Title page for ETD etd-05112004-101625

Type of Document Master's Thesis
Author Wagner, Rachel Cain
URN etd-05112004-101625
Title An Examination of the Reference Watershed Approach for TMDLs with Benthic Impairments
Degree Master of Science
Department Biological Systems Engineering
Advisory Committee
Advisor Name Title
Dillaha, Theo A. III Committee Chair
Mostaghimi, Saied Committee Member
Voshell, J. Reese Jr. Committee Member
Yagow, Eugene R. Committee Member
  • benthic impairment
  • water quality
  • TMDL
  • water quality model
  • Reference Watershed Approach
Date of Defense 2004-04-22
Availability unrestricted
This research addresses the Reference Watershed Approach (RWA) in the TMDL process for benthic impairments. In the RWA, do different land use sources (DOQQ and NLCD) or use of alternative water quality models (GWLF and SWAT) result in different stressor loadings? Is there a difference in stressor loadings when different reference watersheds are used?

Study results showed that using different land use sources resulted in required stressor reductions that were different by greater than 10%. In one scenario, use of the NLCD-based land use parameters results in 3.5 times greater reductions than use of DOQQ-based land use parameters. With respect to water quality model selection, in two of the three scenarios considered, a difference in stressor reduction requirements of greater than 10% resulted from using different models. Differences in load reduction requirements are also seen when different reference watersheds are used, regardless of the water quality model or the land use source used. Different references result in a difference of as much as 73% in required sediment reductions in the impaired watershed: the required reductions using one reference watershed are 6.2 times as great as when another is used.

Possible alternatives to the RWA include water quality standards to set the target level for many of the common stressors on the benthic assemblage, regression equations that relate benthic stressors to the RBP II score, or averaging of stressor reduction requirements obtained from using the Reference Watershed Approach on several different reference watersheds.

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