In Soil and Water Assessment Tool (SWAT), oftentimes, Critical Source Area (CSA),
the minimum upstream drainage area that is required to initiate a stream, is used to
subdivide a watershed. In the current literature, CSA has been used as a trial and error
process to define the subwatershed levels. On the other hand, the ongoing collaboration
of the United States Environmental Protection Agency Office of Water and the United
States Geological Survey has promoted a national level predefined catchments and
flowlines called National Hydrography Dataset (NHD) Plus to ease watershed modeling
in the United States. The introduction of NHDPlus can eliminate the uncertain nature in
defining the number of subwatersheds required to model the hydrologic system.
This study demonstrates an integrated modeling environment with SWAT and NHDPlus
spatial datasets. A spatial tool that was developed in a Geographical Information System
(GIS) environment to by-pass the default watershed delineation in ArcSWAT, the GIS
interface to SWAT, with the introduction of NHDPlus catchments and flowlines, was
used in this study. This study investigates the effect of the spatial size (catchment area) of the NHDPlus and the input data resolution (cell/pixel size) within NHDPlus
catchments on SWAT streamflow and sediment prediction. In addition, an entropy based
watershed subdivision scheme is presented by using the landuse and soil spatial datasets
with the conventional CSA approach to investigate if one of the CSAs can be considered
to produce the best SWAT prediction on streamflow.
Two watersheds (Kings Creek, Texas and Sugar Creek, Indiana) were used in this study.
The study shows that there exists a subwatershed map that does not belong to one of the
subwatershed maps produced through conventional CSA approach, to produce a better
result on uncalibrated monthly SWAT streamflow prediction. Beyond the critical
threshold, the CSA threshold which gives the best uncalibrated monthly streamflow
prediction among a given set of CSAs, the SWAT performance can be improved further
by subdividing some of the subwatersheds at this critical threshold. The study also
shows that the input data resolution (within each NHDPlus catchments) does not have an
influence on SWAT streamflow prediction for the selected watersheds. However, there
is a change on streamflow prediction as the area of the NHDPlus catchment changes.
Beyond a certain catchment size (8-9% of the watershed area), as the input data
resolution becomes finer, the total sediment increases whereas the sediment prediction in
high flow regime decreases. As the NHDPlus catchment size changes, the stream power
has an influence on total sediment prediction. However, as the input data resolution
changes, but keeping the NHDPlus catchment size constant, the Modified Universal Soil
Loss Equation topographic factor has an influence on total sediment prediction.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2009-12-7227 |
| Date | 2009 December 1900 |
| Creators | Mylevaganam, Sivarajah |
| Contributors | Srinivasan, Raghavan |
| Source Sets | Texas A and M University |
| Language | English |
| Detected Language | English |
| Type | Book, Thesis, Electronic Thesis, text |
| Format | application/pdf |
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