Development of an Infiltration Index and Its Application to Site Assessment in the Piedmont Region of the Southeastern USA.

Soils in the Piedmont region of the southeastern USA are well developed and characterized by a sandy surface over a subsurface clayey Bt horizon.  Housing and other construction projects can vastly alter the landscape, exposing the lower Bt and BC horizons, which can result in higher than natural runoff due to low infiltration.   The objective of this study was to develop an infiltration index through the use of readily available soil information to assess potential runoff from soils that are impacted by construction and other land-uses in this region. We used a hydraulic soil properties database to generate runoff scenarios for various soil conditions in HYDRUS 1D.  These runoff scenarios were then used with the NRCS soils map to calculate an infiltration index.  Based on common soil types, a best and a worst case infiltration scenarios were created. To showcase pre and post development soils, a case study was conducted within the area around the NC State University Centennial Campus in Raleigh. This area was farmland in 1968, but is currently well developed and contains several buildings and a golf course. The infiltration index was adjusted for development using changes in the land surface between 2001 and 2013. Using the elevation change data, a modified soil map with different horizons was constructed, and infiltration capacity was re-calculated. Based on our assessment, due to drastically reduced infiltration capacity of the soils, a five-year storm can result in a significant runoff from the developed areas.