Posted October 7, 2020
By Judy Powers, Special Correspondent to DredgeWire
The U.S. Bureau of Reclamation (Reclamation) is sponsoring a competition to seek a method of moving sediment downstream from reservoirs above dams on a continuing, sustainable basis.
Called the Guardians of the Reservoir Challenge, it is open to all persons over 18 years old from all countries except the few under sanction by the U.S. Government.
Reclamation is partnering with the Corps of Engineers, the National Aeronautics and Space Administration (NASA) Tournament Lab and HeroX, a social network for crowdsourcing innovation and human ingenuity, to put the competition on and manage submissions.
The United States has more than 90,000 reservoirs created by damming rivers.
Built beginning in the 1950s, the dams have formed a barrier to downstream transport of sediment, which settles out in the reservoirs and over time reduces the water storage capacity.To date, the nation’s reservoirs have lost a significant portion of their storage capacity.If they are allowed to completely silt in, the flood control, irrigation, water supply and hydroelectric power they supply will be gone.
In 2018, the National Reservoir Sedimentation and Sustainability Team (NRSST) comprising engineers and scientists from federal and local agencies, universities, consultants, and industry, published a white paper describing the state of the reservoirs and the concerns for the country.
Reclamation’s challenge builds on those facts.Two webinars held in August and September described the topic for the dredging and soils industries.
DR. GREGORY MORRIS, P.E., Ph.D. of GLM Engineers, is a member of the NRSST, a co-author of the 2018 white paper, and author of two books on reservoir management.He led off the August 24th webinar with an explanation of the dynamics of “dead zone” sedimentation in a reservoir – sediment that builds up below the dam outlets over time, eventually blocking the outlets, impinging on the water storage ability and threatening to fill in the reservoir completely.
“We’re not building any more reservoirs, and our (water storage) capacity is in trouble,” he said. There is 6 billion cubic yards per year of water storage loss from sedimentation in U.S. reservoirs, he said.
Reservoirs in some other countries have reached the critical stages where action had to be taken to save the reservoirs.Dr. Morris’s work has been done primarily on those reservoirs, and he gave examples of four large projects in Colombia where sediment removal, bypasses and reconfiguration of the reservoir were used to save their storage and flood control ability.
The goal in the U.S. is to balance sediment inflow and outflow to create a long-term balance, he said.What is needed is 21 st century reservoir management for 20th century construction, and dredging has been the most economic method to date.
Dr. Morris co-authored with Jiahua Fan the Reservoir Sedimentation Handbook -- Design and Management of Dams, Reservoirs and Watersheds for Sustainable Use. It can be downloaded, along withExtending the Life of Reservoirs, at www.reservoirsedimentation.com
MORE THAN JUST TRAPPING WATER
JOHN SHELLEY, Ph.D., P.E., is a project manager at the Corps of Engineers Kansas City District. He described some innovative methods for sediment management that have been used in his and other Corps Districts.
A reservoir is more than just trapping and storing water, he said.Sediment management is a necessary part of the process.
Tuttle Creek Lake is a 19.3 square mile reservoir on the Big Blue River in the Flint Hills region of northeast Kansas.The need for sediment management is huge, with 9.2 million cubic yards of sedimentation per year above the dam and sediment starvation downriver of the dam, he said. Because the native downstream species of fish depend on turbid water, elimination of the sediment wiped out those fish populations.
He showed photos taken of Tuttle Creek Lake in 1962 and 2010,showing the water capacity close to eliminated in that time.The District is in an ongoing search to solve the problem.
He quoted Dr. Rollin Hotchkiss, of the USACE Environmental Advisory Board saying, “The only way to sustainably manage the nation’s reservoirs is to pass the sediment downstream.”
Shelley described four methods for accomplishing this.
- 1. Pressure flushing
Pressure flushing involves opening an outlet at the sediment end of a lake and allowing water to rush through, carrying the sediment with it.This can only be done where water conservation is not an issue.It is performed twice a year at Cherry Creek Lake, an 850-acre flood control lake in Aurora, Colorado near Denver. The flush moves through four gates, with each flush lasting 15 minutes, for a total of 90 minutes for the entire operation.A multibeam survey in the reservoir doesn’t show a difference in the volume of the lake, but the sediment near the outlet is removed.
