Preserving the Land That Water Flows Over

When rain falls on the ground, some of it soaks into the ground where it falls, and some of it flows away as runoff, also called stormwater. Most of the water in streams and lakes, and all of the water in aquifers, comes from runoff. The land in the drainage area that contributes runoff to a specific stream or aquifer is called a watershed. One way to think about a watershed is as a bowl, because all of the rain that falls in this drainage area will flow to its lowest point. Texas has thousands and thousands of these bowls, since every stream — from the biggest rivers to the tiniest creeks — has its own watershed. When the upper edge of one watershed bowl meets the upper edge of another one, they form a miniature Continental Divide. For example, consider the watershed boundary for the Brazos and Colorado Rivers — rain that falls north of this divide will flow into the Brazos, while rain that falls south of this divide will flow into the Colorado.

This is why our mission to protect the water in streams and aquifers also means that we work to protect the land in watersheds. Since rain both soaks into the ground and flows over it, problems can develop when this ground is covered with new construction. Buildings, roads, parking lots, and sidewalks are all called impervious cover, since rain can’t soak through them and instead turns into new runoff.

Building new impervious cover can produce several problems:
• It can reduce the amount of water that can seep into an aquifer.
• It can increase the amount of runoff into a stream, which can increase the volume of floods during storms.
• It can pollute the runoff that flows into a stream or seeps into an aquifer, because runoff will pick up pollutants on the surfaces that it flows over. Studies have shown that the first inch of rain, which picks the most surface pollutants, can be as dirty as raw sewage.

Adding impervious cover in a watershed can be especially risky if it’s done in a stream’s riparian zone (the land immediately next to the stream) or in an aquifer’s recharge zone (the area where surface water seeps underground into the aquifer).

There are three solutions to this problem:
• Using land conservation to prevent impervious cover from being built.
• Using impervious cover limits to reduce the amount of new construction.
• Using green stormwater infrastructure and nature-based solutions to improve the quality and reduce the quantity of additional runoff that’s created by new construction.

Save Texas Streams has promoted several measures to implement these solutions:

Land conservation: We strongly supported the creation of the Greenbelt and the Wilderness Park along Barton Creek, which has preserved hundreds of acres from development. We’ve also supported The Nature Conservancy in its acquisition and management of the Barton Creek Habitat Preserve, and the Shied-Ayres family in their conservation of Shield Ranch, both of which have removed thousands of acres along Barton Creek from development. We also backed the creation of the Water Quality Protection Lands program in Austin. Hill Country Conservancy, which is working on land conservation at a regional level, was founded by George Cofer, one of our organization’s longtime leaders.

Impervious cover limits: We actively worked for the passage of Austin’s Save Our Springs Ordinance in 1992. Under this landmark policy, developers can’t build on more than 15 percent of a property if it’s over the Barton Springs Recharge Zone, and on no more than 25 percent if it’s over the Contributing Zone for the Springs.

Green infrastructure: We supported a change to Austin’s Land Development Code that requires new projects to incorporate green infrastructure features such as rain gardens, green roofs, rain harvesting, and permeable pavement in order to cleanse and reduce the new runoff created by their construction. Austin is the largest city in the country to voluntarily adopt a measure like this; other cities were required to do so because of consent decrees with the Environmental Protection Agency.