Environmental Management

, Volume 60, Issue 1, pp 1–11 | Cite as

How Misapplication of the Hydrologic Unit Framework Diminishes the Meaning of Watersheds

  • James M. Omernik
  • Glenn E. GriffithEmail author
  • Robert M. Hughes
  • James B. Glover
  • Marc H. Weber


Hydrologic units provide a convenient but problematic nationwide set of geographic polygons based on subjectively determined subdivisions of land surface areas at several hierarchical levels. The problem is that it is impossible to map watersheds, basins, or catchments of relatively equal size and cover the whole country. The hydrologic unit framework is in fact composed mostly of watersheds and pieces of watersheds. The pieces include units that drain to segments of streams, remnant areas, noncontributing areas, and coastal or frontal units that can include multiple watersheds draining to an ocean or large lake. Hence, half or more of the hydrologic units are not watersheds as the name of the framework “Watershed Boundary Dataset” implies. Nonetheless, hydrologic units and watersheds are commonly treated as synonymous, and this misapplication and misunderstanding can have some serious scientific and management consequences. We discuss some of the strengths and limitations of watersheds and hydrologic units as spatial frameworks. Using examples from the Northwest and Southeast United States, we explain how the misapplication of the hydrologic unit framework has altered the meaning of watersheds and can impair understanding associations between spatial geographic characteristics and surface water conditions.


Watersheds Hydrologic units Rivers/streams Aquatic ecology Watershed management 



The authors would like to thank Jim Harrison, now retired from the U.S. Environmental Protection Agency, for encouraging the exploration and documentation of this topic. Support for this research has been provided in part by the U.S. Geological Survey and U.S. Environmental Protection Agency. This manuscript has been subjected to U.S. Geological Survey and U.S. Environmental Protection Agency review and has been approved for publication.

Conflict of interest

The authors declare that they have no competing interests.


