Jun 06, 2017

Going Deep

Deepening detention basin provides drainage relief

Deepening the detention basin added 20 acre-ft of volume to the site. Right: Six vertical retaining walls were constructed at varying heights.

Located in west Houston, between Interstate 10 (IH-10) Frontage Road and Northbrook Drive, is Lumpkin Road. It runs along Houston Community College (HCC) and is used by the college’s nearly 8,000 students. Constructed in the mid-1970s, the roadway was built as a 22-ft narrow, undivided asphalt road devoid of shoulders and sidewalks, and with open ditches on either side. This caused mobility and safety issues for the students who commuted to the school and community residents. Additionally, the surrounding community faced flooding problems during extreme rain events.

Concerned with these issues, Houston’s Tax Increment Reinvestment Zone No. 17 (TIRZ 17)—an agency focused on developing and rehabilitating public infrastructure—added Lumpkin Road to its capital improvement program. The project’s main goals were to improve drainage, safety, mobility and quality of life. The improvements included widening the roadway to a 40-ft concrete curb and gutter section that would meet current geometric design standards, providing improved pedestrian access to HCC by adding wider sidewalks and a bus shelter with a seating area for students to congregate, and upgrading traffic operations. In addition, TIRZ 17 wanted to address the drainage deficiencies in the surrounding area and replace existing aging public utilities. To this end, TIRZ 17 retained Lockwood, Andrews & Newnam Inc. (LAN)—a planning, engineering and program management firm—as the engineer of record to evaluate and develop solutions that would improve Lumpkin Road’s drainage and roadway problems.

Creative Solution

LAN performed a drainage and conveyance analysis and considered several alternatives. During the analysis, the project team identified a significant opportunity to increase the capacity of the city of Houston’s Westview Basin (located at the northwest corner of Lumpkin Road and Westview Drive) due to the lower depth of the storm sewer along IH-10’s Frontage Road, which served as the outfall for the basin and Lumpkin Road. The IH-10 storm sewer was approximately 10 ft lower at Lumpkin Road than the existing Lumpkin storm sewer system.

Connecting the proposed Lumpkin Road trunk line to the IH-10 drainage system at a lower elevation and extending it back at a minimal grade would provide a deeper outfall for the Westview Basin. This change would allow for additional storage. By deepening the Westview Basin, the total detention storage capacity would increase from 16.1 acre-ft to 30.1 acre-ft, nearly doubling the existing capacity. To convey the flow south along Lumpkin Road, LAN recommended using a combination of 4-by-4-ft and dual 8-by-8-ft storm sewer boxes that extend all the way from IH-10 Frontage Road to the Westview Basin for approximately 3,700 ln ft. This solution provided approximately a 20-acre-ft net increase in detention volume (14 acre-ft basin and 6 acre-ft storm sewer).

“The existing detention basin was an offline basin limited by its configuration and wasn’t fully utilized,” said Derek St. John, P.E., vice president of LAN. “Whenever the system in Lumpkin Road filled up, then water would start bleeding into the basin. We improved the basin function by increasing the flow to the basin with larger boxes and reducing the discharge with a precisely sized outfall. We also added additional basin volume by deepening and reshaping the basin to assist the area north of Westview.”

In order to provide increased drainage capacity to the nearby residential community, the project team also proposed connecting a 54-in. relief storm sewer from the adjacent community to the improved Lumpkin Road drainage system. This also would allow future storm sewer improvements in the neighborhood. The recommended drainage improvements provided a number of benefits, including increasing the region’s detention capacity, meeting the city of Houston’s drainage criteria, reducing overland flow leaving the project area, and improving mobility, safety and access along the existing roadway.

Deepening the Basin

The existing basin was an offline basin with a single 36-in. storm sewer pipe feeding and exiting the basin. Built with mostly earthen slopes, berms and sides, the L-shaped basin had a 6-ft-wide concrete pilot channel inside of it. The basin was redesigned to a parallel system where all flows upstream were directed to the basin and then restricted to the downstream areas by a standard concrete headwall using a 36-in. outfall pipe. Because limited space was available for expansion, deepening the basin was the only way to get additional storage. The basin was designed to be approximately 22 ft deep from the top of the berm to the toe of the wall. A 20-ft-wide berm with swales was considered the minimum to allow the maintenance access required by design guidelines. Therefore, steeper basin side slopes were required. A number of alternatives were evaluated to increase the side slopes, and a segmented gravity wall system was selected as the best option.

During the bidding process, the contractor, SER Construction Partners of Pasadena, selected the Redi-Rock system as the preferred option. A total of 3,880 blocks were used in the project, varying in sizes and offsets. Six vertical walls were constructed at different heights. The Westview Basin also consisted of a 20-ft-wide access road, from the berm to the bottom of the basin. Concrete slope paving with weep holes was installed to prevent erosion and for vehicle access in locations where offsite overflows were expected. To support the weight of the new block walls, all the vertical walls were placed on 150-psi cement-stabilized foundations, replacing the existing poor clay soils. The cement-stabilized foundations of the walls were approximately 20 ft wide by 5 ft tall. In addition, the west side top of bank was lowered to allow overland flow to enter the basin and reduce overflow to the adjacent road.

A segmented gravity wall solution was selected to increase the side slopes.

Project Challenges

The scale, size and complexity of the project provided a number of challenges. Chief among them was the relocation of two large-diameter transmission water lines along Westview Drive to accommodate the addition of the deep, large storm sewer boxes so that the basin could be deepened. The basin could not be deepened to 22 ft without adjusting these water lines. The city mandated that the water lines could be relocated only during the low-demand season.

“The city gave us specific dates between January and April when we could adjust the water lines,” St. John said. “And in some cases, the contractor had to work around the clock so we could meet the strict deadlines."

Another issue was maintaining access for students. This required coordination between the construction management team, contractor and HCC to work around the students’ schedules, especially during critical times of the year, and ramping up the construction during breaks and holidays.

Lastly, constructing the 22-ft-drop vertical walls at the Westview Basin, which required an approximate slope of 1:1.5 to 2, also was a challenge. To accomplish this, 22-ft-tall steel plates were placed behind the walls to support the backwall area and to provide safety for workers during the block installation. The walls were placed in half sections and granular fill was used behind all walls.

Despite these challenges, TIRZ 17 completed the $14.3-million project in March 2016. The results were evident immediately afterward. During the April Tax Day deluge, the Westview Basin filled up while the surrounding neighborhood did not have any flooding issues, showing that the basin was being fully utilized. The project is an example of how an existing infrastructure can be expanded and utilized cost-effectively to mitigate drainage problems.

“The board is extremely proud of the improvements made to Lumpkin Road; it will reduce flooding and provide safety and mobility to the HCC campus and the surrounding neighborhood,” said Ann Givens, TIRZ 17 chair.

About the author

Muhammad Ali, P.E., is senior associate and team leader for Lockwood, Andrews & Newnam Inc. Ali can be reached at [email protected].