The Automated Geospatial
Watershed Assessment Tool
A CIS-Based Hydrologic Modeling Tool
EPA/600/C-07/015
ARS/218468
Key words: watershed assessment; hydrologic model; runoff; erosion; geographic information systems
Background
Planning and assessment in land and water resource management are evolving from simple, local-scale problems toward
complex, spatially explicit, regional ones. 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.
The U.S. EPA Office of Research
Development and the USDA-ARS Southwest
Watershed Research Center have developed a
tool to facilitate this process. A geographic
information system (GIS) provides the
framework within which spatially distributed
data are collected and used to prepare model
input files and evaluate model results.
The Automated Geospatial Watershed
Assessment (AGWA) tool uses widely
available standardized spatial datasets that are
readily obtained via the Internet. The data are
used to develop input parameter files for two
watershed runoff and erosion models:
KINEROS and SWAT.
KIN EROS
The Kinematic Runoff and Erosion Model is an
event-oriented, physically based model
developed at the USDA-ARS to describe the
processes of interception, infiltration, surface
runoff and erosion from small watersheds
characterized by overland flow. The watershed
is represented by a cascade of planes and
channels, thereby allowing rainfall, infiltration, runoff, and erosion parameters to vary spatially. KINEROS can
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 KINEROS, please visit
www.tucson.ars.ag.gov/kineros.
SWAT
The Soil and Water Assessment Tool is a quasi-distributed model developed at the USDA-ARS to predict the impact of land
management practices on water, sediment and agricultural chemical yields in large, complex watersheds with varying soils,
land use and management conditions over long periods of time (> 1 year). SWAT is a continuous-simulation 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.
Example of a watershed discretized by AGWA
(Walnut Gulch, San Pedro River Basin, Arizona).
-------
Automated Geospatial Watershed Assessment
Digital Elevation Model (DEM)
M) £+
W
Watershed Discretization
AGWA Description and Uses
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 Digital
Elevation Model (DEM) information. The watershed elements are then
intersected with soil, land-use/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. Model outputs that can be displayed in AGWA are shown in the
table to the right. This feature allows managers to identify problem areas
for further monitoring and management activities. Additional functionality
can generate alternative future land-use/cover scenarios and display
differences between simulation outputs (potential change), designed to
provide decision support when combined with planning efforts
AGWA is designed to provide qualitative estimates of runoff and erosion
relative to landscape change. 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.
Availability
AGWA is publicly available for download in two different versions,
AGWA 2.0 for ArcGIS and AGWA 1.5 for Arc View. Additionally,
DotAGWA, an Internet version sharing the AGWA 2.0 codebase, is under
development.
AGWA 2.0 requires ArcGIS 9.x, Spatial Analyst 9.x, and the .Net •
Framework. AGWA 1.5 requires Arc View 3.1 or later and version 1.1 of
the Spatial Analyst extension.
For further information contact:
William G. Kepner or Darius J. Semmens
U.S. Environmental Protection Agency
P.O. Box 93478
Las Vegas, NV 89193-3478
http ://www. epa. gov/nerlesd 1/land-sci/agwa/index. htm
David C. Goodrich or Mariano Hernandez
USDA-ARS Southwest Watershed Research Center
2000 East Allen Road
Tucson, AZ 85719-1596
http://www.tucson.ars.ag.gov/agwa
Results
Output variables that can be displayed in AGWA
KINEROS
SWAT
Infiltration (mm, m /km)
Infiltration (in, ac-ft/mi)
Runoff (mm, m3)
Peak flow (m3/s, mm/hr)
Sediment yield (kg/ha)
Channel scour (mm/m2)
Sediment discharge (kg/s)
Precipitation (mm)
ET(mm)
Percolation (mm)
Surface runoff (mm)
Transmission loss (mm)
Water yield (mm)
Sediment yield (t/ha)
dss
US EPA Office of
Research &
Development
USDA-ARS
Southwest Watershed
Research Center
------- |