2020/07/29
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Threats to Natural Streams and Rivers

 

Deterioration of Water Quality

 

Good water quality is essential for all aquatic life. One of the major threats faced by Hong Kong’s stream organisms is the possible deterioration of water quality owing to the discharges of agricultural, industrial, construction or domestic waste from development and human activities. Stream fauna that are sensitive to water quality changes could be affected by the deterioration of water quality.

A polluted stream

 

Developments

 

Developments of new towns and infrastructures in the rural areas often change the land uses around the streams/rivers in these areas. Streams and rivers may have been turned into channels and culverts or even filled up for development. As different species have different habitat requirements for its survival and reproduction, alteration of aquatic habitats, such as silting up of a gravel stream bed, will change the species composition and abundance of aquatic organisms.

 Development next to a natural stream

 

River Training

 

To protect human lives and properties, river training works have been carried out in certain natural streams/rivers mostly downstream in the past to increase their hydraulic conveyance capacity for flood control. The streams/rivers were often “improved” by conventional methods such as widening, deepening or straightening, and their banks were mostly constructed of hard lining materials such as concrete. These engineered channel works might have unavoidably caused alteration or destruction of natural streams/river habitats which would drive away most of the original fauna and flora.  In addition, some of these streams/rivers might have already lost their ecological importance due to the development of human activities in the vicinity over the years.

 Old river channel constructed by conventional method

 

 

In recent years, efforts have been made by concerned departments to incorporate as much as practicable ecological considerations and measures in its design of river channels and floodways. Examples include the use of different types of grassed lining for river embankments and bed; creating 2 stage channels with intermediate platform; creating curves and aquatic planting bays/ponds in the channel; creating marshland and ecological reed beds as compensatory measures; preservation and enhancement of old river meanders as wetland. Green Groups were also involved and consulted in a number of cases in the design on ecological aspects.

 Sheung Yue River Channel completed in recent years

 

Unauthorized Damage/Destructions

 

Natural stream would sometimes be damaged by unauthorized works or unintentionally by development in the vicinity. For instance, a section of the lower course of the TungChungStream was found tampered with by some private individuals in late 2003. The streambed was excavated to a large extent and boulders and pebbles on the streambed were removed. The stream flow was impeded by earth filling activities along the river and the remaining flow inside the stream was filled with sediments. The stream section and riparian habitats were damaged severely. The incidence attracted wide public attention and the tampered stream section has been reinstated subsequently. The offenders have also been prosecuted.
 

 The tampered section of Tung Chung Stream, November 2003

 

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