Stream channel recharge in the Tucson Basin and its implications for ground-water management

Abstract

Recent legislation requires ground water in the Tucson Basin to be managed under a safe yield concept which restricts pumpage to annual recharge. This study develops a knowledge of ephemeral flow recharge and its implications for management under a safe yield concept. Analyses of several types of hydrologic data from the Tucson Basin indicate the following about ephemeral flow recharge: (1) most recharge along piedmont-draining channels occurs in the summer and most recharge along mountain-draining channels occurs in winter; (2) the winter flow regime has the highest recharge rate of 90 percent of flow into a reach on the Rillito Creek system; the summer flow regime recharges 80 percent and the extreme event flow regime only 45 percent; (3) near-surface ground-water levels lead to low recharge conditions along the Santa Cruz River until 1950 when water levels began dropping; and (4) the period of 1930-1960 was characterized by summer flow dominance and lower average annual flow volumes than the period of 1960- 1980, which began an episode of heavy winter flow and higher average annual flow. These results are used to recommend: (1) the time period from which to calculate the highest natural recharge value; (2) well field locations; and (3) artificial recharge program considerations.