ground water hydraulics

1. Asst. Prof. Suman Kundapura
Dept. of Civil Engineering
GROUND WATER DEVELOPMENT
(15CV742)

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Water dowsing" refers in general to the practice of using a forked stick, rod, pendulum, or similar device to
locate underground water, minerals, or other hidden or lost substances, and has been a subject of discussion
and controversy for hundreds, if not thousands, of years.

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MODULE V WELLS:
A well is defined as an artificial hole or pit made in the ground for the purpose of tapping water. In India 75 to
85% of Indian population has to depend on wells for its water supply.
COST OF WELLS
A 20-feet-deep well costs Rs. 15,000 to dig. If special rings are used, the cost can go up to Rs. 35,000 for the
same depth. Well-diggers charge by the foot. The asking rate is between Rs. 300 and Rs. 400 per foot
The three factors which form the basis of theory of wells are
- Geological conditions of the earth’s surface
- Porosity of various layers
- Quantity of water, which is absorbed and stored in different layers.
The following are different types of wells and their methods of construction
- Shallow wells
- Deep wells
- Tube wells
- Artesian wells

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He says these are not good days for well-digging due to plot sizes becoming smaller and borewells costing
lesser and taking little space. But Vedaraj is content earning Rs. 500 a day desilting wells.
In place of 20 wells a month, he and his team of men now dig only five. “I still work throughout the year,
desilting wells,” he says.
Digging wells is hard work and a 20-feet-deep one takes 13 hours of strenuous digging, pulling up buckets of
mud and ensuring the earth does not cave in.

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Shallow Wells:
Shallow wells are constructed in the uppermost layer of the earth’s surface. The diameter of well varies from 2 to 6
m and a maximum depth of 7m. Shallow wells may be lined or unlined from inside. Fig below shows a shallow well
with lining (steining). These wells are also called draw wells or gravity wells or open wells or drag wells or
percolation wells.
Fig: Shallow Well
Quantity of water available from shallow wells is limited as their source of supply is uppermost layer of earth only
and sometimes may even dry up in summer. Hence they are not suitable for public water supply schemes. The
quantity of water obtained from shallow wells is better than the river water but requires purification. The shallow
wells should be constructed away from septic
tanks, soak pits etc because of the contamination of effluent. The shallow wells are used as the source of water
supply for small villages, undeveloped municipal towns, isolated buildings etc because of limited supply and bad
quality of water.

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Deep Wells:
The Deep wells obtain their quota of water from an aquifer below the impervious layer as shown in fig below.
The theory of deep well is based on the travel of water from the outcrop to the site of deep well. The outcrop is
the place where aquifer is exposed to the atmosphere.
The rain water entered at outcrop and gets thoroughly purified when it reaches to the site of deep well. But it
dissolves certain salts and therefore become hard. In such cases, some treatment would be necessary to remove
the hardness of water.
The water available at a pressure greater atmospheric pressure, therefore deep wells are also referred to as a pressure wells.

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Tube Wells:
The tube well is a type of water well in which a long 3.9inch -7.9inch wide stainless steel tube is bored into an
underground aquifer.
The lower end is fitted with a strainer and a pump lifts water for irrigation. The required depth of the well depends
on the depth of the water table.
Advantages of Tube Well irrigation:
• Groundwater is easily available
• The water table is fairly close to the surface
• Able to irrigate larger area
• Reliable even during drought when surface water dries up
• Suitable for small holdings

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Artesian wells
An artesian well is simply a well that doesn't require a pump to bring water to the surface; this occurs when there
is enough pressure in the aquifer. The pressure forces the water to the surface without any sort of assistance. A
Free Flowing Artesian Borehole.

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Dug wells
Dug wells are holes in the ground dug by shovel or backhoe. Historically, a dug well was excavated below the
groundwater table until incoming water exceeded the digger’s bailing rate. The well was then lined (cased) with
stones, brick, tile, or other material to prevent collapse. It was covered with a cap of wood, stone, or concrete.
Since it is so difficult to dig beneath the ground water table, dug wells are not very deep. Typically, they are only
10 to 30 feet deep. Being so shallow, dug wells have the highest risk of becoming contaminated. To minimize the
likelihood of contamination, your dug well should have certain features. These features help to prevent
contaminants from traveling along the outside of the casing or through the casing and into the well.

