CHAPTER 9 ARTIFICIAL RECHARGE

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CHAPTER 9

ARTIFICIAL RECHARGE

9.1 GENERAL

The groundwater storage and the recharge is the fundamental

component of hydrological system. It is the result of water percolating

through various layers of soil and rocks due to the atmospheric precipitation

and snow. The amount of percolation varies from place to place and it

depends on rainfall, characteristics of soils and characteristics of rocks, nature

of terrain, temperature and humidity. Hence the, availability of sub-surface

water will also vary from place to place. In most of the low rainfall areas, the

availability of utilizable surface water is very low. People of those areas have

to depend on groundwater for domestic and agriculture uses. Excessive

pumping of groundwater in those areas has resulted in depletion of the

groundwater levels. Open lands available for natural recharge is reduced due

to large-scale urbanization. In hard rock areas, there are large variations in

groundwater availability. In order to improve the groundwater availability, it

is necessary to artificially recharge the depleted groundwater aquifers.

9.1.1 Advantages of artificial recharge

The advantages of artificial recharge and the benefits which could

be added by this technique are enumerated below (GARGW 2000).

1. To enhance the groundwater yield in depleted the aquifer due

to urbanization.

2. Conservation and storage of excess surface water for future

requirements.

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3. To improve the quality of existing groundwater through dilution.

4. To remove bacteriological and other impurities from sewage

and waste water by natural filtration, so that water is suitable

for re-use.

The basic purpose of artificial recharge of groundwater is to restore

supplies from aquifers depleted due to excessive groundwater withdrawl. This

technique is taken up in this work to improve the quality of the groundwater

of the study area.

9.2 BASIC REQUIREMENTS FOR ARTIFICIAL RECHARGE

The basic requirements for recharging the groundwater reservoir as

per groundwater recharge guidelines (GARGW 2000) are given below.

1. Availability of non-committed surplus monsoon run-off in

space and time.

2. Identification of suitable hydro geological environment and

sites for creating subsurface reservoir through cost effective

artificial recharge techniques.

9.3 PLANNING OF ARTIFICIAL RECHARGE SYSTEM

The planning for an artificial recharge system in this work is mainly

attempted to improve the quality of groundwater of the study area. The following

issues are considered during the planning of artificial recharge system.

1. Selection of area where the groundwater quality is to be improved.

2. The availability of water sources for the recharge.

3. The recharge potential of the study area.

4. The type and geometry of the aquifer.

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5. The type of recharge techniques that could be applied in the

selected area.

9.3.1 Selection of area

The purpose of this research work is to improve the quality of

groundwater at the areas which have adequate availability of groundwater and

their quality not pertaining to IS 10500:1991 standards. The first step in

planning a recharge system is the identification of areas for which the

recharge techniques are required.

9.3.2 Water sources for recharge

The availability of water sources for recharge is to be assessed

before planning a recharge system. The possible sources that are available in

the study area are given below. The sources are to be assessed for their

adequacy.

1. Amount of annual rainfall in the selected area.

2. Availability of large roof areas from where rainwater can be

collected and diverted for recharge.

3. Availability of properly treated municipal and industrial

wastewaters. This water should be used only after ascertaining

its quality

9.3.2.1 Rainwater

The availability of water source is basically assessed in terms of

monsoon run off. At present, the runoff water resource is discharged

unutilized. The amount water available from run off can be assessed by

analyzing the monsoon rainfall pattern, its frequency, the number of rainy

days, maximum rainfall in a day and its variation in space and time. The

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rainfall pattern and infiltration rate of any locality can be considered for

assessing the surplus surface water available in that locality (GARGW 2000).

9.3.2.2 Rainwater from roof top

The roof top rainwater can be conserved and used for recharge of

groundwater. This approach involves collecting rainwater from roof top and

connecting the collection pipe to either existing wells or tube wells or bore

wells or specially designed wells. The urban housing complexes or

institutional buildings have large roof area and can be utilised for harvesting

roof top rainwater to recharge aquifer in urban areas. Table 9.1 shows

availability of rainwater through roof top rainwater harvesting.

