EHRA Engineering uses the Low Impact Development (LID) land planning and engineering design approach to manage stormwater runoff as part of aligning with green infrastructure. An example of this is a road expansion and bioswale project on Sjolander Road in East Harris County, near Baytown. A new way of approaching drainage for the flood-prone area, LID was used to reduce the potential of flooding while decreasing pollution found in stormwater runoff. Added advantages also include the improvement of roadway aesthetics and savings to the local government.
In 2013, Baytown had seen economic growth in the form of an expansion of a nearby chemical plant. In response to this growth and the increasing number of heavy trucks who needed access, Harris County looked to expand a 1.5-mile section of Sjolander Road, adding two lanes with a continuous left turn center lane. EHRA was brought on the project by Harris County to provide engineering design and construction oversight.
LID design, was chosen for this project in coordination with the Chevron Phillips Cedar Bayou plant and Harris County Engineering Department. After consideration, it was determined that an environmentally friendly road was the appropriate application for this design.
Besides the LID elements, construction of the roadway was standard. Steel rebar was added to the new concrete to strengthen the load-bearing capability, creating a layer of pavement 12 inches thick, much thicker than typically used to accommodate the stress of heavy truck traffic.
Workers began work on the southbound lane. LID elements were introduced to the process as the southbound side began to progress through construction. A 60-foot wide bioswale, sloping wide ditches which contain native drought resistant vegetation, filter media and provide erosion protection was installed. These take the place of a typical stormwater drainage structure, such as manholes and concrete pipes, as well as detention ponds.
Sjolander Road is located in the Cedar Bayou watershed, and a major benefit from the LID design is reducing the number of silts, oil and any heavy metals that travel with the runoff that eventually reaches the bayou. Cedar Bayou flows from saltwater marshes important to wildlife just before it reaches Galveston Bay. The bayou is already considered by state agencies to be environmentally impaired and reducing pollution in Galveston Bay is crucial to the economically important seafood industry.
“Using LID design is hugely beneficial to areas that have contaminants in the soil,” said Adam McGovern, RLA, ASLA, Landscape Architecture Practice Area Supervisor for EHRA. “We can use plants to reduce the toxic material that is passed through our stormwater system. This method also reduces erosion by reducing water velocity.”
Slowing down fast flowing water is also important by creating a more natural system of flood control and detention. Low Impact Development reduces the amount of land needed for detention and eliminates or reduces the cost of underground storm sewer pipes. In this case, the cost savings was unusually high, twenty million dollars.
“This project cost approximately $5M. Typically, this project would have been about $7M if we had implemented traditional construction with storm sewers” said John Blount, Director, Harris County Public Infrastructure Department. “However, because there were thirty pipelines and a water canal, it would have cost an additional $18M if we had to adjust all the pipelines in the water canal, which we didn't have to do because of using this type of construction.”
Aesthetic appeal is another significant benefit of low impact development. Instead of building more concrete structures, this design works with nature to manage stormwater flows. For all these reasons, LID is changing the approach to road construction industry wide.
The LID construction, including the bioswale was inspected for substantial completion in March of 2021.