Land Use/Land Cover Change and Its Hydrological Impacts from 1984 to 2010 in the Little River Watershed, Tennessee

Land use/land cover (LULC) change, especially the conversion from farmland to residential and commercial land, has led to significant environmental issues in changing fluvial dynamics, accelerating sediment erosion and degrading water quality. The Little River, which provides drinking water for over 100,000 residents in Blount County, Tennessee, and serves as a source of agriculture and recreational activities, was listed as one of the U.S. Environmental Protection Agency’s (EPA) Targeted Watersheds because the water quality of its tributaries has become impaired due to several reasons. In this study, a detailed record of LULC change in a roughly 2-year interval was documented from 1984 to 2010 based on the classification of Landsat TM/ETM+ images. The classification accuracy was assessed by the comparison of Google Earth high resolution images in 2010. Then, the Soil and Water Assessment Tool (SWAT), a physically-based distributed hydrological model, was used to quantify the impacts of LULC change on streamflow and water quality in this watershed over this period.

The results showed that Landsat TM/ETM+ images can be classified accurately using the Maximum Likelihood Classification (MLC) algorithm, and the SWAT model can effectively simulate the long-term impact of LULC change on streamflow and non-point source (NPS) pollution in this watershed. Above 80% overall accuracy and the kappa coefficient were achieved in the accuracy assessment of the classification of year 2010. Long-term classified LULC records indicated that urban areas (residential and commercial lands) and forest increased in 1984-2010 from 6.3 to 11.1% and from 65.0 to 69.5%, respectively, whereas agricultural land decreased from 28.3 to 18.9% over the same period.

After calibration and validation, the simulation results indicated that stream flow increased 3% in this whole watershed, but with a very distinct spatial pattern. The model also suggested sediment load and nutrients (total nitrogen and phosphorus) had different degrees of decline. The statistic analysis showed that the increase of streamflow and urban expansion demonstrated a very strong and positive relationship, and water quality change is highly related to the decrease of agricultural land that occurred in this watershed in recent years.