Is Your Borehole Running Dry?

During the recent drought, a borehole owner expressed concern that her ‘sprinklers were becoming very weak’ and she was worried that her borehole might be running dry.

So we thought we'd explain the situation in this article, so that borehole water end users would get a better idea of how the water in their boreholes was recharged.

John Tonkin from BWA (Borehole Water Association) shares tips…

Why the decrease in water?

Let’s consider some of the possible reasons for the decrease in water.

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.

These reasons, however, 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. The term ‘recharge’ is used to describe water on the surface of the ground percolating downwards into an aquifer.

Groundwater can be compared to water in a sponge. It exists through rainfall that happened recently or 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 slowly through clay or fractured granite, but a lot faster through loose sand. This affects the rate of recharge of an aquifer.

Other factors such as tarred roads, paved areas and large expanses of rooftops reduce the ground surface area. Rainwater ends up in storm water drains and does not reach the aquifers in the area.

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 rain plus high abstraction rates equals a diminishing (or vanishing) resource.

In the case of the borehole owner with the ‘weak sprinklers’, a few weeks after the rains returned, the sprinklers ‘miraculously’ returned to their expected performance.

Personal experience with numerous commercial installations has shown how quickly water levels in boreholes can recover after a few good downpours. But is this always the case?

How do I know how much water can be safely pumped out of my borehole?

Each borehole will have its own characteristics. Boreholes that are only metres apart can have completely different water levels and delivery capabilities. But, if you and your neighbour are pumping from the same aquifer, over-pumping your borehole could cause their borehole to dry up.  

The best way to find out what your borehole can deliver is to have a recognised yield test done by a professional. This is usually carried out when the borehole is drilled, especially if the borehole water is being used in a mine dewatering project, a large-scale farming irrigation scheme, or to supply drinking water to a town. -John Tonkin

Article courtesy of www.bwa.co.za.