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PUMPS
The function of pump is to raise the water or any fluid to higher elevation. Pumps are driven by electricity, diesel or
steam power. They are helpful in pumping water from the sources that is from intake to the treatment plant and from
treatment plant to the distribution system or service reservoir. At homes the pumps are used to pump the water to higher
floors or to store water in tanks over the buildings.
TYPES OF PUMPS AND THEIR SUITABILITY
Based on the mechanical principle of water lifting pumps are classified as the following
https://www.youtube.com/watch?v=V9bOAqOOEQw

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Latest Centrifugal Pumps Models Expected Price
Sameer I-Flo 1.5HP Monoblock Force
Water Pump
Rs. 2704
Kirloskar Chhotu Star 1HP Single Phase
Monoblock Pump
Rs. 3167
Kirloskar Chhotu 0.5 HP Monoblock
Water Pump
Rs. 1802
Usha 2557 1HP Self Primping Water Pump Rs. 3347

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COMPONENT PARTS OF CENTRIFUGAL PUMP
Centrifugal force is made use of in lifting water. Electrical energy is converted to potential or pressure energy of water.
Centrifugal pump consists of the following parts as shown in fig below (Open and semi impeller type are also
available; However this is an closed type of impeller) shaft connects.

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Centrifugal pump
1) At the heart of the system lies the impeller
2) It has a series of curved vanes fitted inside a plate
3) Impeller is always filled with water
4) When the impeller rotates it makes the fluid inside also rotate
5) This imparts centrifugal force to the water particles and the water moves outwards
6) The rotational mechanical energy is transferred to the fluid at this side both pressure and kinetic energy will rise and at
suction side the water is getting displaced so negative pressure will get induced in the eye (P<Patm)
7) This low pressure will suck the water into the system again; this process continues
8) This is the reason why PRIMING is important for centrifugal pumps
9) If the impeller rotates without water initially, then negative pressure developed initially will be negligibly small to do any
suction from fresh stream of water
10) Impeller is fitted inside the casing and the water rotating will be collected in the casing, water moves in the same direction
as the direction of the impeller towards discharge nozzle
11) Specialty of casing is it has increasing area along flow direction, this increasing area accommodates newly added water,
also help in reduction of exit flow velocity, hence resulting in increase in static pressure which is required to overcome
resistance of pumping system
12) Impeller vanes are backward curved vanes
13) CAUTION : If P < Pvapour of water @ suction side of impeller, a dangerous phenomena known as Cavitation will occur.
Here the water will form vapor bubbles which breaks on the surface creating shockwaves inside the pump and spoils
impeller parts by forming cavities

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Types of Reciprocating Pump :
The following are the types of reciprocating pump according to the source of work and mechanism :
▪ Simple hand-operated reciprocating pump
▪ Power-operated deep well reciprocating pump
▪ Single-acting reciprocating pump
▪ Double-acting reciprocating pump
▪ Triple-acting reciprocating pump
▪ Pump with air vessels
▪ Pump without air vessels

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COMPARISION OF CENTRIFUGAL PUMP AND RECIPROCATING PUMPS

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Maintenance may be
1) Preventive maintenance Locating the sources of trouble and keeping the equipment in good operating condition. It
involves oiling, greasing of stuffing boxes, observing the temperature of the motor and the pump bearings, checking the valves,
strainer, electrical contacts, earthings etc.
2) Break down maintenance : Involves replacement of worn-out components and testing. Sufficient amount of spares of
impellors, bearings, slip-ring brushes(flange and wires), stater-contacts, gland packing(stuffing gap between shaft and pump),
greases, oils, jointing materials, valves are to be kept in stock to attend to the emergencies. It is usual to have one stand by
pump in addition to the required number of pumps.
POINT TO BE OBSERVED IN SELECTING A PUMP
1.Capacity and efficiency – The two basic types of water pumps:
Centrifugal pumps
Positive displacement pumps
-Rotary
-Linear
-Reciprocating pumps
Both types are designed to move water from one place to another continuously.

