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The Automated Geospatial Watershed Assessment (AGWA) tool is a multipurpose hydrologic analysis system for use by watershed, water resource, land use, and biological resource managers and scientists interested in performing watershed- and basin-scale studies. AGWA is a GIS tool developed by the U.S. Environmental Protection Agency, the U.S. Department of Agriculture (USDA), Agricultural Research Service, and the University of Arizona. This tool can run two different hydrologic models: Soil Water Assessment Tool (SWAT) and KINematic Runoff and EROSion (KINEROS2). These two models can produce results at multiple temporal and spatial scales. For large river basins, typically SWAT is employed. AGWA’s current outputs are runoff (volumes and peaks) and sediment yield, plus nitrogen and phosphorus when using the SWAT model.
AGWA employs GIS data to parameterize, execute, and display results from both SWAT and KINEROS2 models. By means of an interactive interface, users choose an outlet from which AGWA delineates and discretizes the watershed using a Digital Elevation Model (DEM) based on the individual model requirements. The elements selected for the watershed model are combined with soils and land cover data layers. This combination comprises the required model input parameters. AGWA can currently use STATSGO, SSURGO and FAO soils and nationally available land-cover/use data such as the National Land Cover Data (NLCD) datasets. Furthermore, users can employ any customized land-cover/use data classification method. The selected hydrologic model is then executed, and the results are imported back into AGWA for visualization. The results help decision-makers to detect potential problem areas where additional monitoring might be necessary. AGWA can differentiate results from multiple simulations to compare and contrast changes predicted for each option input scenario (e.g., climate/storm change, land-cover change, present conditions, and alternative futures). In addition, a variety of new capabilities have been incorporated into AGWA, including pre- and post-fire watershed assessment, watershed group simulations, implementation of stream buffer zones, and installation of retention and detention structures. A land-cover modification tool is provided for the development of prescribed land-cover change scenarios, with a number of options from uniform, spatially random, and patchy change to single or multiple land-cover classes. There are currently two versions of AGWA available: AGWA 1.5 for users with Environmental Systems Research Institute (ESRI) ArcView 3.x GIS software (ESRI, 2005), and AGWA 2.0 for users with ESRI ArcGIS 9.x and ArcGIS 10.
Planning and assessment in land and water resource management are shifting from local-scale problems to regional and spatially correlated issues. Such problems have to be addressed with distributed models that can compute runoff and erosion at different spatial and temporal scales. The extensive data requirements and the difficult task of building input parameter files, however, have long represented an obstacle to the timely and cost-effective use of such complex models by resource managers. AGWA presents decision-makers with an opportunity to facilitate this process.
Input layers displayed in ArcGIS. Source: AGWA website. http://tucson.ars.ag.gov
AGWA uses widely available standardized spatial datasets that can be obtained via the Internet. The data are used to develop input parameter files for two watershed runoff and erosion models: KINEROS2 and SWAT.
1. To provide a simple, direct, and repeatable method for hydrologic model parameterization
2. To use only basic, attainable GIS data
3. To be compatible with other geospatial watershed-based environmental analysis software
4.To be useful for scenario development and alternative futures simulation work at multiple scales.
How does AGWA Work?
Using digital data in combination with the automated functionality of AGWA greatly reduces the time required to use these two watershed models. Through a robust and intuitive interface the user selects an outlet from which AGWA delineates and discretizes the watershed using the DEM. The watershed elements are then intersected with soil, land cover, and precipitation (uniform or distributed) data layers to derive the requisite model input parameters. The model is then run, and the results are imported back into AGWA for visual display.
Soil Water Assessment Tool (SWAT)
SWAT, developed by the U.S. Agricultural Research Service, is a long-term simulation model for use in large (river-basin scale) watersheds. The Soil and Water Assessment Tool is a quasi-distributed model to predict the impact of land management practices on water, sediment and agricultural chemical yields in a complex watersheds with varying soils, land use and management conditions over long periods of time (> 1 year). SWAT is a continuous-time model (i.e. a long-term yield model) using daily average input values, and is not designed to simulate detailed, single-event flood routing. For more information on SWAT, please visit www.brc.tamus.edu/swat.
Kinematic Runoff and Erosion (KINEROS2)
KINEROS, also developed by the U.S. Agricultural Research Service, is an event driven model designed for small semi-arid watersheds. The AGWA tool has intuitive interfaces for both models that provide the user with consistent, reproducible results in a fraction of the time formerly required with the traditional approach to model parameterization. This model displays the processes of interception, infiltration, surface runoff and erosion from small (less than about 100 km2) watersheds. The watershed is represented by a variety of planes and channels. These planes and channels allow rainfall, infiltration, runoff, and erosion parameters to vary spatially. KINEROS2 may be used to determine the effects of various artificial features such as urban developments, small detention reservoirs, or lined channels on flood hydrographs and sediment yield. For more information on KINEROS2, please visit www.tucson.ars.ag.gov/kineros.
Data used in AGWA include Digital Elevation Models (DEMs), land cover grids, soils data, and precipitation data. Most input layers are available at no cost over the Internet for North America, and other areas around the world. In addition, output from one model may be used as input in others, which can be particularly valuable for scenario development and alternative futures simulation work.
