Rivers monitored

The Southwestern New Territories and Kowloon area runs in a wide sweep from Black Point west of Tuen Mun right through to the eastern end of Victoria Harbour. Of the five rivers monitored, Tuen Mun River is in the vicinity of Tuen Mun, Pai Min Kok Stream and Sam Dip Tam Stream are near Tsuen Wan, Kau Wa Keng Stream is in Kwai Chung and the Kai Tak Nullah in Kowloon.

	Map of rivers monitored in the Southwestern New Territories and Kowloon, showing their Water Quality Index gradings in 2005

General survey

The wide geographical range of the Southwestern New Territories and Kowloon area means that each of these five rivers has quite different characteristics and historical problems. The Tuen Mun River is a major watercourse that in the 1980s suffered from a wide range of pollution sources, including effluent discharged from livestock farms, unsewered villages, cottage industries, and expedient connections. Further east, the Pai Min Kok Stream running into the sea at Angler’s Beach was primarily affected by livestock waste, while the Sam Dip Tam Stream, closer to Tsuen Wan, was moderately polluted by industrial effluent. Continuing east, the Kau Wa Keng Stream was largely affected by expedient connections, as was the Kai Tak Nullah, classified as a major urban storm channel rather than a stream.

Overall WQO compliance in 1986 stood at 49%. This statistic, as with all the overall figures cited in this chapter, excludes the Kai Tak Nullah because, as a storm channel, it is not subject to WQO compliance. As for the WQI gradings in 1986, only 13% of monitoring stations were graded ‘Good’ (and none ‘Excellent’). ‘Fair’ gradings were recorded for 7% of stations, but the bulk of the gradings were either ‘Bad’ (47%) or ‘Very Bad’ (33%). To reduce pollution in these watercourses, a number of measures were taken in the 1980s and 1990s with the aim of improving water quality.

	Compliance with the Water Quality Objectives in the rivers of the Southwestern New Territories in the 1980s and in 2005

The major initiatives that led to water quality improvements were those already discussed throughout this report: the implementation of the Livestock Waste Control Scheme in June 1988, and the enforcement of the WPCO as new Water Control Zones were set up. The North Western WCZ was established on 1 April 1992, covering Tuen Mun; the Western Buffer WCZ was established on 1 June 1993 and covered western Tsuen Wan; the Victoria Harbour (Phase I) WCZ was established on 1 April 1994, covering Tsuen Wan and Kwai Chung; and the Victoria Harbour (Phase II) WCZ was established on 1 September 1995, taking in Kowloon. In addition, the implementation of Sewerage Master Plans across these areas from the 1990s has further helped bring down river water pollution.

	Water Quality Index gradings for rivers in the Southwestern New Territories and Kowloon, 1986 and 2005

By 2005, overall WQO compliance had risen to 88%, and major improvements were also evident from the WQI results. In that year, 28% of monitoring stations were graded ‘Excellent’ and 66% ‘Good’. Just 6% were graded ‘Bad’, and none were graded either ‘Fair’ or ‘Very Bad’. The turnaround has been very substantial. However E. coli levels in the area’s rivers and nullah were still high in 2005, especially in the upstream part of the Tuen Mun River (TN1), where the annual geometric mean was 240,000 cfu/100 mL due to bacteriological pollution from unsewered villages. The situation should improve once the Government’s plans to provide public sewers to the villages in the area are put into effect.

Case study #1: The Tuen Mun River

The Tuen Mun River no longer suffers from livestock waste pollution

The Tuen Mun River is the major river of the Tuen Mun district, flowing southward from Lam Tei through a relatively narrow valley into Tuen Mun town centre and past the Tuen Mun Typhoon Shelter into the sea. It has a total catchment area of 17 square kilometres.

In the late 1980s the river was severely polluted, with pollution being worse upstream than downstream. The two upstream monitoring stations were both graded ‘Very Bad’ at this period, while the downstream stations were graded ‘Bad’ as they were further away from the pollution sources.

Ammonia Nitrogen concentration (NH3-N) in the Tuen Mun River (TN1)

The first problem to be dealt with was livestock effluent. The Livestock Waste Control Scheme of June 1988 led as elsewhere to a rapid decline in the pollution load from livestock farms operating in the catchment area. By the early 1990s most farms had already gone, and by 1996 none remained. The graph shows the effects of the scheme on reducing typical pollution caused by livestock waste.

The North Western Water Control Zone was declared on 1 April 1992, upon which the EPD began enforcing the provisions of the WPCO in the area. Most of the expedient connections in Tuen Mun town centre were removed over the next couple of years as a result, as factories were required to provide proper treatment to their waste.

The accompanying graphs show two parameters relating to industrial and sewage pollution respectively. The first illustrates the reduction in chromium pollution from industry as a result of WPCO enforcement in the early 1990s. The second shows reduction in E. coli levels since the late 1990s following WPCO enforcement and the completion of various sewerage projects along the river, such as the construction of a dry weather flow interceptor near Tseng Tau Tsuen, improvements to the interceptor near Siu Hong Court, and the replacement of faulty sewers.

Chromium concentration (Cr) in the Tuen Mun River (TN3)

E. coli levels in the Tuen Mun River (TN5)

By 2005, WQO compliance had risen to 83% and five of the six monitoring stations on the river achieved gradings of ‘Good’ or ‘Excellent’. One particularly happy side-effect of the rise in river water quality was the subsequent improvement of water quality at the picturesque beaches on the coast near Tuen Mun, which became safer and more pleasant to swim at. One of these beaches, Castle Peak Beach, had been closed for over twenty years primarily because of its poor water quality, but was finally reopened in 2005.

