Geology Reference
In-Depth Information
greater user capability, and security. Importantly,
watershed models are typically more complex
then hillslope erosion models and take longer to
execute, which requires more processing power
or user patience. In the future distributed systems
(n-tier architecture) would address some of these
issues where datasets would be stored and
accessed from different host servers with applica-
tion datasets assembled as needed. Distributed
systems will require high bandwidth access,
which is not always present. Examples of Internet-
based watershed model applications that address
erosion and sediment yield include AGWA and
Web-based SWAT (Park
et al
., 2009). AGWA is
discussed below.
One of the first watershed applications was
AGWA ('Dot AGWA'), the Internet version of
AGWA that grew out of the PC-based Automated
Geospatial Watershed Assessment (AGWA) tool
developed by the USDA's Agricultural Research
Service, in cooperation with the Environmental
Protection Agency and the Universities of Arizona
and Wyoming. Many of the initial concepts for
AGWA were conceived by Miller
et al
. (2004)
and the system was fully developed and imple-
mented as an alpha version (Cate
et al
. 2005,
2006; Cate, 2008). AGWA was developed as a
multipurpose hydrological analysis system for
use by watershed, water resource, land use, and
biological resource managers and scientists devel-
oping watershed and basin-scale studies (Miller
et al
., 2007; Semmens
et al
., 2008). AGWA incor-
porates several spatial datasets, GIS mapping,
analysis and visualization tools, and two water-
shed and erosion models into one package,
providing easy access to these features. The two
watershed models embedded within AGWA are
SWAT (Arnold & Fohrer, 2005; http://www.brc.
tamus.edu/swat/) for relatively large basin appli-
cations, and KINEROS2 (Goodrich
et al
., 2006;
Semmens
et al
., 2008; http://www.tucson.ars.
ag.gov/kineros) for small to medium watershed
applications. This enables rapid multiscale water-
shed analysis.
AGWA employs ESRI's ArcIMS and Spatial
Data Engine (SDE) as well as Oracle's spatial data-
base to provide the GIS data and interactions.
Java-based web server technology is used to con-
nect AGWA to the watershed models in the
application. The web application is based on the
Model-View-Controller (MVC) design pattern.
This design pattern is useful in separating the
presentation components of the system architec-
ture from the data storage and processing compo-
nents. In this architecture, the Model component
allows the different system components to be
represented as individual entities. The View is
simply the user interface, and the Controller ties
the Model and View components together. This
separation is useful as it allows changes, replace-
ments or alterations to one of the three compo-
nents without major changes in other parts of the
system. For example, if MySQL is the initial sup-
porting database used in the system and it
becomes inadequate when the user base expands
greatly, then another database like PostgeSQL
can be inserted into the existing system with
minimal effort or interruption.
Users can define management scenarios, and
like AGWA, have the application parameterize
and run the models for the defined management
plan. Both of the watershed models are spatially
distributed so that simulation results for erosion
and sediment transport, as well as hydrology, can
be imported back into AGWA and mapped back
onto upland or channel elements within the inter-
net view. Different output formats (i.e. XML, Word
doc, HTML) for the resulting simulation output
can also be specified by the user. As noted, the tool
leverages client-server architecture so that changes
and improvements in core components will not
disrupt end-user interaction with the application.
The alpha-based application is currently undergo-
ing further development and is not supported for
general Internet access at this time.
17.6
Example of an Internet-Based
Application
Flanagan
et al
. (2004) described the Internet-
based WEPP-GIS application (WEPP-GIS; http://
milford.nserl.purdue.edu/wepp/gis2.php?IES
1).
The application utilizes the core procedures
=
