Lower Catawba River Basin - Nutrient TMDLs Development


Phosphorus and nitrogen are essential nutrients for aquatic life. In surface waters, they control algal growth, typically measured by chlorophyll-a. Excessively high nutrient levels can lead to water quality problems such as algal blooms, hypoxia (low dissolved oxygen), and elevated pH.

Within the Catawba River Basin of South Carolina, the following reservoirs are considered to be impaired due to excessive nutrients and microscopic algal growth:

  • Cedar Creek Reservoir
  • Fishing Creek Reservoir
  • Great Falls Reservoir
  • Lake Wateree Reservoir

Monitoring Locations

More than 30 ambient monitoring locations within the Catawba reservoir system are currently included on the state's 2016 303 (d) List of Impaired Waters (the most recent biennial list submitted to and approved by the EPA).

Many of these monitoring locations have also been included on the 303(d) list for total phosphorus, total nitrogen or chlorophyll-a since South Carolina adopted water quality standards for these pollutants in 2004.

Elevated pH has also been observed at monitoring locations within the system. Long-term monitoring data have demonstrated these conditions existed prior to 2004, although more recent data are demonstrating some improvement as nutrient reductions have been implemented by utilities upstream of the impaired reservoirs.

Nutrient Model and TMDL Development

In accordance with the Clean Water Act and 40 CFR Part 130, Total Maximum Daily Loads (TMDLs) are required to address impaired locations included on a state's 303(d) list.

South Carolina is developing TMDLs to address these impairments in the Lower Catawba River Basin. Once these TMDLs are implemented through permits and voluntary measures, the reservoir system should continue to respond and, over time, achieve the water quality standards as outlined in Regulation 61-68, Water Classifications and Standards.

Watershed Risk Management Framework

South Carolina is using an existing model application known as Watershed Risk Management Framework (WARMF) to effectively make use of resources and develop defensible nutrient TMDLs for implementation in the Catawba River Basin.

With private funding, Systech Water Resources Inc. (Systech) originally developed a model application for the entire river basin in both North and South Carolina (Completed 2000). Subsequent refinements have been made to the model since that time. Systech and the University of South Carolina further enhanced the model (Completed 2003) for the South Carolina portion of the watershed basin. The North Carolina Department of Environmental Quality - Division of Water Resources (NCDWQ-DWR) and Systech provided model updates for the North Carolina portion of the basin (Completed 2004). The model simulation period has also previously been extended in the South Carolina portion to include water quantity and water quality data through 2005 (Completed 2007).

Beginning in October 2012, DHEC entered an agreement with Systech to do additional model refinements for the South Carolina portion of the watershed basin. This project was funded by the USEPA under a Section 319 grant through the DHEC. These enhancements are necessary in order to represent current conditions and document model performance. The longer-term goal will be to use the model application to develop defensible nutrient TMDLs in the Catawba River Basin. The scope of work has been broken down into two phases:

  • Phase I: Extended the model simulation period by including water quantity and water quality data through 2012. In addition, updated physical land use characteristics in the model application were needed in order to better account for development changes in the South Carolina portion of the Catawba River Basin since 2000. Some refinements occurred to more accurately characterize contributions from urban, or more developed, areas in the watershed. A review of the overall model calibration, or the ability of the model to accurately predict observed conditions, was needed once the initial tasks were completed. Each of these major tasks in Phase I were completed in August 2013. The findings have been documented in a Phase I Memorandum.
  • Phase II: Based on the findings from Phase I, a scope of work was developed for the next steps. Additional calibration work was needed for the WARMF model application for both hydrology (water quantity) and water quality. There have been additional refinements to more accurately characterize contributions from urbanized, or urban, areas in the watershed. Systech developed a draft calibration report for the South Carolina portion of the WARMF model application. DHEC provided the draft calibrated model and report for stakeholder review in early 2014 (see below) and requested comments before the model calibration and report were finalized in July 2014.

Catawba-Wateree Basin Advisory Commission

The Catawba-Wateree Basin Advisory Commission, established by law, is composed of members from the State of North Carolina and the State of South Carolina. The Commission is charged with considering issues affecting the river basin's water quantity and quality. It may provide guidance and recommendations to legislative and administrative bodies, promote coordination among stakeholders, identify problems and recommend solutions, undertake studies, and other activities as needed. For more information on the Commission, please visit Catawba-Wateree Basin Advisory Commission. Department staff attended the September 27, 2013, Commission meeting to give an update regarding the Lower Catawba Basin Nutrient TMDL effort.

Public Meeting November 19, 2013

DHEC held a public meeting in Rock Hill on November 19, 2013, to update Catawba River Basin stakeholders and other interested parties on the status of the most recent model updates. The goal of the meeting was to discuss recent model updates and the next steps as DHEC moved forward with nutrient TMDL development. A brief presentation by DHEC staff was followed by a question and answer session.

Lower Catawba Basin Nutrient TMDL Model Update
Date/Time: Tuesday, November 19, 2013 3:00pm-5:00pm
Location: Rock Hill City Operations Center, Training Rooms 132 and 133
757 South Anderson Road
Rock Hill, SC 29730

WARMF Model Calibration and Report

DHEC provided the preliminary WARMF Lower Catawba Basin model calibration for a 45-day stakeholder review from January 28 - March 13, 2014.

Comments received indicated a robust stakeholder review. The comments guided improvements for the final model calibration and documentation. The final version of the modeling report, as well as DHEC's response to comments received, are available (links below).

This effort precedes nutrient TMDL development.

Calibrated WARMF Model Nutrient Reduction Scenarios NEW!

DHEC utilized the calibrated model provided in 2014 to develop preliminary nutrient reduction scenarios for the Catawba River Basin. These scenarios provide aggregate nutrient reductions from all regulated and non-regulated nutrient sources in the Basin in order to achieve numeric nutrient criteria applicable to reservoirs in the mainstem Catawba River system.

The preliminary reduction scenarios are outlined in a memorandum and are being presented as a starting point for the allocation process. DHEC expects that the allocation process will result in individual nutrient reductions for regulated and non-regulated nutrient sources in the Basin. DHEC will coordinate allocation discussions with regulated facilities, Municipal Separate Storm Sewer Systems (MS4s), NCDEQ-DWR, and the USEPA.

Once the allocation process is complete, a draft nutrient TMDL document will be will be made available to the public for review and comment. A stakeholder meeting may be requested during the public comment period in accordance with SC Regulation 61-110.

The final version of the 2014 calibrated Catawba River Basin model, additional model scenarios and a memorandum outlining preliminary nutrient reduction scenarios are being provided. Note that DHEC is not requesting comments at this time.

WARMF Model and Supplemental Information

Contact Us

For more information, contact Wade Cantrell, manager, DHEC 303(d), Modeling and TMDL Section, 2600 Bull Street, Columbia, SC 29201 or email him at cantrewm@dhec.sc.gov.