UCLA

A semi-automated modeling framework for generating hydrographic watersheds for cryo-hydrologic systems using Geographic Information Systems (GIS) tools is presented. The framework derives two alternate types of watersheds i) hydraulic pressure potential (Shreve 1972; Cuffey & Paterson 2010; Banwell et al. 2013), which determines surface/subsurface flow paths from the hydrostatic equation, using surface and basal topography DEMs; and ii) surface (i.e. surface flow paths) as inferred from a surface topography DEM alone. The framework utilizes standard hydrologic modeling tools available in the ArcGIS 10.2 and the ArcPy library. Specifically, DEM depression filling, flow direction, flow accumulation, basin and watershed tools are used in conjunction with custom ArcPy routines to aggregate sub basins, identify hydrologic flow divides and delineate ice sheet hydraulic pressure potential and surface ice watersheds. Both watershed types are delineated for seven nested watersheds in southwest Greenland, derived from remotely sensed pour points along the Aussivigssuit River and its tributaries. The two alternate methods produce watersheds with dissimilar outcomes, particularly at higher elevations (670 m and above) on the ice sheet. For the Aussivigssuit River hydrologic network, surface DEM watersheds tend to be both larger in size and extend to higher elevations when compared to the hydraulic potential watersheds.