Study on Sedimentation and Overspills from Dredging Operation using Numerical Model

Trailing Suction Hopper Dredger (TSHD) is commonly used to dredge soft
bed material. Problem .arises when the fme sediment which has low settling ability is
often released along the overflow of TSHD as suspended sediment. This contributes
to high turbidity which could continue over a time span. The objective of this study is
to measure the overspill's volume from hopper and to establish relations between
inflow discharge (Qi), hopper area (AI=50 m x 15m, Az=25 m x 15m and A3=12.5 m
x 15 m), settling velocity of sediment (i) v,=0.0004 m/s (ii) v,=0.0001 m/s (iii)
v,=0.000027 m/s, sediment concentration (i) Ci=IO kglm3 (ii) Ci=S kg/m3 (iii) Ci=3
kg/m3 (iv) C1=1 kg/m3
, and overspills (OV0 ). The scope of study will cover modelling
of sedimentation of fine sediment in Trailing Suction Hopper Dredger (TSHD) using
MIKE 21 Hydrodynamic (HD) and Mud Transport (MT) software. The constant
overspills is acquired through line discharge function and from there the trapping
efficiency is calculated. All values are plotted in Graph Trapping Efficiency versus
A/Qi. The result shows a function of trapping efficiency D A/Qi, where the trapping
efficiency will increase if inflow is decreased (inversely proportional) and efficiency
will increase if hopper area is increase (directly proportional). The inflow
concentration does not affect the trapping efficiency. However, low inflow
concentration and low inflow discharge will lengthen the dredging loading time which
is uneconomical and unproductive. The study provides good estimates on trapping
efficiency for a hopper. The higher the trapping efficiency the lesser the overspills
and there will be less negative impact towards the environment