COMPARISON OF DRAINAGE DENSITY AS A FUNCTION OF LITHOLOGY AND METHODOLOGY IN THE LEHIGH VALLEY, EASTERN PENNSYLVANIA

The Lehigh Valley in eastern Pennsylvania is part of the Great Valley (GV) section of the Valley and Ridge physiographic province. The Great Valley is bounded by Blue Mountain to the northwest and the Reading Prong ridges to the southeast. The Great Valley consists primarily of two lithotypes: erodible karst terrain, underlain by limestone and dolomite in the southern half, and the Martinsburg slate in the northern half. The bedrock is mantled by Wisconsinan-age glacial drift in the northeast portion of the GV in Pa. Blue Mountain, which forms the northern boundary of the GV is underlain by very resistant sandstone and conglomerate, and the Reading Prong ridges bounding the GV on the south are relatively resistant metamorphic and igneous rocks. Germanoski et al. (2012) compared the drainage densities between the carbonate and slate in Eastern, PA using permanent streams depicted by blue line streams on 7.5-minute topographic maps and also using the drainage network mapped during a peak flow event. The comparison showed higher drainage density in slate than in carbonate for both data sets.

Delineation of drainage basins and drainage networks using DEM’s provide the opportunity for detailed morphometric analysis, yet such delineation can require large number of man hours, even as increased computing power has made automation models possible (Stanton, 2001). The most prominent model is the Deterministic 8 method (O’Callaghan and Mark, 1984), however, these models can be difficult to use for those without the requisite experience with the software. Here we use a combination of pre-packaged programs, ArcMap, and manual delineation to determine the feasibility of more user-friendly models in automated delineation. We compare the results produced by different methodologies to assess the variability inherent in using different software to perform morphometric analysis. The overarching objective is to determine the morphometric relationships between drainage basins underlain by different lithologies in the Lehigh Valley, and how the results vary with procedure.