This document discusses water supply systems based on groundwater. It provides information on different components of groundwater systems including aquifers, zones of saturation and aeration, porosity and specific yields. It also discusses factors that affect tubewell discharge capacity such as permeability, thickness, and radius of influence. Methods for estimating screen length and tubewell design considerations such as diameter, gravel pack, and drilling techniques are summarized.

1. WATER SUPPLY SYSTEM
BASED ON GROUND WATER
INTRODUCTION
Water is a blessing from Allah and the most important
element for the survival of living. However, we, the human
being, need safe drinking water as we do not have the
necessary resistance, like animals and plants, to consume
unsafe drinking water. More than 70% of diseases in the
developing countries are due to use of unsafe drinking water.

2. GLOBAL DISTRIBUTION OF WATER
More than 70% of the earth surface is covered with water, in form of oceans and
seas. This water, comprises 97% of the total water on earth, but this whole
quantum is saline and unfit for human use.
The remaining 3%, which is sweet water, about 75% (or 2.25% of total
available water on earth) is in the form of glacier and only 25% of sweet water (or
0.75% of the overall total water on earth) is in the form of surface water (Rivers,
Lakes & Stream etc.) and ground water.
This 0.75% of global water is the fresh water that we human being
are struggling to develop, consume, use and or waste and contaminate through our
negligence.

3. UNDER GROUND WATER
Under ground water source includes well (deep / shallow) spring and
horizontal infiltration galleries. Understanding of ground water occurrence
requires a study of vertical distribution of water in the sub surface geological
formation. Geologist call the earth’s crust the, litho-sphere, when they speak
of the lithology of a section through earth crusts, they mean the kinds of
rock that occur in a succession of layers or strata below the surface that
makeup any part of litho-sphere. Geologist refer to all the material of the
earth’s crust as rock, whether they be unconsolidated (sand or clay) or
consolidated material (granite & sand stone).

4. The outer part of the earth crust is normally porous to a greater or
lesser depth. This part is called the zone of rock fracture. The pores or
opening in this portion of lithe sphere may be partially or completely
filled with water.
The upper strata, where the openings are only partial filled
with water is called “Zone of Aeration”. Immediately below this, where
all the opening are completely filled with water, is the “Zone of
Saturation”.
The zone of aeration is divided into these belts:
- The belt of soil water.
- The intermediate belt.
- The capillary fringe.

5. These belts very in depth and area / location.
Water in the zone of saturation is the only part of all sub surface water
which is properly referred to as “ground water”. The saturated zone may be
viewed as huge natural reservoir where capacity is the total volume of the
pores or opening in the rocks that are filled with water.
Ground water may be found in one continues body or in
several separate strata’s.

7. The thickness / depth of zone of saturation various form a few feel to
many hundreds of feet’s. Factors that determine its thickness are:
- The local geology.
- The availability of pores or opening in the soil formation.
- The recharge mechanism.
- The movement of water within the zone from areas of recharge
toward the point of discharge.

8. BASIC PRINCIPALS OF GROUND WATER FLOW
What is Aquifer: Rocks which can store and transmit water in large
quantities e.g. Sand, gravel, sand stone or fractured lime stone.
What is Aquitard: Rocks which can stone and transmit water in small
quantities e.g. silt, clay, poorly fractured rocks.
What is Aquiclude: A rocks which under normal conditions, does
not store and transmit water e.g. clay, shale, and consolidated rock.
(Clay can absorb water like sponge but it cannot transmit it).

9. Aquifer Functions:
As disused above, an aquifer perform two important functions:
- Storage of water like reservoir.
- Transmission of water like pipe line.
The opening or pores in a water bearing formation serve
both as storage spaces and as a network of conduits. The underground
water is constantly moving from point of recharge to areas of discharge,
and this movement is very slow with velocity measured in feet per day
or even in feet per year.
Two properties of an aquifer related to its storage function are:
- Porosity.
- Specific yields.

10. Porosity.
- Porosity of a water bearing formation is that part of its total
volume which consists of opening or pores / portion of total volume
not occupied by solid material.
- Porosity is an index of how much ground water can be stored in
the saturated material.
- Or it is defined as the ratio of the volume of voids to the total
volume of material”
Porosity = Volume of Voids = Total Volume – Volume of Solids
Total Volume Total Volume

11. For example, if 1 Cft. Of sand contains /holds 0.3 cft of water (or there
are 0.3 cft opening voids) we say its porosity is 0.3 or 30% while
porosity represent the amount of water an aquifer will hold, it does not
indicate how much water the porous material will yield.

12. Specific yields.
When water is drained from a saturated material by gravity force, only
part of the total volume stored in its pores / voids is released. Hence
the quantity of water that a unit volume of the material will give up,
when drained by gravity, is called its specific yield, expressed in
percentage.
The part of water that is not removed by gravity drainage is held
against the force of gravity by molecular attraction and capillary action.
The quantity that unit volume retains when subjected to gravity
drainage is called its specific retention, expressed in percentage.

