Surface Water Supply Project Segment C2 Program and Construction Management

Vital water management infrastructure initiative ensures reliable water supply for West Houston residents

The City of Houston, Texas, and its surrounding areas have relied heavily on groundwater – mainly underground aquifers – for their drinking water supply. These aquifers have provided readily available water resources for the region’s rapidly growing population. Over the past several decades, the extraction rate has increased to meet residential, commercial, and agricultural demand. However, the long-term over-reliance on groundwater has led to significant land subsidence.

Land subsidence is the gradual sinking or settling of the ground’s surface, often caused by excessive groundwater withdrawal. As groundwater is pumped out, the earth compresses and subsides, leading to increased flooding, infrastructure damage, and changes in natural drainage patterns.

Across Texas, this phenomenon significantly threatens the water supply and infrastructure. To address subsidence and ensure sustainable water demand management, the West Houston area has been shifting from groundwater to surface water sources, such as rivers and reservoirs.

Our Client’s Challenge

Groundwater extraction in Harris and Galveston counties is overseen by the Harris-Galveston Subsidence District (HGSD), a special-purpose district mandating that water providers in three regulatory areas decrease their groundwater usage in accordance with local subsidence rates. While Areas 1 and 2 have transitioned to surface water sources, Area 3 is required to shift to alternative water sources, achieving a 60% reduction in groundwater use by 2025 and an 80% reduction by 2035.

To comply with HGSD’s mandate, the West Harris County Regional Water Authority (WHCRWA) joined forces with the North Fort Bend Water Authority to design and construct the Surface Water Supply Project (SWSP). Once complete, the project will include 55 miles of pipeline, ranging from 42 to 96 inches in diameter, and two large pump stations that enable the regional water authorities to supply municipal utility districts with treated surface water from Lake Houston.

Our Solution

In 2024, Gannett Fleming acquired DEC – the program and construction manager (PM/CM) for the SWSP, which includes Segment C2. Now, with combined resources, our team continues to deliver excellence in the PM/CM role. SWSP Segment C2 is a 4.8-mile section of 84-inch waterline with seven tunnels running from State Highway 6 to Brittmoore Road. This waterline will keep 150 million gallons per day (MGD) of water moving west toward WHCRWA’s Central Pump Station.

Constructing an 84-inch pipeline through an urban corridor presented significant challenges that needed to be addressed during the design and construction phases. Early in the design process, minor route adjustments minimized public impact and reduced construction costs. Once the route was established, several design innovations enhanced the project’s contractor and operator friendliness. These innovations included changing the approach sections toward deep tunnel crossings from a 45-degree slope to a vertical pipe section, reducing the overall depth of cover on the approaches, and using the tunnel shaft for vertical piping construction. This approach provided a clear tunnel entry point and an ideal air valve location, reducing the overall risk at each tunnel shaft site.

A particularly challenging project aspect was the Langham Creek crossing. In potentially flowing ground conditions, a 50-foot-deep, 260-linear-foot tunnel had to be constructed below the groundwater table. A geotechnical baseline report prepared during design outlined the difficult geotechnical conditions, while the design specifications mandated either an earth pressure balance machine or microtunneling due to the pressurized face requirement.

Further soil testing revealed the need to deepen the tunnel’s profile to reach a stable layer, mitigating risk during construction. Significant groundwater ingress at the shafts during construction prompted extensive dewatering efforts, including adding deep and eductor wells to manage inflows effectively. Despite these challenges, the microtunneling proceeded smoothly, without over-excavation or loss of face pressure.

The team initiated a pipeline embedment prove-out process during the design phase for all installation crews. This field operation involved installing one or more pipeline joints in the ground with proper trench shoring, backfilling up to the springline, and removing them to verify the support of the pipe haunches. This standardized process ensured successful pipe-laying and established a baseline for the inspection team and the contractor. This approach benefited the client by enhancing product quality, the community by minimizing rework in suburban areas, and the construction industry by promoting method documentation and standardization.

The project also used monolithic insulating joints (MIJ), a relatively new technology, to isolate pipeline sections for cathodic protection. This strategic implementation of MIJs met design pressure requirements and provided effective cathodic isolation, extending the pipeline’s design life.

The success of the Segment C2 project hinged on extensive coordination with utility owners, public entities, and residents. The program and construction management team employed various dynamic methods to keep the public informed and engaged, including regular drone flights, interactive public meetings, and advanced construction management software. This transparent communication approach facilitated stakeholder collaboration and addressed public concerns promptly.

The Segment C2 project exemplifies the successful integration of innovative engineering, meticulous planning, and effective stakeholder collaboration. By overcoming complex technical and logistical challenges, the project team delivered a vital infrastructure solution that meets regulatory requirements, enhances community resilience, and sets a new standard for large-diameter pipeline construction in urban environments. The team’s expertise and commitment to quality ensured the safe and efficient installation of the Segment C2 waterline, contributing to West Houston water demand management and reduction of land subsidence.

Key Features

More than 4.8 miles of 84-inch pipeline.
Trenchless and open-cut construction methods.
Seven tunnels minimized community disruption and navigated complex crossings.
Effective groundwater management and dewatering efforts.

Outcomes

Achieved compliance with HGSD regulatory requirements.
Enhanced water supply reliability and sustainability for West Houston residents.
As part of the SWSP, contributed to mitigating land subsidence and reducing groundwater dependence.
Delivered under the original project budget.