Arroyo Bacteria Modeling
Problem/Need Statement
The Arroyo Colorado currently has elevated levels of bacteria within the tidal and non-tidal segments, not meeting the primary contact recreation standard established by the state. There are many challenges associated with restoring water quality in the Arroyo Colorado Watershed. With the majority of the watershed being agricultural (cropland) and urban acreage, it is easy to attribute high nutrient contents to those land uses; however, determining bacteria loadings can be more challenging. In addition to this, the urban landscape is rapidly growing, increasing the threat for bacterial impairments. The Arroyo Colorado Watershed Protection Plan: Phase I (ACWPP) currently in place was created to address these impairments, but primarily addresses low dissolved oxygen in the tidal segment (Segment 2201) of the Arroyo Colorado by focusing on reducing nutrients entering the Arroyo Colorado. The TCEQ conducted a TMDL on the Arroyo Colorado from 1998-2002. As a result of the TMDL, A Pollutant Reduction Plan for the Arroyo Colorado was developed to address the wastewater infrastructure component of the larger watershed protection plan (WPP) for the Arroyo Colorado. The plan was designed to achieve reductions in concentrations of total nitrogen, total phosphorus, BOD, and sediment in the tidal segment of the Arroyo Colorado. Reductions in the concentration of fecal pathogens (including e-coli) in the above-tidal segment of the Arroyo Colorado were also expected as an ancillary result of the implementation of the pollution reduction plan. Neither the ACWPP or the PRP address Urban Stormwater and/or other nonpoint sources of bacteria. Load reductions for all existing and emerging sources of bacteria entering the watershed need to be established in order to implement specific BMP's to address all sources of bacteria to improve water quality in the Arroyo Colorado. The ACWPP was published in 2007, before the 2008 EPA Handbook for Developing Watershed Plans to Restore and Protect our Waters and generally follows the EPA’s 9 Key Elements for Watershed-Based Plans. By incorporating the bacteria modeling, resulting load reductions and milestone's table into the update of the plan, the ACWPP will meet EPA's 9 Key Elements for Watershed Plans.
General Project Description
This project will build on TCEQ project 582-13-30048 and work towards establishing loading reductions for bacteria necessary to meet water quality standards in the Arroyo Colorado Watershed as well as provide management measures and milestones for the update of the ACWPP. Bacteria loading reduction benefits to water quality in both the tidal and above tidal segments will be established by a state-of-the-art modeling system (flow for SWAT calibrated under the TSSWCB 06-10 project) that links a watershed model to a hydrodynamic and water quality model (H/WQ). Predictions from the modeling system will be the basis for determining new milestones, timelines, and management measures needed to update the ACWPP. All of work in this project will build upon previous efforts to restore water quality in the Arroyo Colorado Watershed.
Through this project, historical data will be collected, analyzed, and utilized in an effort to calibrate the SWAT and H/WQ modeling component. SWAT, a watershed model that predicts watershed pollutant loadings and changes in loadings with different management measures and BMPs, will be utilized as well as the H/WQ component to predict bacteria loadings to the Arroyo Colorado tidal and above tidal segments. The modeling system results will be used to determine the expected load reductions and resulting elevated levels of bacteria from management measures specified in the current WPP. It is important that all data is accurate since SWAT and H/WQ modeling results are essential components to the update of the ACWPP.
Several components of the project will require environmental data operations. Specifically, these tasks will include: data review, watershed and H/WQ modeling, and the development of Geographic Information System (GIS) maps.
The watershed and H/WQ modeling system to be developed for this project provides a state-of-the-art tool that will predict 1) pollutant load reductions in the watershed of the Arroyo Colorado resulting from implementation of specific suites of management practices and 2) improvements in bacteria levels, in the Arroyo Colorado resulting from the watershed load reductions. The tool will be applied to predict necessary load reductions and management practices to restore water quality and to meet applicable standards. Once necessary load reductions and management practices have been established, these findings will serve as a guide for stakeholders to utilize to improve water quality in the Arroyo Colorado. All modeling activities in this project will utilize existing models develop under previous projects (TSSWCB 06-10 and TCEQ 582-13-30048) for the Arroyo Colorado and add the bacteria component that is necessary to determine loading reductions and update the Arroyo Colorado Watershed Protection Plan in future projects. Bacteria, being an added parameter to the modeling system, will require some additional formatting of the modeling files to ensure the linkage between the two models.
Funding Source
Funding provided by the Texas Commission on Environmental Quality as part of a Clean Water Act Section 319(h) Grant.