The one blemish on this record was the grading of the monitoring station furthest upstream (TN1). Its ‘Bad’ grade and high recorded E. coli levels (240,000 cfu / 100 mL) reflected the continued presence of unsewered village houses in the vicinity. The Tuen Mun Sewerage Master Plan and its Review, however, lay out plans to provide public sewers to over 40 villages around Tuen Mun over the next decade, so further improvements are expected.

Case study #2: The Kai Tak Nullah

The Kai Tak Nullah runs through the densely populated Southeastern Kowloon area

The urban area of Kowloon, as on Hong Kong Island, contains few natural watercourses. Most have over time been covered and converted into storm drains. The Kai Tak Nullah is also a storm channel situated upstream of the old Kai Tak Airport in south-east Kowloon. Its catchment includes some densely populated areas such as San Po Kong, Diamond Hill, Tsz Wan Shan, Wong Tai Sin and Kowloon City. It suffered severe pollution in the 1980s from large numbers of expedient connections from factories, raw sewage emanating from nearby squatter huts, and overflows from old and overloaded sewers. All six monitoring stations recorded grades of ‘Bad’ or ‘Very Bad’ in the late 1980s and early 1990s.

Improving the sewerage situation was the first step in cleaning up the Kai Tak Nullah. Various sewerage works were outlined in the East Kowloon and North & South Kowloon Sewerage Master Plans drawn up for the area, and these began to be carried out in the 1990s. They included construction of a number of dry weather flow interceptors along the nullah to intercept polluted storm flow, along with the replacement of worn-out and often overloaded sewerage facilities. This period also saw the clearance of some squatter areas in the catchment, reducing the quantity of untreated sewage flowing into the nullah.

The Victoria Harbour (Phase II) Water Control Zone was declared in 1995, and this in turn enabled the EPD to begin the task of identifying and removing expedient connections that were polluting the nullah. The job was by no means easy given the dense population in the area, the complex tangle of drainage connections and misconnections, and resistance from some long-standing polluters.

In December 2001 the EPD’s Regional Office (East) launched “Operation Starfish”, establishing a team specifically to address the pollution problems in the nullah. Over the following years, the team systematically combed the catchment for misconnections, carried out investigations, initiated enforcement action against polluters where necessary, and worked closely with the property management sector to improve the situation.

First to be targeted were old residential buildings and squatter areas. The team carried out three drainage surveys and four closed-circuit TV surveys covering extensive areas. Dye-tracing was used to track misconnections back to where they originated, and the EPD also cracked down on illegal back-lane dishwashing at food stalls and restaurants. The task required patience and perseverance, as EPD staff traced misconnections along tangled downpipes and under manhole covers, facing occasional hostility from building owners. Operation Starfish ended up identifying some 90 misconnections, and to date it has overseen the rectification of over 90% of these.

Chemical Oxygen Demand (COD) in the Kai Tak Nullah (KN4)

Interestingly, the Kai Tak Nullah has also benefited from a scheme that was primarily designed to reduce marine water pollution many miles away. The Tolo Harbour Effluent Export Scheme began in 1995 as a move to improve water quality in Tolo Harbour by redirecting treated sewage effluent from the Sha Tin and Tai Po Sewage Treatment Works away from the harbour. This redirected treated effluent was piped to the Kai Tak Nullah for discharge where it brought new benefits. The greatly increased flow in the nullah enhanced water aeration and improved the nullah’s flushing ability, leading to better water quality overall.

At the end of 2003, the dry weather flow interceptors that had been installed along the Kai Tak Nullah were upgraded and turned into an enclosed conduit that helped reduce the odour problem. Since then, polluted storm flow has been intercepted and channelled along the enclosed conduit to receive proper treatment at sewage treatment facilities.

By 2005, the six monitoring stations in the Kai Tak Nullah had all improved substantially, recording WQIs of either ‘Good’ or ‘Excellent’. These grades were further boosted by the recent upgrading of the Sha Tin and Tai Po Sewage Treatment Works, which meant that the exported treated sewage flowing through the Kai Tak Nullah was cleaner than ever before. Egrets have now returned to the nullah, which is teeming with fish once again.

Streams in Tsuen Wan and Kwai Chung

The Sam Dip Tam Stream has maintained ‘Good’ to ‘Excellent’ water quality in recent years

The other three rivers monitored in the Southwestern New Territories and Kowloon area (Pai Min Kok Stream, Sam Dip Tam Stream and Kau Wa Keng Stream) are comparatively minor, with small catchments. They have all benefited from the range of measures introduced to reduce pollution over the past twenty years, and achieved WQO compliance rates of between 87% and 97% in 2005. In recent years, all monitoring stations for these rivers have returned WQI grades of either ‘Good’ or ‘Excellent’.

However, the E. coli levels in some of the monitoring stations remain fairly high (>10,000 cfu / 100 mL), due to faecal pollution from unsewered premises in the catchments. To minimise this pollution, sewer connections for some of the premises in the vicinity of the Sam Dip Tam Stream are in progress, and a public sewer for the catchment area of the Pai Min Kok Stream is being constructed in phases, with a scheduled completion date of 2009.