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GROUNDWATER

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GROUNDWATER


Groundwater is water located beneath the ground surface in soil pore spaces and in the fractures of lithologic formations. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water. The depth at which soil pore spaces or fractures and voids in rock become completely saturated with water is called the water table.

Groundwater is recharged from, and eventually flows to, the surface naturally; natural discharge often occurs at springs and seeps, and can form oases or wetlands.

Groundwater is water located beneath the ground surface in soil pore spaces and in the fractures of lithologic formations. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water. The depth at which soil pore spaces or fractures and voids in rock become completely saturated with water is called the water table.

Groundwater is recharged from, and eventually flows to, the surface naturally; natural discharge often occurs at springs and seeps, and can form oases or wetlands. Groundwater is also often withdrawn for agricultural, municipal and industrial use by constructing and operating extraction wells. The study of the distribution and movement of groundwater is hydrogeology, also called groundwater hydrology.

In the previous article we have looked at the pump test stage of drilling a borehole, and for many this seem to be the final stage of groundwater development. However, to complete the picture and take cognizance of the fact that groundwater is a resource that needs to be managed, we have to now look at the different phases as a summary, as well as considering the information and strategies that will assist in managing this resource effectively.

The activities described in the previous articles can now be summarized for groundwater development. The development of groundwater resources generally takes place in three phases namely exploration, evaluation and finally the exploitation or management phase.

During the exploration phase, surface and subsurface geological and geophysical techniques are applied to assist in finding suitable aquifers. During the evaluation phase, boreholes are drilled, constructed, developed and tested to establish Hydrogeological parameters and calculate possible borehole, aquifer and basin (or catchment) yields. The final (and ongoing) phase in groundwater development is the exploitation or management phase. This is the stage whereby groundwater monitoring and aquifer performances are monitored and fine tuned to assist in the consideration of the optimum development strategies as well as the interactions between groundwater abstraction and the hydrological cycle. In all the areas where groundwater is either the sole source of water, or where groundwater is used to augment water supply, the management of this resource will become increasingly important. The pressure on this resource worldwide will increase as the demand for increased production and from increased populations will require more utilization of this scarce resource.

Every borehole owner will benefit from keeping the following information on his/her borehole: Geological description of samples as encountered during drilling; borehole specifications e.g. borehole diameter drilled, final depth, length and type of casing installed, and static water level after drilling. Additional information for the borehole includes the blow yield as measured during drilling and the test pump information. The details to be kept on the borehole pump include the type of pump installed, the pump depth as well as the date of initial installation.

To furthermore ensure a continuous supply of water from a borehole additional information should be measured on a regular basis. This information should be kept in a data basis and could be represented in graphical manner for ease of understanding. This include the water level measurement on a weekly or monthly basis (depending on the pumping schedule as well as the importance of the borehole), rainfall on a daily weekly or monthly basis, and finally the volume of water pumped on a weekly or monthly basis, or alternatively the time the borehole was pumped.

A borehole water user can now, based on this information start to manage this resource by adhering to some basic groundwater management principles. To become an effective businessman or farmer sound financial control and planning is essential. Similarly if a person depends on groundwater for a large percentage of his income, proper management of this valuable resource is of utmost importance. By analyzing the data recorded on a regular basis, by means of graphical presentation or modeling**, one can have an early warning system setup. Steady declines in borehole water levels, even approaching the pump inlet, will provide a clear indication of over pumping of the borehole. Based on this up to date information one can immediately implement remedial action by either reducing the pump rate or the pumping periods.

Modeling refers to the simulation of borehole, aquifer and basin groundwater responses by means of a computer generated mathematical model. There are number computer codes developed specially for the simulation of groundwater flow and abstraction patterns as well as the movement and remediation of groundwater pollution. Modeling is an important tool used in combining all available hydrological, hydrogeological and geological information to assist in the planning of exploration, development, exploitation and management of a groundwater resource.

As noted from the above discussion, groundwater management should take place on various levels, starting from the localized borehole owner and user to the regional aquifer, basin and catchment area. Ultimately groundwater development will rely heavily on management principles applied by Local authorities, Government and Inter Governmental development planning and management strategies. In this regard the South African Water Law has been developed with specific outcomes and responsibilities in mind. Next week we look at the South African Water Law and how it affect the local borehole owner and user as well as the role that is envisaged for Local Authorities and Government.

Economic value of groundwater Water is the true wealth in a dry land; without it land is worthless or nearly so. And if you control water, you control the land that depends on it. Wallace Stegner (1954) At my visit to the recent Nampo Expo I overheard a pump salesman and a farmer talking. The farmer was enquiring about protection for his borehole pump to prevent it from burning out and about problems he is experiencing with the water level in his borehole. The salesman had a hundred and one devices that he could sell in order to protect this farmer Considering the economic value of groundwater this was, and remains a shocking answer!

Although one cannot generalise I was wondering how many irrigation farmers still have the same outlook on this matter? Here you are spending hundreds of thousands of Rand on capital equipment to irrigate crops, more on working and planting, and more money on protecting the pump, yet it is considered too expensive to test the borehole? The very reason opting for irrigation is economics and profits, yet it is concluded that it is too expensive to test this resource! Having a borehole tested means amongst other things that one knows how much water one can extract to retain sustainability as well as the quality of water you extract. Can you justify spending a large capital outlay on an irrigation system without the assurance that you will have a constant water supply? A proper borehole test and resource evaluation will cost you a fraction of your capital outlay but/and will give you the peace of mind that you will have water to irrigate. The notion of ll just drill another and carry on does groundwater have an economic value at all? If it does why do so few groundwater user in Southern Africa actually contemplate spending money on the scientific evaluation and exploration of this valuable resource? According to the Water Research Commission (WRC) of South Africa, 55.8% of water used in South Africa is used in the agricultural industry. This water is made up of both surface water and groundwater. Irrigation agriculture contributes in the order of 25 to 30 % of the gross agricultural production and is of great importance in the economic activities in rural areas. This, while groundwater in many areas around the world is considered as either an invaluable good or as a good.