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ORIGIN OF THE HORSEPOWER UNIT
- Before steam power became widespread during the Industrial Revolution, horses were the main source of energy
for applications like pulling carts, turning grinding mill wheels, and providing movement to industrial machines. As
the availability of steam engines increased, a means of providing understandable power ratings became important.
- Comparing the power output of a steam engine to a corresponding number of horses was an easy way for
prospective engine owners to understand and compare power ratings.
- James Watt, an engineer, inventor, and entrepreneur of the late 1700s, determined that by recording the distance a
horse traveled in a specific time while pulling a known weight against gravitational force, a measurement could be
made of the power the horse produced.
- After several observations, Watt concluded that a strong horse could provide 550 foot-pounds per second of power,
or one horsepower (Fig. 1).
Figure 1. Diagram demonstrating the definition of horsepower.

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WATER AND PUMP HORSEPOWER
The energy is defined as the capacity to do work and Power is the amount of energy that is used to do work or how
quickly work can be done. Water horsepower (1 horsepower is equal to 746 watts.)is the minimum power required
to run water pump. In other words, it is the power that the pump would require if the pump were 100% efficient.
The water horsepower can be determined if the flow rate of the water and the force (pressure) required to produce that
flow are known.
WHP= HQ(SG)/3960
Example : If an irrigation pump located at ground level is pumping 460 gallons of water per minute from a well whose
water level is 112 feet below the ground level and discharging that water at ground level, the water horsepower that the
pump is delivering is:
WHP = (112 x 460) / 3960 = 13.0
3960 = a conversion number we get by dividing 8.333 (the weight, in pounds, of one gallon of water)
into 33,000 ( foot pounds in one horsepower).
PUMP EFFICIENCY
No pump can convert all of its mechanical power into water power. Mechanical power is lost in the pumping process due to
friction and other physical losses. It is because of these losses that the horsepower going into the pump must be greater than
the water horsepower leaving the pump. The efficiency of any given pump η
is a ratio defined as the water horsepower out divided by the mechanical horsepower into the pump.
η = water Hp out / Hp into pump 0 < η < 1
W. H. P
Break Horse Power = ----------------
Efficiency

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CONJUNCTIVE USE OF GROUNDWATER
Conjunctive use combined use of surface water resources & groundwater, in a unified way, to optimize resource &
minimize adverse effects of using a single source. Conjunctive use - actively managing aquifer systems as an
underground reservoir. During wet years, when more surface water is available, surface water is stored
underground by recharging the aquifers with surplus surface water. During dry years, the stored water is available
in the aquifer system to supplement or diminished surface water supplies
NECESSITY OF CONJUNCTIVE USE
Groundwater and surface water are closely linked. Groundwater maintains the base flow of rivers, and water in
rivers can infiltrate into the ground. Abstraction of surface water and groundwater cannot be planned in isolation —
one will affect the other.
eg. abstraction of groundwater can reduce base flow contribution to rivers by lowering water table.
If carefully planned, however, the conjunctive use of rivers and groundwater can even out the seasonal variations
in river flow. In the summer when the river flow is low, water moves from the aquifer into the river, so that more
water can be drawn from the river d /y , s. Rainy season, water flows from River to aquifer. Pumping from wells
also intercepts some of the natural base flow to the river.

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Artificial recharge
Artificial recharge is a process by which the groundwater reservoir is augmented artificially.
Green revolution of 1960’s gave them technology of ground water. However GW started depleting within few decades
The rapid urbanization and deforestation have considerably reduced the groundwater recharge in many parts of the
world.
The reduction in groundwater recharge and over exploitation of groundwater due to increasing demands, the
groundwater table has been depleted in many parts of the world. For example, the groundwater table in some parts of
Delhi has been depleted by 20 to 30 meters in a span of 60 years. Same is the condition in other major cities in India
and other parts of the world.
As such there is a need to increase the groundwater recharge by some artificial means. In this lecture, we will discuss
some of the methods use for artificial recharge and also the methods use in estimation of groundwater recharge.
Often, the quality improvement of the water is actually the main objective of recharge, and the system is operated
specifically using the soil and the aquifer to provide additional treatment to the source water. Systems used in this way
are called soil-aquifer treatment (SAT), or geopurification, systems.

