Downeast Drainage: Characterization of Upland Drainage Attributes for Parameterization of Gulf of Maine Watersheds

Abstract:

Research undertaken by the New England Sustainability Consortium includes use of multi-scale elevation data ranging from one arc-second (~30m) NED to two-meter LiDAR for delineation and subsequent characterization of watersheds draining to the Gulf of Maine. Watersheds within the study area range from the Penobscot River (drainage area > 22,000 km²) to small coastal streams with drainage basins <1km². The research seeks to relate fresh water flows to water quality conditions within bathing beaches and shellfish harvesting areas along the Maine coast.

Although spatial analysts typically pursue topographic data with the highest available resolution, use of multi-scale elevation data is necessary in regions where datasets are created from different survey methods. The sizes of the watersheds draining to the Gulf of Maine vary substantially, with several large interior-reaching watersheds dwarfing most of the coastal basins. An elevation raster at a two meter grid size can produce large file sizes and long processing times, presenting cost-benefit considerations due to the relatively low level of detail necessary for comparison of the largest watersheds to the rest of the study basins. Our watershed delineation method involves a multi-step approach to capture the inland portions of large watersheds using 10m and 30m USGS DEMs, while maintaining use of two-meter coastal LiDAR to accurately delineate the small coastal basins.

Our delineated watersheds are parameterized based on multiple geomorphological and land use characteristics to facilitate evaluation of the relation between watershed and coastal water quality conditions at monitoring stations along the Maine coast. Landscape characteristics under consideration include watershed size (drainage area), surface drainage network density, soil drainage, vegetation cover, and impervious surface area.