From page 15
aquifer. In addition, in
developed areas, rainwater
ends up in storm water drains
and does not reach the
aquifers in the area.
The number, proximity and
depth of other boreholes in
your area will also affect your
hole, especially if they are
drawing on the same aquifer.
Pumping too much water out
of your borehole without
adequate rainwater to
recharge the aquifer will result
in your borehole delivering
less water. The dynamic
becomes quite simple: no
Graph showing borehole yields over four years
rain plus high abstraction
(removal) rates equals a
diminishing (or vanishing)
resource. If you are lucky,
after a few weeks of good
rains your borehole may
return to its former strong
output. Experience with
numerous commercial
installations have show n how
quickly water levels in
boreholes can recover after a
few good downpours. But is
this always the case?
For, what happens if a
borehole is being over
pumped?
The accompanying graph
shows data that was collected
from a borehole over a period
of 30 months. The top graph
shows how much water was
taken out of the borehole. An
installed totalising water
meter will give you this
reading. The red trend line
shows that the rate of
abstraction increased slightly
over the 30 months that the
hole was monitored.
17
www.sasmallholder.co.za
WATER
The bottom graph shows that
the rainfall was erratic but the
trend was constant.
The middle graph, however,
shows that even though rain
had fallen in the area, the
water level in the borehole
dropped from about 25m
below ground to 46m. That's
a drop of 21m in the water
content in the aquifer. The
good rainfall in December of
Year 2 did not have a
significant influence on the
overall situation. The owner
of this borehole was clearly
taking out more than what
Continued on page 18