WATER
Why boreholes can weaken over time
I
n Gauteng at least, the
drought may be over, but
that doesn't mean that
your borehole will instantly
become a gushing fountain.
And, you may have memories
of it becoming weaker and
weaker as the drought wore
on.
Here, therefore, are some of
the reasons why a borehole's
output may lessen over time,
courtesy of John Tonkin,
editor of the Borehole Walter
Association's journal.
In addition, this article may
help you to calculate what
you can reasonably expect
from your borehole over
time.
Let's consider some of the
possible reasons for water
delivered by a borehole
becoming less and less.
It could be that the pump's
inlet has been blocked by a
plastic bag, cable ties or other
foreign objects in the
borehole. There is also the
possibility that the pipe in the
borehole carrying the water to
the surface has developed a
leak. This is especially true of
long-established boreholes
where the metal connectors
may have corroded through
with age and burst under the
pressure of the pump output.
However, these reasons are
more the exception than the
rule during times of drought.
The more likely explanation is
that due to the very low
rainfall, not enough rainwater
was added to the aquifer from
which the pump is drawing its
water. The term "recharge" is
used to describe water on the
surface of the ground
percolating downwards into
an aquifer.
Groundwater can be com-
pared to water in a sponge. It
exists through rainfall that
happened recently or many
thousands of years ago and is
stored in various types of
formations. The type of
formation determines how
quickly water moves through
it. Water moves very slowly
through clay or fractured
granite but a lot faster through
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loose sand. This affects the
rate of recharge of an aquifer.
Other factors on the surface
such as tarred roads, paved
areas and large expanses of
rooftops reduce the ground
surface area into which water
can be absorbed to eventu-
ally percolate into the
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