Abstract:
This research work was undertaken to study the process
of shore erosion along the coast of Karachi.
The area under investigation is the coastline from Manora
Island to Cape Monze. Six different locations in this area
were selected for taking observations and collections of
samples.
Due to the limitations regarding instruments and sea-going
facilities, the study was carried out near the shore only.
The observations from the six fixed reference points along
the coast were taken after every fortnight, including the
recording of visual wave data, wind data and samples of
sediments and sea water. In order to track the offshore
movement of suspended load, satellite imageries were visually
interpretated.
In the laboratory the sediment samples were dried and sieved
for the determination of variations in grain size in surf zone
at each station for diffferent seasons. From the visual wave
data an attempt is made to work out the longshore energy
flux in surf zone due to breaking waves.
It is observed that during SW-monsoon the dissipation of
wave energy causes considerable changes on the beaches and
surf zone, and large amount of sediment are brought into
suspension by the collapsing waves. During this season of high
wave energy the waves predominantly approach the coast lineobliquely resulting transport of sediment along the
coast and "on and Off" shore. It is observed that during
the post-monsoon and pre-monsoon period the beaches and
nearshore zone, are subjected to only moderate to low wave
energy conditions and rebuilding of beaches takes place
in these periods.
However it is observed that the beach material removed due
to erosion is greater than the beach material deposited
back and thus there is a net loss of beach material in the
area. At station No.2 near Paradise Point erosion is quite
severe as the waves attack causes landslides. On the otherhand at sandspit the most crucial area is near station No.6
where sea water is observed to cross the sandspit on
several occasions. Protective measure must be taken here
immediately to protect the sandspit.
