Construction of a drainage channel at Inner Deep Bay, Hong Kong: mitigating ecological and landscape impact through an environmentally friendly design

In order to alleviate a flooding problem of the upper catchment area, it was proposed to construct a drainage channel across the fishponds of Inner Deep Bay which were considered as having high ecological value particularly for wetland birds. The potential loss of 34.6 ha of fishponds, which would be converted into the footprint of the drainage channel, was the major controversial issue of the environmental impact assessment study of the project even though an environmentally friendly design of the channel was proposed as a mitigation measure. Construction works were commenced in 1993 and completed in 1997. Post-construction monitoring of the drainage channel was conducted in 2001 and 2002 and its utilization by wetland birds was reported. The results indicated that the drainage channel with the unlined earth bottom and mangrove plantation provided a favorable habitat for wetland birds especially Ardeids and wintering ducks during low-tide periods. As the channel was connected to the estuary, its ecological function was similar to that of a tidal creek which promoted natural flushing and nutrient recycling. The exposed mudflat during low tide provided an important foraging habitat for wetland birds of the Inner Deep Bay area. The construction of the environmentally friendly drainage channel not only enhanced habitat diversity but also enriched the landscape element of the study area which used to be only fishponds in a homogeneous setting.[PUBLICATION ABSTRACT]