In order to put the economic value of groundwater into perspective the United States Government commissioned a project in 1994 to determine the economic value of groundwater. According to that study the first and fundamental step in valuing of a groundwater resource is recognizing and quantifying that resourceIs it too expensive to test a resource and make sure of it In the next article we look at the occurrence of groundwater as well as the legal environment and recent legislation changes in South Africa.

Farmers Weekly: Ground water Part One: Economic value of groundwater

Water is the true wealth in a dry land; without it land is worthless or nearly so. And ifyou control water, you control the land that depends on it. Wallace Stegner (1954)

At my visit to the recent Nampo Expo I overheard a pump salesman and a farmer talking. The farmer was enquiring about protection for his borehole pump to prevent it from burning out and about problems he is experiencing with the water level in his borehole. The salesman had a hundred and one devices that he could sell in order to protect this farmer’s pump. As a matter of interest I stepped closer and asked the salesman if he knows how people actually test boreholes? He answered – “they talk about a step drawdown test, but it is really so expensive to test a borehole that it is really not worth it!” Considering the economic value of groundwater this was, and remains a shocking answer! Although one cannot generalise I was wondering how many irrigation farmers still have the same outlook on this matter? Here you are spending hundreds of thousands of Rand on capital equipment to irrigate crops, more on working and planting, and more money on protecting the pump, yet it is considered too expensive to test the borehole? The very reason opting for irrigation is economics and profits, yet it is concluded that it is too expensive to test this resource!

Having a borehole tested means amongst other things that one knows how much water one can extract to retain sustainability as well as the quality of water you extract. Can you justify spending a large capital outlay on an irrigation system without the assurance that you will have a constant water supply? A proper borehole test and resource evaluation will cost you a fraction of your capital outlay but/and will give you the peace of mind that you will have water to irrigate. The notion of – water is always there and will always be available, if my borehole packs up I’ll just drill another and carry on – will be much more costly than just gaining the know how of proper aquifer testing, management and maintenance.

Economic decisions in the farming business are often taken with the aid of complex financial and crop models, but seldom on an economic model of your groundwater resource. Precision farming with the aid of satellite imagery is also fast winning ground, but is this the case for groundwater? This lead me to ask the question – does groundwater have an economic value at all? If it does why do so few groundwater user in Southern Africa actually contemplate spending money on the scientific evaluation and exploration of this valuable resource?

According to the Water Research Commission (WRC) of South Africa, 55.8% of water used in South Africa is used in the agricultural industry. This water is made up of both surface water and groundwater. Irrigation agriculture contributes in the order of 25 to 30 % of the gross agricultural production and is of great importance in the economic activities in rural areas. This, while groundwater in many areas around the world is considered as either an invaluable good or as a “free” good.

In order to put the economic value of groundwater into perspective the United States Government commissioned a project in 1994 to determine the economic value of groundwater. According to that study the first and fundamental step in valuing of a groundwater resource is recognizing and quantifying that resource’s total economic value.

(TEV). For the purposes of that study groundwater services have been divided into two basic categories: extractive services and in situ services. Each of these is considered to have an economic value which can be summed up as follows: TEV = extractive value + in situ value. The most familiar of these two are the extractive values, which are derived from municipal, industrial and agricultural demands met by groundwater. (In the majority of these cases the economic value of groundwater is only translated in related costs, e.g. cost of exploration and production drilling, pumping equipment and operational costs (such as electricity, lubricants and repairs), but not as a value per unit of groundwater abstracted.) The in-situ services (i.e. services or values that occur or exist as a consequence of water remaining in place in an aquifer) include e.g., the capacity of groundwater to, a) buffer against periodic shortages of surface water supplies, b) prevention or minimizing of subsidence due to groundwater abstraction (sinkholes), c) protect water quality by maintaining the capacity to dilute and assimilate groundwater contaminants, to name but a few.

The valuation of extractive and in-situ services of groundwater requires an understanding of geology, geohydrology and ecology of a certain groundwater resource. Hydrological and geohydrological information includes numerous factors such as rainfall, runoff, depth to groundwater, whether the water-bearing zone if confined or unconfined, the groundwater flow rates and direction, type of vadoze and water bearing zone materials and water quality associated with different strata.

Most groundwater applications in especially the agricultural sectors have focused on the valuation of limited production related services provided by groundwater. This has lead to misallocation of resources in the past as well possible conflict situation where the demand on a certain resource has changed with one user taking legal precedence over another. Enormous amounts have been spend in attempting to augment water supplies in agriculture, trying to clean up polluted groundwater resources and fighting court battles resolving water allocation issues.

It is clear from the above discussion that estimating and quantifying the TEV of groundwater is not a simple issue, but remains a pressing and important issue for industry, and agriculture throughout the world. The big questions now for my friend the pump salesman, is this: “Is it too expensive to test a resource and make sure of it’s sustainability before you embark on major capital projects, or would you prefer to work and build on a proven, and well understood, sustainable resource?”

In the next article we look at the occurrence of groundwater as well as the legal environment and recent legislation changes in South Africa.

GROUNDWATER