Land Use Change and Its Effect on Water Quality: A Watershed Level BASINS-SWAT Model in West Georgia...
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![Page 1: Land Use Change and Its Effect on Water Quality: A Watershed Level BASINS-SWAT Model in West Georgia Gandhi Raj Bhattarai Diane Hite Upton Hatch Prepared.](https://reader030.fdocuments.in/reader030/viewer/2022032703/56649cfa5503460f949cb9b1/html5/thumbnails/1.jpg)
Land Use Change and Its Effect on Water Quality: A Watershed Level BASINS-SWAT
Model in West Georgia
Gandhi Raj BhattaraiDiane Hite
Upton Hatch
Prepared for presentation at the Alabama Water Resource Conference and Symposium, Orange Beach, Alabama, October 12-14, 2005
![Page 2: Land Use Change and Its Effect on Water Quality: A Watershed Level BASINS-SWAT Model in West Georgia Gandhi Raj Bhattarai Diane Hite Upton Hatch Prepared.](https://reader030.fdocuments.in/reader030/viewer/2022032703/56649cfa5503460f949cb9b1/html5/thumbnails/2.jpg)
Introduction
• Non-Point Source Pollution (NPP) is caused by the movement of water over and through the ground
• NPP threatens majority of the water bodies in the US
• Increasing urbanization coupled with increasing use of fertilizers and chemicals in agricultural lands create significant challenges to maintain water quality
• Biophysical water quality models facilitate the spatial analysis of sources and effects of point and non-point pollutants with reference to their origin and locations
• Level of nitrogen, phosphorus and sediment loads are estimated to help in formulating control policies
![Page 3: Land Use Change and Its Effect on Water Quality: A Watershed Level BASINS-SWAT Model in West Georgia Gandhi Raj Bhattarai Diane Hite Upton Hatch Prepared.](https://reader030.fdocuments.in/reader030/viewer/2022032703/56649cfa5503460f949cb9b1/html5/thumbnails/3.jpg)
Objective
• Find the relationship between land use change and water quality by simulating levels of nitrogen, phosphorus and sediment with two contrasting land use scenarios over time
![Page 4: Land Use Change and Its Effect on Water Quality: A Watershed Level BASINS-SWAT Model in West Georgia Gandhi Raj Bhattarai Diane Hite Upton Hatch Prepared.](https://reader030.fdocuments.in/reader030/viewer/2022032703/56649cfa5503460f949cb9b1/html5/thumbnails/4.jpg)
The Modeling Approach
The BASINS framework
(Better Assessment Science Integrating Point and Non-point Sources)
• Provides a centralized platform for data extraction and descriptive analysis
• Helps in setting up individual watershed based models
• Includes four specific watershed level biophysical models for the estimation of in-stream and watershed loading and transportation (QUAL2E, PLOAD, HSPF and SWAT)
![Page 5: Land Use Change and Its Effect on Water Quality: A Watershed Level BASINS-SWAT Model in West Georgia Gandhi Raj Bhattarai Diane Hite Upton Hatch Prepared.](https://reader030.fdocuments.in/reader030/viewer/2022032703/56649cfa5503460f949cb9b1/html5/thumbnails/5.jpg)
The Modeling Approach
Soil and Water Assessment Tool (SWAT)
• Soil and Water Assessment Tool (SWAT) is integrated in components of the BASINS model
• The program integrates ArcView Geographic Information System interface to derive the model input parameters and simulation
• Inputs are DEM, digital land use maps, soils maps, historical temperature and precipitation data, management parameters etc.
• Starts with hydrological boundary delineation
![Page 6: Land Use Change and Its Effect on Water Quality: A Watershed Level BASINS-SWAT Model in West Georgia Gandhi Raj Bhattarai Diane Hite Upton Hatch Prepared.](https://reader030.fdocuments.in/reader030/viewer/2022032703/56649cfa5503460f949cb9b1/html5/thumbnails/6.jpg)
(a) (b)
(c) (d)
Figure 2. Automatic watershed delineation using the DEM and NHD stream network; (a) National Elevation Model data loaded, (b) watershed area and NHD networks loaded as focus area and burn-in option, (c) digitized stream networks and nodes created, (d) sub-basins created and parameters calculated.
