INFILTRATION AND PERCOLATION OF WATER AT SELECTED SITES IN SINGAPORE
GRACE LEE CHENG YEE
GRACE LEE CHENG YEE
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Abstract
Studies on water movement in Singapore have
generally been confined to monitoring the process of
infiltration, as it occurs under various conditions.
Relatively little has been done to monitor the rates and
direction of soil water movement during and after
infiltration.
This study aimed to monitor soil water behaviour,
in terms of variation in flow rates laterally and
vertically during infiltration. In addition to this,
changes in soil moisture were monitored prior to and
following infiltration.
In view of the above, and the various factors
influencing the process of infiltration and percolation,
four sites were selected based on the following criteria:
1) Soil type : Only the Harimau and Rengam series
were chosen.
2) Vegetal cover reflects the degree of surface
disturbance. Two types of vegetation were selected
Forested (undisturbed) and Mown grass (disturbed)
The main source of data for this study was obtained
in the field. Infiltration rates were measured by the
ponding process, using the double ring infiltrometer. Flow
rates and direction within the soil profile were determined
in terms of suction measurements,by means of tensiometers
installed to various depths and at various points in the
field. Infiltration and suction measurements can both be
employed to monitor the rates and direction of soil water
movement as explained in chapters 2 and 5.
In view of the massive amount of data procured in
this exercise, the results were graphically presented in
chapter 4. For practical analysis, this manner of
presentation provides a visual presentation of soil water
behaviour in the form of trends and changes. In addition
to this, wetting front diagrams were used to depict water
movement with time during infiltration in chapter 5.
Results from this study revealed the significance
of soil type, vegetal covers and degree of surface
disturbance on flow rates and direction.
On the basis of soil type, it was observed that
differences between vertical and lateral flow rates were
less marked in the relatively fine textured Rengam soil.
However, very rapid vertical flow was observed at Seletar
Lawn. This was found to be the direct effect of high
antecedent moisture conditions following a heavy downpour.
In particular, the slope gradient at Seletar was pertinent
in influencing the direction of flow. The foregoing
demonstrated the influence of external factors on soil
water movement.
The rate and direction of flow was more difficult
to predict for sites under the Old Alluvium soil profile
in view of its inconsistent nature. The highest and lowest
infiltration and perrcolation rates were recorded at Loyang
Forested and Loyang Lawn respectively. The study concluded with a recommendation that, a
local classification system of flow rates and direction
based on varying factors of influence be compiled. It is
believed that this can be useful to future related studies
when quick and systematic references need to be made.
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Date
1985
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