Committing to conserving the habitat at Lam Tsuen River
During Chinese New Year, many people will visit the “wishing trees” and Tin Hau Temple in Lam Tsuen, Tai Po. But do you know about the Lam Tsuen River nearby? Its upstream is one of the some 30 ecologically important streams in Hong Kong, providing habitats for rare wildlife species, such as the Hong Kong Newt. Given the extraordinary conservation value of Lam Tsuen River, the Drainage Services Department (DSD) has been committed to conserving the river ecosystem while undertaking river improvement works in Upper Lam Tsuen River to alleviate flood risk in the region. Recently, accompanied by the Director of Drainage Services, Mr Edwin TONG, I visited the Lam Tsuen River to learn more about the achievements of the conservation measures adopted in the project.
Lam Tsuen River stretches 10 kilometers from Tai Mo Shan, running through Ng Tung, Lam Tsuen Valley, Tai Wo and Kwong Fuk before discharging into Tolo Harbour. In the 1990’s, the Lam Tsuen River Valley was susceptible to flooding during heavy rainstorms. After detailed planning, the DSD conducted the “River Improvement Works in Upper Lam Tsuen River” by straightening, widening and deepening 2.6 kilometers of the upper river between 2007 and 2012 to enhance drainage capacity. A series of conservation measures were put in place during the design, construction and post-construction stages to preserve the original course of the stream, maintain biodiversity, and to minimise the environmental and ecological impacts brought by the works.
Appropriate conservation measures to restore the original habitats
On the day of our visit, the river was so clean that the riverbed could be seen with fish swimming in the streams, and birds were staying on the boulders. Engineer of the DSD, Mr Marcus CHENG, said in the design of the works, the DSD endeavoured to retain the river’s natural habitat. For example, the excavated in-situ soil and rocks on riverbed were temporarily stored off site during river deepening and were put back onto the river upon completion of works. Besides, gabion walls were used to fortify the river banks instead of concrete. This allowed plants to grow between the rocks, and trees were planted back at the banks on both sides of the river.
Mr Marcus CHENG specially introduced the zigzag fish ladders designed by the DSD. The idea of the design came after the DSD discussed with green groups. At present, there are three fish ladders in the upper course of Lam Tsuen River. The fish ladders are laid in the reaches with steeper gradient to allow fish and other creatures to swim or leap upstream. The fish ladders also provide recesses which offer fish and other creatures places to rest on during their journey upstream.
Increasing populations of wildlife species
The Lam Tsuen River is a breeding site of the Hong Kong Newt, Paramesotriton hongkongensis, classified as “Near Threatened” by the International Union for Conservation of Nature. Pre-construction capture surveys were conducted by the DSD. Endemic Hong Kong Newt and other fauna species in the affected channel section were relocated to other parts of the river prior to work commencement. According to the monitoring data, it was demonstrated that after the works, the newts migrated back to the original sections of river channel.
Meanwhile, the DSD has appointed an ecological consultant to conduct four years of post-construction ecological monitoring, which was completed at the end of 2017. The results show that the numbers of wildlife species including birds, fish and dragonflies has returned to pre-construction levels. The number of newts in the Lam Tsuen River is higher than before as it increased from 200 in the pre-construction baseline monitoring to more than 500 lately. It is testimony to the success of the project team’s ecological conservation measures. The result is encouraging. That day, the ecology consultant of the DSD, Dr Mark SHEA, were present on site to observe the newts and found that they were in good health.
Continuing with river channel revitalization
Apart from Upper Lam Tsuen River, the DSD has successful experiences with river channel revitalization, including the improvement works for Pak Ngan Heung River and Luk Tei Tong Bypass Channel in Mui Wo. The department also incorporates green, natural and ecological features into the current works at Kai Tak River in Wong Tai Sin in order to transform it into an urban green river corridor.
In order to make Hong Kong a better city to live, the DSD continues to maintain efforts to revitalize river channels across the territory in the years ahead. Since the end of 2015, the DSD has commenced a consultancy study on revitalizing the water bodies in 228 major river channels in Hong Kong which will build up a database of the river channels, including river channel features, geographical location and ecological features, etc. The revitalization potential of channels will be assessed systematically based on more than 10 criteria including the environment, social and economic benefits.
At present, the initial result has identified four rivers with high revitalization potential for further in-depth studies, including Tai Wai Nullah, Fo Tan Nullah, mid-stream of Tuen Mun River and Jordon Valley Nullah. In order to integrate the idea of revitalization into the community and gain public support, local residents, district councils and green groups will be consulted. We hope we can share more stories of river revitalization in the near future. Let’s join hands to protect the ecological environment for wildlife species to co-live and prosper.
25 February, 2018