Sensitivity of the Reference Watershed Approach in Benthic TMDLS

Wagner, Ricardo; Dillaha, Theo A.; Yagow, E. R.; Mostaghimi, Saied; Benham, Brian Leslie; Brannan, Kevin M.; Wynn, J.; Zeckoski, Rebecca W.

doi:10.13031/2013.15561

Cited by 2 publications

(4 citation statements)

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“…Research has shown that the choice of the TMDL reference watershed can greatly affect both the TMDL load and the relative reduction required from the impaired watershed (Wagner, 2004). The Generalized Watershed Loading Function (GWLF) model has been used for most of the modeling performed for benthic impairments in Virginia.…”

Section: Discussionmentioning

confidence: 99%

“…The basic assumption of the reference watershed approach is that if the unit‐area pollutant load in the impaired watershed is reduced to the same level as in the reference watershed, then the health of the benthic community in the impaired watershed will be restored. Additional details on the reference watershed approach are available from Wagner (2004)…”

Section: Methodsmentioning

confidence: 99%

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Development of Bacteria and Benthic Total Maximum Daily Loads

et al. 2005

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Two total maximum daily load (TMDL) studies were performed for Linville Creek in Rockingham County, Virginia, to address bacterial and benthic impairments. The TMDL program is an integrated watershed management approach required by the Clean Water Act. This paper describes the procedures used by the Center for TMDL and Watershed Studies at Virginia Tech to develop the Linville Creek TMDLs and discusses the key lessons learned from and the ramifications of the procedures used in these and other similar TMDL studies. The bacterial impairment TMDL was developed using the Hydrological Simulation Program-Fortran (HSPF). Fecal coliform loads were estimated through an intensive source characterization process. The benthic impairment TMDL was developed using the Generalized Watershed Loading Function (GWLF) model and the reference watershed approach. The bacterial TMDL allocation scenario requires a 100% reduction in cattle manure direct-deposits to the stream, a 96% reduction in nonpoint-source loadings to the land surface, and a 95% reduction in wildlife direct-deposits to the stream. Sediment was identified as the primary benthic stressor. The TMDL allocation scenario for the benthic impairment requires an overall reduction of 12.3% of the existing sediment loads. Despite the many drawbacks associated with using watershed-scale models like HSPF and GWLF to develop TMDLs, the detailed watershed and pollutant-source characterization required to use these and similar models creates information that stakeholders need to select appropriate corrective measures to address the cause of the water quality impairment when implementing the TMDL.

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Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Development of Bacteria and Benthic Total Maximum Daily Loads

et al. 2005

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“…Some of the DOQQ-based land use used in this study was developed by Virginia Department of Conservation and Recreation (DCR) and some was developed by the Virginia Tech TMDL Development Group. Areas digitized by Virginia Tech were checked and approved by DCR (Wagner, 2004). …”

Section: Alternative Land Use Sources Used In Tmdl Developmentmentioning

confidence: 99%

“…However, since the DOQQ-based land use was available, DOQQ-based land use was chosen for land use parameter development for the SWAT model. The land use types used in the DOQQ land use development were converted to the land uses in the SWAT databases based on best professional judgment and on advice from the SWAT User's Manual (Neitsch et al, 2002a;Wagner, 2004). After the reclassification of land uses into the categories in the SWAT databases, an overlay of the land use and soil layers was used to create the hydrologic response units (HRUs) in SWAT.…”

Section: Swat: Soil and Water Assessment Toolmentioning

confidence: 99%

An assessment of the reference watershed approach for TMDLs with biological impairments

Wagner

Dillaha

Yagow

2006

Water Air Soil Pollut

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The Reference Watershed Approach (RWA) is used in TMDL development for biological and other impairments with narrative water quality criteria. The questions addressed in this research include: (1) With the RWA, how do land use classifications from different data sources (Digital Ortho-Quarter Quads (DOQQ) and National Land Cover Dataset (NLCD)) impact simulated pollutant loadings? (2) With the RWA, what is the impact of alternative water quality models (GWLF and SWAT) on pollutant loadings? (3) With the RWA, how sensitive are simulated pollutant loadings to the use of different reference watersheds? Various combinations of land use, water quality model, and reference watershed resulted in pollutant reductions that ranged from −13 to 88%. In a comparison of the use of NLCD versus DOQQ-based land use data with the GWLF model, differences in required reductions ranged from 13 to 74% for three different reference watersheds. Use of alternative water quality models with DOQQ land use data resulted in differences in required sediment reductions from −43 to 8% for the three reference watersheds. Differences in load reduction requirements were also seen when different reference watersheds were used, regardless of the water quality model or the land use source used. With DOQQ land use, required sediment reductions ranged from 18 to 88% and 37 to 82%, for the SWAT and GWLF models, respectively. These results suggest that explicit margins of safety used to account for modeling uncertainties during TMDL development may need to be substantially greater than 20% when using the reference watershed approach.

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Sensitivity of the Reference Watershed Approach in Benthic TMDLS

Cited by 2 publications

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Development of Bacteria and Benthic Total Maximum Daily Loads

Development of Bacteria and Benthic Total Maximum Daily Loads

An assessment of the reference watershed approach for TMDLs with biological impairments

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