Before You Drill A Borehole In Zimbabwe - Read This!
Water Systems Zimbabwe is looking forward to your call or WhatsApp Message.
Please feel free to leave a message on our WhatApp number or alternatively please call us and we will be able to help you straight away. If you would prefer, send us an email with your details and an outline of your enquiry and we will be pleased to come back to you.
We respond to all enquiries usually within 24 hours, but guarantee within 48 hours.
Our Contact Numbers Are:
Water Systems Sales: +263 77 389 8979.
Water Systems Sales: +263 71 961 3479.
Solar Systems Sales: + 263 78 922 2847.
Water Systems Sales: +263 71 884 5891.
Water Systems Zimbabwe is looking forward to your call or WhatsApp Message.
Please feel free to leave a message on our WhatApp number or alternatively please call us and we will be able to help you straight away. If you would prefer, send us an email with your details and an outline of your enquiry and we will be pleased to come back to you.
We respond to all enquiries usually within 24 hours, but guarantee within 48 hours.
Our Contact Numbers Are:
Water Systems Sales: +263 77 389 8979.
Water Systems Sales: +263 71 961 3479.
Solar Systems Sales: + 263 78 922 2847.
Water Systems Sales: +263 71 884 5891.
Please feel free to leave a message on our WhatApp number or alternatively please call us and we will be able to help you straight away. If you would prefer, send us an email with your details and an outline of your enquiry and we will be pleased to come back to you.
We respond to all enquiries usually within 24 hours, but guarantee within 48 hours.
Our Contact Numbers Are:
Water Systems Sales: +263 77 389 8979.
Water Systems Sales: +263 71 961 3479.
Solar Systems Sales: + 263 78 922 2847.
Water Systems Sales: +263 71 884 5891.
It is important that certain procedures be followed to ensure a clean, reliable, productive Borehole in any location in Zimbabwe.
These important steps include siting, drilling and pump testing the borehole.
In addition to the siting considerations discussed above which pertain to finding adequate water, boreholes should be located at least 15 to 20 metres from sewers and septic tanks; at least 30 metres from pastures, on-lot sewage system absorption fields, cesspools and barnyards; and at least 10 metres from a silo. Areas, where groundwater comes to within 3 metres of the soil surface, should also be avoided.
2. Borehole Drilling and Casing: Drilling a borehole is more than boring a hole into the earth. A finished borehole will consist of a borehole cut into the aquifer at a diameter large enough to accept the borehole casing which will receive the pump. The borehole itself can be drilled using any one of several types of drill rigs including impact, rotary, or various combinations.
Development is accomplished by surge pumping, bailing or any operation which will force water through the development zone at high velocities. Developing a borehole is the responsibility of the borehole driller. Properly developed boreholes will yield more water than poorly developed boreholes.
With the borehole in place, the question remains "How much water can be pumped from the borehole on a sustained basis?" The sustained pump rate is determined by the aquifer rocks ability to move water toward the borehole under the influence of gravity while the borehole is being pumped. To determine the sustained pumping capacity of a borehole a pump test must be performed on the borehole. The pump test should be completed by the borehole drilling contractor as part of the contract to drill the borehole. The desire for a pump test must be made clear to the driller before drilling begins since some drillers are not able to do pump testing. Be sure to use a driller who can complete the work including a pump test.
Several types of pump tests have been developed, but all are designed to establish the long term equilibrium rate at which water will flow towards and enter the borehole. The simplest, most straightforward pump test is to place a pump in the borehole, after the development phase is complete, and pump water from the borehole at a constant rate. The discharged water must be dumped some distance from the borehole so it can not recirculate back into the borehole during the pump test.
Figure 2 is a schematic of the water levels within the geologic structure while a pump is drawing water from a borehole. The cone of depression is produced when water is removed from the borehole by the pump, causing the water level in the borehole to drop. This drop in the borehole water level means the water surrounding the borehole is at a higher elevation and the gravitational water in the rock begins to flow into the borehole. As this continues, the distance between the original water table and the water level in the borehole, or drawdown, increases forming a large cone of depression. At some point, the drawdown reaches a point of equilibrium, where the water flows to the borehole at the same rate as it is being pumped from the borehole. This equilibrium usually occurs after 24 to 48 hours of continuous pumping at a constant flow rate.