  1. Affuso E, Duzy LM (2013) The impact of US biofuel policy on agricultural production and nitrogen loads in Alabama. Econ Resear Internat doi: 10.1155/2013/521254. Accessed 17 Dec 2016
  2. Al-Chokhachy R, Roper BR, Archer EK (2010) Evaluating the status and trends of physical stream habitat in headwater streams within the Interior Columbia River and Upper Missouri River basins using an index approach. Trans Am Fish Soc 139:1041–1059CrossRefGoogle Scholar
  3. Alexander DH, Smith RA, Schwartz GE (2000) Effects of stream channel size on delivery of nitrogen to the Gulf of Mexico. Nature 403:758–761CrossRefGoogle Scholar
  4. Berelson WL, Caffrey PA, Hamerlinck JD (2004) Mapping hydrologic units for the national Watershed Boundary Dataset. J Am Water Res Assoc 40:1231–1246CrossRefGoogle Scholar
  5. Bisson PA, Gregory SV, Nickelson TE, Hall JD (2008) The Alsea watershed study: a comparison with other multi-year investigations in the Pacific Northwest. In: Stednick JD (ed) Hydrological and biological responses to forest practices. Springer, New York, pp 259–289CrossRefGoogle Scholar
  6. Brenden TO, Clark RD Jr, Cooper AR, Seelbach PW, Wang L (2006) A GIS framework for collecting, managing, and analyzing multiscale landscape variables across large regions for river conservation and management. In: Hughes RM, Wang L, Seelbach PW (eds) Landscape influences on stream habitats and biological assemblages. Symposium 48. American Fisheries Society, Bethesda, pp 49–74Google Scholar
  7. Bryce SA, Omernik JM, Larsen DP (1999) Ecoregions: a geographic framework to guide risk characterization and ecosystem management. Environ Pract 1(3):141–155CrossRefGoogle Scholar
  8. Currens, JC, Ray JA (2001) Discrepancies between HUC boundaries and karst basin boundaries. Kentucky Geological Survey. Accessed 10 July 2016
  9. Daggupati P, Deb D, Srinivason R, Yeganantham D, Mehta VM, Rosenberg NJ (2016) Large-scale fine-resolution hydrological modeling using parameter regionalization in the Missouri River basin. J Am Wat Res Assoc 52:648–666CrossRefGoogle Scholar
  10. Daniel WM, Infante DM, Hughes RM, Tsang Y, Esselman PC, Wieferich D, Herreman K, Cooper AR, Wang L, Taylor WW (2014) Characterizing coal and mineral mines as a regional source of stress to stream fish assemblages. Ecol Indic 50:50–61CrossRefGoogle Scholar
  11. Dodds WK, Whiles MR (2004) Quality and quantity of suspended particles in rivers: continent-scale patterns in the United States. Environ Manage 33(3):355–367CrossRefGoogle Scholar
  12. Eagles-Smith CA, Ackerman JT, Willacker JJ, Tate MT, Lutz MA, Fleck JA, Stewart AR, Wiener JG, Evers DC, Lepak JM, Davis JA, Pritz CF (2016) Spatial and temporal patterns of mercury concentrations in freshwater fish across the western United States and Canada. Sci Tot Environ 568:1171–1184. doi: 10.1016/j.scitotenv.2016.03.229 CrossRefGoogle Scholar
  13. Entrekin SF, Maloney KO, Kapo KE, Walters AW, Evans-White MA, Klemow KM (2015) Stream vulnerability to widespread and emergent stressors: a focus on unconventional oil and gas. PLOS ONE 2015:1–28. doi: 10.1371/journal.pone.0137416 Google Scholar
  14. Fausch KD, Torgersen CE, Baxter CV, Li HW (2002) Landscapes to riverscapes: bridging the gap between research and conservation of stream fishes. Bioscience 52:483–498CrossRefGoogle Scholar
  15. Flotemersch JE, Leibowitz SG, Hill RA, Stoddard JL, Thoms MC, Tharme RE (2015) A watershed integrity definition and assessment approach to support strategic management of watersheds. River Res Appl doi: 101002/rra.2978Google Scholar
  16. Foran CM, Narcisi MJ, Bourne AC, Linkov I (2015) Assessing cumulative effects of multiple activities in New England watersheds. Environ Syst Decis 35:511–520. doi: 10.1007/s10669-015-9575-0 CrossRefGoogle Scholar
  17. Ghimire S, Johnston J (2013) Impacts of domestic and agricultural rainwater harvesting systems on watershed hydrology: a case study in the Albemarle-Pamlico river basins (USA). Ecohydrol Hydrobiol 13:159–171CrossRefGoogle Scholar
  18. Glover JB, Domino ME, Altman KC, Dillman JW, Castleberry WS, Eidson JP, Mattocks M (2010) Mercury in South Carolina fishes, USA. Ecotoxicol 19:781–795CrossRefGoogle Scholar
