Rivers monitored

Lantau Island is large, and relatively unpopulated by Hong Kong standards. Two major rivers are monitored by the EPD, with a total of eight monitoring stations in all: they are Mui Wo River on the south-eastern side of the island, and Tung Chung on the north-western side.

[Photo of Map of rivers monitored on Lantau Island, showing their Water Quality Index gradings in 2005]

 

The regions through which each of these rivers flow are mainly rural and quite remote, with little human population. In the 1980s, though, there were a number of livestock farms in the Mui Wo area, which formed the main source of pollution. The EPD began its monitoring activities on Lantau when it set up three monitoring stations on the Mui Wo River in 1986. At that stage, the river achieved 72% compliance with the WQO, and all the stations were graded ‘Fair’. In 1988, two further monitoring stations were added to the Mui Wo River. Monitoring of the Tung Chung River began in 1993.

 

The fact that pollution in Lantau rivers was primarily caused by livestock waste meant that the introduction of the Livestock Waste Control Scheme in June 1988 led to major and rapid improvements in water quality. On Lantau, all livestock farms closed down during the 1990s as a result of the scheme.

[Photo of Compliance with the Water Quality Objectives in the rivers of Lantau Island in the 1980s and in 2005]

 

Overflow and seepage from septic tanks and soakaways in unsewered villages, though not such a major problem on Lantau as in other parts of Hong Kong, still contributed to river water pollution. With the establishment of the Southern Water Control Zone in August 1988 (which covers the Mui Wo River in south-east Lantau), the EPD was able to implement the Water Pollution Control Ordinance there and require villagers to maintain their septic tanks properly and treat any effluent before discharging it. The establishment of the North Western Water Control Zone in April 1992 enabled the EPD to do the same for villages in the Tung Chung River catchment area.

[Photo of Water Quality Index gradings for rivers on Lantau Island, 1986 and 2005]

 

By the late 1990s, both rivers displayed highly satisfactory water quality. In 2005, WQO compliance had reached 99%, and the WQI for the two rivers produced 88% of ‘Excellent’ grades and 12% of ‘Good’.

 

 

Mui Wo River

[Photo of Mui Wo River water quality improved significantly after the Livestock Waste Control Scheme was implemented]

Mui Wo River flows down the south-eastern slopes of Lantau and drains into silver Mine Bay. In 1986, its WQI was graded ‘Fair’, and its overall WQO compliance was 72%. By 1989, after the implementation of the Livestock Waste Control Scheme, WQO compliance for the river had risen, and it was achieving a compliance rate of over 95% by the mid 1990s. Its WQI grades also rose, with the three monitoring stations maintaining grades of ‘Good’ or ‘Excellent’ after 1989. The accompanying graph of suspended solids recorded at the MW1 monitoring station on the Mui Wo River makes the improvements after 1986 clear.

[Photo of Suspended Solids concentrations (SS) in the Mui Wo River (MW1)]

 

 

Tung Chung River

[Photo of Monitoring of the Tung Chung River began in 1993]

The Tung Chung River is made up of three main streams. One eastern stream runs through Wong Lung Hang, while two western streams pass through Shek Lau Po and Nim Yuen before entering Tung Chung Wan on the north-western coast of Lantau Island.

 

Monitoring of the Tung Chung River began when the new Chek Lap Kok Airport project near Tung Chung was commissioned, with the aim of checking that the project and related developments in the vicinity would not affect the water quality of the river. Three monitoring stations were selected on the river in 1993, all of which have maintained WQI grades of ‘Good’ or ‘Excellent’ since monitoring first began, along with WQO compliance of over 90%. In 2001, a group of men were arrested and convicted for removing large quantities of rocks from the bank of the Tung Chung River. The culprits were ordered to restore the ecology of the river in addition to being sentenced for imprisonment.