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ABSTRACT
Natural
river is a form of channel that easily changes in term of its physical
shape such as width or depth as well as the changes in water
pollution. Unplanned development couples with human and natural
factors are the biggest contributors to changes in the river
equilibrium. Economics activities such as agricultures, urbanisation,
fishery, sand mining, etc, should be control in ensuring the balance
of river eco-system. Sand mining activities are usually concentrated
at the sandy-bed natural rivers. River sands are an important element
in development factors, where its demand increases linearly with
Malaysian infrastructure development.
The
research was conducted to identify the changes of riverbed due to sand
mining activities at Muda River in Kedah because of currently active
sand mining operations along the river. This research consists of
river cross-sectional survey, sediments sampling and water level
records at seven stations along a 5 km river reach.
The
extensive sand mining activities along the research area requires
closed supervision and control by related authority in ensuring that
erosions are minimised. The mining depth needs to be closely monitored
so that sand miners do not exceed the permitted depth of Sand Mining
Guideline established by Jabatan Pengairan dan Saliran Malaysia (JPS).
Based on survey works that have been carried out in year 2001 and
2002, it has been found out that the sand miners have failed to fulfil
the requirements of the Sand Mining Guideline given by JPS. Almost all
the cross-section within the research area having width more than 50
m, have been mined exceeding 1.5 m depth of the allowable tolerance.
A
mathematical model, FLUVIAL-12 (Mathematical Model for Erodible
Channel, Chang, 1988) was used to forecast the changes of Muda
riverbed. The calibration carried out shows that the Manning
Coefficient, n = 0.040 is suitable for Muda River analysis. Yang
Equation also gives almost an accurate result to the actual condition
at research site. Selected simulation cases have successfully shown
that the changes of riverbed are due to sand mining activities and
flood. The results also show that the past flooding (1988, 1998) have
given major effect to physical stability of the research area compared
to sand mining activities.
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