4 minute read
Hartlepool Headland Coastal Protection
Hartlepool, England, United Kingdom
Placing rock features strategically for complex habitats. Hartlepool, an internationally important site for waterbirds, is the site of the first known engineering project that used passive ecological enhancement techniques on a rock revetment. The project combined passive and active multiscale ecological enhancements, such as careful positioning of the rocks in the revetment construction and the use of textured form liners to cast the wall panels, both of which provided key habitats for intertidal prey species. Within just two years of project completion in 2018, the area has shown a significantly higher biodiversity. The project proves that simple, inexpensive methods with little change in cost or procedure will improve ecological outcomes of hard engineering structures. The project now serves as an example for the Environment Agency’s replacement coastal engineering scheme based in Elmer, England, which uses optimal rock types, the positioning of natural features, and the selection and positioning of rocks with quarrying features such as blastlines and blastholes to mimic natural habitats. These methods increase the local population of intertidal species such as limpets (Patella vulgata)— and the oystercatchers (Haematopus ostralegus), redshanks (Tringa tetanus), turnstones (Arenaria), and red knots (Calidris canutus) that feed on them.
Producing Efficiencies
The University of Glasgow provided biogeomorphology guidance on the most ecologically optimal granite: the lightest granite with the coarsest grain and the greatest number of decimeter-to-meter scale features, such as concavities and ledges. The project team used limestone to fill the void spaces in the granite, but the natural limestone along the rocky shore itself was far too difficult and expensive to procure. Instead, the team locally sourced a darker limestone, increasing the long-term ecosystem potential by providing a boreable material for micro- and macroboring species such as cyanobacteria and limpets.
Using Natural Processes
The team maximized available habitat space by carefully selecting, orienting, and modifying topographically complex rocks to mimic natural rocky shore geomorphology. During construction, the project team trained the lead installer to identify features such as depressions, concavities, and ledges that increased the complexity and water-holding capacity of natural rock boulders. Installing the rocks with depressions that faced sufficiently upwards and horizontal trapped water during low tide, which mimicked natural pools. Placing the rocks to create overhangs established shelter from the sun or waves. These measures improved the habitat value of the revetment rocks, increasing limpet abundance compared to nearby rocks without these features.
Broadening Benefits
Changes made to the conventional design broadened the revetment’s engineering and environmental benefits. The flattened top and strengthened base make it more adaptable and better able to withstand future sea-level rise and climate-change pressures since future rock layers can be added to address these challenges. The various enhancements to the rock revetment created no significant increase in construction or long-term costs while increasing the ecological value of the conventional scheme, adding habitat for intertidal prey species and encouraging biodiversity in an internationally designated bird habitat.
Promoting Collaboration
Altering the original design to include passive ecological enhancement was pivotal to securing timelimited funding for the engineering scheme, a grant-in-aid for flood defense through the UK government’s Environment Agency. A team spanning many sectors worked together to design the installation, combining the expertise of Mott MacDonald, the University of Glasgow, the Hartlepool Borough Council, PD Ports, Hall Construction, and Poundfield Products. Further, the Hartlepool Council and PD Ports provided additional funding to the scheme. The support and collaboration resulted in multiple construction excellence awards, including for innovation, value, and sustainability.
