USGS just presented this topic at their quarterly USGS Hydrography Community Call yesterday (April 22, 2025)
Abstract: Hydrographic features on topographic maps and the National Hydrography Dataset classified a feature's flow characteristics into three categories – perennial, intermittent, or ephemeral. These determinations were usually made by crews conducting field surveys for the original paper topographic maps (1947-1992). These classifications were subject to differences in field interpretation, changes in definitions through time, and even bias based on whether the field survey was conducted in a wet or dry year. The 3D Hydrography Program will replace these categorical classifications with a continuous value probability and uncertainty estimates. This presentation will describe the process to develop the first iteration of these values using survival regression techniques, illustrate some of the results, and discuss some of the limitations based on both the available data and the approach.
A recording of this meeting should be available soon - I'll share the link here as a comment when I get it!
Notes:
This new approach, that will be released later this year, totally replaces the Cartography (Blue Lines on the Quad Map) with a Data Driven (statistical likelihood of 0 flow days calculated for each HUC-4 Region using 4 different time period attributes). Steve Achiel from USGS stated that the USGS is getting out of the stream classification business, and it will be up to you [Fed Agencies, States, and Locals] to determine the classification of stream periodicity in their AOI by whatever statistical data threshold or criteria they define.
So, what does this mean to State and Local Governments who have laws, ordinances, and regulations based on these legacy perennial, intermittent, and ephemeral categories (blue lines on a map)?
Thoughts???
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Philip Worrall
Retired
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