HOUSTON – (By Michael F. Bloom, P.E.) – Houston area developers have traditionally used concrete parking areas, concrete streets, and pre-cast concrete storm sewer systems to convey rain water quickly and efficiently to “end-of-pipe” detention basins. From there, the collected rainwater is discharged into nearby streams or bayous at a restricted rate to avoid downstream flooding.
Developments are typically disconnected from their nearby streams in favor of locating homes and businesses around the detention basins, which are often designed with permanent pools of water and are viewed as manicured “lakes” by future residents.
There is an alternative, however: natural drainage systems – also known as “low impact development.”
Natural drainage systems simulate natural headwater streams and bayous, more closely mimicking the natural flow of water across the landscape. They can extend the existing bayou and stream corridors up into the development, serving as natural open-space, creek or bayou style amenities that support adjacent trails and parkland.
The use of natural drainage can replace the use of concrete storm sewers, and because the water runs off the site more slowly, the system requires less detention. This allows the development site to accommodate a higher number of homes or commercial buildings, reduces drainage system costs, and provides for an open-space amenity, such as parks or trails.
Natural drainage systems are a marketing differentiator for developments. They capitalize on the market demand for natural and environmentally friendly neighborhoods. They can serve as a framework for trail systems, which are ranked among the highest in consumer-requested amenities. They can provide a polished and manicured look along entryways and community front doors, while maintaining a wild and rustic look along paths and leading away from back doors.
Finally, natural drainage systems serve a drainage utility function under the Texas Water Code. This means that developers can be reimbursed by a special district for the cost of their construction with the proceeds from tax free municipal bond sales.
Let’s look at a few examples.
Audubon Grove, a large-lot, single family residential subdivision in Springwoods Village near the new Exxon-Mobil, campus features 57 lots on about 24 acres. Designed by Costello, Inc. for Taylor Morrison, the development includes trail systems along natural swales (see Figure 1).
The concrete roadways do not include curbs so that stormwater runoff can drain directly into the swales. Front yard swales have been landscaped with cobbles to create a more refined and polished look (see Figure 2).
Camellia, is another single-family subdivision that has used natural drainage systems. Camellia is located in Fort Bend County and includes 323 lots on about 50 acres. Designed by EHRA for Legend Homes, the development includes roads with cross slopes down to depressed vegetated center medians.
The outside edge of the roads are include traditional curbs while the inside edge is curbless to allow for sheet flow into the swale system.
Figure 3 illustrates the overview and Figure 4 shows the roadway and vegetated median area.
The use of natural drainage systems in Camellia reduced overall project infrastructure costs by $1.6 million, increased lot yield by 99 homes, and reduced the volume of detention required to comply with floodplain regulations. *See footnote.
Lastly, let’s look at Stonebrook Estates in the Champions/Spring area. Designed by R. G. Miller Engineers, Inc. and Aguirre & Fields for Terra Visions, LLC., the development includes 135 lots on about 51 acres (see Figure 5).
About 70% of the development is served by a natural drainage system with landscaped and manicured ditches (called “swales”) and biofiltration, which is basically a high flow rate sand filter for stormwater that removes pollutants.
The rest of the development is served by traditional storm sewer.
Roadways are sloped to one side and have curbs but feature “false back inlets” that drain stormwater to vegetated swales instead of expensive underground storm sewer pipes (see Figure 6).
The use of natural drainage reduced the site detention requirement by 24%, which increased lot yield.
The business case for natural drainage in the Houston area is clear. Natural drainage:
- Reduces the volume of detention required to comply with floodplain regulations;
- Increases lot yield;
- Reduces the cost of drainage infrastructure;
- Allows for reimbursement for the cost of drainage facilities;
- Provides an open space and natural amenity to more of the homes in the development, allowing the developer to charge higher sale prices;
- Capitalizes on the market demand for environmentally friendly and natural communities; and
- Differentiates the development from all the rest.
For more information about Houston-area natural drainage projects, check out the Houston-Galveston Area Council’s Designing for Impact: A Regional Guide to Low Impact Development.
AUTHOR: Michael Bloom, P.E., is the manager of the Sustainability Practice of R. G. Miller Engineers, Inc. He specializes in helping clients enhance the economic, social, and environmental outcomes of their projects. Bloom utilizes his 24 years of planning, design, and permitting experience to meet the sustainability and compliance objectives of clients, especially relating to the Clean Water Act and stormwater management. He is a nationally recognized expert on natural drainage systems and stormwater management. Follow Bloom on Twitter and check out his Linkedin.
*Footnote: Ring, J. 2015. Talking Dollars and Sense: LID Construction Costs. Presented at the ASCE International LID Conference. Houston, Texas. January.
Jan. 4, 2017 – Content by R.G. Miller Engineers Inc.