About the Upper San Marcos River Watershed and Edwards Aquifer

Spring Lake is a unique ecosystem and serves as the headwaters of the Upper San Marcos River. Artesian spring water from the Edwards Aquifer emerges into the lake from hundreds of spring openings, creating one of the most productive spring-fed systems in Texas. The Edward’s Aquifer is one of the world’s most prolific artesian aquifers and the sole source of drinking water for two million people in central and south central Texas.
The Upper San Marcos River segment (Segment 1814) is 4.5 miles long and extends from its headwaters to its confluence with the Blanco River. The River is primarily spring-fed and receives periodic inputs of stormflow from four major tributaries. This segment of the river is classified for Contact Recreation, Exceptional Aquatic Life Use, and drinking water supply for downstream users.

Spring Lake and the Upper San Marcos River are also habitat for federally- and state-listed taxa. The San Marcos salamander (Eurycea nana), Texas wild rice (Zizania texana), fountain darter (Etheostoma fonticola), Comal Springs riffle beetle (Heterelmis comalensis), and Texas Blind Salamander (Typhlomolge rathburni) are all present in the headwaters, and the Edwards Aquifer immediately below Spring Lake and are listed by US Fish and Wildlife Service as endangered or threatened. The Guadalupe Roundnose minnow (Dionda nigrotaeniata) and the Bigclaw River Shrimp (Macrobrachium carcinus) also occur in the headwaters, and have been identified by the Texas Comprehensive Wildlife Conservation Strategy as species of “high priority” for conservation. These species are sensitive to pollution and rely on suitable flows for survival, including lowered temperatures made possible through cooler springflows into the upper reaches of the system.

Because of these unique features and the clear, pristine nature of the flowing river, it is visited by thousands each year seeking recreation, reflection and tourism. The City of San Marcos and Texas State University have seen unprecedented growth over the past decade. The City has been listed for the past 3 years as the fastest growing small sized city in the United States and more recently as the fastest growing mid-sized city. It is located along the IH 35 corridor that according, to recent Census projections, is expected to increase from 11.3 million in 2010 to 17 million in 2040.

Adverse effects on water quality resulting from urbanization and development within the Upper San Marcos watershed already have been observed. Growth in the watershed and surrounding area is rapidly changing land use, putting pressure on surface water quality and groundwater resources.

Sampling data show that water quality in Spring Lake and the Upper San Marcos River decline after storm flow events, especially with regard to TSS and nutrients. Elevated levels of bacteria in the river and its tributaries also are associated with stormflow. As more people move to the area, the watershed and river become more burdened with increased stormwater runoff and pollutant loading as rainfall that once soaked into native fields is forced to run off of manmade impermeable surfaces to the storm sewers, creeks and river. The water quality is degraded from additional pollution and litter brought by increased urbanization and population. This explosion in human growth in an area with a critically sensitive watershed will surely bring decline unless knowledge and sound engineering controls can be introduced into the urbanization design.

In 2010, the Upper San Marcos River was cited on Texas Commission on Environmental Quality’s 303(d) list of impaired waterways for exceeding total dissolved solids (TDS) water quality standards. Several other pollutants also have been identified as a concern by stakeholders in the watershed. The stakeholders realized that to adopt standards meant for the “average” Texas river would be to allow great increases in a number of pollutants in the San Marcos River. The stringent, above-average standards are intended to maintain the quality of water in the River, to avoid degradation and the necessity of rectifying  a future problem

These water quality targets are part of a comprehensive, voluntary and stakeholder-driven plan to manage surface water resources in the Upper San Marcos River watershed. The WPP, known locally as the San Marcos Watershed Initiative (SMWI), will be submitted to TCEQ and EPA, as well as the community for final review in Spring 2017, and addresses the listed impairment (5c) for Total Dissolved Solids (TDS), as well as E. coli, nutrients, sediment and other pollutants associated with future growth and development.

This WPP is unique in that is was developed in coordination with several other significant watershed level water quality protection efforts, including a regional Habitat Conservation Plan, City and University led Water Quality Protection Plan, City led Comprehensive Watershed Master Plan and City and University MS4 permitting process. The SMWI Stakeholders worked together to weave these efforts into a holistic management plan to restore and protect water quality in the Upper San Marcos River, complete with long term technical implementation schedules, coordinated educational efforts and funding strategies.

These interwoven initiatives will ensure funding and support for implementation of the WPP. Stakeholders selected a suite of structural and nonstructural best management practices (BMPs) to mitigate current and future potential water quality impairments in the watershed. A subset of these BMPs was prioritized for immediate implementation, while others will be implemented over a number of years, as required to mitigate nonpoint source pollution from future development and other activities in the watershed.

The first Implementation Phase will include coordination of partner water quality monitoring efforts to address data gaps, demonstration projects, urban BMPs, education and outreach activities, and an assessment of the effectiveness of newly developed water quality and land development ordinances. The demonstration projects will act as functioning BMPs in highly visible areas and will not only remove pollutants and educate the public, tourists, students, residents and local leaders, but also will validate the future use of low impact design and green infrastructure in the watershed and guide future City and University efforts to implement additional measures to protect water quality.