Modeling Urban Hydrology: A Comparison of New Urbanist and Traditional Neighborhood Design Surface Runoff

Urban development affects the amount of potential surface runoff generated during storms by changing the amount of impervious cover across the landscape. However, the degree of surface runoff alteration depends on the type of urban development in place. New urbanist developments are designed with higher densities and encourage a diversity of land uses, while traditional neighborhood developments have a monotone land use pattern with medium-to- low densities. Two neighborhoods within the city of Austin, Texas- Mueller, a new urbanist development, and Circle C Ranch, a traditional neighborhood development- were used to study the effect of development type on potential surface runoff. Using satellite imagery coupled to the HEC-HMS model nested within the Watershed Modeling System (WMS), potential surface runoff was calculated for the two different neighborhoods for a 10-year 24 hour storm scenario. Results initially suggest that total runoff volume and peak surface runoff significantly increase for the new urbanist neighborhood over the traditional development as a function of the higher density urban footprint associated with the new urbanist design. However a higher number of residential units are available at Mueller over the same area as Circle C Ranch. When taking this into account the increased potential surface runoff is negated at the new urbanist site. Although new urbanist neighborhoods will usually contain more residential units than traditional developments when compared at the same scale, the higher urban density associated with these developments necessitates the construction of more efficient stormwater retention measures within these neighborhoods