Friday, 26 January 2018 09:22

Borehole Yield Testing 101: How It Works

Would you like your borehole to continue providing water for a long time? Are you interested in a sustainable yield? Then a borehole yield test is mandatory.

A yield test consists of an evaluation to determine the balance between the highest volume of water which can be pumped from the borehole as well as the amount of water that flows back from nearby underground water sources.

After testing, we will present a certificate on which the date, level of the test pump installation, fixed water level, pumping rate and water colour is documented.

How do we test?

Test pumping involves pumping a borehole at a selected rate and logging the volume in the pumping well, in addition to your local observation wells at particular periods of time. Anytime these specifications are replaced in suitable flow equations; specific hydraulic variables can be determined. These guidelines, in addition to a qualitative review of discharge-drawdown elements, will be used for the analysis of a suggested yield of the boreholes and or aquifers.

It is normal to carry out a six-hour test which after a pump is installed with the potential of approximately 40-50% of water flow after the test. This 40-50% safety perimeter is enough in many instances, however, not always. We will discuss with the end user to identify what their requirements are and which type of test will be perfect their needs.

Boreholes that will be used every day and should be able to supply an efficient water supply every day, such as mass water supply for the public, commercial or irrigation, will require more advanced and lengthier water yield tests which can be more expensive. Despite this, the extra initial cost can save lots of money in the long run. Unless necessary, never pump the borehole at its full capacity.

How long does yield testing take?

During the step test, the pump rate is raised in steps at frequent periods. This particular test is especially beneficial to establish the effectiveness of the borehole, although not valuable in creating the long-term sustainable supply of a borehole.

In the Constant Rate Test (CTR), the well is pumped at a consistent discharge rate over the course of 8 - 48 hours. The release is kept steady throughout the test, and water levels are documented in the pumping boreholes together with monitoring boreholes. The time-drawdown information extracted from the CRT will then be examined. The analysis offers helpful feedback to judge the maintainable output of individual boreholes plus the perspective of aquifers.

Right after the CRT, once the pump is turned off, recovering water levels are calculated in the pumping borehole. This recovery test is incredibly valuable in researching the pumping result and possible dewatering of the aquifers which could result because of the confined scope of an aquifer. Additionally, the recovery test will reveal the volume to which the aquifer is in fact dewatered by determining the rest of the drawdown as soon as the borehole is ready to recover.

Water is a precious resource that should not be abused.

Published in Blog

Roelf Burger - Managing Director

Cell: 079 490 2314 | 072 792 8026

Physical Address
Plot 11, Randfontein–South, Randfontein, Gauteng, 1759

Postal Address
P.O Box 2633, Kocksvlei, Randfontein, 1760

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