The capacity of a borehole can be estimated by first determining the specific capacity of the borehole. Specific capacity Sc of a borehole is the pump rate, Q in gallons per minute during the pump test, divided by the drawdown, s (in feet) after 24 hours or at equilibrium. In other words, the specific capacity is the flow rate per foot of drawdown.
Sc = Q(gpm)/s(ft)
Knowing the depth of the borehole and where the permanent pump will be placed, the maximum permissible depth to water in the borehole can be taken to be 3 metres above the permanent pump intake location. The difference in elevation between the original water table and the maximum permissible depth to water is the maximum drawdown, Smax. The maximum sustainable discharge for the borehole is then the specific capacity times the maximum drawdown.
Qmax = Sc (Smax)
After the pump test is completed, you will have developed knowledge about how much water the 10 feet can be expected to produce. You are now ready to proceed with your irrigation design.
Even though following the recommendations on this page will not guarantee all the clean water you may need or desire to have, it will greatly increase your chances of having a clean, reliable, productive borehole that is able to meet your needs.
1. Borehole Siting: Groundwater exploration is not a hit or miss (or random) proposition. Excess rainwater percolates into the soil and rock beneath the earth's surface accumulating in zones of saturation called aquifers.
A borehole is a hole drilled into the aquifer from which a small portion of the groundwater can be pumped to the surface for man's use. It is true that any borehole penetrating an aquifer will yield water but the amount of water produced from a randomly sited borehole may be very small. Such low producing boreholes often provide adequate water for domestic or farmstead uses. If a borehole is to provide irrigation water a more highly productive borehole will usually be needed.
Scientific methods have been developed for locating boreholes where they will penetrate into zones of fractured rock buried beneath the soil surface. Borehole located on a fractured rock zone will produce much larger quantities of water than boreholes drilled into zones where the rock is not fractured. Finding the fractured rock zones, or better yet, finding the intersection of two fractured rock zones can be a time consuming and expensive procedure.
Scientific methods have been developed for locating boreholes where they will penetrate into zones of fractured rock buried beneath the soil surface. Borehole located on a fractured rock zone will produce much larger quantities of water than boreholes drilled into zones where the rock is not fractured. Finding the fractured rock zones, or better yet, finding the intersection of two fractured rock zones can be a time consuming and expensive procedure.
Only geologists and engineers with training in aerial photo interpretation and hydrogeology are qualified to locate boreholes by the fracture-trace technique.
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| Before You Drill A Borehole In Zimbabwe - Read This! |
If a high producing borehole is desired, however, the consultant's fee for siting the borehole is worth the extra benefit.
In addition to the siting considerations discussed above which pertain to finding adequate water, boreholes should be located at least 15 to 20 metres from sewers and septic tanks; at least 30 metres from pastures, on-lot sewage system absorption fields, cesspools and barnyards; and at least 10 metres from a silo. Areas, where groundwater comes to within 3 metres of the soil surface, should also be avoided.
2. Borehole Drilling and Casing: Drilling a borehole is more than boring a hole into the earth. A finished borehole will consist of a borehole cut into the aquifer at a diameter large enough to accept the borehole casing which will receive the pump. The borehole itself can be drilled using any one of several types of drill rigs including impact, rotary, or various combinations.
After the borehole has been drilled into or through the water-bearing aquifer, the borehole screen should be installed in the producing zone. The zones above the producing aquifer must be cased to prevent cave-ins, and the annulus between the borehole and casing must be filled with grout to keep surface contaminants from entering the borehole.
4. Borehole Development: Developing a borehole is the process of clearing the borehole of fines left by the drilling operation, and flushing these fine particles out of the gravel and aquifer between the borehole screen and the first few feet of the aquifer.
