US Army seeks new dredging solutions for reservoirs

The US Army Corps of Engineers will trial water injection dredging (WID) for the first time, while another novel solution is also being considered, in a bid to address sediment build up in its lakes and reservoirs through its deepest dredging contract to date.

Article by Gary Howard, Intent Communications, supplied to SWZ|Maritime by CEDA, ceda@dredging.org

Reservoir dredging poses unique challenges to dredging companies due to access restrictions to often isolated bodies of water, and stringent environmental and water quality requirements.

Many reservoirs have experienced decades of sediment build up, which reduces storage capacity and the surface area of bodies of water often used for recreation as well as flood defence and water storage. The US Army Corps of Engineers (USACE) manages 419 dams and reservoirs, many of which are now experiencing negative impacts of sedimentation after fifty years of using reservoirs with sediment storage pools designed for fifty to 100 years of operation.

The difficulties in reservoir dredging have spurred innovation in the sector, and a search for new technologies to relieve reservoirs of sediment build up after prolonged neglect.

‘Transitioning to a more sustainable use model requires a shift in design and operational strategies for dams and reservoirs that will require the development and application of active sediment management strategies not previously employed in US reservoirs. One such method is water injection dredging,’ says the USACE.

After carrying out lab tests at the US Army Engineer Research and Development Center in Vicksburg, the USACE believes it can use water injection type technologies to move reservoir sediment downstream in a sustainable manner.

Also read: Van Oord christens new water injection dredgers and USV

Dredging’s essential role

Tuttle Creek Reservoir, a 20-mile long reservoir in Kansas, held an open tender for a water injection dredging demonstration to take place in spring 2025 to help address its sediment build up and dwindling water capacity.

The reservoir’s multipurpose pool provides a conservation pool for water supply, fish and wildlife enhancement, recreation, navigation flow support and helps to maintain water quality for downstream communities. It is around 49 per cent full of sediment and without dredging, the forecast is for near total loss of the pool in fifty years’ time.

The plan is to use flushing and sluice gates to create flow through the reservoir, and a water injection type technology to lift the sediment. According to the US Army, it will be the first time WID will be used in a lake. An extra 7.2 feet of water will be stored at the reservoir to offset drawdown from the outflow of nine-day dredging operations three times per year, with flow adjustments to control sediment concentration levels in the outflow during dredging.

Pre-dredging, active, and post-dredging monitoring will take place at five locations on the Big Blue and Kansas Rivers, along with continuous monitoring of water quality and sediment quality, and other analysis of the impact of the novel dredging approach. The primary goals of the demonstration are to quantify how much sediment can be moved by WID, the cost per cubic yard of sediment moved, and the short term downstream effects. Long term downstream effects are among the secondary questions, along with how the findings can be generalised for sediment management at other lakes.

Tiamat, a novel solution

The US Army’s search for dredging solutions has not been limited to traditional WID systems.

‘We’ve recently had the US Corps of Engineers over from America… They first introduced the idea of using Tiamat in reservoirs,’ Jake Storey, chief financial officer at Harwich Haven Authority and executive director of Haven Dredging tell CEDA Industry News.

Tiamat is a dredging technology invented by Harwich Haven Authority harbour engineer Jim Warner, and developed by the authority alongside Birkett Long, Martens en Van Oord, Royal HaskoningDHV, and HR Wallingford. The authority offers Tiamat to dredging organisations, companies, ports and harbours through Haven Dredging Ltd.

The technology can be deployed by a standard workboat and works by pumping water into the seabed, then pumping the agitated sediment up and releasing it into the water column at the appropriate height to be taken away by the tide. The pumping of the sediment into the water column is one of the system’s differentiators.

Cost benefits

With reservoir dredging, often the responsibility of public bodies and utility companies, cost efficiency is a key consideration for any solution. Cost saving is one of the Tiamat’s advertised benefits, cutting asset requirements through its ability to be deployed on a standard small workboat, and saving fuel costs by using natural movement of the water to take sediment away rather than transporting the heavy loads to disposal sites using vessels and barges.

Storey said the team was initially surprised at the potential use of Tiamat in reservoir dredging. They knew from extensive operational experience in Harwich and elsewhere that the system worked better with a strong tidal current to move sediment over long distances, and reservoirs are not known for their strong currents.

The downward slope of the reservoir at Tuttle Creek plays to one strength of traditional WID systems, but Haven Dredging is working with US partners to put forward a bid using Tiamat as the proposed high outflow during dredging will create a moving water column to transport sediment. The tender called for an operational depth of 15 to 90 feet alongside specifics on nozzle sizing, spacing, angle, and a minimum transit speed of 2 knots in operation.

‘The advantage of Tiamat is that you don’t have the long steel arms traditional water injector vessels have, so you can deploy at a greater depth without having a big pontoon to deploy from,’ says Storey.

Also read: SWZ|Maritime’s March 2024 issue: Ports, dredging, and strategy

Proof of concept

‘We think Tiamat can work quite well in a reservoir. However, we’ve not used it in a reservoir, so it is a proof of concept. We feel that trying to use a traditional water injector design in a reservoir would be very difficult. The deepest water injectors go to maybe 30 metres, but the steel and cost would be astronomical in comparison to Tiamat,’ explains Storey.

Tiamat’s maximum operating depth has not been tested, but one theoretical limitation could be pump operation at depth. ‘We use Damen pumps, and Damen has used its pumps in reservoirs down to about 150 metres. It’s basically down to buoyancy and the size of the pontoon, but we think we can cover a huge amount of reservoirs down to 35-40 metres.’

Storey believes the high cost of reservoir dredging projects has prevented any generalisation in approach, and that a change of concept like Tiamat could have a big impact. ‘If we’re successful in this trial then that could open up these markets a lot,’ he says. ‘We think it could be very useful in Taiwan and also Japan, where there are huge issues in reservoirs and availability of water. We’ve had some interest from China because again, they have a lot of reservoirs.’

Picture (top): The USACE has been exploring the use of WID to remove sediment from its reservoirs (photo by USACE, supplied by CEDA).