Assessing the Hydrologic Implications of Land Use Change for the Upper Neuse River Basin

Abstract

Land cover plays a vital role in the chemistry and the quantity of runoff, and therefore can indirectly have an immense impact on the water quality of stream and river systems. Simulation models have become extremely useful tools available to watershed managers as geospatial environmental datasets become increasingly more available. The Soil and Water Assessment Tool (SWAT) is a deterministic hydrologic model that can predict hydrologic conditions over various temporal and spatial scales. This project evaluates the accuracy of the SWAT model for the Upper Neuse River Basin, while comparing two land use scenarios in an effort to identify sensitive regions in the watershed. A regression analysis between observed and predicted stream velocity demonstrated that the initial model required calibration of stream parameters in order to more accurately model the natural system. After calibration, stream sedimentation values were compared by subbasin between a current (2001) and future (2010) land use scenario, in order to identify areas in the watershed that were the most susceptible to degradation via urbanization. Out of the 138 catchments delineated in the watershed, 29 experienced no relative change while the remaining 109 all displayed an increase in the relative difference of the sedimentation rate between scenarios. Subbasins with the greatest potential for degradation were identified and prioritized for conservation efforts or further analysis. The subbasins experiencing the highest increase in both the relative change as well as the percent change in sediment yield are all in either Wake or Durham County, suggesting a need for conservation planning in these regions. Moreover, through examining the spatial variability of these results, the influence of regional characteristics like slope, land use and soil type can be exemplified. The tremendous variation in sediment yield that occurs with urbanization suggests that local spatial conditions can exert a noticable influential on water quality and should be taken into account to maximize future management efforts. Overall, environmental tools such as the SWAT model demonstrate their usefulness in helping inform land use decisions, and can assist environmental managers in protecting water quality.