The Upper San Marcos River Watershed
Watershed Tour
Introduction into the Upper San Marcos River Watershed
The Upper San Marcos River (USMR) Watershed and its spring-fed waters have remained a priceless resource valued by the community, tourists, and many species, including eight critically listed species . San Marcos has experienced major growth over the years, and such growth is projected to continue well into the future. Aiming to meet the growing demand for infrastructure through the implementation of sustainable and environmentally conscious development is important in unique ecologic and hydrologic areas such as the USMR watershed to protect the water quality from harmful pollutants.
The Upper San Marcos River extends from its headwaters at Spring Lake to its confluence with the Blanco River, the USMR is primarily fed from the Edwards Aquifer and periodic flows from four major tributaries: Sink Creek, Sessom Creek, Willow Creek, and Purgatory Creek. Below is an interactive map of the watershed:
Upper San Marcos River Watershed Interactive Map
Best Management Practices
The USMR Watershed Protection Plan addresses issues such as water quality and quantity through the implementation of best management practices (BMPs). BMPs are structural, vegetative, or managerial practices used to slow down stormwater runoff and treat, prevent, or reduce water pollution. Stormwater runoff is precipitation that cannot soak into the ground and flows across hard surfaces, carrying pollutants such as sediments and bacteria with it. By slowing down stormwater runoff, BMPs remove pollution before they enter our creeks, rivers, and lakes. There are various types of BMPs that target different types of stormwater runoff: agricultural, commercial and institutional, municipal, industrial, and wholesale. Because each type of runoff contains different pollutants, BMPs are tailored for different sectors.
This interactive StoryMap guides people through existing BMPs in the USMR watershed. Simply click through each step to see the BMPs or, follow along through the StoryMap on your phone as you make your way around town.
To download the ArcGIS Companion App, please follow the link for your compatible device:
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Matthews Street Hogtrap
The ‘hogtrap’ was a collaborative project between USMR staff, and Texas State University. The hogtrap is a stormwater feature on campus that has been remodeled to help manage the quantity and quality of stormwater runoff from the northern edge of the Texas State University campus. Runoff occurs when the ground can no longer absorb rainwater and instead flows over the land surface. The newly upgraded hogtrap is designed to receive runoff from approximately nine acres that is 74% impervious cover. The hogtrap itself is a series of inlets that divert runoff into underground piping, eventually discharging runoff into Sessom Creek.
Upgrades to the existing project included repairing and increasing the capacity of the piping, restoring and filling the eroded hillside, and adding vegetation to prevent further erosion during runoff events. To see what the hillside looked like, check out these before and after photos!
The hogtrap has the potential to significantly reduce pollutant loads and is estimated to remove approximately:
• 435 pounds of Total Phosphorus (TP)
• 43 pounds of Total Suspended Solids (TSS)
• 23 pounds of Total Nitrogen (TN)
2
Hutchison Street Biofiltration Pond
The Hutchison Biofiltration Pond was a collaborative project between USMR staff and the City of San Marcos. Biofiltration areas capture and treat stormwater runoff onsite, similarly to rain gardens, except they function a little differently:
1) Vegetated, shallow depression made of engineered soil captures stormwater runoff
2) The captured stormwater percolates through the soil and native vegetation, removing pollution
3) The treated stormwater is temporarily stored, and then passed through an underdrain below the surface into the San Marcos River.
By capturing and treating stormwater runoff onsite, this biofiltration pond has the potential to remove approximately 2,000 pounds of total suspended solids (TSS) and 5 pounds of total phosphorous pollutants per year, as well as reduce the potential for landscape erosion.
Hutchison Biofiltration pond is just one of five biolfiltration ponds the City has installed on CM Allen Drive. In addition to the biofiltration ponds, educational signage and native landscaping was also added by the City. CM Allen receives drainage from downtown San Marcos and consequently all of the pollution that comes along with it after rain events. Due to it's close proximity to the River, it acts as a last line of defense to stop pollutants from reaching the River.
We are proud to have been a part of the reconstruction of CM Allen Drive , which was recently awarded 2nd place in the Professional Category of the 2020 Outstanding Green Infrastructure and LID Project Competition from the EPA’s Region 6 . You can view a video of the improvements and green stormwater infrastructure elements that were included in the project by clicking here.
Partner Recognition
We thank all the individuals and organizations shown for their outstanding contributions of time, effort, and commitment to the development of the watershed protection plan.
Visit our website to learn more about the USMR Watershed Protection Plan:
For questions about the USMR Watershed Protection Plan, please contact:
SMWatershed@txstate.edu
