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Framework for Estimating TMDLs with Minimal Data
Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.orgCitation: Pp. 6-12 in Total Maximum Daily Load (TMDL) Environmental Regulations: Proceedings of the March 11-13, 2002 Conference, (Fort Worth, Texas, USA) 701P0102.(doi:10.13031/2013.7522)
Authors: James V. Bonta
Keywords: duration curve, TMDL, water quality, erosion, risk assessment
Current regulations specify the derivation of total maximum daily loads (TMDLs) for surface waters. Yet these standards are often derived from incomplete information. In some cases these quantities are assigned to watersheds for which there are little data, and are established in terms of loads when only concentration data are available. Furthermore, they are often assigned under conservative conditions with no estimation of risk and uncertainty of the estimate. Flow-duration curves and regressions between flow rate and constituent concentration have historically been used to compute average total loads to determine water-quality trends. However, intermediate calculations in this methodology, not often used, have utility for TMDL estimation. From these intermediate calculations, one can determine the percent of time that a concentration and load (TMDL) will be exceeded, the duration of concentrations/loads, etc. The method can be used by itself or as a supplement to more complex watershed modeling. It is useful for determining the range of concentrations expected from a watershed, for characterizing actual in-stream conditions, and for tracking actual in-stream conditions after implementation of best-management practices. The method is simple to use, and is promising for areas where there are no flow data, and for which there are only a few samples. The concepts of the method are presented, along with those for using this method when data are scanty and for determining uncertainty in the TMDL estimates.(Download PDF) (Export to EndNotes)