- 2. Drawdown flushing
This method involves opening a low-level gate on the dam and allowing the water to draw down to the river level, taking excess sediment downstream. This method is used for small, hydropower reservoirs.
It was used on the Spencer Dam reservoir in Nebraska, which was able to maintain 10 percent of its original storage by flushing twice a year for two weeks.(Spencer Dam, built in 1927, was destroyed by ice in March 2019 and will not be rebuilt.)
The challenges of drawdown flushing is that all the water is used, so is not an option for water supply reservoirs, and the resulting storage capacity is less than the original because sediment remains in the floodplain area of the reservoir, and the discharge downstream has a high sediment concentration with short duration.
If hydraulic dredging or agitation dredging is performed during the drawdown, more sediment will be in suspension and move out of the reservoir.
“There is a market for small-scale dredging to make pressure flushes more effective,” said Shelley.
- 3. Hydraulic Dredging
At Millsite, an irrigation reservoir in Utah, Ferron Creek deposits a large sediment load.To maintain the storage area, a small dredge operates above the dam and discharges into the clear water flowing over the spillway, creating a natural sediment level in the discharge.
By moving the dredged material downstream in this manner, 40 to 60 percent of the project cost for maintaining the reservoir can be saved, Shelley estimated, and there is a good potential for positive ecosystem benefits.
“As a sediment engineer, I loved this solution,” he said.
- 4. Water Injection Dredging (WID)
WID has not been used in lake or reservoir maintenance, but the State of Kansas is seeking to do a WID pilot project at the Tuttle Creek Lake.WID introduces sediment into low-elevation gate releases, pressure flushes and drawdown flushes.If the pilot project is successful it will create a market for these dredges in reservoir management, Shelley estimates.
MICHAEL WHELAN, P.E., is a dredging engineer with Anchor QEA.He contrasted dredging applications in reservoirs to dredging in coastal, river or industrial settings.
Reservoirs are inland, freshwater impoundments.They are flooded canyons or valleys, sometimes with steep sides that are hard to access.
There are distinct conditions at inlet and outlet ends, he explained.The inlet may contain coarse and crystalline granular materials in mountainous country, logs, organics and rocks in forested areas, chemicals in agricultural areas, andspikes in sediment eroded and delivered to the reservoir following wildfires.
At the dam end there is deep water and infrastructure features such as outlets and gates.
In managing sediment, it is desirable to move it downstream, but if that is not possible, an upland permanent placement facility is possible to store dredged material that is a resource and has value. It can be used in a sediment-starved downstream ecosystem or in the commercial market.
“Sediment is accumulating where it’s not wanted and can be removed and placed where it is wanted,” said Whelan, such as using the material to create wildlife habitat.
DAVID OLSON is the Regulatory Program Manager at Corps Headquarters in Washington D.C. He explained the permitting requirements and procedures required for sediment management activities in reservoirs.
Permits are required under three laws:
Section 10 of the Rivers and Harbors Act of 1899 refers to construction dredging in navigable waters, and regulates any modification of the course, condition, location or capacityor condition of a navigable waterway.It may apply in some cases todredging inland reservoirs.
Section 404 of the Clean Water Act, regulates the discharge of sediment into the waters of the United States, including wetlands.Permits refer to dredged materials or fill materials.Dredged materials are defined as materials that do not change the elevation of the water’s bed or bottom.Fill material has the effect of replacing a portion of water with dry land, or changing the bottom elevation of any portion of the waters of the U.S.
and Section 103 of the Marine Protection Act, which regulates transport of dredged material into the ocean for disposal.
“How the activity will deviate from naturally occurring transport events is how we determine if a 404 permit is required,” said Olson. For example, aSection 404 permit is required for discharge of a substantial amount of sediment that will change the ability of the reservoir to hold water.
REGULATING RESERVOIR SEDIMENT
In 2005, the Corps issued Regulatory Guidance Letter 05-04 that settled a question regarding reservoir sediment management.The letter stated thata Section 404 permit is required for sluicing sediment through a dam in a manner consistent with hydraulic dredging and defined this activity as discharge of dredged material.It also stated that a Section 404 permit is required for discharges of sediment from a dam that raises the bottom elevation of downstream waters to a discernable, substantial degree, and defined this activity as discharge of fill material.