Development is accomplished by surge pumping, bailing or any operation which will force water through the development zone at high velocities. Developing a borehole is the responsibility of the borehole driller. Properly developed boreholes will yield more water than poorly developed boreholes.
With the borehole in place, the question remains "How much water can be pumped from the borehole on a sustained basis?" The sustained pump rate is determined by the aquifer rocks ability to move water toward the borehole under the influence of gravity while the borehole is being pumped. To determine the sustained pumping capacity of a borehole a pump test must be performed on the borehole. The pump test should be completed by the borehole drilling contractor as part of the contract to drill the borehole. The desire for a pump test must be made clear to the driller before drilling begins since some drillers are not able to do pump testing. Be sure to use a driller who can complete the work including a pump test.
5. Pump Testing: With the borehole in place, the question remains "How much water can be pumped from the borehole on a sustained basis?" The sustained pump rate is dependent upon the aquifers ability to move water toward the borehole under the influence of gravity while the borehole is being pumped.
To determine the sustained pumping capacity of a borehole a pump test must be performed on the borehole. The pump test should be completed by the contractor as part of the borehole drilling contract. The desire for a pump test must be made clear to the driller before drilling begins because some drillers are not able to do the pump testing. Be sure to use a driller who can complete all drilling work including the pump test.
Several types of pump tests have been developed, but all are designed to establish the long term equilibrium rate at which water will flow towards and enter the borehole. The simplest, most straightforward pump test is to place a pump in the borehole, after the development phase is complete, and pump water from the borehole at a constant rate. The discharged water must be dumped some distance from the borehole so it can not recirculate back into the borehole during the pump test.
The pump rate should be great enough to stress the borehole, but not so great as to cause the borehole to be pumped dry. During the pump test, the water level in the borehole must be measured and recorded at regular intervals starting at the time pumping begins and continuing until pumping stops. Pumping should continue for at least 24 hours (without interruption) or until the water level in the borehole remains at the same elevation for three consecutive half-hour readings.
Figure 2 is a schematic of the water levels within the geologic structure while a pump is drawing water from a borehole. The cone of depression is produced when water is removed from the borehole by the pump, causing the water level in the borehole to drop. This drop in the borehole water level means the water surrounding the borehole is at a higher elevation and the gravitational water in the rock begins to flow into the borehole. As this continues, the distance between the original water table and the water level in the borehole, or drawdown, increases forming a large cone of depression. At some point, the drawdown reaches a point of equilibrium, where the water flows to the borehole at the same rate as it is being pumped from the borehole. This equilibrium usually occurs after 24 to 48 hours of continuous pumping at a constant flow rate.
The capacity of a borehole can be estimated by first determining the specific capacity of the borehole. Specific capacity Sc of a borehole is the pump rate, Q in gallons per minute during the pump test, divided by the drawdown, s (in feet) after 24 hours or at equilibrium. In other words, the specific capacity is the flow rate per foot of drawdown.
Sc = Q(gpm)/s(ft)
Knowing the depth of the borehole and where the permanent pump will be placed, the maximum permissible depth to water in the borehole can be taken to be 3 metres above the permanent pump intake location. The difference in elevation between the original water table and the maximum permissible depth to water is the maximum drawdown, Smax. The maximum sustainable discharge for the borehole is then the specific capacity times the maximum drawdown.
Qmax = Sc (Smax)
After the pump test is completed, you will have developed knowledge about how much water the 10 feet can be expected to produce. You are now ready to proceed with your irrigation design.
Water Systems Zimbabwe is looking forward to your call or WhatsApp Message.
Please feel free to leave a message on our WhatApp number or alternatively please call us and we will be able to help you straight away. If you would prefer, send us an email with your details and an outline of your enquiry and we will be pleased to come back to you.
We respond to all enquiries usually within 24 hours, but guarantee within 48 hours.
Our Contact Numbers Are:
Water Systems Sales: +263 77 389 8979.
Water Systems Sales: +263 71 961 3479.
Solar Systems Sales: + 263 78 922 2847.
Water Systems Sales: +263 71 884 5891.
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