Rock armour for birds and their prey: ecological enhancement of coastal engineering

Abstract

The authors present key design, construction and ecological enhancement criteria for sustainable coastal defence structures at Hartlepool, UK, a high-energy wave climate. Such 'ecologically favourable' coastal defences fulfil the habitats directive and key engineering and cost criteria. Bird, rocky intertidal ecological and biogeomorphological data underpin recommendations for 'passive' enhancement mitigation to maximise ecological potential involving rock armour material choice (partially enhanced) and its smart positioning (enhanced). Within 12-18 months of installation, key intertidal species (e.g. limpets, barnacles, fucoid seaweeds) had successfully colonised the rock revetment, matching the initial baseline biotope. However, species abundance and overall mobile and sessile species were not significantly different between the two enhanced treatments after 12-18 months. Importantly, key prey species (the limpet, Patella vulgata) on enhanced rock armour showed statistically significant abundances similar to the baseline shore platform and significantly higher than partially enhanced rock armour. These preliminary data show that well-chosen rock armour material and boulder enhancement using positioning can match baseline biotope conditions in 12-18 months and that for some key prey species, positioning-enhanced rock armour rapidly matches baseline conditions. This facilitates rapid rock revetment colonisation, enabling good recruitment of food species and favourable conditions for internationally designated waterbird species.

Hard Structures for Coastal Protection, Towards Greener Designs

“…As with foreshore structures, smooth surfaces, such as concrete, should be avoided as far as possible (Wiecek 2009;Firth et al 2014;Coombes et al 2015) or can be made rougher by casting irregular finishes (Wiecek 2009) or by chiselling grooves or drilling holes (Martins et al 2010;Nordstrom 2014;Hall et al 2018). Naylor et al (2017) showed how a rock revetment can be ecologically enhanced by informed selection and intentional positioning of armour rocks. Rock pools can be incorporated in seawalls to provide habitat for intertidal organisms by adding water-retaining features (Chapman and Blockley 2009;Firth et al 2016b;Chapman and Underwood 2011;Firth et al 2014).…”

From ocean sprawl to blue-green infrastructure – A UK perspective on an issue of global significance

“…Despite a wealth of proof-of-concept evidence, a clear policy pull and cross-sectoral support (all discussed in 1.2 and 1.3 above), there have been few examples of non-research-driven implementation of blue-green artificial structures in the UK (but see Naylor et al, 2017b), or indeed globally (but see Harris, 2003;Perkol-Finkel and Sella, 2016;Scyphers et al, 2015;Toft et al, 2013). So what are the barriers that remain?…”

“…We are beginning to see the start of a gradual shift from research-driven experimentation to practice-driven implementation. Naylor et al (2017b) report an example of practice-driven implementation of ecologically-sensitive design in a coastal defence scheme in the northeast of England. The implementation was driven by the local authority and regulators, who sought advice from the researchers.…”

“…using alternative construction materials and installing retrofit rock pools). This was reportedly based on cost implications (Naylor et al, 2017b). Further examples of the shift from research-driven trials to practice-lead implementation in the UK have stemmed from experiments undertaken by Hall (2017) and Hall et al (2018).…”

Present-day use of an empirical wave prediction method

“…The final paper by Naylor et al (2017) shows how relatively low cost changes to traditional hard engineering solutions can greatly enhance its biodiversity value. The work presents detailed ecological information to show how the proposed solution performed.…”