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Headwater Stream Spatial Dataset Overview
The NC Division of Water Quality's Headwater Stream Spatial Dataset (HSSD) program uses a combination of field-truthed headwater stream data, GIS analysis, and statistical modeling to create updated headwater stream maps for select areas of the state.
Why do we need updated stream maps? Existing maps, such as the USGS topographic quads and NRCS soil surveys, were never intended to provide an accurate depiction of streams on the ground and so a range of issues have been noted with them; see the figure below for an example. In some cases, these maps show streams that do not exist on the ground, and in other cases, the opposite problem occurs. They also are inconsistent in under- or over-representing streams as you go from one map to an adjoining map.
This inconsistent accuracy of existing maps makes resource management difficult, and therefore more time-intensive and expensive, for regulatory agencies such as NC DWQ and the US Army Corps of Engineers (USACE). It also makes project planning in regards to environmental impacts more resource-intensive for members of the regulated community, such as the NC Department of Transportation (NCDOT). The benefits to NCDOT of updated, accurate GIS data, both in terms of planning efficiency and cost-savings, are detailed in an Interagency Leadership Team policy statement available from the NC Geographic Information Coordinating Council (GICC) website.
As of mid-2012, the HSSD program has mapped the intermittent and perennial headwater streams in 83 watersheds statewide-- this represents a total area of 105,000 acres and over two million feet of streams. The data set includes nearly 1700 stream origins (the GPS location of where a stream starts) and stream transitions (the GPS location of where a stream changes from intermittent to perennial). These data are used to create models that accurately predict the location of headwater streams in areas where field data are unavailable. To date, models have been developed for the Carolina Slate Belt, Triassic Basins, Sand Hills, Rolling Coastal Plain, and Carolina Flatwoods Level IV ecoregions.
This innovative program received national recognition in 2011 from the Federal Highway Administration, who awarded a joint Environmental Excellence Award to the HSSD and a similar modeling effort at NCDOT that focuses on wetlands. Both of the programs were also recently profiled by SAS.