Identifying areas sensitive to land use/land cover change for downstream flooding in a coastal Alabama watershed

This paper explored the linkage between historic, current and future land use/land cover (LULC) conditions and peak flow and runoff volumes in a coastal community in Alabama in an effort to identify critical areas for downstream flooding. The study demonstrated that critical areas cannot be determined intuitively without conducting modeling studies. The study watershed, Eightmile Creek, experienced approximately 48 % forest loss between 1966 and 2011 largely due to urbanization. Residential development is expected to continue mostly in the central part of the watershed in the near future. Historic, current and future LULC maps were developed by processing aerial imagery, which were used in the HEC-HMS hydrologic model to study flood risk. An index method was applied to estimate the contribution of different parts of the watershed to downstream peak flows. The model showed a significant increase in peak flow and runoff volume from 1966 to 2011 and from 2011 to 2022 due to urbanization. The sensitivity of peak flows to LULC change decreased with increasing storm return periods, but the order of importance of different parts of the watershed, in terms of flooding, did not change significantly. Results of this study demonstrate the need for sustainable development by targeting areas that can have the least impacts on downstream flooding. The methodology presented in this paper can help decision makers propose land use alternatives to minimize adverse environmental impacts.