To solve flooding problems, part
of the middle and lower courses of the natural river
has been channelized. Channelization straightened
the natural and meandering river, and deepened and
widened the riverbed. It increased the carrying capacity
of the new channel, hence containing floodwaters that
originally overflowed onto the floodplain, and discharging
the water into the sea within a short period.
To reduce water resistance and make
it convenient to maintain, the riverbed and river
banks are mostly covered with concrete. The channel
after Tai Po Tau of Lam Tsuen River has been straightened
into a flood control ditch made of bricks and concrete.
River works not only alter the appearance
of natural rivers, they also change the river structure.
(1) Hydrological impacts
Channelization directly increases the flow rate and
flow volume of the river. It also disconnects the
river from underground water, leading to an extreme
river hydrology. During dry seasons, the concrete
surface prevents underground water from entering the
river. During rainy seasons or rainstorms, overflowing
water cannot seep underground.
(2) Impacts on Water Quality
River training projects convert the riverbed and riverbanks
into concrete. Water flow and temperature are no longer
be suitable for most of the original flora and fauna,
including microorganisms. The populations of different
species decrease, and the river ecology is severely
damaged. The self-purification ability of the river
is greatly reduced, and the water quality deteriorates.
(3) Other Impacts
Lam Tsuen River is among Hong Kong's few remaining
natural rivers with relatively complete river geomorphology
and ecology, which can serve as educational and research
resources for subjects including hydrology, ecology,
geography, and urban planning. Yet past river works
have already ruined many of the natural resources
and geographical features. We have lost a wealth of
scientific and educational resources.