Table 9.1 Availability of rainwater through roof top rainwater

harvesting (GARGW 2000)

Rainfall

(mm)100 200 300 400 500 600 800 1000 1200 1400 1600 1800 2000

Roof Toparea

(sqm)Harvested water from Roof top (cum)

20 1.6 3.2 4.8 6.4 8 9.6 12.8 16 19.2 22.4 25.6 28.8 32

30 2.4 4.8 7.2 9.6 12 14.4 19.2 24 28.8 33.6 38.4 43.2 48

40 3.2 6.4 9.6 12.8 16 19.2 25.6 32 38.4 44.8 51.2 57.6 64

50 4 8 12 16 20 24 32 40 48 56 64 72 80

60 4.8 9.6 14.4 19.2 24 28.8 38.4 48 57.6 67.2 76.8 86.4 96

70 5.6 11.2 16.8 22.4 28 33.6 44.8 56 67.2 78.4 89.6 100.8 112

80 6.4 12.8 19.2 25.6 32 38.4 51.2 64 76.8 89.6 102.4 115.2 128

90 7.2 14.4 21.6 28.8 36 43.2 57.6 72 86.4 100.8 115.2 129.6 144

100 8 16 24 32 40 48 64 80 96 112 128 144 160

150 12 24 36 48 60 72 96 120 144 168 192 216 240

200 16 32 48 64 80 96 128 160 192 224 256 288 320

250 24 40 60 80 100 120 160 200 240 280 320 360 400

300 24 48 72 96 120 144 192 240 288 336 384 432 480

400 32 64 96 128 160 192 256 320 384 448 512 576 640

500 40 80 120 160 200 240 320 400 480 560 640 720 800

1000 80 160 240 320 400 480 640 800 960 1120 1280 1440 1600

2000 160 320 480 640 800 960 1280 1600 1920 2240 2560 2880 3200

3000 240 480 720 960 1200 1440 1920 2400 2880 3360 3840 4320 4800

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Based on the annual rainfall and the roof top area, the amount of

water that can be collected from roof top can be found out from the Table 9.1.

This water can be used as the source for recharging of aquifer or the source

for dissolution of groundwater.

9.3.3 Recharge potential of the study area

The recharge potential of any location is a primary factor for the

promotion of artificial recharge. The groundwater quality improvement

methods using artificial recharge require good recharge potential. Based on

the surface and subsurface parameters, the recharge potential of any location

can be found out using the effective tools of remote sensing techniques.

9.3.3.1 Remote sensing

Hydro-geological science makes use of remote sensing and

geographic information system as tools to assess, monitor and to conserve

groundwater resources. One of the greatest advantages of using remote

sensing data for hydrological investigations and monitoring is, its ability to

generate information in spatial and temporal domain, which is very crucial for

successful analysis, prediction and validation (Saraf and Choudhury 1998).

GIS technology provides necessary facilities for efficient management of

large and complex databases. In recent years, the increasing uses of satellite

and remote sensing data have made easier to define the spatial distribution of

different groundwater prospect classes on the basis of geomorphology and

other associated parameters. Analysis of remotely sensed data along with

Survey of India topographical sheets and collateral information with

necessary field-data help in generating the base line information for

groundwater recharge zones. It is used for analyzing and modeling the

interrelationship between the layers. The remotely sensed data at the scale of

1:50000 and topographical information from available maps, have been used

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for the preparation of groundwater recharge potential zone map by integrating

geology, geomorphology, drainage-density and lineaments map of the study

area.

9.3.3.2 Assignment of weightages and ranks

Weighted Index Overlay Analysis (WIOA) in spatial analysis is a

simple and straight forward method for a combined analysis of multi-class

layers. In WIOA, the individual thematic layers and also their classes are

assigned weights on the basis of their relative contributions towards the

output. There is no standard scale for a simple weighted overlay method

(Saraf and Choudhary 1998). The determination of the weights of each class

is an important part in the integrated analysis. The assignment of appropriate

weights controls the value of input in the weighted index overlay method.

Consideration of the relative importance between the parameters leads to a

better representation of the actual ground situation (Choudhary 1999). The

potential zones for artificial recharge of groundwater are also controlled by

various factors. Each factor considered is assigned a weight depending on its

influence on the storage and transmission of groundwater. Lithology and the

geomorphology of the area play a prominent role in groundwater recharging

(Elango and Mohan 1997). The deep water level is given the highest

weightage because it provides space for the recharge. Land use influence over

recharge is assigned less weight. As the role of soil depends on various factors

in recharge, it is given a lower weight, (Saraf et al 2007).