13. Conclusion
Porosity = Specific Yield + Specific Retention
Further to above example, if 0.1 Cft. of water is drained from 1 cft of
saturated sand, the specific yield of this sand sample is 0.10 or 10% and
its specific retention is 0.2 or 20%
Porosity = 0.1 + 0.2 = 0.3 Or 30%

14. Example:
Consider a water table aquifer extended over an area of 2
square miles and with an average thickness of about 40 ft.
-Total Volume of aquifer = 2 x 5280 x 5280 x 40 = 2230272000 Cft.
= 2.230 billion cubic ft.
- Assume Porosity = 25% 0.25
Hence Total volume of water = 2230272000 x 0.25 = 557578000 Cft. of
saturated strata.
Assume specific yield = 0.1 and only upper 5 ft. of aquifer was
drained by lowering the water table by 5 ft.

15. The total yield would be:
= 557578000 x 0.1 x 5 = 278784000 Cft of water
= 278784000 x 6.24 = 1739612160 Imperial water gallons
Is available (specific yield)
If we are going to install 01 tubewell of 1.00 cusec discharge capacity to
work for 12 hours a day.
The total yield of water of the tubewell= 1 x 6.24 x 60 x 60 x 12 = 270000
gallons / day
Total days of working of tubewell = 1739612160 = 6443 days
270000 Or = 17.65 years

16. It means this saturated strata would supply water for tubewell having 1.00 cusec
discharge, working for 12 hours a day for about 17.65 years. This pumping would be
sustained by the ground water stored in the upper 5 ft. of the aquifer in the absence of
any replacement / recharge to the aquifer for a period of about 17.65 years. If number
of tubewell are increased for 1 to 2, the time period to deplete above aquifer will be
decreased by half and so on. Similarly if the time of pumping hence is increased this
time period will also decreased further.
FACTORS AFFECTING THE DISCHARGE OF A TUBEWELL
- Permeability of a aquifer material, the characteristic of the rock to treatment
particular amount of water under a unit hydraulic head.
- Thickness of the aquifer material being tapped or the length of screen.

17. - Radius of influence of well or core of depression.
- Permissible draw dawn.
(We can pump a well at high rate than its normal discharge, but in that case
the draw dawn will increase and possibly results into some damage to the well)
MUTUAL DISTANCE OF PUMPING WELL
When a well is pumped the water level, not only inside the well but also
to certain the distance from the well, is depressed as the water from the
surrounding areas move towards the well to meet the discharge capacity. The
distance upto which a well affects the ground water level is known as the
radius of influence of the pumping well. If another well is installed with in the
radius of influence of the already existing well, effect of water level lowering
will be compounded with the two well called interference of wells.

19. In Punjab, the experiment of hundreds of installed tubewells indicate that
the cone of influence of the pumping well (also called core of depression)
various from less than 1000 ft to more than 4000 ft. depending upon the
discharge and the aquifer characteristics .
TYPE OF TUBEWELLS
Well are classified a shallow and deep tubewells, there is not
general agreement on the definition of deep and shallow well. However,
more frequently adopted definition are:

20. Shallow well
Shallow wells which derives its water from a water bearing surface
formation below an impervious strata. A shallow well is general are
particularly liable to pollution, hence a shallow well / skimming well
installed near the canal or stream gives a good quality water. Water
channel loose water through evaporation from the water surface and also
seepage from the wetted area of the water lost through seepage a
significant amount percolates down to the ground water table, forming a
source of recharge and resulting in the rise of water table.
Shallow tubewells are drilled along the canals for tapping fresh
ground water, overlying the deep saline ground water over a period of
decades, a fresh layer has formed over the saline ground water. Thickness
of this layer generally maximum in the close vicinity of canals. These type
of tubewells are generally drilled for small capacity discharge.

22. These shallow tubewells are installed in B’Nagar, Bahawalpur, T.T. Sing.
Faisalabad & Sargodha Districts along the canals for drinking water
purpose to extent fresh ground water.
DEEP TUBEWELL.
A well which derives its water from below an impervious
strata which prevents local rainfalls from existing the well, by virtue of
its depth, and either an impervious lining or an overlying an impervious
strata does not receive the water of local rain fall.
Deep tubewells are installed in the Pothowar Platean,
Gujranwala, Lahore, Multan Civil Divisions etc.

24. DESIGN OF TUBEWELL
The includes:
i. Discharge of tubewell (water requirement)
ii. Depth and diameter of bore hole to be drilled for the installation
of tubewell.
iii. Depth/length and diameter of pipe and screen required to pump
the required quality of water with permissible draw down. This
will include the type of construction material for the pipe and
screen, keeping in view the discharge, depth and water quality of
ground water.
Length and diameter of housing pipe – suitable for the lowering of
the required pump and water level in the well (Material may be MS,
GRP, SS, PVC etc.)

25. - Length or diameter of screen, alongwith the slot size of the
screen and tis material (like be brass, SS, PVC & Fiberglass etc.)
iv. Size and gradation of gravel pack to be used as shrouding material
to avoid sand blowing wells.
DESIGN OF LENGTH OF SCREEN
Length of screen for the tubewell may be estimated by
equation (developed by WAPDA based on design, operation, and
performance of around 15000 SCARP tubewells in Pakistan).

