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Comparing the extent and permanence of headwater streams from two field surveys to values from hydrographic databases and maps
Citation:
Fritz, K., E. Hagenbuch, E. D'Amico, M. Reif, Parker Wigington, S. Leibowitz, R. Comeleo, J. Ebersole, AND T. Nadeau. Comparing the extent and permanence of headwater streams from two field surveys to values from hydrographic databases and maps. JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION. American Water Resources Association, Middleburg, VA, 49(4):867-882, (2013).
Impact/Purpose:
Recognizing the limitations of hydrography databases and maps in representing the actual extent and flow permanence of headwaters is important for several reasons. In particular because headwater streams represent a dominant interface between terrestrial and freshwater ecosystems, hydrology is a critical factor influencing pattern and process in river networks, and hydrography is such a fundamental tool used in water resource monitoring, modeling, and decision making. The objective of this study was to compare the extent and permanence of headwater streams from field surveys to existing values from national databases and maps. In this document we present two case studies comparing the extent and permanence of headwater streams to existing hydrography resources.
Description:
ABSTRACT: Recent US Supreme Court cases have questioned the jurisdictional scope of the Clean Water Act. Headwater streams are central to this issue because many headwater streams do not have year-round flow, and also because little is known about their contributions to navigable waters. An accurate account of the geographic extent and flow permanence of headwater streams is critical to understanding their downstream contributions. The study goal was to evaluate how accurately these characteristics are portrayed on existing mapping resources across several regions in the US. This was done by comparing the extent and permanence of headwater streams from two field surveys to values from existing databases and maps. The first survey used geographical and hydrological data from 29 headwater streams distributed among nine US forests, whereas the second survey included data from 178 headwater streams in Oregon. Synthetic networks developed using survey data from the nine forests indicated that 33 to 93% of the channel lengths did not have year-round flow. Seven of the nine forests were predicted to have >200% more channel length than portrayed in high resolution National Hydrography Dataset (NHD). The NHD and topographic map (ranging from 1:24,000 to 1:250,000 scale) classifications of flow permanence only agreed with ~50% of the field determinations across almost 300 headwater stream sites. Classification accuracy relative to the field determinations generally increased with increasing resolution. However, the flow permanence classification on National Resource Conservation Service soil maps only agreed with ~30% of the field determination despite having the highest mapping resolution and often portraying a greater extent of headwater channel than the NHD and topographic maps. An accurate national map that includes all water bodies, including headwater streams regardless of flow permanence and size, is a fundamental step in improving national water quality monitoring and models.
