Topographical Wetness Index of Pleasant Stream Watershed in Lycoming and Sullivan Counties, PA

Elaine Langone Center, Terrace Room

To study the impact of new dirt and gravel roads, and new land development related to the unconventional natural gas development on watershed drainage and instream turbidity in the Pleasant Stream watershed LAS LiDAR data was used to create a high resolution DEM image using the IDW spatial analyst tool. The TauDEM Tool and Raster Calculator were used on the DEM raster to create Topographic Wetness Index (TWI) of the study area. Since this TWI model only took elevation into consideration during this calculation, ArcSWAT was used to delineate the Pleasant Stream watershed taking into consideration soil type (USSURGO database), land use, and elevation. Even though there is relatively little to no new natural gas development in this watershed, it was greatly impacted by the logging industry in the early 1900s. The old system of logging roads and railroad grades still clearly showed up on the TWI and they have an impact on how runoff drains from the watershed. The output from ArcSWAT allows us to identify regions of the watershed that are prominent sources of turbidity and nutrient discharge during and immediately after precipitation event. To ground truth the TWI, soil samples were collected after a rainstorm and soil moisture content was analyzed. These sample locations were then plotted onto the TWI map and the measured moisture content values correlated really well with the TWI model. The TWI and ArcSWAT output maps will prove to be very useful in having baseline data to compare to watersheds where extensive natural gas development has already occurred and as well if the Pleasant Stream watershed is ever further developed.