Recharge studies on the High Plains in northern Lea County, New Mexico

The area described in this report is that part of the southern High Plains principally within northern Lea County, N. Mex. ; it comprises about 1,400,000 acres. Hydrologic boundaries isolate the main aquifer of the area, the Ogallala Formation, from outside sources of natural recharge other than precipitation on the area. Natural recharge to this aquifer from the 15-inch average annual precipitation for the period 1949-60 is estimated to be about 95,000 acre-ft (acre-feet) which is between the 59,000 and 118,000 acre-ft a year obtained from the This estimate (1934) of ? to 1 inch a year. About one-sixth of the water pumped for irrigation, or an average of about 23,000 acre-ft a year in the period
1949-60, returns to the aquifer. The estimated long-term (1939-60) average
annual recharge to the aquifer is about 77,000 acre-ft.

Discharge from the aquifer is by pumping and underflow from the area. Gross pumpage averaged about 151,000 acre-ft a year in the period 1949-60. Underflow from the area is estimated to have been about 36,000 acre-ft a year. Thus, the estimated average annual discharge from the aquifer was about 187,000 acre-ft a year, and this exceeded recharge by about 69,000 acre-ft a year. This overdraft is reflected in a general net decline of the water table of 10 ft in the period 1950-60 and net declines of as much as 30 feet in local areas.

Data obtained during this study indicate that about 100,000 acre-ft of water collects in closed depressions on the surface of the High Plains in years when precipitation is normal. Studies of water losses from ponds in selected depressions indicate that between 20 and 80 percent of this loss recharges the groundwater body and the balance is lost to evapotranspiration, principally evaporation. Artificial recharge facilities constructed in the depressions could put at least 50,000 acre-ft of water underground annually that otherwise would be lost to evaporation. Recharging through pits or spreading ponds would cost less per unit volume of water than recharge through wells.