Bois d’Arc Lake Receives Excellence Award from U.S. Society on Dams

The Bois d’Arc Dam received the 2025 Excellence in Constructed Project Award from the U.S. Society on Dams.

Owner: North Texas Municipal Water District
Designer: Freese and Nichols, Inc.
Construction Manager at Risk: Archer Western
Contractor: Phillips and Jordan

From the award submission:

Freese and Nichols designed the Bois d’Arc Dam that created the 16,600-acre Bois d’Arc Lake in Fannin County, Texas, the first major reservoir in the state in nearly 30 years. The $173 million dam is the focal point of the North Texas Municipal Water District’s new $1.6 billion Bois d’Arc Lake Water Supply Program, which can store 367,600 acre-feet of water and add 121,000 acre-feet each year to the area’s water supply.

The dam comprises a 2-mile-long earthen embankment more than 90 feet high with 5.2 million cubic yards of earth fill. The zoned embankment features a soil-bentonite slurry trench cutoff to a shale foundation, soil cement erosion protection on the upstream face and an intricate internal drainage system to control potential seepage and to enhance embankment stability.

The service spillway features a 60-foot-wide, three-cycle labyrinth weir control section. The emergency spillway is a 1,500-foot-wide earthen channel designed to operate during extreme floods greater than the 100-year flood.

The 110-foot-tall multilevel intake tower transfers water from the lake through dual 78-inch encased conduits through the dam to a 236-MGD raw water pump station located immediately downstream. The tower and conduits were used as a temporary bypass during much of the construction, and all future low flow environmental releases will be pulled from the suction line to the pump station.

The Challenge

North Texas Municipal Water District (NTMWD) supplies water to 2+ million people in more than 71 communities in an area that has consistently been among the fastest-growing parts of the U.S. for decades. Current demands for water are about 400,000 acre-feet per year and are projected to roughly double by 2060. NTMWD has emphasized maximizing their current resources, purchasing available water from adjacent providers, growing conservation programs, and extensive reuse facilities, but these additions to their capacity will not be sufficient to keep up with the growth in demand.

NTMWD’s ambitious project to develop an entirely new surface water supply source included a new major dam and 16,600-acre reservoir, transmission systems and treatment plant. Permitting the massive new system took up most of the available time, so the District obtained most of the land needed and completed the design of the dam and portions of the transmission system prior to issuance of the needed permits. All project elements were accelerated, requiring massive coordination and program management, using four construction manager at risk packages and a full-service provider to construct about $1.1 billion of infrastructure in 5 years. The system started providing a crucial new water source in spring 2023, ahead of one of the hottest and driest summers on record.

Sustainable Water Resources Management

NTMWD has an extensive, diversified range of water supply sources, and the District’s long-standing commitment to their award-winning water conservation program paved the way for permitting the project. NTMWD collaborated with environmental, landowners and local interests to receive the first uncontested water rights permit issued by the Texas Commission on Environmental Quality for a major reservoir in the last 50 years.

Throughout the permitting process, NTMWD worked with multiple state and federal resource agencies to avoid and minimize the environmental impacts of the project and to mitigate those unavoidable impacts that would occur. The mitigation efforts included more than 17,000 acres of restoration and enhancement. This included approximately 8,500 acres of constructed wetlands, more than 70 miles of enhanced or restored streams, and planting of more than 6.3 million trees. This area is one of the largest Permittee Responsible Mitigation (PRM) sites ever authorized by the U.S. Army Corps of Engineers.

The Bois d’Arc site, located just six miles from the creek’s mouth to the Red River also maximizes the available supply of fresh water from that source. The water in the Red River is brackish and cannot be used for water supply without blending or expensive treatment, so the water in Bois d’Arc Creek would be lost to potential water supply if not captured at this site.

Innovation and Overcoming Challenges

The design of the various components of the dam included several innovative concepts that resolved dam safety risks, reduced construction costs by approximately 10% to 20% of construction and allowed for the delivery of the water supply ahead of one of the hottest summers on record.

Intake Structure

State permitting required that the water supply intake to use screens openings less than 1 square inch with flow velocities less than 1 fps. This resulted in the screens needing to be much larger than the required control gates, each of which are 7’ x 7’ sluice gates. This rendered the traditional manner of placing screens and stop logs immediately in front of the gates impractical. The design team’s approach was to separate the tower into two separate chambers. The screens and stop logs were placed at the entrance to the outer chamber while flow into the inner chamber would be controlled by four sluice gates. The configuration cut the footprint in half, saving more than $7 million, while improving operability and worker safety.

Permanent Stop Logs

The intake structure was designed to be able to take water from any possible level in the reservoir. This, however, effectively leaves no dead storage for silt deposition over time. The concern was that silt might block the lowest gates in the intake structure, rendering them useless. The response was to develop a system of smaller “permanent” stop logs that would be set in place in the intake tower prior to any impoundment that would serve as a block for silt accumulation over a long period of time, but, if needed, could be removed individually to the appropriate height to allow for sufficient water to be withdrawn at very low levels.

Stream Diversion Sequence

A significant challenge at the site was the wide presence of high plasticity clays, which are prone to significant consolidation and settlement, bulging and the risk of slope stability problems from high pore pressure buildup. These risks are exacerbated when such embankments are placed rapidly. A normal full height closure section in the river channel would need to be placed very quickly to reduce overtopping risk, but this would likely be too rapid for stability of the fat clays.

Freese and Nichols’ innovative response was to re-sequence the dam construction to hold the embankment at roughly one third its height, divert stream flows through the partially completed intake structure, place the reduced stream closure section, and then place the remainder of the embankment at a more gradual and consistent pace across the full length of the main portions of the embankment.

Though this added flood risk and had to be coordinated with a new bridge and other roadway improvements in the reservoir area, the design protected the structure from the 100-year flood while the embankment was still relatively low. The innovative sequence produced several benefits and cost savings, including the installation of the slurry trench cutoff without a remobilization for a late closure section and the placement of the soil cement erosion protection full length rather than leaving a gap for the closure section. This saved significant costs and provided a safer construction sequence, while reducing the risks from the fat clays.

The biggest benefit to the owner was that permanent impoundment of the reservoir could begin six to nine months earlier than would have happened with a standard closure section. Partial impoundment began in March 2021, which turned out to be crucial because spring runoff provided more than 100,000 acre-feet that could be captured, roughly a third of the lake’s storage. The area then experienced a significant dry period starting in June 2021, so the spring runoff gave the system more than a year’s worth of storage ahead of testing and treated water production. That proved critical to being able to start delivering the water supply when it was needed.