26. Length of / aquifer or Screen = 1.32 Q/{K x h}
Where
Q = Discharge of tubewell in cusecs
K = Coefficient of permeability of aquifer (feet / sec)
H = Draw dawn in feet.
Length of screen estimated, as above, will be somewhat
on the higher/ side as core of depression is considered as less than
1000 feet in this equation.

27. For “K” = Coefficient of permeability feet /sec.
-Fine to medium sand (loose dense soil) = 5.6 to 13
10000 10000
-Fine to medium sand (medium dense soil) = 4.9 to 9.8
10000 10000
-Fine to medium sand (dense soil) = 3.3 to 6.6
10000 10000

28. Generally the value of “K” adopted in Punjab (Plain Region) is 0.00116 ft/sec.
Some adjustment keeping in view the field condition/ experience may have to
be made.
Example:
Calculate the length of screen for tubewell having 0.25 cusec
discharge in plain region of Punjab.

29. Length of / aquifer or in otherwords Screen = 1.32* Q/[K x h]
Q = 0.25 Cusec
K = 0.00116 (feet / sec) it is assumed for plain Punjab areas
S = Draw dawn =10 ft assumed.
L = 1.32 x 0.25 = 28 ft.
0.00116 x 10
Add 10% safety margin on account of blocking of some
screen slots with general pock particles and on incrustation.
Length = 28 + 2.8 approx. = 31 ft.or 32 ft is sufficient

30. Checking for Entrance Velocity
Slot opening = 10% of total circumference
Dia of screen = 8” (assumed)
Total Slot opening = 0.1x (8/12) x 3.143 x 30 ft.
= 6.284 Sft.
V = Q= 0.25 = 0.038 ft/sec. (hence within permissible limits)A 6.284
Maximum range of entrance velocity = 0.1 ft/sec.

31. DIAMETER OF SCREEN AND TUBEWELL DISCHRGE
Relationship between discharge of the tubewell and its
diameter is logarithmically proportional and hence by doubling the
diameter of the screen, the discharge may increase by only 10% with
other parameter kept same.
Normally 6” dia of screen is adopted for tubewell having discharge upto
0.5 cusec.
8 dia ” of screen is adopted for tubewell having discharge upto 1.00
cusec.
10 to 12” dia of screen is adopted for tubewell having discharge more
than 1.0 cusec

32. GRAVEL PACK OR SHROUDING MATERIAL
In Punjab, the aquifer material compressing of sand of various
grades intercepted with layers of silt and clay, gravel and kankers. As this sand
formations are unconsolidated and heterogeneous (mixture of various grain sizes).
The screen opening / slot size has to be selected as based on the dominant grain
size of sand. There is possibility that some fine material continuously pass through
the well screen and come in the pumped water, rendering it unfit for drinking.
Accordingly, as layer of gravel is provided around the well screen to provide that
strength against collapse pressure and to stop the fine particle from entering into
the well screen. This gravel pack well:

33. -Create a more permeable zone around the well.
Increase the hydraulic efficiency of the tubewell keeping in
views the experience and study of SCARP tubewells Pea gravel from
Attock quarries is generally selected around and keeping in view the
grain size of dominant sand particle in Punjab, slot size of 1/32” inch is
generally adopted.
DRILLING METHOD
i. Direct Rotary drilling technique.
ii. Reverse Rotary drilling technique.
iii. Percussion drilling method.

34. i. Direct Rotary Drilling Technique
Under this technique, the hole is drilled by rapid rotation of rotating
bit, the cuttings of the underground formation are removed by
continuous circulation of drilling fluid. In direct rotary system the
drilling is fluid is forced driven under pressure, with the help of mud
pump through the drilling pipes and comes out through the nozzle of
the bit.

36. The drilling fluid moves upward alongwith the cuttings through the
annular space around the drill pipe and bore.
ii. Reverse Rotary Drilling Technique.
It work on the same principle as the direct rotary method except that the
drilling fluid is circulated in a reverse direction as compared to direct
rotary method. In this method, the drilling fluid is generally feed into the
bore from the pit through the annular space and this drilling fluid, along
with cuttings, are moved upward through the drill pipe and is discharged
by the mud pump into settling pit. The bore hole is not provided with
casing and is prevented from caving by the hydraulic pressure of water in
the bore hole and also due to film / layer of fine grained material
deposited on the walls of bore hole by the circulating water.

38. TUBEWELL CONSTRUCTION / LOWERING OF WELL ASSEMBLY
PRECAUTIONS
- Pipes end should be properly beveled for the MS, housing, joints
to be welded.
- Screen should be checked before lowering for any possible
damage to the slots during field handling.
- Verticality and straightness of the well should be ensured.
- Gravel pack should be sieved at the site to remove the fines and
pouring should ensure uniform distribution.

39. DEVELOPMENT AND TESTING OF TUBEWELL
Objective of the development of tubewell is to create a
more permeable zone around the well screen by pumping out fines.
Development of the well should be started at 25 to 30% of
the design discharge and generally be increased to 100% capacity or
1.25 times capacity