Armfield S12-MKII, Instruction Manual

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61
Exercise K - Ground water flow between two canals with
and without rainfall
Theory
When two neighbouring canals have their water surfaces maintained at different
levels, there will be a flow of ground water between them from the higher to the
lower. If, at the same time, there is surface recharge by rainfall, a water divide may
form in the intervening water table and this means that a small proportion of the
recharge is entering the upper canal and the larger part the lower canal.
It is suggested that students read the theory of superposition described in Exercise I
before proceeding with this experiment.
Procedure
Form the two canals by excavating two trenches across the catchment tank, one
near each end. Build up the intervening ground with the sand excavated from the
canals. Connect the flexible tubing from the 3 l/min flow meter to the French drain on
the same side as the highest of the two canals and turn on the water supply. This will
establish the ground water flow without recharge and the correct flow can be found
by experiment.
Connect the flexible tubing from the 5 l/min flow meter to the self-sealing connection
for the spray nozzles. When the water table has been determined, turn on the spray
nozzles until the water table between the two canals is elevated above the water
level within the canals. It will be necessary to adjust the rainfall flow rate and the
valves for the two French drains in order to achieve a constant level in the two
canals. This is another experiment in which the principle of superposition can be
tested by allowing the water surfaces in both canals to equalise while the rain is
falling. This can be done by careful regulation of the appropriate valves.
Results
Tapping
position
m
Manometer
reading
(rainfall only)
m
Manometer
reading
(groundwater
only)
m
Manometer
reading
(rainfall only +
groundwater only)
m
Manometer
reading
(rainfall and
groundwater)
m