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The USDA-ARS Southwest Watershed Research Center (SWRC) operates the Walnut Gulch Experimental Watershed (WGEW) in southeastern Arizona as an outdoor laboratory for studying semiarid rangeland hydrologic, ecosystem, climate, and erosion processes. Since its establishment in 1953, the SWRC in Tucson, Arizona, has collected, processed, managed, and disseminated high-resolution, spatially distributed hydrologic data in support of the center’s mission. Data management at the SWRC has evolved through time in response to new computing, storage, and data access technologies. In 1996, the SWRC initiated a multiyear project to upgrade rainfall and runoff sensors and convert analog systems to digital electronic systems supported by data loggers. This conversion was coupled with radio telemetry to remotely transmit recorded data to a central computer, thus greatly reducing operational overhead by reducing labor, maintenance, and data processing time. A concurrent effort was initiated to improve access to SWRC data by creating a system based on a relational database supporting access to the data via the Internet. An SWRC team made up of scientists, IT specialists, programmers, hydrologic technicians, and instrumentation specialists was formed. This effort is termed the Southwest Watershed Research Center Data Access Project (DAP). The goal of the SWRC DAP is to efficiently disseminate data to researchers; land owners, users, and managers; and to the public. Primary access to the data is provided through a Web-based user interface. In addition, data can be accessed directly from within the SWRC network. The first priority for the DAP was to assimilate and make available rainfall and runoff data collected from two instrumented field sites, the WGEW near Tombstone, Arizona, and the Santa Rita Experimental Range (SRER) south of Tucson, Arizona. This web map describes the associated GIS layers.
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The Walnut Gulch Experimental Watershed (WGEW) runoff database has the longest period of record of runoff in the world for a semiarid location, with data collection beginning in 1953. Runoff occurs at Walnut Gulch primarily as a result of convective thunderstorms during the months of July through September. Runoff volume and flow duration are correlated with drainage area as a result of the limited areal extent of runoff producing rainfall and transmission losses or infiltration of the flood wave into the channel alluvium. Runoff is measured at three ranges of watershed size: small, 0.0018-0.059 km2; medium, 0.35-1.60 km2; and large, 2.27-149 km2. The small watersheds are termed ‘‘unit source area watersheds'' and were established to quantify the interaction of rainfall intensity patterns, soils, vegetation, and management on the rates and amounts runoff and sediment production. The medium watersheds were established at preexisting small earthen dams or stock tanks to obtain inexpensive measurements of storm runoff volume and annual sediment yield. The large watersheds were established to quantify the effects of the spatial and temporal variability of thunderstorm rainfall and channel characteristics on water yield, peak discharge, and sediment yield. Runoff was originally measured using a stilling well, float, and analog stage recorders (Stevens A-35, Friez FD-4, Friez FW-1) with mechanical clocks to record the timing of the event. In 1999, digital recorders consisting of potentiometers attached to the stilling well gear mechanism and a Campbell Scientific CR-10 data logger were added to all of the runoff measurement stations. At present, both the analog and digital data are being collected and are archived.
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The Southwest Watershed Research Center (SWRC) has operated Walnut Gulch Experimental Watershed (WGEW), located in the vicinity of Tombstone, Arizona, for more than 50 years. A 17 year (1990-2006) meteorological and soil hydrology database has been established by the USDA Agricultural Research Service, SWRC. Data have been acquired at 3 automated weather stations, 5 soil profile trench sites, and 19 locations dispersed across the watershed colocated with recording rain gauges. Meteorological elements measured at the weather stations include air temperature, relative humidity, wind speed, wind direction, barometric pressure, solar radiation, photosynthetically active radiation, and net radiation. Net radiation is measured at LHMet and KENMet. A single sensor is used to measure each variable at each AWS. Barometric pressure is sampled once and output at the output time step; all other sensors are sampled every 10 seconds and averaged at the output time step, either 20 or 60 minutes. Manufacturer supplied calibration or conversion factors are employed to report output in standard units.
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The meteorological data and Bowen ratio energy balance systems (BREB) (Model 023/CO2 Campbell Scientific Inc., Logan, Utah, USA) data are used to calculate carbon dioxide and evapotranspiration (ET) fluxes at Lucky Hills. The stored Bowen ration instrument data from the measurement site were transmitted by radio daily to our research station in Tombstone, AZ. From there, they were transferred through an Internet connection to Tucson, AZ. The data were then divided into 5-day increments and inserted into a Quattro1 Pro spreadsheet file which had all the formulations to calculate flux of soil heat, latent heat, sensible heat, evapotranspiration rates (ET), and CO2 rates on the 20-min time step of the data. All instrument and calculated data were graphed in the spreadsheet file and thoroughly reviewed for any instrument problems or data stream collection issues. The shrub site is known as Lucky Hills, elevation 1372 m. The soil at this site is coarse-loamy, mixed, thermic Ustochreptic Calciorthids) with 3 to 8% slopes [NRCS Soil Survey, 2003]. The surface A horizon (0-6 cm) contains 650 g kg1 sand, 290 g kg1 silt, and 60 g kg1 clay with 290 g kg1 coarse fragments >2 mm, 8 g kg1 organic carbon, and 21 g kg1 inorganic carbon. Vegetation is dominated by creosotebush (Larrea tridentata (D.C.) Cov.), whitethorn Acacia (Acacia constricta Benth. (Fabaceae)), and tarbush (Flourensia cernua D.C. (Asteraceae)). Vegetation canopy height maintained an almost constant 1 m height. Carbon dioxide and water fluxes are important components of watershed function. In order to study carbon dioxide and water flux as they exist over the Walnut Gulch Experimental Watershed (WGEW), two sites were selected on the basis of their ecosystem composition, one site being dominated by shrubs and the other a grass dominated plant community. Lucky Hills is the shrub site. Measurements were made from 1997 through the present at the two sites.
