New map identifies small and buried streams west of the Chesapeake Bay
By Jeffrey Brainard, Maryland Sea Grant
University of Maryland researchers have built a novel, detailed map that shows streams in Maryland not recorded on other maps. The new map, which identifies small and buried streams west of the Chesapeake Bay, provides a tool that promises to help efforts to protect streams from development and to improve the region’s water quality.
The research was funded by Maryland Sea Grant and conducted by Andrew Elmore and colleagues at the Appalachian Laboratory, part of the University of Maryland Center for Environmental Science.
Streams, especially small ones, can play an important role in improving water quality, a key problem in the Chesapeake region. The stream habitat removes excess nutrients, sediment, and other contaminants before they reach the Bay. That makes the new map “an important tool for improving our understanding of how to keep the Bay clean,” says Christine Conn, director of the Maryland Department of Natural Resources’ integrated policy and review unit. “If we don’t know where these streams are, we have difficulty managing the resource, both for conservation and restoration.”
Elmore’s map identifies a network of streams across Maryland that is denser than those shown on maps based on a widely used, nationwide database about surface waters, the National Hydrography Dataset (NHD.) In some portions of Maryland, the “stream density” in Elmore’s map (measured as kilometers of stream length per square kilometer) is 2.5 times that shown in maps of the same area based on NHD data. Elmore’s map filled in blank spots on the NHD with many new, thin squiggly lines representing streams not previously identified.
The difference between the two maps stems from how they were created. Streams in cities like Baltimore and Washington, D.C. have been buried steadily by roads, houses, and other construction. The NHD data does not record streams filled in before the U.S. Geological Survey began creating the database during the 1990s.
Elmore’s map is based on data that include stream locations in forested areas, which are relatively untouched by the effects of development. The scientists combined this information with other, statewide data about topography and soil characteristics that can indicate the presence of streams. They constructed a computer model to predict the location and course of streams flowing downhill from the upland, forested areas.
The scientists then extended the model to predict where streams would probably flow today across all of Maryland west of the Bay, including in non-forested, suburban and urban areas.
Officials in several Maryland counties have contacted Elmore about using the map to help comply with the new mandatory water-quality standards, called Total Maximum Daily Loads (TMDLs), that govern the Chesapeake region. The new stream map could help inform where to plant streamside buffers of trees to help remove nutrients and sediments from runoff. This “opens up the amount of land where we could potentially plant buffers to meet those TMDLs,” Elmore says.
Conn says that her agency may incorporate Elmore’s data into its next update of maps used to create Maryland’s GreenPrint tool, a statewide website that identifies lands and watersheds as priorities for conservation because of their high ecological value.
