STILLING BASIN AT JOHN MARTIN DAM GETS FIRST FULL INSPECTION IN MORE THAN 75 YEARS

BY TUCKER FEYDER, Sacramento District; ELIZABETH LOCKYEAR, Albuquerque District; AND JONATHAN TAGUE, Albuquerque District

A 12-person multi-disciplinary team of engineers from the U.S. Army Corps of Engineers (USACE) Albuquerque District found the concrete of John Martin Dam’s stilling basin to be in good condition during an inspection, Feb. 21-25, 2019.

The concrete stilling basin sits immediately downstream of the concrete dam and contains nearly 200 8-foot-tall concrete baffle blocks, which dissipate the energy of the water that is released from 16 massive tainter gates. Without this important feature, the water released by the tainter gates could undermine the dam’s foundation.

Photo taken Jan. 10, 2019, of the stilling basin as seen from the end sill at the John Martin Reservoir, in Colorado. Baffle blocks are on the left; on the right are pump lines to remove water from the basin.

Photo Courtesy of U.S. Army Corps of Engineers Albuquerque Division

“The inspection found very little damage in the stilling basin. In fact, some areas of concrete looked nearly new,” said Tracy Aragon, civil engineer in the Albuquerque District’s Operations Support Branch and inspection team lead.

The inspection team was primarily looking for damage in the concrete that would expose the reinforcing steel to corrosion and offset in the joints that would indicate instability of the structure.

“The results of the inspection showed that the structure is performing as designed and also exposed a few additional unanticipated concerns, which the engineering team was able to correct before the contract was complete,” said Aragon. “The biggest surprise of the inspection was that the 2,000-plus drain holes in the stilling basin floor were partially clogged. These drains were cleaned before refilling the stilling basin.”

Drain holes serve to relieve water pressure from underneath the concrete of the stilling basin floor, said Aragon.

“In every dam, some water ‘leaks’ through the foundation and under the dam,” she said. “If we trap this water, it can create a buoyant force underneath the dam that could destabilize it. The drain holes need to be kept clear to relieve the pressure under the dam from this leakage water.”

John Martin Dam is a gravity dam, consisting of a concrete middle section and two earthen wing dams on either end. The concrete section contains the 16 tainter gates at the top of the dam, and six service gates near the bottom. The service gates control most of the water released into the stilling basin, and ultimately, control the flows downstream on the Arkansas River. The 64-feet-tall and 30-feet-wide tainter gates are used during flood control releases.

The contractor uses an excavator to remove equipment from the stilling basin, March 25, 2019. Baffle blocks are visible on the left.

Photo by Jeff Horton

To ensure the stilling basin performs as expected during flood releases, USACE regulations recommend inspecting a dam’s stilling basin every 10 to 25 years, depending on the dam.

After several years of including this project in the budget request, Congress authorized and appropriated funding for this project in fiscal year 2018.

At John Martin, the concrete of the stilling basin has been underwater since it was completed more than 75 years ago. In addition to removing the water, approximately 55,000 cubic yards of sediment that had built up from regular conduit releases over the years also had to be removed to inspect the concrete.

According to the John Martin Dam Concrete Spillway Investigation report, the baffle block concrete is overall in good condition. The majority of the baffle blocks appeared to have been covered with sediment, which reduced the possibility of damage from erosion or abrasive water flows.

The dewatering portion of the $4.8 million John Martin Reservoir Stilling Basin Sediment Removal and Dewatering project began Nov. 1, 2018. Contractors installed six high-powered pumps in the stilling basin to begin the process of removing the basin’s water for the first time since the dam was constructed in the 1940s.

Due to the high nutrient content of the water in the stilling basin, this area has become a high-quality, well-known “honey hole” for local anglers. In fact, the stilling basin has produced multiple state record bass and catfish in the past.

USACE John Martin project staff teamed up with local Colorado Parks and Wildlife (CPW) staff and a few hardworking volunteers to relocate the game fish from the stilling basin to the main body of the reservoir. The fish were collected through various means, including electrofishing, seine-netting, and dip-netting.

Electrofishing involves a high-tech boat that is capable of delivering high-voltage currents through the water, which essentially stuns the nearby fish, causing them to float to the water’s surface.

Upon breaching the surface, USACE and CPW employees captured the fish via dip-net and placed them in an oxygenated holding tank on the boat. After a few minutes in the holding tank, the fish recovered from being shocked and were back to normal.

Once the holding tank was full, the fish were transferred by hand to a hatchery truck that was provided by CPW’s Las Animas Fish Hatchery. The hatchery truck shuttled the fish up and over the dam to the main body of the reservoir, where they were released into the lake to continue life in their new, much bigger home.

The fish salvaging lasted for 14 days, with tens of thousands of fish relocated to the main body of the reservoir. The fish species relocated included channel catfish, blue catfish, flathead catfish, saugeye, walleye, white bass, striped bass, wiper, drum, bluegill, crappie, and shad, as well as the undesirable common carp.

With most of the water and the fish finally safely out of the way, crews were able to begin hauling sediment out of the stilling basin. Backhoes, skid-steers, excavators, and dump trucks worked tirelessly to move the water-saturated dirt from the stilling basin to a settling area for the dirt to dry out.

Once dried out, the sediment was used to improve the grade of one of John Martin’s numerous food plots to make irrigation easier and more effective, said Jonathan Tague, project office manager at John Martin Reservoir. The John Martin staff also grows crops that support local wildlife. “We generally grow triticale – which is similar to winter wheat – buckwheat, pumpkins, and other crops to enhance the food available for local wildlife. They primarily support wild turkeys and deer, but there are also others like rabbits and other small rodents,” said Tague. “We have somewhere around 30 wild turkeys and an unknown number of deer, as they have a larger territory.”

“The project delivery team did an outstanding job designing and monitoring the construction to completion. The project was constructed on time, no fatalities, and within budget,” said Felton Prosper, project manager in USACE’s Albuquerque District Civil Project Management Branch.

The USACE Albuquerque District began construction on its second major dam project, the John Martin Dam, known as the Caddoa Reservoir Project in 1940. After a three-year delay during World War II (1943-1946), the dam was completed in 1948.