  19. Graf WL (2001) Damage control: restoring the physical integrity of American rivers. Ann Assoc Am Geog 91:1–27CrossRefGoogle Scholar
  20. Griffith GE, Omernik JM, Woods AJ (1999) Ecoregions, watersheds, basins, and HUCs: how state and federal agencies frame water quality. J Soil Water Conserv 54:666–677Google Scholar
  21. Griffith MB (2014) Natural variation and current reference for specific conductivity and major ions in wadeable streams of the conterminous USA. Freshwater Sci 33:1–17CrossRefGoogle Scholar
  22. Gurung DP, Githinji LJM, Ankumah RO (2013) Assessing the nitrogen and phosphorus loading in the Alabama (USA) River Basin using PLOAD model. Air Soil Water Res 6:23–36. doi: 10.4137/ASWR.S10548 Google Scholar
  23. Herlihy AT, Larsen DP, Paulsen SG, Urquhart NS, Rosenbaum BJ (2000) Designing a spatially balanced, randomized site selection process for regional stream surveys: the EMAP Mid-Atlantic pilot study. Environ Monit Assess 63:92–113CrossRefGoogle Scholar
  24. Hocutt CH, Wiley EO (1986) The zoogeography of North American freshwater fishes. Wiley, New YorkGoogle Scholar
  25. Hollenhorst TP, Brown TN, Johnson LB, Ciborowski JJH, Host GE (2007) Methods for generating multi-scale watershed delineations for indicator development in Great Lakes coastal ecosystems. J Great Lakes Res 33(Suppl. 3):13–26CrossRefGoogle Scholar
  26. Horn CR, Hanson SA, McKay LD (1994) History of the U.S. EPA’s River Reach File: a national hydrographic database available for ARC/INFO applications. U.S. Environmental Protection Agency, Office of Water, Washington, DCGoogle Scholar
  27. Houghton Mifflin Company (1982) The American Heritage Dictionary. Houghton Mifflin, BostonGoogle Scholar
  28. Hudy M, Thieling TM, Gillespie N, Smith EP (2008) Distribution, status, and land use characteristics of subwatersheds within the native range of brook trout in the eastern United States. N Am J Fish Manage 28:1069–1085CrossRefGoogle Scholar
  29. Hughes RM, Omernik JM (1981) Use and misuse of the terms watershed and stream order. In: Krumholtz LA (ed) The warmwater streams symposium. Am Fish Soc, Bethesda. pp 320–326Google Scholar
  30. Hughes RM, Omernik JM (1983) An alternative for characterizing stream size. In: Fontaine TD, Bartell SM (eds) Dynamics of Lotic Ecosystems. Ann Arbor Press, Ann Arbor, pp 87–102Google Scholar
  31. Hughes RM, Kaufmann PR, Weber MH (2011) National and regional comparisons between Strahler order and stream size. J N Am Benth Soc 30:103–121. doi: 10.1899/09-174.1 CrossRefGoogle Scholar
  32. Hughes RM, Paulsen SG, Stoddard JL (2000) EMAP-Surface Waters: a multiassemblage probability survey of ecological integrity in the U.S.A. Hydrobiologia 422/423:429–443CrossRefGoogle Scholar
  33. Hughes RM, Herlihy AT, Sifneos JC (2015) Predicting aquatic vertebrate assemblages from environmental variables at three multistate geographic extents of the western USA. Ecol Indic 57:546–556CrossRefGoogle Scholar
  34. Hynes HBN (1975) [The stream and its valley]. Verandlungen der Internationalen Vereinigung für theoretische and angewandte Limnologie 19:1–15Google Scholar
  35. Jones KB, Ritters KH, Wickham JD, Tankersley Jr RD, O’Neill RV, Chaloud DJ, Smith ER, Neale AC (1997) An ecological assessment of the United States Mid-Atlantic region: a landscape atlas. U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-97/130Google Scholar
  36. Jordan SJ, Benson WH (2015) Sustainable watersheds: integrating ecosystem services and public health. Environ Health Insights 9(S2):1–7CrossRefGoogle Scholar
  37. King KW, Smiley Jr PC, Baker BJ, Fausey NR (2008) Validation of paired watersheds for assessing conservation practices in the Upper Big Walnut Creek watershed, Ohio. J Soil Wat Cons 63:380–395CrossRefGoogle Scholar
  38. Kolok AS, Beseler CL, Chen X, Shea PJ (2009) The watershed as a conceptual framework for the study of environmental and human health. Environ Health Insights 3:1–10Google Scholar
  39. Laitta MT, Legleiter KJ, Hanson KM (2004) The national Watershed Boundary Dataset. Hydro Line, Summer 2004, ESRI Water Resources Group, p 1, 7. Accessed 10 July 2016
  40. Lanigan S, Miller S, Anderson H, Raggon M, Eldred P (2013) Aquatic and riparian effectiveness monitoring program – 2012 annual report. Interagency Monitoring Program – Northwest Forest Plan Area. Accessed 9 July 2016
