The USDA-ARS Walnut Gulch and Santa Rita Experimental Watersheds

The Walnut Gulch Experimental Watershed (WGEW) was selected as a research facility by the United States Department of Agriculture (USDA) in the 1950's to quantify the influence of upland conservation on downstream water supply and quality. The watershed encompasses a 149 sq. km drainage area in SE Arizona. It is representative of roughly 60 million hectares of grass and brush covered rangeland found throughout the semiarid southwest and northern Mexico. The initial overall rainfall and runoff instrumentation for the experimental watershed was completed in 1964 and consists of 103 recording rain gauges and 22 nested watersheds creating one of the densest rain gauge networks in the world for drainages over 100 sq. km. Extensive monitoring of erosion and sediment transport is also conducted on eight of the smaller sub-watersheds within Walnut Gulch and eight additional source area watersheds instrumented in the nearby Santa Rita Experimental Range. In 1990 additional instrumentation was added to the watersheds to characterize the meteorology, soil temperature and soil moisture. In 1996 energy balance and CO2 flux measurements were initiated at these stations, and currently, two long-term Ameriflux eddy covariance sites are located both in Walnut Gulch and the Santa Rita Range. Long-term remote sensing acquisitions with ground support and biotic characterization has also been ongoing. Since its creation, the mission of the USDA-ARS Southwest Watershed Research Center, who maintains and conducts research at WGEW, has expanded to include research on global change; decision support systems; rangeland health; remote sensing; development and transfer of hydrological, erosion, and natural resource models; and, sustainable intensification of U.S. agriculture as one of 18 Long-Term Agroecosytems Research (LTAR) sites. This poster presentation will provide an overview of the Walnut Gulch and Santa Rita Experimental Watersheds as well as major scientific accomplishments and social benefits derived from research on these outdoor laboratories.