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 for presentation at the Alabama Water Resource Conference and Symposium, Orange Beach, Alabama, October 12-14, 2005

2. 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

3. 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

4. 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)

5. 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

7. 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

8. Limitations of the study Left out small land cover areas in unique uses (model limitation) Lack of model calibration and validation (data limitation)

12. 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 UnitsNLCD-92NLCD-01 # HRUs created20892158 # HRUs per Sub-basin6.36.5 Average size of HRU (ha.)27.9 27.0

13. Effects of Land Use Change on Water Quality (60 years Annual Average)

17. 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

18. 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