  41. Lanigan S, Miller S, Anderson H, Eldred P, Beloin R, Raggon M, Gordon S, Wilcox S (2014) Aquatic and riparian effectiveness monitoring program – 2013 annual report. Interagency Monitoring Program – Northwest Forest Plan Area. Accessed 9 July 2016
  42. Likens GE (2013) The Hubbard Brook ecosystem study: celebrating 50 years. Bull Ecol Soc Amer 94:336–337CrossRefGoogle Scholar
  43. Lomnicky GA, Whittier TR, Hughes RM, Peck DV (2007) Distribution of nonnative aquatic vertebrates in western U.S. streams and rivers. N Am J Fish Manage 27:1082–1093CrossRefGoogle Scholar
  44. Macedo DR, Hughes RM, Ligeiro R, Ferreira WR, Castro M, Junqueira NT, Silva DRO, Firmiano KR, Kaufmann PR, Pompeu PS, Callisto M (2014) The relative influence of multiple spatial scale environmental predictors on fish and macroinvertebrate assemblage richness in Cerrado ecoregion streams, Brazil. Landscape Ecol 29:1001–1016CrossRefGoogle Scholar
  45. Marzin A, Verdonschot PFM, Pont D (2012) The relative influence of catchment, riparian corridor, and reach-scale anthropogenic pressures on fish and macroinvertebrate assemblages in French rivers. Hydrobiologia 704:375–388CrossRefGoogle Scholar
  46. McKay L, Bondelid T, Dewald T, Johnston J, Moore R, Rea A (2012) NHDPlus version 2: user guide. U.S. Environmental Protection Agency. Accessed 2 July 2016
  47. Merriam-Webster (1986) Webster’s new world dictionary of American language. World Publishing Company, New YorkGoogle Scholar
  48. Morisawa M (1957) Accuracy of determination of stream lengths from topographic maps. Trans Am Geophys Union 38:86–88CrossRefGoogle Scholar
  49. Mulvey M, Leferink R, Borisenko A (2009) Willamette basin rivers and streams assessment. Oregon Department of Environmental Quality, Salem, Oregon. Accessed 2 July 2016
  50. Mylavarapu R, Hines K, Obreza T, Means G (2012) Watersheds of Florida: understanding a watershed approach to water management. SL367, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, p 7Google Scholar
  51. Nadeau T, Raines MC (2007) Hydrologic connectivity between headwater streams and downstream waters: how science can inform policy. J Am Water Res Assoc 43:118–133CrossRefGoogle Scholar
  52. Oberdorff T, Guegan JF, Hugueny B (1995) Global scale patterns in freshwater fish species diversity. Ecography 18:345–452CrossRefGoogle Scholar
  53. Omernik JM (2003) The misuse of hydrologic unit maps for extrapolation, reporting, and ecosystem management. J Am Water Res Assoc 39:563–573CrossRefGoogle Scholar
  54. Omernik JM, Bailey RG (1997) Distinguishing between watersheds and ecoregions. J Am Water Res Assoc 33:935–949CrossRefGoogle Scholar
  55. Omernik JM, Griffith GE (1991) Ecological regions versus hydrologic units: frameworks for managing water quality. J Soil Water Conserv 46(5):334–340Google Scholar
  56. Omernik JM, Griffith GE (2014) Ecoregions of the conterminous United States: evolution of a hierarchical spatial framework. Environ Manage 54:1249–1266. doi: 10.1007/s00267-014-0364-1 CrossRefGoogle Scholar
  57. Pai N, Saraswat D, Daniels M (2011) Identifying priority subwatersheds in the Illinois River drainage area in Arkansas watershed using a distributed modeling approach. Trans Am Soc Ag Biol Engineers 54:2181–2196Google Scholar
  58. Paulsen SG, Mayio A, Peck DV, Stoddard JL, Tarquinio E, Holdsworth S, Van Sickle J, Yuan LL, Hawkins CP, Herlihy A, Kaufmann PR, Barbour MT, Larsen DP, Olsen AR (2008) Condition of stream ecosystems in the US: an overview of the first national assessment. J N Am Benthol Soc 27:812–821CrossRefGoogle Scholar
  59. Pont D, Hughes RM, Whittier TR, Schmutz S (2009) A predictive index of biotic integrity model for aquatic-vertebrate assemblages of western U.S. streams. Trans Am Fish Soc 138:292–305CrossRefGoogle Scholar
  60. PRISM Climate Group (2016) Average annual precipitation for Washington (1981-2010). Accessed 2 July 2016
  61. Rathert D, White D, Sifneos JC, Hughes RM (1999) Environmental correlates of species richness for native freshwater fish in Oregon, USA. J Biogeogr 26:257–273CrossRefGoogle Scholar
  62. Ruhl JB (1999) The (political) science of watershed management in the ecosystem age. J Am Water Res Assoc 35:519–526CrossRefGoogle Scholar
