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Jul 24, 2010
Has train tunnelling played a part?
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THUS far, one factor that has not been raised is how the many underground MRT tunnels criss-crossing our island are contributing to the boutof flooding, which we are now told is unavoidable.
Under natural conditions, the surface vegetation and the entire volume of soil underneath it (assuming it is 100m deep) will absorb 'x' amount of rainfall. However, when we create an MRT tunnel, say, 30m underground, the volume of soil available to absorb the same amount of rainfall will now be only 30m deep as the remaining depth is cut off by the tunnel. Therefore, the rest of the water becomes surface run-off.
Thus, several conditions must exist for flash floods to occur:
There must be a train tunnel running underground in the vicinity of that flood area, which explains why we are discovering new flood-prone areas.
That flood area must be at a lower ground level relative to its surroundings.
The drainage system in that area must have been designed before the MRT tunnel was built, and so is inadequate to handle the run-off.
The situation is compounded by covering open drains, which are more efficient at draining surface water.
Should we trace the physical tunnel network of the MRT over the recent flood areas?
Tan Tiong Chye
Has train tunnelling played a part?
<!-- by line --><!-- end by line -->
<!-- end left side bar --><!-- story content : start -->
THUS far, one factor that has not been raised is how the many underground MRT tunnels criss-crossing our island are contributing to the boutof flooding, which we are now told is unavoidable.
Under natural conditions, the surface vegetation and the entire volume of soil underneath it (assuming it is 100m deep) will absorb 'x' amount of rainfall. However, when we create an MRT tunnel, say, 30m underground, the volume of soil available to absorb the same amount of rainfall will now be only 30m deep as the remaining depth is cut off by the tunnel. Therefore, the rest of the water becomes surface run-off.
Thus, several conditions must exist for flash floods to occur:
There must be a train tunnel running underground in the vicinity of that flood area, which explains why we are discovering new flood-prone areas.
That flood area must be at a lower ground level relative to its surroundings.
The drainage system in that area must have been designed before the MRT tunnel was built, and so is inadequate to handle the run-off.
The situation is compounded by covering open drains, which are more efficient at draining surface water.
Should we trace the physical tunnel network of the MRT over the recent flood areas?
Tan Tiong Chye
