Hydrology and soil erosion

We review research on surface water hydrology and soil erosion at the Santa Rita Experimental Range (SRER). Almost all of the research was associated with eight small experimental watersheds established from 1974 to 1975 and operated until the present. Analysis of climatic features of the SRER supports extending research findings from the SRER to broad areas of the Southwest with similar climates. Conceptual models for annual water balance and annual sediment yield at the SRER were developed and supported by data from four very small experimental watersheds. The impacts of rotation and yearlong grazing activities, and of mesquite removal were analyzed using data from four small experimental watersheds. The analyses suggested that mesquite removal reduced runoff and sediment yield, but differences in hydrologic response from paired watersheds due to soil differences dominated grazing and vegetation management impacts. The 28 years of monitoring under the same experimental design on the four pairs of watersheds provides us with a long period of "pretreatment" data on the paired watersheds. New treatments could now be adapted and designed based on lessons learned from monitoring over nearly three decades. There is a unique opportunity to institute long-term adaptive management experiments on these experimental watersheds.