  63. Sály P, Takács P, Kiss I, Bıró P, Erös T (2011) The relative influence of spatial context and catchment- and site-scale environmental factors on stream fish assemblages in a human-modified landscape. Ecol Freshw Fish 20:251–262CrossRefGoogle Scholar
  64. Seaber, PR, Kapinos FP, Knapp GL (1987) Hydrologic unit maps. U.S. Geological Survey Water-Supply Paper 2294. U.S. Geological Survey, Denver, Colorado. Accessed 1 July 2016
  65. Simley JD, Carswell WJ Jr (2009) The national map – hydrography. U.S. Geological Survey Fact Sheet 2009-3054, p 4. Accessed 1 July 2016
  66. Stoddard JL (2004) Use of ecological regions in aquatic assessments of ecological condition. Environ Manage 34(Suppl. 1):S61–S70. doi: 10.1007/s00267-003-0193-0 CrossRefGoogle Scholar
  67. Stoddard JL, Herlihy AT, Peck DV, Hughes RM, Whittier TR, Tarquinio E (2008) A process for creating multi-metric indices for large-scale aquatic surveys. J N Am Benthol Soc 27:878–891CrossRefGoogle Scholar
  68. Strahler AN (1975) Physical geography, 4th edn. Wiley, New YorkGoogle Scholar
  69. Swank WT, Meyer JL, Crossley Jr DA (2001) Long-term ecological research: Coweeta history and perspectives. In: Barrett GW, Barrett TL (eds) Holistic science: the evolution of the Georgia Institute of Ecology (1940-2000). Sheridan Books, Ann Arbor, pp 143–163Google Scholar
  70. U.S. Environmental Protection Agency (1995) Watershed protection: a statewide approach. EPA841-R-95-004, Office of Water, Washington, DC. Accessed 12 June 2016
  71. U.S. Environmental Protection Agency (1996) Watershed approach framework. EPA840-S-96-001. Office of Water, Washington, DC. Accessed 12 June 2016
  72. U.S. Environmental Protection Agency (2016) A practitioner’s guide to the biological condition gradient: a framework to describe incremental change in aquatic ecosystems. EPA-842-R-16-001. Office of Water, Washington, DC. Accessed 12 July 2016
  73. U.S. Geological Survey (2013) Hydrologic unit maps. Accessed 7 June 2016
  74. U.S. Geological Survey (2015) What is the WBD? Accessed 7 June 2016
  75. U.S. Geological Survey and U.S. Department of Agriculture–Natural Resources Conservation Service (2013) Federal standards and procedures for the national Watershed Boundary Dataset (WBD), 4th edn. U.S. Geological Survey, Techniques and Methods 11–A3, p 63. Accessed 7 June 2016
  76. Vannote RL, Minshall GW, Cummins KW, Sedell JR, Cushing CE (1980) The river continuum concept. Can J Fish Aquat Sci 37:130–137CrossRefGoogle Scholar
  77. Van Sickle J, Hughes RM (2000) Classification strengths of ecoregions, catchments, and geographic clusters for aquatic vertebrates in Oregon. J N Am Benthol Soc 19:370–384CrossRefGoogle Scholar
  78. Wardrop DH, Bishop JA, Easterling M, Hychka K, Myers W, Patil GP, Taillie C (2005) Use of landscape and land use parameters for classification and characterization of watersheds in the Mid-Atlantic across five physiographic provinces. Environ Ecol Stat 12:209–223CrossRefGoogle Scholar
  79. White GF (1969) Strategies of American water management. University of Michigan Press, Ann ArborGoogle Scholar
  80. Zank B, Bagstad KJ, Voigt B, Villa F (2016) Modeling the effects of urban expansion on natural capital stocks and ecosystem service flows: a case study in the Puget Sound, Washington, USA. Landsc Urban Plan 149:31–42. doi:org/10.1016/j.landurbplan.2016.01.004CrossRefGoogle Scholar
  81. Zuellig RE, Schmidt TS (2012) Characterizing invertebrate traits in wadeable streams of the contiguous US: differences among ecoregions and land uses. Freshwater Sci 31:1042–1056CrossRefGoogle Scholar

Copyright information

© Springer Science+Business Media New York (outside the USA) 2017

Authors and Affiliations

  1. 1.U.S. Geological Survey (Emeritus)c/o U.S. Environmental Protection AgencyCorvallisUSA
  2. 2.U.S. Geological Survey (Emeritus)Western Geographic Science CenterCorvallisUSA
  3. 3.Amnis Opes InstituteCorvallisUSA
  4. 4.Aquatic Biology Section, Bureau of Water, South Carolina Department of Health and Environmental ControlColumbiaUSA
  5. 5.National Health and Environmental Effects Research Laboratory, Western Ecology DivisionU.S. Environmental Protection AgencyCorvallisUSA

Personalised recommendations