Using the National Hydrography Dataset Plus for Drainage Area Delineation and Site Matching
By Kirsten Cassingham1 and Silvia Terziotti1 1
U.S. Geological Survey, North Carolina Water Science Center, 3916 Sunset Ridge Road, Raleigh, North Carolina 27607
Abstract
National Hyrography Dataset Plus (NHD-Plus) linework and associated subwatersheds (catchments) are
being used in the U.S. Geological Survey (USGS) National Water-Quality Assessment (NAWQA)
Program to accelerate the completion of tasks that previously have been extremely time-intensive, such as
drainage area delineation and site matching for water-quality sites. The lines, representing streams from
the NHD-Plus are corrected so all are pointing upstream, and a one-to-one relation exists between each
stream segment and the subwatershed that drains to it. In basin delineation, the outflow point (usually a
streamgage) is used to initiate a trace of upstream reaches, collecting the catchments as the stream
network is traced. This process is being used to automate the delineation of hundreds of basins, much
more quickly and accurately than using elevation data alone.
The NHD-Plus also is extremely valuable in matching drainage characteristics of two separate data sets.
The study area includes a large number of water quality monitoring sites without stream flow data.
Drainage area ratio was used as the criterion for a goodness of match between monitoring site and gaging
station; a paring with a ratio between 0.75 and 1.25 was considered an acceptable match. The trace
command was automated to find the closest NHD stream to the ungaged site and collect associated
catchments and calculate the drainage area. If any gaged sites were within the upstream or downstream
catchment areas, drainage areas were compared to see if they were within the threshold. The program
creates screen snapshots of each site and a file listing potential matches. The NHD-Plus enables accurate
basin delineation and site matching more consistent with national data.
Citation:
Cassingham, Kirsten, and Terziotti, Silvia, 2006, Using the National Hydrography Dataset Plus for drainage area delineation and Site matching: Proceedings of the National Water-Quality Monitoring Council National Monitoring Conference, May 8-12, 2006, San Jose CA.
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