The “living seawalls”
I introduced the latest progress of near-shore reclamation of the Tung Chung New Town Extension in My Blog some time earlier, and mentioned that the project adopted eco-shorelines for the first time in the extension area with an objective to further conserve the ecological habitats and enhance biodiversity. The Civil Engineering and Development Department (CEDD) is working in partnership with The University of Hong Kong (HKU) to conduct a feasibility study by introducing eco-shoreline features at the seawalls in Sai Kung, Lung Kwu Tan in Tuen Mun and Ma Liu Shui in Sha Tin for field trials. This time, I have invited a colleague from the CEDD and a professor from the School of Biological Sciences at HKU to introduce the details and initial findings of the study.
Mimicking the physical conditions of natural inter-tidal zones
In general, artificial shorelines consist of vertical seawalls or rubble mound seawalls, of which the materials are mostly concrete and granite with smooth surfaces that are unfavourable for allowing organic matters and micro-organisms to attach and grow. Artificial shorelines also lack the habitats that are commonly found in natural rocky shores, such as rock pools and crevices. Therefore, the inter-tidal marine life may die from dehydration or heatstroke during a hot afternoon at a low tide, leading to relatively low biodiversity on the seawall.
Senior Engineer of the CEDD, Mr LEE Chi-kin, Clive, says the adoption of eco-shorelines aims to mimic the physical conditions of natural inter-tidal rocky shores as far as practicable for retaining seawater and offering shade and holes in order to provide a suitable habitat and shelter for the inhabitation and growth of marine species to enhance biodiversity and create a “living seawall”. Besides, eco-shorelines can provide a good leisure place for the public and tourists, and can also facilitate environmental education and scientific studies.
Selected trial locations for the study belong to different water bodies
Since Hong Kong has little experience in adopting eco-shorelines, CEDD would like to carry out field trials to study the effectiveness of adopting eco-shorelines to promote marine ecology and biodiversity on artificial shoreline. The selected trial locations for this study at Sai Kung, Ma Liu Shui and Lung Kwu Tan in Tuen Mun are identified as oceanic, semi-enclosed and estuarine types of water bodies respectively. Such arrangement helps assess the feasibility of application and development of eco-shorelines in different types of water bodies in Hong Kong. The study, including two-year on-site monitoring, commenced in January 2018 and is expected to complete at the end of 2021.
Testing various components for “eco-seawalls”
According to Professor LEUNG Mei-yee, Kenneth, of the School of Biological Sciences of HKU, field monitoring has been conducted since March this year. Various components for “eco-seawalls”, including ecological armouring units, oyster baskets, tidal pools and enhanced seawall panels, are being tested.
Mimicking the physical properties of natural rocky shores such as cavities, cracks and uneven surfaces, ecological armouring units are for the inhabitation and feeding of marine organisms. Bivalve shellfish, such as oysters and mussels, are placed in the oyster baskets. As such shellfish feed on suspended microalgae and organic matters in seawater, they help purify the water body. The pit at the centre of a tidal pool can retain seawater during low tides, which can prevent marine species from dying of dehydration due to long exposure to the sun. The uneven and rather rough surfaces of the enhanced seawall panels can facilitate the growth of microbial films and microalgae.
Study showing encouraging initial results
Professor Kenneth LEUNG says to us that the field monitoring of the first six months of the trials has shown encouraging initial results. Quoting the initial data collected during the field monitoring conducted at the Ma Liu Shui trial site as an example, he says that 11 types of species, including algae, coralline algae, crabs and various kinds of gastropods (e.g. cowries), have been found to have settled on some of the “eco-seawall” components. As these species are not found at the neighbouring vertical or rubble mound seawalls, the results show that the components have effectively created new habitats that can enhance biodiversity and promote ecological functions.
The Government has always attached great importance to maintaining a balance between development and environmental protection. There are successful overseas examples of eco-shoreline implementation. For instance, the large-scale eco-shoreline at Sydney’s Barangaroo Reserve, Australia, and the eco-seawall at Haifa Bay, Israel, have both effectively enhanced biodiversity at the local seashores. I hope that, in the near future, eco-shorelines can serve multiple purposes - not only can they protect the shores from waves, but also facilitate conservation of coastal ecosystem and promote a water-friendly culture to the public.
8 December, 2019