Output Variables available in AGWA
|Infiltration (mm; m3/km)||Channel Discharge (m3/day)|
|Infiltration (in;ac-ft/mi)||ET (mm)|
|Runoff (mm)||Percolation (mm)|
|Runoff (m3)||Surface runoff (mm)|
|Sediment yield (kg/ha)||Transmission loss (mm)|
|Peak flow (m3/s)||Water yield (mm)|
|Peak flow (mm/hr)||Sediment yield (t/ha)|
|Sediment discharge (kg/s)||Precipitation (mm)|
This table shows models’ results that can be displayed in AGWA. Observing the outputs allows managers to identify problematic areas where management activities can be focused, or to anticipate sensitive areas in association with planning efforts. Simulation results must be imported following the successful execution of SWAT or KINEROS.
KINEROS Plane Outputs
Infilt_m: infiltration (mm) Infilt_e: infiltration (in) Runoff_mm: runoff (mm) Runoff_m3: runoff (m3) Sed_out: sediment yield (kg) Pflow_m3s: peakflow (m3/s) Pflow_mmh: peakflow (mm/hr) PSedQ_kgs: peak sediment discharge (kg/s) Percent Error: mass balance error (%)
KINEROS Stream Outputs
Infilt_m: infiltration (mm) Infilt_e: infiltration (in) Runoff_mm: runoff (mm) Runoff_m3: runoff (m3) Sed_out: sediment yield (kg) Pflow_m3s: peakflow (m3/s) Pflow_mmh: peakflow (mm/hr) PSedQ_kgs: peak sediment discharge (kg/s) Z_change: channel scour (mm/m2) Percent Error: mass balance error (%)
SWAT Subwatershed outputs
Precip_mm: total precipitation for the subwatershed for the given time period (mm) ET_mm: estimated evapotranspiration (mm) Perc_mm: estimated percolation for the subwatershed (mm) Surq_mm: estimated surface runoff for the subwatershed (mm) Tloss_mm: estimated transmission loss for the subwatershed (mm) Watyld_mm: estimated water yield (mm) SedYld_t_h: estimated sediment yield (t/ha) OrgN_kg/ha: Organic Nitrogen contributed by the subwatershed to the channel (kg/ha) OrgP_kg/ha: Organic Phosphorus contributed by the subwatershed to the channel (kg/ha) SedP_kg/ha: Mineral Phosphorus attached to sediment contributed by the subwatershed to the channel (kg/ha) SurN_kg/ha: NO3 contributed by surface runoff from the subwatershed to the channel (kg/ha) SolP_kg/ha: Soluble Phosphorus contributed by surface runoff from the subwatershed to the channel (kg/ha)
SWAT Stream Outputs
Watyld_mm: estimated water yield (mm) 3 Tloss_m3s: estimated transmission loss (m /s) SedYld_mtn: sediment yield (tons) Q_cmd: channel runoff (m3/day) SedCon_mg/kg: Sediment concentration (mg/kg) OrgN_kg: Organic Nitrogen transported by water from the channel (kg) OrgP_kg: Organic Phosphorus transported by water from the channel (kg) NO3_kg: Nitrate transported by water from the channel (kg) NH4_kg: Ammonuim transported by water from the channel (kg) NO2_kg: Nitrite transported by water from the channel (kg) MinP_kg: Mineral Phosphorus transported by water from the channel (kg)
SWAT HRU outputs
Same as the subwatershed results but separated for each HRU in a subwatershed. These results cannot be displayed in the view.
IMPORTANT NOTE: AGWA is designed to evaluate relative change and can only provide qualitative estimates of runoff and erosion. It cannot provide reliable quantitative estimates of runoff and erosion without careful calibration. It is also subject to the assumptions and limitations of its component models, and should always be applied with these in mind.
AGWA 2.0 requires ArcGIS 9.x or ArcGIS 10, Spatial Analyst 9.x or 10, and the .Net Framework. AGWA 1.5 requires ArcView 3.1 or later and version 1.1 of the Spatial Analyst extension.
AGWA is publicly available for download in two different versions: AGWA 2.0 for ArcGIS and AGWA 1.5 for ArcView. Additionally, DotAGWA, an internet version sharing the AGWA 2.0 codebase, is under development (As of June 2012).
AGWA allows various download options. For more information click the following link. http://tucson.ars.ag.gov/agwa/index.php?option=com_jdownloads&view=viewcategories&Itemid=58
Rangeland Use Examples
Miller et al. 2007. Used KINEROS2 model to observe probability errors of omission in land cover classes.
Miller et al. 2002. Compared SWAT and KINEROS2 results over two watersheds in North America.
Rangeland Studies References
Miller S., Kepner W., Mehaffey M., Hernandez M., Miller R., Goodrich D., Devonald K., Heggem D., and Miller W. 2007. Integrating Landscape Assessment and Hydrologic Modeling for Land Cover Change Analysis. In In Journal of the American Water Resources Association. 38 (4): 915-929.
Miller S., Guertin P., and Goodrich D. 2007. Hydrologic Modeling Uncertainty Resulting from Land Cover Misclassification. In Journal of the American Water Resources Association. 43 (4): 1065-1075.
Technical Resources & References
AGWA website. http://tucson.ars.ag.gov
AGWA manual. www.epa.gov/esd/land-sci/agwa/pdf/agwa_manual_2-0.pdf