann (1980), and those shown on plate 1. Differences are generally a result of more and sometimes better data; therefore, changes in storage in the regional aquifer are zero-inflow equals outflow. A total water budget could not be computed because records of total surface outflow are not available; therefore, only a low-flow budget was evaluated as a first approximation of flow in the regional aquifer. Inflow to the regional aquifer is by infiltration of precipitation and streamflow. Outflow is by spring and seepage discharge to streams, pumping and flowing wells, and evapotranspiration.
The data available for use in estimating the water budget include records of streamflow, pumpage, and water levels in wells. Investigations of evapotranspiration, seepage, and land use have also provided estimates of flow quantities for use in the water budget. Outflow is discussed first because the outflow quantities are the easiest to estimate, and inflow is based on that estimate and the assumption that the change in storage equals zero.
Outflow
Ground water that leaves the regional aquifer is discharged to streams and springs, lost to evapotranspiration, or withdrawn by wells. Streamflow and spring flow are the largest components of outflow and have remained fairly constant since 1915 north of Clarkdale and since 1935 between Clarkdale and Chasm Creek. Underflow out of the area is assumed to be negligible. No significant gains in base flow in the Verde River were detected south of Beasley Flat.
Gaging-station records and seepage investigations along the Verde River indicate that the river is a gaining stream, although it does contain some short losing reaches. Net base flow leaving the valley is measured at Verde River near Camp Verde gaging station. The annual base flow for the 1977 water year was 80,000 acre-ft (table 9), which is 21,000 acre-ft/yr lower than the average value calculated for the 1934-45 water years of 101,000 acre-ft/yr. The data for water year 1977 were used because this water year is the only complete year of recent base-flow data. The value for the base flow may be anomalous because 1977 was a dry year and more water probably was used for irrigation than was used in 1934-45. The seepage investigation of June 1979 indicates no appreciable gains or losses between the Verde River near Camp Verde gage to the outflow point except the gain from Fossil Springs. The outflow is adjusted for the base flow of Fossil Creek by adding the discharge of Fossil Springs, which averages 43 ft3/s or 31,150 acre-ft/yr (U.S. Geological Survey, 1979, p. 413) (table 9). Therefore, the total base flow leaving the study area at the outflow point is 111,000 acre-ft/yr (rounded).
Evapotranspiration losses from the regional aquifer were determined using the estimated evapotranspiration figures from Anderson (1976) for the main stem of the Verde River, Oak Creek, Wet Beaver Creek, and West Clear Creek. Calculations (Anderson, 1976) were for particular reaches of the streams and include the transpiration from the riparian zone and the evaporation from soil and open-water surfaces along stream channels. Where a reach did not fall totally within the study area, a proportional amount was determined by the ratio of length of the reach in miles that is in the study area to total length of the reach in miles. The evapotranspiration losses by reach are listed as follows:
Length Evapotranspiration of reach losses,in Reach or stream in miles acre-feet per year Verde River 3.4 mi downstream of Sullivan Lake to Paulden gage 6.4 400 Paulden gage to Clarkdale gage 28.2 2,200 Clarkdale gage to Camp Verde 47.1 18,000 Camp Verde to East Verde River 32.1 3,800 Oak Creek 46.9 4,700 Wet Beaver Creek 27.4 3,500 West Clear Creek 32.5 2,400Surface water, mainly from the Verde River, is diverted through a system of ditches for irrigation. Unused water returns to the river. In the Verde Valley 7,781 acres is irrigated by surface water (Northern Arizona Council of Governments, 1979, p. 123). The amount of water used per acre depends on soil type, crop type, and the method of irrigation. The Soil Conservation Service (J. E. Alam, oral commun., 1979) estimated consumptive use of water to be 4 acre-ft/acre; therefore, using this estimate, the amount of water used for irrigation is about 31,000 acre-ft/yr (table 9). Surface-water returns from the fields to the river are not common because of the nature of the irrigation systems employed by most of the irrigation ditch users and because most of the crops are close-grown, thereby minimizing overland flow (Northern Arizona Council of Governments, 1979).Total 35,000
Prior to 1950, ground-water use was sparsely scattered in the Verde Valley. During the 1950's, development of ground water for public and domestic use started increasing. Ground-water withdrawal for the upper Verde River area was estimated to be 8,000 acre-ft/yr for 1978 (U.S. Geological Survey, 1980a) (table 9). Ground water is used for domestic and public supplies. Estimates by the Soil Conservation Service (J. E. Alam, oral commun., 1979) indicate that less than 5 percent of the land being irrigated uses ground water as the water supply.
Total annual outflow from the study area is estimated as 185,000 acre-ft. Subtracting Fossil Springs discharge, the total annual outflow at the Verde River near Camp Verde gaging station is about 154,000 acre-ft. This value compares well with the minimum value for total outflow of 150,000 acre-ft/yr estimated by Twenter and Metzger (1963) for the Verde River near Camp Verde station.
Table 9 -- Estimated average inflow to and outflow from the regional aquifer including surface-water inflow in acre-feet per year for the upper Verde River area Inflow Infiltration of precipitation and streamflow 169,000 Base flow of Verde River near Paulden 16,000 Total 185,000 Outflow Base flow of Verde River near Camp Verde 80,000 Fossil Springs 31,150 Evapotranspiration 35,000 Irrigation, consumptive use 31,000 Ground-water withdrawal 8,000 Total (rounded) 185,000
Inflow
Inflow to the regional aquifer is from infiltration of precipitation and streamflow. Some infiltration occurs throughout the entire study area. The largest amount of infiltration probably occurs in the Plateau uplands where the average annual precipitation is about 20 in. and permeable volcanic rocks and limestone crop out. The average annual precipitation on the upper Verde River area is 16.6 in. or 2.1 million acre-ft.
The amount of infiltration from precipitation and streamflow was estimated by balancing the water budget, assuming equilibrium conditions existed. Surface-water base flow into the area is accounted for by calculating the base flow at the gaging station, Verde River near Paulden. Annual base flow is fairly constant at 16,000 acre-ft (table 9). Sycamore and Oak Creeks where they enter the study area and East Clear Creek where it leaves the study area are ephemeral and have no base flow. Underflow into the area is assumed to be negligible. The only other source of recharge is through infiltration of precipitation, which is estimated to be 169,000 acre-ft/yr (table 9) or 8 percent of the average annual precipitation. This value agrees with the 8-percent recharge calculated by Twenter and Metzger (1963, p. 75).