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Techniques of groundwater recharge
The artificial techniques use for groundwater recharge can be divided in two groups, i.e. direct method and
indirect method.
Further, the direct method can be sub grouped as surface method and sub-surface method.
The main objective of the surface method is to enhance groundwater infiltration by providing more residence
time with the help of structural and nonstructural measures. Residence time is defined as the amount of water in
a reservoir divided by either the rate of addition of water to the reservoir or the rate of loss from it.
Some of the structural measures are contour bunding, percolation tank, check dams, etc .
On the other hand, afforestation falls under the category of nonstructural measures. The induced recharge
method and aquifer modification method falls under the category of indirect method.

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1. Percolation tank
In this method, series of earthen dams are constructed on suitable sites for storing of adequate quantity of surface water.
The tank area should be selected in such a way that significant amount of water infiltrates through the bed of the tank and
reaches the groundwater table. This method is very effective in alluvial area as well as in areas with hard rock. This method
is very useful in providing continuous recharge after the monsoon.

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2. Flooding

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Contour bund
Contour bund is a small embankment constructed along the contour in hilly region to retain the surface runoff for
longer time. This scheme is adopted for low rainfall area where internal subsurface drainage is good.

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Subsurface methods
1) Recharge well
Recharge wells are used to recharge water directly to the aquifer. Recharge wells are similar to pumping wells. This method is
suitable to recharge single wells or multiple wells. This method is costlier than the other method as wells are required to be bored.
However, sometimes abandoned tube wells can be used for recharging water into the aquifer.

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Subsurface methods
Dug wells can also be used to artificially recharge the groundwater. Generally, water level of dug wells depletes during the
non monsoon period. Sometime the dug wells even dried up in the non- monsoon period. These dug wells can be used for
recharging groundwater. The water from various sources can be collected through a distribution system and can be
discharged at the dug wells.
Pits and shafts
Recharge pit of variable dimensions are used to recharge water to unconfined aquifer. Most of the time, especially in case
of agricultural field, a layer of less permeable soil exist. Due to the existence of the less permeable strata, the surface
flooding methods of recharge do not show satisfactory performance. For such type of cases, recharge pit can be excavated
which are sufficiently deep to penetrate the less permeable strata. On the other hand recharge shaft is similar to the recharge
pits, but the cross sectional size of the recharge shaft is much lesser than the recharge pits. Like the recharge pits, recharge
shafts are also used to recharge water to unconfined aquifer whose water table is deep below the land surface and a poorly
impermeable strata exist at the surface level

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Indirect method
I) Induced recharge
It is an indirect method of artificial recharge. In this method water is pumped from the aquifer hydraulically connected to
the surface water sources like stream, river or lake. Due to pumping, a reverse gradient is formed and water from the
surface water source enters into the aquifer and thus the aquifer is recharged . This method is good, especially when quality
of the surface water is poor. The filtration of surface water through soil strata removes the impurities of the water. Thus the
quality of the water received in the wells is much better than the surface water.
2) Aquifer modification method
This is also an indirect method of artificial recharge. In this method, some techniques are used to change the aquifer
characteristic so that aquifer can store more water and also can transmit more water. After application of these techniques,
more recharge takes place under natural condition as well as under artificial condition. The most commonly used techniques
are, bore blasting method, hydro- fracturing method, jacket well techniques, fracture seal cementation and pressure injection
grouting, etc.

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Bore blasting method
This method is used to increase the fracture porosity of an aquifer. Shallow bore wells are drilled in the area where fracture
porosity of the aquifer is planned to increase. These bore holes are blasted with the help of explosive which creates fracture
porosity in the aquifer.
Hydro-fracturing method
Hydro-fracturing is used to improve the yield of a bore well. In this technique, water is injected at a very high pressure to
widen the existing fracture of the rock. The high pressure injection of water also helps in removing of clogging, creates
interconnection between the fractures, and extends the existing length of the old fracture. The high pressure injection also
creates new fracture in the rock strata. As a result of these, the water storing and transmitting capacity of the strata
increases.
Jacket well techniques
Jacket well technique is used to increase the yield of a dug well. In this method, the effective diameter of the well is
increased by drilling small diameter bores around the well in a circular pattern.
Fracture seal cementation and pressure injection grouting
This technique is used to control the outflow from an aquifer. Cement slurry is injected into the aquifer using mechanical
means or manually near to the aquifer outlet like spring, etc. The injection of cement slurry helps in reducing the fracture
porosity of the aquifer near the outlet which will eventually reduce the outflow from the aquifer.

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