John Martin Stilling Basin is Cleaned Out for First Time in 70 Years

Stilling Area at Base of Dam, February 17, 2019

The cleaning project, underway since this past November, is nearing completion at John Martin Dam in Bent County. A trip to the dam this past Sunday, February 17^th, shows that the water from the stillway has been drained and earth moving equipment has scraped clean, almost all the accumulated sediment that has built up over the decades.  Access to the ground work is denied to the public while vehicles can still pass freely over the top of the dam.

Dry Out Area for Sediment

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 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 tainter gates are used to release flood water. The stilling basin sits immediately downstream of the concrete dam, and contains large concrete baffles, to dissipate the energy of the water that is released from the dam’s tainter gates.

Winter Sunlight on Water

To ensure the stilling basin performs as expected during flood releases, it is recommended that the stilling basin be completely dewatered, and inspected, every ten years. Before the inspections can begin, all of the sediment, which has accumulated from the normal water releases, must be removed. Since the completion of the dam, John Martin’s stilling basin has never been cleaned. That is over 70 years’ worth of sediment – equal to 60,000 cubic yards!

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 (both of which have since been broken).

On Nov. 1, 2018, work began to dewater, and clean, the stilling basin, as contracted workers placed one-half dozen high-powered pumps in the stilling basin, to begin the dewatering process.

Knowing that there were likely to be thousands of fish that were soon to be left high and dry by the dewatering process, USACE John Martin project staff teamed up with local Colorado Parks and Wildlife 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, which was generously 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.

This process fish salvaging continued for 14 days. During this time, tens of thousands of fish were relocated to John Martin Reservoir. The variation in species was very broad, and 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. The sheer number of fish, and the size of them, surprised even the local CPW aquatic biologists!

Multiple “potential” Colorado state record catfish, and striped bass, are now lurking around John Martin Reservoir waiting for anglers to test their skill, and maybe a little luck, at catching them.

With most of the water and the fish finally 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 dirt will then be relocated to its final resting ground, on one of John Martin’s numerous food plots. The dark sediment will be used to enhance the food plots, where the John Martin staff grows crops, which support the local wildlife.

The final steps of the project include cleaning and inspecting the now-empty concrete stilling basin, and performing any needed repairs. Work is scheduled to continue throughout February and March 2019.

By Tucker Feyder, John Martin park ranger and Jonathan Tague, John Martin Project Office manager