For the $49 million Exploration Green project, Lockwood, Andrews & Newnam, Inc., (LAN) of Houston, Texas, designed five massive detention ponds that each hold up to 100 million gallons of stormwater. When complete, the project will protect more than 2,000 homes from flooding.
However, Exploration Green goes beyond drainage solutions to create a 200-acre urban green space. The site will offer 6 miles of 10-foot-wide, concrete hike-and-bike trails; two athletic fields; numerous open spaces; and 105 acres of natural habitat with wetlands and native grasses to support birds, butterflies, and other wildlife. Even the detention ponds mimic the shape of natural lakes rather than the typical square or rectangular stormwater basins.
With the site nestled in a master-planned community built more than 50 years ago, construction contractors deal with numerous challenges working around the residential neighborhood and adjacent schools while coping with wet soils, wildlife, and massive storm events. Crews already excavated about 1.6 million cubic yards of dirt, with a total of 2.5 million cubic yards expected by the end of the project.
Because LAN has an ongoing contract as district engineer for the CLCWA, they were given the opportunity to design and provide construction administration for the project’s 5 detention ponds. LAN started preliminary design in 2011 and began final design on phase 1 after completion of the master plan in 2013.
Funded by the CLCWA, local authorities, grants, and private donations, the project has been built in five main phases, some split into sub-phases (see “Step-by-Step Construction”). The first phase began construction in November 2015 and the last phase is scheduled to finish in late 2022. Construction contracts for each phase are awarded to the lowest qualified bidder.
Throughout the work, “We’ve had hurricanes and tropical storms that greatly impacted our schedule, but overall construction of the entire project remains on schedule,” said Kelly Shipley, P.E., LAN’s Project Manager.
In 2017, Hurricane Harvey ravaged the area. Although crews had excavated only 80 percent of the phase 1 pond, it helped detain 100 million gallons of water, protecting as many as 200 homes from flooding. Tropical Storm Imelda hit during phase 2 of the work and Tropical Storm Beta during phase 3A.
“The excavation is very dependent on weather,” Shipley said. “There’s a level at which the ponds will drain out, but ultimately there’s a permanent pool of water. When we get to that level and it rains, it can delay the project as the contractor pumps out the water and waits for it to dry before continuing their operations.”
In phase 4, the contractor needed additional drying procedures.
“Our biggest challenge in that phase was existing water hazards from the old golf course,” Shipley explained. “When we started excavation in those locations, the soils were very mushy and wet.”
To prepare the excavated soil for hauling offsite, “The contractor stockpiled the materials off to the side and tried to turn them and dry them out – but every time they got to a certain point, it rained again and they had to repeat the process,” Shipley said.
Eventually the contractor needed to excavate the area where they stored the material.
“Luckily, phase 5 is right across the street from phase 4,” Shipley said. “They were able to get the material out of their way and spread it into a thinner layer to dry more easily. We decided to leave that soil there and haul it off during phase 5 construction.”
The sand seams can’t always be found before construction. “In one phase, we bored within 20 feet of a sand seam, but the bore didn’t expose it,” Shipley said. “We’ve come to expect the sand, so we plan ahead.”
Other lessons learned through the different phases help contractors finish their work more quickly.
For instance, “Because of the nature of Exploration Green, we use all native plants instead of the Bermuda grass we use in most detention ponds for turf establishment,” Shipley said. “Before phase 1, we worked with many consultants who had planted similar seeds and they gave us recommendations on compost, topsoil mix, and how the seed is laid out.”
However, “In each phase, we’ve used a different method in placing the seeds,” Shipley added. “Even the seedbed and what that looks like has changed. As we worked with the various contractors and their subcontractors who put in the seed, they presented variations that appeared to work better than a previous phase in getting that turf established.”
“When we get to the point of tying in the ponds, we have to make sure we don’t cause any issues with an existing pond that’s already established an ecosystem,” Shipley said.
For example, in constructing the box culvert that ties together phases 1 and 2, “We had to make sure we didn’t drop the water level on phase 1 too significantly or too long to cause stress to the fish, birds, or wetland grasses,” Shipley said. “The contractor needed a week for the culvert, and once they got in there, they needed to restore that area as soon as possible. We’d get prepared to go, then it would rain. It took a lot of monitoring.”
“The contractor can be onsite at 7 a.m. but we don’t allow them to start any equipment until 8,” Shipley said. “They can generally work until 5 p.m., but if school is in session their hours are more restrictive.”
That’s because phases 1, 2, and 4 are located near an elementary school; phases 3A and 3B near a middle school; and phase 5 near a high school.
“Lots of kids walk to school,” Shipley said. “We want to make sure those kids get to school safely and we don’t interfere with school traffic.”
Access to the site comes with additional challenges. In every phase except 3A, equipment and workers enter and exit from residential streets.
In addition, “Most of the phases are sandwiched around a ditch for the existing drainage channel,” Shipley said. “We usually have a bridge on one side or the other, so construction traffic has an entrance about 20 feet wide; if we get lucky, sometimes it’s 30 feet. The contractors create a circular traffic pattern to avoid conflicts. We also make sure we have the proper traffic control so we don’t create issues with trucks coming in and residents trying to get home.”
Ultimately, “It’s a really important project for the community so we want to make sure we meet their expectations and deliver a beautiful pond for them,” Shipley said.
- Owner – Clear Lake City Water Authority
- Design Engineer – Lockwood, Andrews & Newnam, Inc., Houston, Texas; Kelly Shipley, P.E., Project Manager; Abby Stanhouse, P.E., Jake Kocurek, P.E., Adam Anderson, P.E., and Kenrick Piercy, P.E., Project Engineers; Chris Edwards, P.E., Drainage Impact Analysis
- Construction Contractors –
- 1A: Paskey, Inc., La Porte, Texas
- 1B and 1C: LECON, Inc., Houston, Texas
- 2: Triple B Services, LLP, Huffman, Texas
- 3A, 3B, and 4: SERCO Construction Group Ltd., Houston, Texas
- 1A: Started November 2015 and finished April 2016
- 1B: June 2016 to August 2017
- 1C: March 2017 to February 2018
- 2: May 2018 to November 2019
- 3A: November 2019 to May 2021
- 3B: October 2021 to summer 2022
- 4: July 2020 to December 2021
- 5: January 2022 to last quarter 2022
Photos courtesy of Lockwood, Andrews & Newnam, Inc.