Hydrography Seminar Series, Seminar 4 (Main) - September, 2015

Abstract - Digital hydrologic networks, which comprise stream reaches depicting surface-water pathways and their associated drainage catchments, are a key component to hydrologic analysis and modeling. Collectively, stream reaches and catchments form common spatial units that can be used to frame the descriptions of aquatic and watershed processes affecting water quality and streamflow. In addition, the topology of a hydrologically connected network allows for the simulation of water movement, providing the ability to route constituents throughout the landscape. Digital hydrologic networks have evolved from derivatives of mapping products to detailed, interconnected, spatially referenced networks of water pathways, drainage areas, and stream and watershed characteristics. These properties are important because they enhance the ability to spatially evaluate associated factors that affect the sources and transport of water-quality constituents over land and in streams at local and regional scales. An example of a modeling application that depends on a digital hydrologic network is SPARROW, a process-based/statistical/spatial model that establishes relations between quantities of monitored contaminant flux, contaminant-sources, aquatic transport processes, and the physical characteristics affecting contaminant transport.

The USGS NWAQA program is enhancing the qualities of the medium resolution NHDPlus geospatial dataset (based on the 1:100,000-scale National Hydrography Dataset) in order to support regional and National SPARROW models estimating water quantity and quality. Topological improvements to the network have been conducted, providing the basic foundation for the spatial framework used to geographically reference and route necessary monitoring, contaminant source, and transport characteristics within the SPARROW modeling structure. Impoundments, long-term water-quality and stream-gaging stations also have been associated to the network and quality controlled for accuracy. This talk describes the utility of the NHDPlus network supporting SPARROW applications, and describes some of the methods and data associated to the network.

Biography – John Brakebill is a Supervisory Geographer in the Maryland-Delaware-DC Water Science Center (WSC), serving as a senior manager for the center and a geospatial data coordinator for the NAWQA Cycle 3 program. John has 27+ years of USGS experience, including developing GIS applications and data supporting regional and national SPARROW models with the NAWQA program and USGS Chesapeake Bay studies.