Page 205 - Biosystems Engineering

GIS-Based W atershed Modeling Systems 183

requires efficient acquisition, storage, organization, reduction, and
analysis of model input data accompanied by manipulation, interpre-
tation, reporting, and display of model output data (DePinto et al.
1994). Input data required by the models are currently available in
varying spatial and temporal scales, resolutions, uncertain quality
(because of errors associated with measuring, digitizing, editing,
etc.), and a multiplicity of formats. The large quantity of complex
data can be overwhelming, and model users may spend dispropor-
tionate amounts of time on data manipulation and systems integra-
tion to perform each application.
The only solution to this problem is a GIS-interfaced tool that
supports flexible interactive analysis and visualization. The use of
GIS can make the task of compiling necessary spatial data, nonspatial
data, and required hydrologic parameters for modeling watershed
runoff and water quality more manageable (Bhasker et al. 1992).
Interfacing GIS with a NPS pollution model results in a powerful tool
that is capable of storage, acquisition, organization, reduction, and
analysis of input and output data as well as visualization of input and
model simulated data, thereby reducing the time required for inter-
preting, reporting, and displaying model results. The interfacing of
GIS and hydrologic and NPS models also enables users to identify
critical areas of pollution and to perform various “what if?” scenarios
to better understand the effect of various alternative management
strategies on NPS pollution.
In the past, a number of researchers have attempted to interface
spatially distributed NPS, and other environmental models, with
GIS. For example, Roaza et al. (1993) interfaced a finite element
model of an aquifer with GIS to develop a system for optimal man-
agement of resources for a sand and gravel aquifer in Escambia
County, Florida. Ross and Tara (1993) interfaced a commercial GIS
[Tydac Technologies, Inc., Spatial Analysis System (SPANS)], a pub-
lic domain surface-water model [USEPA-supported HSPF], a
groundwater model [MODFLOW (McDonald and Harbaugh 1988)],
and an evapotranspiration code to aid P-mining–reclamation design.
Hay et al. (1995) interfaced a hydroclimatic model, GIS, Scientific
Visualization System (SVS), and an advanced statistical tool (STAT–
StatSci S-PLUS) as part of the U.S. Geological Survey’s Gunnison
River Basin Climate Study. Bromberg et al. (1995) developed the Sci-
entific Geographic Information System (SGIS) integrating Genamap
(GIS), S-Plus (Statistical Tool), Geo-EAS (Geostatistical Tool), and the
CENTURY model for ecosystem modeling. Geter et al. (1995)
described the development of the Hydrologic Unit Water Quality
Model (HU/WQ) GIS interface. This interface was developed for
four Agricultural Research Service (ARS) pollutant-loading models:
AGNPS (Young et al. 1987), SWRRBWQ (Arnold et al. 1990), EPIC
(Sharpley and Williams 1990), and GLEAMS (Knisel et al. 1992).