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SECTION
5 ASSIMILATIVE CAPACITY CAPITAL STOCK
| 5.3 |
Assimilative
Capacity of Freshwater Systems |
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| River
Water Quality
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| 5.3.1.4 |
The
water quality of all major rivers and streams
in Hong Kong has been routinely monitored
by EPD since the mid 1980s. Monitoring is
conducted to give an understanding of the
present state of river water quality, allow
the assessment of the effectiveness of the
various pollution abatement measures being
implemented and to evaluate the progress
in achieving and maintaining water quality
objectives (WQOs). Monitoring of over 40
parameters is currently undertaken at 81
stations along 34 inland watercourses, and
involves measurement of physico-chemical
characteristics, organics, nutrients, toxic
metals and coliform bacteria in order to
assess compliance against the WQOs which
are specific to each WCZ. Data on compliance
with WQOs and EPD's index of river water
quality are discussed below to indicate
trends and the extent to which each waterbody
is polluted.
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| 5.3.1.5 |
The
status of each river is assessed using EPD's
Water Quality Index (WQI) which reflects
the degree of organic pollution in the river.
The index is based upon the level of dissolved
oxygen, 5-day Biochemical Oxygen Demand
(BOD5) and ammoniacal nitrogen and is constructed
by assigning observed measurements of the
three parameters to one of five categories
and awarding 1 to 5 points according to
the category assigned. Each parameter is
weighted equally and the points are summed
across the three parameters to provide a
cumulative score of 3 to 15. The range of
the score is then ranked according to one
of five water quality gradings from 'Excellent'
to 'Very Bad'. The WQI is applied to each
river water quality monitoring station on
a yearly basis to track the trends in water
quality.
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| 5.3.1.6 |
Table
5.3a presents the percentage of monitoring
stations classified within each WQI ranking
category for the years 1988 to 1998.
| Table
5.3a River Water Quality Trends, 1988-1998 |
Table
5.3a River Water Quality Trends, 1988-1998
| Year |
No.
Station(1) |
WQI
Ranking by Percentage of Monitoring
Stations : Excellent
|
WQI
Ranking by Percentage of Monitoring
Stations :
Good
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WQI
Ranking by Percentage of Monitoring
Stations :
Fair
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WQI
Ranking by Percentage of Monitoring
Stations :
Bad
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WQI
Ranking by Percentage of Monitoring
Stations :
Very Bad
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1988
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57
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12.7
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14.3
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20.6
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25.4
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27.0
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1989
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68
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18.4
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18.4
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21.1
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17.1
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25.0
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1990
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76
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19.7
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22.4
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21.1
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23.7
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13.1
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1991
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75
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9.5
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29.7
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20.3
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18.9
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21.6
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1992
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75
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2.7
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43.3
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18.9
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18.9
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16.2
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1993
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86
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32.4
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18.2
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20.8
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14.3
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14.3
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1994
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86
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28.4
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23.0
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23.0
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14.8
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10.8
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1995
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86
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35.0
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22.1
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18.2
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13.0
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11.7
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1996
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86
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37.7
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22.1
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16.9
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13.0
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10.4
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1997
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82
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37.2
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30.8
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16.7
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12.8
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2.5
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1998
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82
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38.5
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28.2
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17.9
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9.0
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6.4
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Source:EPD
Reports on River Water Quality in Hong Kong
Note
(1) : WQI Ranking by Percentage does not
cover all monitoring stations as per EPD
reports on River Water Quality in Hong Kong
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| 5.3.1.7 |
The
data in the table indicate that river water
quality has generally sustained a territory-wide
improvement over the last ten years. By 1997,
the percentage of monitoring stations receiving
a WQI ranking of 'Excellent' or 'Good' was
68%, the highest recorded to date, although
this declined to 66.7% in 1998 due to significantly
lower annual rainfall than the previous year.
This compares with 44% and 51% of stations
classified as 'Excellent' or 'Good' in 1990
and 1994 respectively. Additionally, in 1997
& 1998 only 15% of stations recorded a
'Bad' or 'Very Bad' ranking compared with
52% in 1988. |
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| 5.3.1.8 |
Analysis
of the WQI gradings of freshwater systems
within individual WCZs over the period 1984
to 1998 (EPD 1999c) show that the WCZs with
the greatest percentage of stations recording
'Excellent' or 'Good' river water quality
were the Southern, Western Buffer and Tolo
Harbour & Channel areas, whilst Junk Bay,
Deep Bay and Victoria Harbour WCZs recorded
the lowest percentages. Conversely, Deep Bay,
Junk Bay, North Western and Victoria Harbour
WCZs had the greatest percentage of monitoring
stations with WQI rankings of 'Bad' or 'Very
Bad' over the last 14 years. Deep Bay WCZ
also had the highest percentage of 'Very Bad'
WQI rankings in 1998, with over one fifth
(21%) of all monitoring station results falling
within this category. The table in Annex
F4 summarises water quality and pollutant
input issues for each Water Control Zone in
Hong Kong in order to provide a qualitative
review of locally important water quality
impacts and assimilative capacity implications. |
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