Water

The Mill Creek/Peaks Branch/State Thomas Drainage Relief Tunnel is a five-mile-long stormwater tunnel that will provide 100-year flood protection for nearly 2,200 commercial and residential properties in East Dallas when completed in 2029. The tunnel is designed to carry a maximum flow of 9 million gallons (34 million liters) per minute. This provides exponential relief from flooding during large rain events.

COWI served as the geotechnical and structural designer as well as the engineer of record for the tunnel, laterals and shafts. The work also included developing a subsurface investigation plan and preparing a geotechnical baseline report.

Spanning 1.5 miles (2.4 km), the Annacis Water Supply Tunnel is designed to significantly improve the resiliency and reliability of water delivery for 3 million residents in Metro Vancouver, particularly during seismic events.

COWI designed two deep vertical shafts and the connecting tunnel, constructed using a 15.3 ft (4.67 m) diameter tunnel boring machine. Working in highly challenging geotechnical conditions, the project required innovative shaft designs with slurry walls, a comprehensive dewatering strategy and carefully planned excavation methods. All solutions were supported by detailed structural and geotechnical analyses, ensuring long-term performance and safety.

Hot Springs, Arkansas, has faced water issues for years. Now, the Lake Ouachita Water Supply Tunnel transports water directly from Lake Ouachita to the treatment system, improving water infrastructure and security for the city’s 38,000 citizens.

The project features an approximately half-mile-long and 60-inch-wide tunnel bored through Blake Mountain. A 54-inch steel intake pipe gravity-feeds up to 23 million gallons a day. The tunnel carrier pipe was installed using a 61-in (1.55 m) direct steerable pipe thrusting method. The tunnel serves as a critical, high-capacity water source and is an integral part of a USD 150 million, 17-mile water improvement project for the Hot Springs water utility system.

The Gilboa Dam Low Level Outlet Tunnel enhances emergency drawdown capacity, improving dam safety and resiliency for the Schoharie Reservoir. The critical upgrade of the reservoir helps secure the drinking water supply for 9 million citizens in New York City and upstate New York.

COWI served as the tunnel designer and engineer of record, providing structural and geotechnical design, subsurface investigation, and baseline reporting, supporting efficient construction, effective risk management, and long-term performance of this vital infrastructure. The project delivers improved safety, reliability, and resiliency through a new high-pressure tunnel, shafts and intake structures designed to withstand extreme hydraulic demands and complex ground conditions.

The DC Clean Rivers project is designed to capture and clean wastewater during rainfalls before it reaches rivers in the Washington area, and the Potomac River Tunnel is the final major component. This 5.5-mile-long (8.9-km) tunnel includes four drop shafts and seven combined sewer overflow connections.

COWI leads the design of the tunnel and horizontal access tunnels and provides geotechnical support for the entire project. Two advanced tunnel boring machines are used for construction in some of the most sensitive and complex urban and geological conditions in Washington, DC.

The Folsom Dam Auxiliary Spillway will help prevent flooding for 500,000 citizens in Sacramento, California. The new spillway increases flood release capacity and allows more flexibility and controlled release of excess water through its 1,100-ft approach channel, six-gate control structure, 3,000-ft spillway chute and stilling basin. Excavation proceeded through challenging foundation materials, including historic fill, lake sediments and hard granitic rock, while rapidly changing reservoir levels necessitated underwater excavation.

COWI supported URS/AECOM with structural and geotechnical engineering for the approach channel and spur dike, addressing hydraulic loading, seasonal water level fluctuations and the project’s complex excavation requirements. 

COWI, together with GFT, is leading construction management for the Syphon Reservoir Expansion in Southern California. The project will increase recycled water storage from 578 to 5,000 acre-feet, strengthening long-term drought resiliency for Irvine Ranch Water District (IRWD). By enabling greater use of recycled water and reducing reliance on imported supplies, the expansion supports sustainable water management while delivering lasting value to communities across central Orange County.

Responsibilities encompass constructability reviews, support during the contractor bidding process, contract administration, resident engineering, quality assurance, and risk management. The team will also support IRWD’s environmental monitoring and public outreach initiatives.

The Chickamauga Lock on the Tennessee River needed replacement due to structural deficiencies and deterioration. The lock is vital to the navigation, transportation, economy, commerce and recreation in East Tennessee. COWI completed feasibility studies, value engineering and detailed design for an innovative landward cofferdam that enables in-the-wet construction while maintaining navigation. The design addressed space restrictions, deep excavation in complex geology, lateral stability and flood risk.

COWI evaluated conventional, float-in and lift-in alternatives, identifying concepts capable of multimillion-dollar savings. The precast modular cofferdam later became part of the permanent lock structure.

COWI provides construction management for the Anderson Dam Tunnel Project, helping Santa Clara Valley Water District enhance regional flood protection and water safety. The new tunnel will enable rapid emergency drawdown and support the future seismic retrofit of the 1950s-era dam.

COWI oversees construction of key infrastructure and supports community and environmental work, contributing to a safer, more resilient water system for Santa Clara Valley residents. The project includes a new outlet system featuring a 1,700-ft underground tunnel, lake tap, outlet structure, discharge channel, reservoir rim and bank stability upgrades, intake improvements, plus road work, utility relocation, traffic control, revegetation and community outreach.

The Olmsted Lock and Dam project replaced aging infrastructure on the Ohio River, significantly improving navigation safety and efficiency on the busiest stretch of U.S. commercial inland waterways. As part of a joint venture, COWI provided detailed design services for the navigation dam and construction design support for the precast yard, including the marine skidway. We developed construction alternatives and supported selection of the in‑the‑wet construction method.

The dam consists of a 654-ft-long tainter gate spillway and a 1,400 ft gated navigable pass, two boat abutment sections, a fixed weir section, and upstream and downstream scour protection. The team addressed major seismic demands, large river level fluctuations and the need to maintain navigation during construction.

COWI is a trusted partner in planning, designing and delivering transportation infrastructure that strengthens connectivity and supports sustainable growth across North America. Drawing on decades of global expertise and strong local presence, we support public and private customers throughout the project lifecycle.

Across North America, COWI delivers water infrastructure solutions, designing dams, hydraulic structures, and water and wastewater tunnels through close customer collaboration, applying global expertise to ensure reliable service, long‑term resiliency and solutions to water challenges.

COWI offers engineering consultancy to federal agencies across North America. In Canada, we work with Parks Canada to inspect and maintain bridge assets. In the United States, we partner with the U.S. Navy, delivering resilient marine infrastructure.

COWI helps customers across North America strengthen climate resiliency through coastal protection and flood control, assessing risk, adapting infrastructure, and protecting communities, assets and ecosystems with robust strategies for extreme weather and rising sea levels.

COWI supports North America’s energy transition through engineering services for offshore wind, green fuels, microgrids and waste‑to‑energy. We combine global expertise and local insight to help customers reduce emissions and strengthen energy security.