SAVING OUR SALTMARSHES

The decline of saltmarsh habitats in the United Kingdom is a significant environmental concern, with multiple factors contributing to their loss and degradation. The expansion of coastal cities, towns, and infrastructure, such as roads and sea defences, has led to the direct loss of saltmarsh areas. Now, civil engineering and environmental firm, Land & Water, alongside sister company Earth Change, is leading the charge to help restore these vital ecosystems.

This award-winning business, founded more than four decades ago by Chairman, Richard Melhuish, and Chief Executive Officer, James Maclean, is made up of people who are passionate about creatively and sympathetically delivering effective solutions for the maintenance and management of the UK’s coastal, canal, and river networks. Over the years, it has designed equipment specifically to solve complex engineering challenges.

Historically, many saltmarshes in the UK were reclaimed for agriculture, industry, and urban development.

This practice has significantly reduced the extent of saltmarsh habitats. As sea levels rise due to climate change, saltmarshes are caught between advancing seas and fixed coastal defences, such as sea walls. This ‘coastal squeeze’ prevents the natural inland migration of saltmarshes, leading to their erosion and loss.

Dams, regular dredging of ports, docks, harbours, and marinas, and other human activities have altered the natural flow of sediments to coastal areas, reducing the ability of saltmarshes to accumulate sediment and keep pace with rising sea levels. Since 1945, over 60% of the saltmarsh habitats around the UK have been lost, and without some inspired interventions, significant further losses will continue.

Saltmarshes not only serve as breeding and nursery grounds for a variety of marine species, including fish, crustaceans, and shellfish, but they act as natural buffers, absorbing wave energy and reducing the impact of storm surges and coastal erosion. This helps protect coastal communities and infrastructure from flooding and storm damage. They trap and stabilize sediments, which helps maintain and build up the coastline, preventing land loss and contributing to the overall stability of the coastal ecosystem.

“Land & Water, alongside sister company Earth Change, is leading the charge to help restore the UK’s declining saltmarshes…

But restoring saltmarshes within an intertidal habitat is not straightforward. The large barges and ships used in commercial dredging operations cannot directly access the shallow waters and mudflats where saltmarsh proliferates.

Historic attempts to place sediments on failing saltmarsh have relied on pumping liquid sediments between the dredgers and the saltmarsh. The need to liquefy the sediments for pumping ultimately releases dirty water onto the saltmarsh, which has high environmental impacts and requires costly, unnatural retaining structures. However, Land & Water, together with sister company Earth Change, is using a modern take on old technology to overcome those challenges.

RESTORATION DRAG/DREDGE BOX

Back in the days of steam engines, drag or dredge boxes, as they were known, were used to dredge lakes by dragging silts between traction engines across sites to disposal areas. The dredge box ran on skids across the softest of ground conditions. It had no bottom but solid sides and a tailgate that pulled shut going forwards and opened in reverse. There really wasn’t a better solution for moving material across land where normal equipment couldn’t travel.

The UK dredges approximately 20 million tonnes of silt and mud a year maintaining ports, harbours, and marinas. The majority of this material is disposed of offshore, in designated disposal sites, but now Land & Water has borrowed modern hydraulic winching technologies from the Canadian Forestry Industry, coupled with a new and enlarged drag/dredge box design to get large quantities of sediment onto marshes that are eroding and drowning – and in very short timescales, with negligible environmental impact.

The first full-scale trials of this re-invented technology, permitted by the MMO (Marine Management Organisation), were successfully completed last year when Land & Water, and Earth Change, partnered with Chichester Harbour Conservancy as part of the Solent Seascape Project to restore the saltmarsh in Chichester Harbour. Land & Water has now applied for a patent for this method of dredging and restoring saltmarsh.

Commented James Maclean, CEO of Land & Water and co-founder of Earth Change along with Tom Godfrey: “This exciting new development shows how we can reuse materials from one industry in a positive way to increase the value of our nation's Natural Capital. Our works are being underpinned by a team of national experts, and we are delighted to have worked with a wide group of stakeholders to unlock this concept.

“Helping nature to help itself is hugely gratifying, and finding an opportunity to provide an alternative beneficial reuse of what is usually a waste material that would previously be disposed of at sea is a truly circular economy concept at work.”

"Modern hydraulic winching technologies, coupled with a new dredge box design, used to move large quantities of sediment on to eroding and drowning saltmarshes..."

When we caught up with the team at Land & Water, work similar to that carried out at Chichester Harbour was taking place to help restore saltmarsh on the Solent Estuary near Lymington Harbour on the Hampshire coast in the South of England.

Lymington Harbour and Boiler Marsh, in particular, have a very high nature conservation value and are highly protected. But they have also lost more than 50% of their saltmarsh since 1945. Similarly, worrying levels of decline in saltmarsh have been documented around the Solent and other sensitive estuaries in the UK.

SPECIALIST EQUIPMENT

At Lymington, Land & Water were employing two 25m long pontoons, several ultra-low ground-pressure amphibious excavators, a multifunctional amphibious Truxor machine used as a service vehicle, and, of course, the specially designed dredge box utilising a dual winch supplied by R J Fukes Forestry Services, which was being operated between the two pontoons.

The dual winch allows the dredge box, which can hold over 15 tonnes of material at a time, to run off a pulley and can then be travelled forwards and backwards from the single winch. As the pull line is returned to the winch, the return line is paid out, and vice versa in the opposite direction.

Land & Water had positioned a spud pontoon with a small service crane out beyond the dump area just off the saltmarsh. The pontoon had the winch pulley on an adjustable rail mounted to it, and 400m away, on the other side of the saltmarsh, was a second spud pontoon with a Hitachi ZX 250 excavator on which the winch was mounted.

The winch pulled the dredge box over the dumped dredgings, and with an adjustable tailgate, silt was dragged the 400m up onto the old marsh to the desired height. The pontoons were repositioned as necessary to allow all the dredgings to be pulled into final position, usually during high tides, with the final height being graded by an amphibious excavator from Land & Water’s remarkable fleet of specialist plant machinery.

PUBLIC AWARENESS

This project, along with other undertakings by Land & Water and Earth Change, is helping to increase public awareness about the importance of saltmarshes, and involving local communities in conservation efforts is crucial for the long-term protection of these habitats.

As we mentioned, the decline of saltmarsh habitats in the UK is a complex issue driven by both natural and human-induced factors. However, through a combination of restoration efforts, managed realignment, and protective legislation, there are opportunities to halt and even reverse the decline of these crucial ecosystems. Going forward, Land & Water, with its evolving technology such as the Saltmarsh Restoration Drag-Box, will remain at the forefront of this vital work.