Abstract:
The state of Kerala in India is a typical example of a region facing droughts
of varying degrees despite receiving high annual rainfall. This is because a lion
share of the precipitation received is going out as runoff without recharging the
groundwater. The subsurface stormflow is considered as the fast moving
component of subsurface runoff on which very little information is available due to
its complex mechanism of movement through subsurface. Hence, this study has
been taken up for gathering more knowledge on the phenomenon of subsurface
stormflow with the help of monitoring of soil moisture movement and tracer
method. For data collection, three experimental setups in two experimental plots
have been setup in KCAET campus, Kerala, India. It is a lateritic terrain having
sandy loam type of soil and a general slope. Through-flow trenches were
constructed for all the three setups and studied the soil moisture variation on the
trench face at three depths (0-40 cm, 40-80 cm and 80-120 cm) in order to study the
subsurface stormflow through different depths. For the experimental setup 1,
simulation of rainfall was done using a butterfly sprinkler as the input. Line
application of water was done for the experimental setup 2. Natural rain was taken
as the input for the experimental setup 3. The subsurface stormflow through the soil
matrix is also studied by the salt tracer experiment for obtaining its velocities. From
the study it was found that the subsurface stormflow discharge is greatly affected
by the soil dry density and soil suction. The subsurface stormflow discharge was
found to have negative correlations with both soil suction and soil dry density. The
subsurface stormflow velocities through 0-40 cm, 40-80 cm and 80-120 cm depths
obtained from the soil moisture variation studies were 23.74 cm day -1 ,
36.23 cm day -1 and 17.41 cm day -1 respectively and the same obtained through the
tracer studies were 27.27 cm day -1 , 30 cm day -1 and 26.67 cm day -1 respectively. It
was also concluded that the prevailing subsurface stormflow in the experimental
sites is due to matrix flow rather than the preferential flow. The results gave the
conclusion that high value of rainfall along with low values of soil dry density and
soil suction can induce the subsurface stormflow even in the area having gentle
slope (<10 %).
