Rebuilding Houston: Natural drainage systems are an important tool after Hurricane Harvey
By Michael F. Bloom, P.E., CFM (@michaelfbloom)
Rebuilding Houston: About the series
This series features perspectives from Houston and the coast about how the region could move forward after Hurricane Harvey in ways that favor wise financial investments, public safety and the long-term health of our state’s rivers, bays and wildlife. The authors are Houstonians who have long advocated for innovative, nature-based approaches to development, as well as storm surge and flood mitigation, in the greater Houston area.
After Hurricane Harvey, newspapers, blogs, social media posts, and television shows have been filled with stories questioning how land development and floodplain management is accomplished in the Houston region. These stories tend to suggest that we “paved paradise and put up a parking lot,” like Joni Mitchell sang in her 1970 song Big Yellow Taxi. The stories don’t, however, describe how engineers reduce the negative impacts of paving over prairie land by using current design approaches. The stories also don’t describe how civil engineering is evolving to use newer, more innovative approaches.
Traditional approaches use concrete curbs, drains, and pipes to speed rainwater quickly away from development and into large landscaped holes in the ground called detention basins. Rainwater is collected and stored in the detention basins and then released slowly to avoid impacting downstream properties.
A new, more nature-inspired approach uses contoured soil, berms, ditches, native grasses, infiltration systems, rain barrels, and similar elements to collect, re-use, infiltrate, evaporate, and store rainwater throughout the development site. These techniques reduce the total volume of rainwater that must be managed, conveyed, and released from the site. When using this approach, rainwater can flow away from the developed land as if the development was not there. I like to say the development is “hydrologically invisible” because a catfish downstream of the project wouldn’t notice any change in the bayou’s response to rain events – large or small.
This new approach is sometimes called “low impact development” because it has a lower impact on downstream properties. It is also called “green stormwater infrastructure” because it uses green grasses and shrubs to manage stormwater. I like to call the approach “natural drainage” because it uses natural elements to manage stormwater.
The natural drainage approach provides multiple benefits to the project sponsor, the public, and the environment. It is a sustainable approach because it provides enhanced economic, social, and environmental outcomes.
Natural drainage in action
Consider the construction of a new residential subdivision on a native prairie area. The traditional approach would require the installation of scores of stormwater drains, hundreds of feet of concrete pipe, and one or more large detention basins. The basins alone might consume 20 percent of the available land. A few homes might have “lake front” views, but most would have a backyard enclosed by a shared cedar fence. The detention basin would limit the rate at which rainwater drains from the site – it would not reduce the total amount of rainwater leaving the site. This would keep water levels in the downstream bayous higher for longer, which could lead to pervasive flooding. Stormwater pollutants would not be addressed, which means more pollution would be dumped into rivers and bayous.
Now consider this same project built using a natural drainage approach. Imagine every home is built on a relative highpoint so that rainwater drains through the grass to the backyard and front yard of each home. Now imagine that rainwater draining along the street is allowed to flow into a small creek, which connects to a slightly larger creek, which connects to a slightly larger creek. Finally, imagine that this creek system runs behind every home, providing a backyard corridor for trails and neighborhood connectedness.
Every child living there can go out his or her back gate and walk or bike along the creek system. Less detention is required than the traditional concrete system. More land is available for homes or open space. Stormwater pollutants are removed in special filters built into the creek system at key locations. The cost per acre of development is reduced. Homes can sell for a higher price because of the creek amenity. The subdivision will attract home buyers interested in an environmentally friendly and active lifestyle. The subdivision is different from all other subdivisions in the market.
Natural drainage systems are an important tool
The benefits of natural drainage systems include:
- Better built-environment aesthetics;
- Improved stormwater runoff quality;
- Increased bayou health;
- Enhanced ecosystem services for wildlife;
- Reduced heat island effect;
- Reduced erosion in downstream areas, due to reduced velocity and volume of stormwater;
- Lower drainage infrastructure costs; and,
- Enhanced financial performance.
Natural drainage systems won’t prevent flooding, but they are an important tool in the policy, planning, and engineering tool box, and they will help reduce flooding risks. We should look at ways to make it easy for private project sponsors to use this approach. We should create incentives to encourage private sector use of natural drainage systems. We should use natural drainage systems frequently in public projects. With careful planning and engineering we can develop Houston in a way that keeps our economy humming, achieves positive social outcomes, and helps the environment.
Michael F. Bloom, P.E., is manager of the Sustainability Practice of R. G. Miller Engineers, Inc., a Houston-based civil engineering firm. An Envision Sustainability Professional and a Certified Floodplain Manager, Mr. Bloom serves on the Steering Committee of the Houston Land and Water Sustainability Forum, is vice chair of the Government Affairs Committee of the Water Environment Association of Texas, and is a member of the Board of Directors of the Bayou Preservation Association.