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SECTION
5 ASSIMILATIVE CAPACITY CAPITAL STOCK
| 5.3 |
Assimilative
Capacity of Freshwater Systems |
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| 5.3.2 |
Assimilative
Capacity Enhancers |
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| 5.3.2.1 |
Freshwater
systems are similar to marine waters in
the types of pollutant input they receive
with wastewaters such as sewage treatment
works effluent, untreated sewage discharges,
agricultural wastes and run-off and industrial
discharges forming a large component of
the overall load. Capacity enhancers such
as sewage treatment works (STWs) discussed
in Section 5.2.2 therefore perform a similar
role in terms of reducing wastewater loads
on the receiving watercourses and thereby
increasing assimilative capacity.
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| 5.3.3.2 |
In
rural areas, discharges of untreated sewage
to watercourses from villages lacking mains
sewerage or treatment has been a significant
source of organic and faecal pollution in
many of the territory's rivers. However,
Sewerage Master Plans have been developed
for each water control zone (see also Paragraph
5.2.2.2), and the phased implementation
of these plans will significantly reduce
discharges of untreated sewage by providing
sewers to connect villages to existing or
proposed treatment works, as well as improving
the level of service to larger towns in
each area. Table 5.3c summarises the SMP
schemes of relevance to freshwater for each
WCZ and details the anticipated cumulative
pollution load relief once they have been
fully implemented.
| Table
5.3c Assimilative Capacity Enhancement
from Sewerage Master Plan |
Table
5.3c Assimilative Capacity Enhancement from
Sewerage Master Plan
| WCZ
and Sewerage Master Plan |
Implementation
Phases (Years) |
Estimated
Population to be Provided with Sewer
(No.) |
Estimated
Pollution Loads Collected by Sewers
(kg BOD day -1) |
| Tolo
Harbour and Channel WCZ, Tolo Harbour
SMP works |
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1993-2004 |
75,400 |
4,200 |
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2005-2007 |
13,000 |
720 |
| Southern
WCZ Outlying Islands SMP(1) |
2004-2008 |
n/a |
n/a |
| Port
Shelter & Junk Bay WCZ, Port Shelter
SMP |
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1993-2000 |
11,500 |
630 |
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1995-2003 |
23,600 |
1,300 |
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2001-2004 |
27,300 |
1,500 |
| Deep
Bay WCZ |
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| North
District SMP |
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1999-2004 |
40,900 |
2,200 |
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2003-2005 |
20,000 |
1,100 |
| Yuen
Long & Kam Tin SMP |
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1999-2005 |
40,000 |
2,200 |
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2001-2008 |
22,000 |
1,210 |
| Yuen
Long & Kam Tin SMP (Review) |
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2003-2006 |
482,000 |
95,000 |
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2005-2008 |
95,500 |
5,300 |
| North
Western WCZ, Tun Mun SMP |
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1995-2006 |
20,000 |
1,000 |
| Western
Buffer WCZ, Ting Kau & Sham Tseng
Sewerage Scheme |
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1999-2003 |
32,400 |
1,800 |
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2001-2004 |
15,900 |
880 |
| TOTALS |
|
919,500
people |
119,040
kg BOD day-1 |
Note(1):
SMP for Outlying Islands due for completion
of review during 2000.
Source: EPD (1999c)
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| 5.3.2.3 |
The
data from the table suggest that the implementation
of the various SMPs will reduce direct BOD
loading discharges by 120,000 kg per day
(equivalent to around one quarter of daily
BOD loadings to the seas around Hong Kong
(WWF 1999)). This figure is an under-estimate
since data were not available on the anticipated
pollution loads to be collected under the
SMPs for Junk Bay, Southern and Victoria
Harbour WCZs. However, the extent to which
the assimilative capacity of the freshwater
or marine receiving environment will ultimately
be relieved, will depend upon the level
of treatment afforded to this newly collected
sewage, and on the capacity of the sewage
treatment systems to handle this additional
load (see Section 5.2.2 for a discussion
of throughputs and capacities of sewage
treatment works).
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| 5.3.2.4 |
Assimilative
capacity enhancement is also afforded through
the extensive network of man-made drainage
systems in Hong Kong, including channelised
streams and rivers, purpose built drainage
conduits and stormwater pipes and nullahs.
This infrastructure provides additional drainage
capacity to the natural rivers and streams
of the SAR, particularly during periods of
high rainfall and storm events. As land continues
to be used for new development, hydrological
patterns will change and surface water run-off
from paved areas will increase, necessitating
attention to drainage parameters, to manage
both the quantity and quality of floodwaters.
Pressure for development is growing outside
of the urban metropolitan areas, and in the
north and north west New Territories there
are significant flooding problems associated
with the natural characteristics of the land
(much of which is a floodplain (DSD 1999)). |
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