In this study, artificial recharge zones are identified based on

integration of the thematic layers in the GIS environment. The area which is

categorized as excellent for an artificial recharge zone possess high

storativity, deep water table and good water holding capacity for constructing

an artificial recharge structure. Eight thematic layers which include geology,

geomorphology, lineament density, land use/land cover, soil, slope, rainfall

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and groundwater level are used to identify recharge potential zones. Various

thematic maps are reclassified on the basis of weightage assigned and brought

into the spatial analysis tool for integration (Saraf and Choudhary 1998). The

different units in each theme is assigned a knowledge-based hierarchy of

ranking from 1 to 5. These were assigned on the basis of their significance

with reference to their influence on identification of groundwater artificial

recharge sites (Selvarani 2010). In this ranking 1 denotes poorly favorable

zone, 2 denotes moderately favorable zone, 3 denotes moderate to good zone,

4 denotes good zone and 5 denotes very good zone for identification of

groundwater artificial recharge sites. The weight influence for identifying

artificial recharge sites are given in Table 9.2 and weightage ranks for

identifying artificial recharge sites are given in Table 9.3. The percentage

influence for identifying artificial recharge sites are given in Table 9.4.

Table 9.2 Weight influence for identifying artificial recharge sites

S. No Thematic map Major relationship Minor relationship Score

1 Groundwater

level

Rainfall, Lineament,

Geology, Slope

Geomorphology

Land use/land cover,

Soil 6

2 Geology Lineament,

Geomorphology,

Groundwater level

Slope, Soil, Land use/land

cover 4.5

3. Geomorphology Groundwater level,

Geology,Lineament

Soil3.5

4 Lineament Groundwater level,

Geology, Geomorphology

Slope, Lineament4

5 Land use /land

cover

Soil Groundwater level Rainfall,

Geology, Lineament3.5

6 Slope Groundwater level Rainfall, Land use /land

cover, slope, Geology3

7 Soil Land use /land cover Groundwater level, Geology,

Rainfall Geomorphology3

8 Rainfall Groundwater level Land use /land cover,

Slope, Soil2.5

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Table 9.3 Weightage and rank for identifying artificial recharge sites

S.

NoThematic map Descriptive scale

Identification of

artificial recharge

Alluvial 5

Red Soil 4

Brown Soil 3

Black Soil 1

1 Soil

Hill Restricted Area

Alluvium 5

Gneissic Rock 4

Granitoid Gneiss with

Pegmatite

4

Pyroxene Granulite 4

Charnockite 3

Dolerite 2

Ultrabasic with Magnesite 2

2Geology

Zone Brecciation 1

Flood plain 5

Bazada zone 4

Shallow pediment 3

Composite slope 2

Plateau 2

3 Geomorphology

Structural hill Restricted Area

0-0.800 1

0.801-1.600 2

1.601-2.400 3

2.401-3.200 4

4

Lineament density

km / km2

3.201-4.000 5

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Table 9.3 (Continued)

S.

NoThematic map Descriptive scale

Identification of

artificial recharge

Water bodies 5

Dense forest Restricted Area

Open forest 4

Forest blank 4

Crop land 3

Land with scrub 2

Land without scrub 2

Fallow land 2

Barren Rocky 1

5

Land use and Land

cover

Built up land 1

0 – 6 1

6.1 – 12 2

12.1 – 18 3

6

18.1 – 24 4

Water Level

(m)

>24 5

< 600 1

600.1 – 700 2

700.1 – 800 3

800.1– 900 4

7 Rainfall

(mm)

900.1 - 1000 5

0 - 1 5

1 - 3 4

3 - 7 3

7 - 15 2

8 Slope

>15 1

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Table 9.4 Percentage influence for groundwater prospects and for

identifying artificial recharge sites

Thematic

MapScore

Very

goodGood

Moderate

to goodModerate Less Total

%

of influence

Groundwater level 6 30 24 18 12 6 90 21

Geology 4.5 20 16 12 8 4 60 14

Geomorphology 3.5 17.5 14 10.5 7 3.5 52.5 13

Lineament 4 17.5 14 10.5 7 3.5 52.5 13

Land use /land cover 5 15 12 9 6 3 45 10

Slope 3 15 12 9 6 3 45 10

Soil 3 15 12 9 6 3 45 10

Rainfall 2.5 12.5 10 7.5 5 2.5 37.5 9

Total 427.5 100.0

9.3.3.3 Artificial recharge sites of the study area

Figure 9.1 Artificial recharge zone map of the study area

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From the weighted overlay analysis, the artificial recharge zones

are of moderate to good category are found in central and south east part of

the study area. 8.8 % of the study area contains moderate to good category

of recharge potential. The artificial recharge zones are found to be of very

good category in west central part and it is found in 2.73% of the study area.

