Serene area of the San Antonio River while padding along the SASPAMCO Paddling Trail

Low Impact Development

An Introduction to Watershed Sustainability

Think for a moment about the word sustainability. What comes to mind? For many people, environmental sustainability means recycling, conserving energy and water, or reducing air pollution. All of these things are essential in creating a healthy environment that can be sustained for generations to come. However, maintaining clean and healthy water in our creeks and rivers is also an essential element of environmental sustainability.

How the River Authority Defines Sustainability

The San Antonio River Authority (River Authority) is dedicated to achieving a sustainable watershed through improving water quality in the San Antonio River Basin. We believe that sustainability is achieved by implementing solutions that balance a set of criteria that is often referred to as “the triple bottom line.” To meet these criteria, sustainability solutions must:

  • Be good for the environment    
  • Be good for people
  • Make sound financial sense.
Triple Bottom Line 2020

How we care for our watershed now will determine the health of rivers and streams for future generations to enjoy. Polluted San Antonio River water harms more than just the fish and wildlife in our local area. Water that drains into the San Antonio River flows all the way to San Antonio Bay where it has direct impact on the health of wildlife in the bay and the Gulf of Mexico.

However, a sustainable watershed is not just good for the environment. In the long run, it will save taxpayer money through reduced infrastructure costs. It will also improve quality of life in our watershed through increased green space, walkability, and landscape beautification.

If we do not take steps now to encourage a healthy watershed, we could be susceptible to federal government intervention in the future. We feel that it is important for the community, not the federal government, to be responsible for decisions made about the river. Below are several key components of a sustainable watershed. These components are not mutually exclusive – they all work together to create a healthy watershed.

What is Low Impact Development?

Low Impact Development (LID) is a sustainable land planning and design approach that manages stormwater on site. It is a set of tools specifically created to mitigate the pollutants and other unhealthy components of stormwater runoff. Examples are rain gardens, stormwater harvesting cisterns, and permeable pavement.

LID design

  • Maintains or enhances on-site natural features to drain the site and manage pollutants after development

  • Reduces impervious cover and/or disconnect impervious areas from the storm drain/stream network.

San Antonio River Basin LID Technical Design Manual Content Overview

The manual addresses the design, specifications, and details of individual LID best management practices (BMPs). Since future maintenance should be considered during the design process, preferably by incorporating maintenance staff into the planning and design process, the manual also includes maintenance guidance. The manual provides guidance both on design considerations influenced by maintenance and on general maintenance practices for each BMP.

The manual also provides a segment on treatment trains, showing three different popular configurations of BMPs working in sequence for enhanced performance. Multiple treatment processes in either individual or multiple BMPs are called a treatment train. Treatment trains maximize the treatment of pollutants within the runoff. For example, vegetated filter strips designed to convey runoff from a road may be directed into an infiltrating bioretention cell that is designed to capture pollutants and provide volume reduction. Another example is the use of manufactured products for pre-treatment, filtering, trash removal, and oil and grease removal as the first structural BMP in a treatment train. Developer flexibility is enhanced by the many treatment train BMP combinations that can be designed.

San Antonio River Basin LID Technical Design Manual
Components of a Sustainable Watershed

Download the San Antonio River Authority's Position Paper On Practices Advancing Watershed Sustainability

Good Water Quality

Creeks and rivers with good water quality have very low levels of pollutants and contaminants. They are safe for recreation such as swimming and kayaking and are a healthy home for wildlife.

Healthy Riparian Habitats

A healthy riparian habitat contains native vegetation that acts as a buffer that filters out pollutants before they enter creeks or streams. Healthy riparian habitats are also able to support a diverse array of native animal species.

Healthy Aquatic Habitats

A healthy aquatic habitat provides a safe home for aquatic animals that live in our watershed. A healthy aquatic habitat is free of pollution and contains a variety of areas for animals to live.

Sustainable Stormwater Infrastructure

In a sustainable watershed, low impact development (LID), green infrastructure, stormwater parks, innovative parking paradigms, and other technologies and policy actually reduce the amount of taxpayer funded infrastructure that is needed.

Threats to a Watershed

The most significant threat to the health of the San Antonio River Watershed is stormwater runoff. Many assume the greatest threat is from manufacturing or industrial waste piped into the watershed. That is not the case here in our basin and in many throughout the United States. 

Below is a listing of some other common threats to sustainable watersheds. These threats usually harm rivers by increasing pollutants and/or increasing the volume, velocity and natural temperature of stormwater runoff that flows to the rivers.

Luckily, there are solutions available to protect our watershed from the threats mentioned below. Sustainable site planning and design methods such as low impact development, green infrastructure including stormwater parks, and stream restoration are a few best management practices that the San Antonio River Authority implements and advocates for a more sustainable watershed.

Threat:

Harms:

Examples:

Why?

Nonpoint source pollution
  • Water quality
  • Aquatic habitat
  • Automotive fluids washing into streams off of roads
  • Pet waste washing into streams from yards

Nonpoint source pollution is pollution that enters waterways from many different sources. This type of pollution harms water bodies by increasing levels of bacteria, nutrients and hazardous chemicals.

Impervious ground cover
  • Water quality
  • Aquatic habitat
  • Riparian habitat
  • Asphalt
  • Concrete
  • Roofs

Hard surfaces do not allow stormwater to absorb into soil. This increases the volume and velocity of stormwater entering waterways, which leads to erosion. Water quality is also harmed because there is no vegetation present to filter out pollutants.

Unnatural animal populations
  • Water quality
  • Aquatic habitat
  • Riparian habitat
  • Large duck populations on the River Walk
  • Feral hog populations

When people feed wildlife rather than allowing animals to be fed by natural food sources in their habitat, populations can grow to unnatural levels. An example of this is the duck population on the River Walk in San Antonio. Another way animal populations can grow out of control is if the animal species is a non-native species that has no natural predators. An example of this is feral hogs that are seen throughout the San Antonio River Basin. Overpopulation of wildlife is bad for the watershed because it tends to result in erosion and elevated bacteria levels in water bodies.

Concrete Drainage Channels
  • Water quality
  • Riparian habitat
  • There are numerous examples throughout the basin

Concrete drainage channels are designed to quickly move water off of streets and property, and they do this job well. However, they also result in erosion to creeks and rivers as water rushes out the concrete and into water bodies. These channels also raise water temperature unnaturally and do not assist in helping filter out contaminants from stormwater coming off of streets and roads. Luckily, there is a method of channel design called “natural channel design” that filters contaminants by mimicking natural stream processes using vegetation. This method also conveys floodwater more efficiently while minimizing erosion to streams. An added benefit is that they can also be much more visually appealing.
What is Stormwater Runoff?

Stormwater is rain that falls onto impervious cover, such as streets, roofs, and driveways, picks up pollutants that are on those surfaces, and carries the pollutants into the street storm drain system and on into our streams. Those pollutants include, but are not limited to, oil, fertilizers, bacteria, heavy metals, gasoline, and sediment. A great stormwater control measure in highly urbanized areas, such as San Antonio, is low impact development (LID).

Did You Know? In San Antonio, stormwater does not drain into a sanitary sewer system. It flows directly into our creeks and rivers primarily from the street storm drain system.

Low impact development fact sheet