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Energy and CO2 Fluxes have been monitored from 1997 to 2007 using Bowen Ratio technique, and since spring of 2004 with eddy covariance. This is located in a small intensively-studied, experimental watershed within USDA-ARS's Walnut Gulch Experimental Watershed.
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The Walnut Gulch Experimental Watershed (WGEW) sediment collection program, established in 1953, provides event-based data for semiarid rangeland erosion, sediment transport, and yield research. Sediment loads carried through the channel network on the WGEW are high, but are typical of semiarid rangelands, and are influenced by soils, geologic parent material, and geomorphology. Typical monsoon thunderstorm generated flows in dryland regions are characterized by high velocities, short durations, and heavy and coarse sediment loads. Sediment is measured in conjunction with discharge measurements [Stone et al., 2008] that are integral to converting sample values to runoff event-based values. Sampling initiated in the 1960s was done with point intake pump samplers. The single point sampler intake tubes were later replaced with tubes that rise in response to flow and are perforated to collect depth integrated samples. Sampling with each of these systems is limited to suspended sediment smaller than the 0.635 cm diameter of the intake slots. Pump samplers are in use at the outlet of small watersheds where overland flow is the dominant hydrologic driver of sediment transport, and particles are small. As watershed size increases on the WGEW, in general, the channel network can dominate sediment delivery processes as it evolves to carry an increasingly coarse, and vertically sorted, sediment load. A traversing slot sediment sampler was designed in response to limitations of alternative sampling methods such as the pump sampler. The data collection network was expanded in 2002 and pit traps were added below the overfall at flumes 63.103 and 63.104. Analysis of these data, and efforts to process and make available the historic data, are ongoing.
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An extensive precipitation database at the 149 km2 Walnut Gulch Experimental Watershed (WGEW) has been developed over the past 53 years with the first records starting in August 1953 and continuing to the present. The WGEW is a tributary of the San Pedro River, surrounds the town of Tombstone in southeastern Arizona, and has a drainage area of approximately 149 km2. Elevation of the watershed ranges from 1220 m to 1950 m above mean sea level (MSL). Average annual precipitation for the period of 1956-2005, as measured with six gauges, is roughly 312 mm, with approximately 60% falling during the summer monsoon. Precipitation consists almost solely of rainfall with relatively rare instances of hail and snowfall. From a historical high of 95 rain gauges, a current network of 88 gauges is operational. This constitutes one of the densest rain gauge networks in the world (0.6 gauges/km2) for watersheds greater than 10 km2. Through 1999, the network consisted of analog recording weighing rain gauges. In 2000, a newly designed digital gauge with telemetry was placed adjacent (1 m) to the analog gauges. Both the analog and digital networks of gauges were in operation from 2000 to 2005 to enable a comparative analysis of the two systems. The analog data were digitized from paper charts and were stored in breakpoint format. The digital data consist of rainfall depths at 1-min intervals during periods of rainfall.
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This dataset contains air temperature, relative humidity, precipitation, solar radiation, wind speed, soil temperature, and soil moisture data from the Soil Climate Analysis Network (SCAN) site 2026, "Walnut Gulch #1," located in Cochise County, Arizona. The dataset links to a National Resources Conservation Service data request form, from which available data can be queried. The data collection site is at an elevation of 4500 feet; data has been continuously collected there since 1999-03-19.
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A stationary camera overlooking the Kendall sub-watershed in the Walnut Gulch Experimental Watershed used to track vegetation phenology (RGB and IR imagery). Images are taken every 30 minutes between 4:00am and 10:30pm local standard time. A link to the Phenocam's network FAQ: https://phenocam.sr.unh.edu/webcam/faq
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A stationary camera overlooking the Lucky Hills sub-watershed in the Walnut Gulch Experimental Watershed used to track vegetation phenology (RGB and IR imagery). Images are taken every 30 minutes between 4:00am and 10:30pm local standard time. A link to the Phenocam's network FAQ: https://phenocam.sr.unh.edu/webcam/faq