Early View article: “Comparing the Extent and Permanence of Headwater Streams from Two Field Surveys to Values from Hydrographic Databases and Maps,” by Ken M. Fritz, Elisabeth Hagenbuch, Ellen D’Amico, Molly Reif , Parker J. Wigington Jr., Scott G. Leibowitz, Randy L. Comeleo, Joseph L. Ebersole, and Tracie-Lynn Nadeau
I’m seeing more articles pointing out problems in accurately identifying headwater streams in the National Hydrography Dataset (NHD). There’s more going on here than just differences in photo interpretation. It comes down to the question of how you define a first-order stream: Presence of a channel? A certain flow frequency (which may have to be modeled)? Or, like the wetland scientists, by the type of biota? Here’s an interesting insight from Oregon.
(From the abstract:) Supreme Court cases have questioned if jurisdiction under the Clean Water Act extends to water bodies such as streams without year-round flow. Headwater streams are central to this issue because many periodically dry, and because little is known about their influence on navigable waters. An accurate account of the extent and flow permanence of headwater streams is critical to estimating downstream contributions. The authors compared the extent and permanence of headwater streams from two field surveys with values from databases and maps. The first used data from 29 headwater streams in nine U.S. forests, whereas the second had data from 178 headwater streams in Oregon. Synthetic networks developed from the nine-forest survey indicated that 33 to 93% of the channel lacked year-round flow. Seven of the nine forests were predicted to have >200% more channel length than portrayed in the high-resolution National Hydrography Dataset (NHD). The NHD and topographic map classifications of permanence agreed with ~50% of the field determinations across ~300 headwater sites. Classification agreement with the field determinations generally increased with increasing resolution. However, the flow classification on soil maps only agreed with ~30% of the field determination despite depicting greater channel extent than other maps. Maps that include streams regardless of permanence and size will aid regulatory decisions and are fundamental to improving water quality monitoring and models.
[Please note: I have quoted and paraphrased freely from the article, but the interpretation is my own.]
