Replacing Harty and Leysdown Pumping Stations – Delivering resilient infrastructure in a constrained landscape

Harty and Leysdown are two pumping stations located on the Isle of Sheppey in Kent. They serve two low lying catchments that are entirely reliant on pumped drainage. The land they protect includes productive agricultural holdings and internationally designated freshwater grazing marsh, supporting significant populations of breeding and overwintering birds.

Both pump stations were built in the 1970s, and in recent years their reliability had deteriorated significantly. Harty failed during the winter of 2019/20 requiring emergency pumping and a 24 hour site presence for several weeks while levels remained high. The experience underlined what we already knew, continual patch repairs were no longer a sustainable strategy.

Lower Medway Internal Drainage Board had long identified a need for replacement, but funding was a constraint. The Board had prudently built reserves towards the project, yet there remained a substantial shortfall. Although properties exist within the protected catchments, neither scheme could attract sufficient Flood Defence Grant in Aid to make delivery viable under the usual partnership funding model.

The breakthrough came through a successful application to Defra’s Tranche 2B (Asset Improvement) element of the IDB Storm Recovery & Asset Improvement Fund. That funding, combined with the Board’s own reserves, enabled the project to proceed. It is a good example of targeted central support unlocking locally developed schemes that might otherwise remain undelivered for some time.

Working within environmental and physical constraints

At concept stage, several key constraints shaped the approach. Firstly, flood protection had to be maintained throughout the works, with limited space to construct entirely offline replacements. Both sites lie partially within The Swale National Nature Reserve, designated as a Site of Special Interest (SSSI), Special Protection Area (SPA), Special Area of Conservation (SAC) and Ramsar site. The working window for intrusive works was narrow, broadly June to October, subject to ongoing bird surveys. Furthermore, the locations are remote, with constrained access for construction and potential implications for highway upgrades and culvert works.

The core requirements for the new installations were clear: energy efficient pumps with long service lives, adaptability to future climate pressures, safe eel passage, minimal habitat disturbance, and reduced whole life carbon footprint.

Rethinking the traditional approach

Traditionally, replacing a land drainage pumping station involves sheet piling and extensive cast-in-situ concrete works to form pump support structures and working areas. On constrained, environmentally sensitive sites, those activities can drive both programme risk and cost.

The detailed design prioritised minimising site works wherever reasonably practicable. On a remote site with ecological constraints and a narrow working window, reducing plant movements and construction activities lowered delivery risk and cut embodied carbon through reduced material and temporary works requirements.

For Harty and Leysdown, the design team – Stantec, working collaboratively with ACE, and precast supplier JKH, developed a prefabricated concrete support structure. The units were designed specifically around the selected pumps and auxiliary equipment, modularised for transport and assembled on site.

Once the concept was fixed, foundations were designed in collaboration with Breheny Civil Engineering. Cased concrete piles were installed using a small piling rig, which allowed the foundations to be delivered with minimal plant machinery. Beyond that, the civil works were deliberately modest: minor earthworks, scour protection, a control kiosk, electrical ducting, drainage, fencing, and hardstanding.

Works commenced in June 2024 following ecological clearance and resolution of power supply issues. Foundations were installed first. Both prefabricated support structures and pumpsets were then installed within a three-week period. Civil works were completed by October 2024, exactly four months from commencement, comfortably within the ecological window. Residual mechanical & electrical works followed, and both stations were brought online in November. Crucially, flood protection was maintained throughout, with no requirement for emergency pumping during the works.

Cost and carbon outcomes

Early cost comparisons indicated that the prefabricated approach to the pump support structure was approximately half the cost of a cast-in-situ equivalent. The savings were driven by reduced material quantities. In addition to the savings associated with reduced construction materials, there were substantial cost and carbon savings associated with the avoidance of: infrastructure upgrade works, temporary works including dewatering, a prolonged site presence, and the associated contingency risks. Environmental and flood risks were also greatly reduced.

Modern pumping technology

Both stations are equipped with modern screw pumps selected for their fish-friendly design, and the new installations incorporate variable speed drives and telemetry, providing far greater control of water levels, and enabling a more energy-efficient pumping regime. For an IDB operating increasingly complex water management duties, that level of operational control is invaluable.

A model for wider adoption

There are many low to medium capacity pumping stations across the country facing similar challenges: ageing assets, constrained sites, environmental sensitivities, and limited funding. The approach taken at Harty and Leysdown demonstrates that modern methods of construction, combined with early contractor collaboration, can materially change the delivery model.

Projects can be delivered more quickly, with lower capital cost, and reduced whole-life carbon, while maintaining environmental safeguards and operational resilience. For IDBs managing entirely pumped catchments, where asset failure carries immediate consequences, accelerating replacement programmes in a cost-effective way is essential.

For the newly amalgamated North Kent Marshes Water Level Management Board, this scheme represents more than a like-for-like replacement. It marks a shift in delivery philosophy; one we intend to refine as lessons are embedded into future projects. With improved control and telemetry now in place, the next logical step is to work more closely with landowners to optimise how water is retained and reused within the catchment, making better use of the resource that is being pumped while maintaining flood resilience.

In a funding landscape where every pound must work harder, innovation in design and construction is not optional. It is fundamental to maintaining resilient water level management in our most vulnerable landscapes.

The success of this approach was recognised, when the project was shortlisted for the Best Project – Innovation category in the Institution of Civil Engineers (ICE) South East Engineering Excellence Awards 2024. It highlights how modern methods of construction and collaborative design can reshape delivery of relatively modest, but operationally critical, drainage assets.

Within a month of completion, water voles had returned to areas around both pumping stations, a quiet but welcome sign of aquatic life continuing alongside essential infrastructure.

 

 

By Priscilla Haselhurst, Chief Officer, North Kent Marshes Water Level Management Board – First published in the ADA Gazette, Spring 2026

For more information about North Kent Marshes Water Level Management Board, or to follow and support their work, visit their website at www.northkentwlmb.org.uk

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