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Geospatial Implications of Considering Various Definitions of Headwater Streams
Citation:
Christensen, J., J. Hammond, C. Jones, C. Lane, A. Price, C. Segura, E. Seybold, M. Zimmer, F. Cheng, H. Golden, A. Husic, K. Jaeger, C. Kelleher, L. Li, D. Mahoney, H. McMillan, R. Sando, AND A. Ward. Geospatial Implications of Considering Various Definitions of Headwater Streams. Water Science Conference 2024, St. Paul, MN, June 24 - 27, 2024.
Impact/Purpose:
Headwaters dominate stream networks in catchments and provide important functions to healthy watersheds. There are numerous definitions of headwaters but it is unclear how the variety of definitions influence our analyses or how they vary across physiographic regions.
Description:
Headwater streams are numerous and variably expand and contract through time and space. An understanding of those spatial and temporal dynamics is crucial to 1) quantify the important hydrologic, biogeochemical and ecological functions in headwaters, 2) quantify how those functions affect downstream systems and 3) identify the degree of protections provided by regulations for headwaters. Despite their importance, the term “headwater” itself is ill-defined, due in part to their variability. We selected eight small catchments representing a range of geophysical and climatic regions across the conterminous US. In those catchments, we considered multiple definitions of headwaters derived from publicly available data: 1) Strahler stream orders (SO) 1 & 2 derived from the National Hydrography Dataset High-Resolution (NHD HR), 2) NHD HR SO 1&2 combined with permanence classification considerations, 3) SO 1 & 2 network derived from a minimum area threshold, and 4) a 1km drainage threshold. We then quantified how such headwater definitions influence the resulting length, stream permanence types, and drainage area of included headwaters. Regardless of definition, across all test catchments the proportion of headwater stream length and area ranged from 70 to 90% of the total catchment. While headwater proportions were similar within a catchment, the spatial location differed among definitions. Headwater stream length varied highly among definitions with the NHD HR typically having the shortest stream lengths. Permanence classifications influenced the total drainage area in semi-arid and arid regions where perennial reaches were located much farther downstream. While multiple definitions can be used to define headwaters, the stream network used will influence the physical characteristics (e.g. stream length) but due to network scaling properties, the proportion of total area or length will still be similar. With headwaters dominating the catchments, this work reiterates the importance of protections and increased study.
