Skip to main content

Developing Bacteria TMDLs Using a Modified Load Duration Curve Approach

Buy Article:

$9.50 plus tax (Refund Policy)

Or sign up for a free trial

In developing E. coli TMDLs for four tributaries to the West Fork White River in Indiana, a modified Load Duration Curve (LDC) approach was applied. This approach typically involves the generation of a flow duration curve for each particular sampling site or location and creation of a LDC by taking the product of the flow duration curve and the water quality standard for the parameter of interest. Sampled loads are also plotted as points, with those that fall above the LDC denoted as violations of the water quality standard. Required load reductions are then determined as the difference between the observational data and the LDC.

The LDC methodology is a simple and well-tested TMDL approach, and is especially pertinent for nonpoint source dominated watersheds. Agricultural row crop land uses are predominant in all four of the watersheds requiring E. coli TMDLs. While a few scattered point source discharges and some combined sewer overflows also contribute to the E. coli loadings in these watersheds, nonpoint sources are the most significant source categories, providing further justification for the selection of the LDC methodology as the approach for determination of the E. coli TMDLs.

Due to its ease of application and affordability, the LDC approach is rapidly becoming a popular method for coliform bacteria TMDLs across the nation. Where deterministic water quality models have achieved limited success in the accurate and consistent quantification of bacteria loadings, the LDC method provides a straightforward, simple approach for assessing these highly unpredictable parameters. Other specific advantages of the method include:

The ability to establish loading capacity for the full spectrum of flows in the water body, rather than for a characteristic critical low flow;

No requirement to establish a critical storm flow or statistical flow for assessment of wet weather conditions;

Quick correlation of loading with flow profiles, which provides insight into the major contributing source categories within a watershed; and,

Comprehensibility of results, to stakeholders, regulators, source contributors, and other interested parties.

Typical LDC methodologies are applied at a single location within a watershed and assess standards violations over a range of flows at that location. Here, an incremental loading estimation method was used for multiple locations within each watershed. This method incorporates existing monitoring data and assesses land use, soils, and source contribution differences between observation points. The approach utilized gauged flow data where available. In ungauged watersheds, flow duration curve estimations were made using flow information from neighboring gauges, drainage area ratios, and relative composite SCS curve number adjustments.
No Reference information available - sign in for access.
No Citation information available - sign in for access.
No Supplementary Data.
No Article Media
No Metrics

Document Type: Research Article

Publication date: 01 January 2005

More about this publication?
  • Proceedings of the Water Environment Federation is an archive of papers published in the proceedings of the annual Water Environment Federation® Technical Exhibition and Conference (WEFTEC® ) and specialty conferences held since the year 2000. These proceedings are not peer reviewed.

    A subscription to the Proceedings of the Water Environment Federation includes access to most papers presented at the annual WEF Technical Exhibition and Conference (WEFTEC) and other conferences held since 2000. Subscription access begins 12 months after the event and is valid for 12 months from month of purchase. A subscription to the Proceedings of the Water Environment Federation is included in Water Environment Federation (WEF) membership.

    WEF Members: Sign in (right panel) with your IngentaConnect user name and password to receive complimentary access. Access begins 12 months after the conference or event
  • Subscribe to this Title
  • Membership Information
  • About WEF Proceedings
  • WEFTEC Conference Information
  • Learn about the many other WEF member benefits and join today
  • Ingenta Connect is not responsible for the content or availability of external websites
  • Access Key
  • Free content
  • Partial Free content
  • New content
  • Open access content
  • Partial Open access content
  • Subscribed content
  • Partial Subscribed content
  • Free trial content
Cookie Policy
Cookie Policy
Ingenta Connect website makes use of cookies so as to keep track of data that you have filled in. I am Happy with this Find out more