HEADWATER STREAM CHANNEL MAPPING AND IMPACT ASSESSMENT IN THE MID-ATLANTIC, USA

Headwater streams provide important ecosystem services such as drinking water, habitat for aquatic life, and biological uptake and increased processing of nutrients, which can reduce delivery of nitrogen and phosphorus to downstream coastal waters. Despite their known importance to humans, many headwater streams are not included in the national hydrography dataset (NHD), either because they were buried during the course of early development or because they were seen as smaller than the minimum mapping size at the time of map generation. Small headwater streams, often with intermittent or ephemeral flow, can provide ecosystem services distinct and complementary to those of larger streams. Therefore, revised maps of headwater stream extent are required for many studies of urban streams and modeling efforts requiring precise measurement of stream length. Here we report research that utilizes field observations of headwater stream channel presence and absence to map the true extent of the stream channel network from terrain variables derived from a digital elevation model. The model correctly predicts the presence of 89% of all 10m stream segments and rarely miss-calculates stream tributary numbers. We apply this approach to several small watersheds within the Potomac River Basin and compare accuracy and the importance of different landscape attributes across this large and varied basin.