![Page 7: Land Use Change and Its Effect on Water Quality: A Watershed Level BASINS-SWAT Model in West Georgia Gandhi Raj Bhattarai Diane Hite Upton Hatch Prepared.](https://reader030.fdocuments.in/reader030/viewer/2022032703/56649cfa5503460f949cb9b1/html5/thumbnails/7.jpg)
(a) Reclassified land use (e.g., NLCD 2001) (b) Reclassified state soils map
Figure 3. Land use and soil reclassification and spatial overlay
Unique hydrological response units (HRU) are created by overlaying land use and soils maps; e.g. 5 land use classes and 3 different soils can produce 5x3 = 15 HRUs with unique land use-soil combinations
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Limitations of the study
• Left out small land cover areas in unique uses (model limitation)
• Lack of model calibration and validation (data limitation)
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5 0 5 Miles
Main Watershed
Study area sub-watershed
County Boundary
Reach File V1
Legend
Stream Network (NHD)
N
EW
S
Location of Study Area in West Georgia
(HUC #0331000212)
Fulton
CobbPaulding
Carroll
Douglas
Coweta
Heard
Meriwether
Troup
TalbotHarris
Muscogee
Randolph
Chambers
Lee
HUC # 03310002
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Weighted Land Use Share in Harris County, GA
Land Use Share Broad Land Use Class 1992 2001 Change* Developed 1.0% 6.2% 515.9% Agricultural 8.2% 16.6% 101.8% Forest 86.6% 70.7% -18.3% Other 4.2% 6.5% 54.3% * Area weighted change
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Land Use Change in Mulberry Creek Subwatershed1992 - 2001
(a) Reclassified NLCD-1992 (a) Reclassified NLCD-2001
Developed LandAgricultural LandForest LandOther Land
Subwatershed Boundary
Legend
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Results
Description of watershed
Number of sub-basins : 331
Mean Elevation of sub-basins : 216 m.a.s.l.
Average size of sub-basins : 176.3 hectares
Hydrological Response Units NLCD-92 NLCD-01
# HRUs created 2089 2158
# HRUs per Sub-basin 6.3 6.5
Average size of HRU (ha.) 27.9 27.0
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Effects of Land Use Change on Water Quality (60 years Annual Average)
NLCD 1992 NLCD 2001 Variable
Mean S. E. Mean S.E.
Change
%
Precipitation (mm) 1277.60 207.86 1277.60 207.86 n/a
Water Yield (mm) 243.15 93.17 251.87 94.20 3.6%
Sediment (t/ha) 13.60 8.49 16.13 9.22 18.7%
Nitrogen (kg/ha) 2.07 1.20 2.23 1.19 8.0%
Phosphorus (kg/ha) 0.24 0.14 0.27 0.14 9.0%
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Average Annual Sediment Yield (t/ha)
0.00
10.00
20.00
30.00
40.00
50.00
60.00
1950 1960 1970 1980 1990 2000
Year
Sed
imen
t (t
/ha)
.
LU-1992 LU-2001
`
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Average Annual Organic Nitrogen Runoff (kg/ha)
0.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
1950 1960 1970 1980 1990 2000
Year
Nitr
ogen
(kg/
ha)
.
LU-1992 LU-2001
`
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Average Annual Organic Phosphorus Runoff (kg/ha)
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1950 1960 1970 1980 1990 2000
Year
Pho
spho
rus
(kg/
ha)
.
LU-1992 LU-2001
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Conclusion
• Land use change from 1992 to 2001 affected water quality:
• Average annual nutrient runoff increased by 8% for nitrogen and 9% for phosphorus
• Average annual sediment loadings increased by 19%
• Water yield in main channel increased by 4% suggesting less ground water recharge
• Less vegetative cover, more impervious surfaces, and increased agricultural land caused less percolation and higher runoff with higher nutrient runoff & sedimentation
![Page 18: Land Use Change and Its Effect on Water Quality: A Watershed Level BASINS-SWAT Model in West Georgia Gandhi Raj Bhattarai Diane Hite Upton Hatch Prepared.](https://reader030.fdocuments.in/reader030/viewer/2022032703/56649cfa5503460f949cb9b1/html5/thumbnails/18.jpg)
Conclusion
• Simulation using two land use maps suggest– Using a fixed set of land use data for a long period of SWAT
modeling may not yield precise results as changes in land use causes significant changes in water quality result
– However, the same result indicates that SWAT can precisely predict the effects on water quality over time, if intermediate land use maps are used for comparative studies