Sustainable Use Of Groundwater

Sustainable Use Of Groundwater

It is no secret that South Africans live in a water scarce country that is experiencing a very tough drought. At home we catch as much water as possible with buckets in the shower to help the dry and oh so thirsty garden. As there is a strict water usage restriction in the area, no sprinklers or hosepipes are used. The JoJo is always ready to harvest of course, yet grass stays brown and the car is dirty. This is just a small effort from our side to be water wise and only use water where absolutely needed.

Then you drive past homes with green grass and a “BOREHOLE” sign outside; where people sometimes water their lawns smack bang in the middle of the day… so you have a borehole; does that entitle you to abuse this precious resource?

Here is some great info from the Department of Water and Sanitation that explains why it is important to use groundwater sustainably.


Sustainable Use Of Groundwater

Why is groundwater not sustainable?

As all water sources in the RSA, groundwater is available in limited quantities. All groundwater comes from rain falling on the surface of the earth, infiltrates through the soil and then into the cracks and fissure in hard rock formations, to reach the water table – this called recharge. Recharge amounts to about 2% – 4% of the annual rainfall. From the aforementioned facts, it will be appreciated that groundwater has limits. These limits are further limited by the amount of cracks and fissure in hard rock formations.

If well managed, groundwater can be used sustainably! For more information see Question on ‘How can groundwater be managed?’

What is a safe yield of a borehole?

The speed with which water can flow through the cracks and fissures determine the yield of a borehole – where the cracks and fissures are very concentrated, the water can flow easily, consequently it will deliver a large volume of water at a time. However, this 4 is only the rate at which water can be abstracted from the relevant aquifer and the volume available in the aquifer is rather the limiting factor. Based on the above description it is clear that a ‘safe yield’ of a borehole is a fallacy. A sustainable abstraction rate would be the correct term to use.

The sustainable abstraction rate will differ for each borehole and need to be determined before any pumping equipment may be ordered. Furthermore, the current practice of the groundwater community to recommend an abstraction rate per hour and an eight, or ten hour duty cycle, need to change. An abstraction rate per 24hour duty cycle must be calculated and recommended.

Is groundwater suitable for its purpose?

Most groundwater in the RSA is suitable for most purposes – domestic and/or stock watering and where it boreholes with high abstraction rates can be established – for irrigation purposes. The areas where groundwater is unsuitable to any of the above purposes are well known. For instance at the town of Bitterfontein – in Namaqualand – the water has to be desalinated to bring it to drinking water standards.

What can be done to achieve the sustainable management of our South Africa’s groundwater resources?

Measuring the water levels in your boreholes, volumes abstracted as well as rainfall figures. Drawing a graph with its parameters you will be able to see how the groundwater levels rise and fall with changing seasons and increase abstractions.

What can be done to achieve the appropriate allocation of our South Africa’s groundwater resources?

If everyone uses groundwater for her/his needs and not her/his greed, there will be enough water for all the citizens of South Africa.

Should groundwater sources, i.e. aquifers, be managed?

If you compare the management of your credit card account with an aquifer, you will find many and relevant parallels and/or similarities.

  • As your credit limit is determined but what you earn the groundwater sources of the country has its limit. In fact South Africa is a water scare country with an extremely variable rainfall (spatially and temporally). All groundwater once fell upon the surface of the earth and infiltrated down to where it is currently abstracted.
  • One cannot use your credit card unabated, nor can you abstract water from an aquifer uncontrolled.
  • As the bank helps one in the management of your credit card account (bank statements and credit limits) groundwater abstraction should be measured by flow meter and limits set by the professional geohydrologist, should be respected.
  • As you ignore your credit limits and bank warnings and eventually land in trouble, the uncontrolled use of groundwater will lead to failure.
  • As you cannot blame the bank for the trouble you are in due to above, you cannot blame groundwater for an unreliable source if you do not manage your groundwater sources properly.

From the above the answer is unequivocally ‘YES’ you MUST manage your groundwater sources.

GROUNDWATER AND DROUGHTS

What happens to groundwater during drought (where does groundwater disappear to)?

For an explanation of how groundwater occurs and where it come from refer to the Question ‘Why is groundwater not sustainable?’

  • Groundwater, unlike surface water, cannot evaporate. However, groundwater may be lost to an aquifer through pumping, spring flows and water a shallow water table through transpiration of plants which then evaporates into the air (term = evapotranspiration). Of these three the uncontrolled pumping has the largest impact.
  • It could also be that the water table has declined below the level of the borehole or dug well, i.e. water table deeper that the borehole and thus the pump inlet is dry.

What is groundwater recharge?

Water under the surface of the earth (groundwater) occurs in cracks and fissures in hard rock formations across about 890% of the RSA. The other 10% is underlain by loose sands (also called primary aquifers) where the water occurs in openings between sand grains.

Water falling on the surface of the earth infiltrates through the soil profile and excess water will infiltrate through the crack and fissures (interstices) in the hard rocks, or openings between the sand grains, until these interstices becomes saturated. The volume of water augmenting the water in the interstices is deemed recharge. It is thus obvious that recharge is driven by rainfall. It is generally accepted that between 2% and 4% of the annual rainfall reaches the saturated parts of an aquifer.

Source: http://www.dwa.gov.za/groundwater/FAQ.aspx

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