The letter also stated that de minimis discharges incidental to normal dam operations and passing sediment-laden water from or through a dam during routine high-water-flow dam operations do not require a permit. In other words, he said, if the sediment load in the water matches the natural yearly variation and can be construed as a normal high flow transport event no permit is required.
In a navigable water, if the sediment changes the water-carrying capacity, it will require a Section 404 permit.
Olson listed the types of permits required for various sediment management approaches.Sediment flushing or sluicing may require a Section 404 and/or Section 10 permit;construction of a sediment bypassing structure may require Section 10 or Section 404 permit; hydraulic or mechanical dredging of reservoir sediments may require Section 10 and/or Section 404 permits depending on how the dredging is done and where the material will be placed; and reducing sediment inputs to a reservoir through watershed best management practices such as check dams or bank stabilization activities may require Section 404 permits.
Permit evaluations are determined by the National Environmental Policy Act, 20 public interest review factors, and Clean Water Act Section 404(B)(1) guidelines for assessing effects of dredged or fill material on aquatic ecosystems.
The final requirement for obtaining a permit for point source discharges into the water is a Water Quality Certification requiring approval by states, tribes, and the U.S. Environmental Protection Agency. Without the certification, the permit will not be issued.
“We hope to issue a supplement to Regulatory Guidance Letter 05-04 to help educate the regulatory staff on regulations affecting reservoir sediment management,” said Olson.Once the letter is issued, the Corps will develop training materials to educate the staff on what reservoir sediment management is, the benefits of it and factors for evaluating permit applications for these activities, he concluded.
TIM RANDLE, Ph.D., P.E., W.RE, retired in April after a 40-year career with Reclamation, and stayed on in a volunteer advisory capacity to design the Reservoir Challenge competition.
“Reservoirs operated by Reclamationirrigate 10 million farm acres, provide drinking water to 31 million people, host 100 million visitors per year for recreation, and create 100 million kW hours of electricity per year,” he said.It is vital to find a method of maintaining the existing water storage capacity.
“If we fail to do anything, the dams will fill and will cost tens of millions of dollars to remove.We need to find a way to sustain them,” he said.
He explained that the competition will interface with a global community of solvers to find an innovative solution to reservoir sedimentation, to identify the most promising ideas and to help develop them.The goal is to connect promising technologies with industrial partners, he said.
“Solutions will be geared toward a commercial application,” he said.
The contest taps the imagination, technological knowledge, and engineering skill of individuals in the soils industry and seeks a method of stopping sedimentation by moving silt downstream instead of letting it settle out in the reservoir.Though the challenge does not call for removing existing sediment, technologies that would regain storage capacity would be of interest if environmentally acceptable, he said.
On September 22, HeroX sponsored an online discussion to describe the contest parameters and to further describe the challenges needed to be addressed.
There are $550,000 in prizes to be awarded.
In Phase 1, submissions are due on October 20, and will be evaluated by the program sponsors.Up to five of the most compelling submissions will receive $75,000 each and advance to the next phase.
Phase 2. December 8, 2020 to February 8, 2022.The top five teams will have 15 months to develop their proposed approaches, perform laboratory-scale demonstrations, and submit a report. The teams will have development support and field-testing opportunities, including assignment to a technical point of contact from Reclamation and 40 hours of access to subject matter experts.
Three winners of Phase 2 will be announced on March 29, 2022, awarded $25,000 and advance to the next phase.
Phase 3.The three chosen during Phase 2 will have nine weeks to prepare a large-scale demonstration for Reclamation, USACE and their partners.
On June 21, 2022, teams will present an overview of their work to Reclamation, USACE and possible commercial partners.The final winner will be announced on June 22 and will receive a $100,000 cash award.
Panelists at the August 24thWebinar were, clockwise from top left, Tim Randle, Greg Morris, Michael Whelan, John Shelley, and David Olson.
Case study: Paonia Dam in Gunnison County, Colorado was built in 1962.The overflow structure in the left photo is 70 feet above the bottom of the reservoir.The picture on the right shows that by 2014, sedimentation near the dam had nearly covered the top of the structure.The reservoir originally held 20,950 acre feet (AF) of water.In 2013, there remained 15,800 AF of storage.Sedimentation is 120 AF per year.