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Walnut Gulch Experimental Watershed, Arizona (Sediment)

posted on 2023-11-30, 08:41 authored by MH Nichols

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.

Resources in this dataset:


Agricultural Research Service


Data contact name

Armendariz, Gerardo


U.S. Department of Agriculture - Agricultural Research Service

Intended use

The WGEW sediment database provides baseline information for characterizing erosion and sediment delivery on semiarid rangelands. Sediment data collected on the WGEW have been critical for developing erosion prediction technologies. The long-term objective of sediment data collection is to support an evolving set of research objectives to understand the interactions among climate, vegetation, and land use that affect erosion, sediment transport, and yield in semiarid regions. The data are also fundamental to developing simulation models and conducting short-term hypothesis driven research.

Use limitations

Sediment data collection in dryland ephemeral channels is notoriously difficult. Early attempts to use V notch weirs for runoff and sediment accumulation measurements failed when hydraulic control required for accurate flow measurement was lost as sediment was deposited behind the structure. Attempts to measure sediment moving through the large flumes along the main channels on the watershed were limited to the suspended load, and collecting those samples took place under less than ideal weather conditions. Collecting sediment during runoff using either a pump sampler or the traversing slot sampler is subject to a range of mechanical problems, such as clogged intake tubes and failure of moving parts. In addition, sample handling and laboratory procedures can introduce errors. Historically, the pen traces for runoff and sediment measurements operated independently, thus potentially introducing timing errors. The recent instrumentation upgrade improved data collection by incorporating electronic clocks for time stamping measurements.

Temporal Extent Start Date



  • Not specified

Geographic Coverage


ISO Topic Category

  • environment
  • farming

Ag Data Commons Group

  • Walnut Gulch Experimental Watershed
  • Long-Term Agroecosystem Research

National Agricultural Library Thesaurus terms

watersheds; sediments; rangelands; sediment transport; pollution load; sediment yield; soil; geomorphology; monsoon season; arid lands; suspended sediment; overland flow; traps; climate; vegetation; land use; semiarid zones; simulation models

OMB Bureau Code

  • 005:18 - Agricultural Research Service

OMB Program Code

  • 005:040 - National Research

ARS National Program Number

  • 211

Pending citation

  • No

Public Access Level

  • Public

Preferred dataset citation

Nichols, MH (2020). Walnut Gulch Experimental Watershed, Arizona (Sediment). U.S. Department of Agriculture - Agricultural Research Service.

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