62.21 % of total area of the study area contains artificial recharge zones of

good category. As the whole study area contains potential artificial recharge

zones of moderate to very good categories, the artificial recharge system can

be implemented in any part of the study area.

9.4 AQUIFER GEOMETRY

The data of the sub-surface hydro geological units, their thickness,

their depth of occurrence and hydraulic properties bring out the presence of

unconfined, semi-confined in the study area. As the discharge through either

pumping well or recharge well is the function of hydraulic conductivity,

thickness of different stratum, radius of influence, radius of the well and the

aquifer geometry becomes very important in the planning of artificial

recharge system. The surface and subsurface strata are to be permeable to

maintain high rate of infiltration during the period of artificial recharge. The

type of aquifer in the study area is unconfined aquifer.

9.5 TYPES OF RECHARGE TECHNIQUES

Various types of recharge techniques are in practice to recharge

groundwater reservoir. The type of artificial recharge technique will vary with

respect to hydro geological conditions. The artificial recharge techniques can

be broadly categorised as follows.

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1. Direct surface techniques

a. Flooding

b. Basins or percolation tanks

c. Stream augmentation

d. Ditch and furrow system

e. Over irrigation.

2. Direct sub surface techniques

a. Injection wells or recharge wells

b. Recharge pits and shafts

c. Dug well recharge

d. Bore hole flooding

e. Natural openings, cavity fillings.

3. Combination surface – sub-surface techniques

a. Basin or percolation tanks with pit shaft or wells.

4. Indirect Techniques

a. Induced recharge from surface water source

b. Aquifer modification.

As the groundwater table is available at very high depth in the

study area, the deep bore well pumps are commonly used to extract ground

water. Hence the recharge wells or vertical shafts are suggested in this work

as appropriate methods for artificial recharge in the study area.

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9.6 DESIGN OF ARTIFICIAL RECHARGE SYSTEM

9.6.1 Design objectives

The design objectives of artificial recharge system for the study

area are as follows.

1. The quality of the groundwater has to be improved by means

of natural system.

2. The groundwater storage has to be replenished so as to keep

the groundwater utilization within safe yield of the well.

9.6.2 Design concepts

The predominant controlling mechanism of the groundwater

chemistry during both premonsoon and postmonsoon seasons of the study

area is rock dominance. As the groundwater moves slowly through an aquifer,

the compositions of water continue to change usually by the addition of

dissolved constituents (Freeze and Cherry 1979). A longer residence time of

percolating water will usually increase concentrations of dissolved solids.

Because of short residence time, groundwater in recharge areas often contains

lower concentrations of dissolved solids than water occurring in other parts of

the same aquifer. The quality of groundwater of the study can be improved by

implementing the suitable system designed based on the following concepts.

1. Reducing the resident time of percolating water by reducing

the distance between source point and yield point.

2. Dissolution of dissolved solids contents by passing excessive

quantum of percolating water through the aquifer.

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The above methods can be implemented in a single system known

as artificial recharge system. Several case studies have given number of feed

backs about the increased groundwater quality due to artificial recharge

system.

9.6.3 Groundwater hydraulics terms

Aquifers: The water bearing geological formations or strata which

yield significant quantity of water for economic extraction from the wells.

Unconfined aquifer: It is the one in which water table varies in

form and slope. It depends on areas of recharge, discharge from wells and

permeability.

Specific yield: The volume of water expressed as percentage of

total volume of the saturated aquifer that can be drained by gravity is called as

specific yield.

Safe yield: The amount of water that can be withdrawn from a well

in the foreseeable future without causing depletion of the aquifer.

Hydraulic conductivity: It is a constant that serves as a measure of

the permeability of the porous medium. The permeability (K) of the study

area ranges between 0.26 m/day and 1.63 m/day (PWD 2001).

9.6.4 Design methodology

The methodology followed in the design of artificial recharge wells

to improve groundwater quality is illustrated in the flow chart given in figure

9.2 below.

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Collection of data

Estimation of annual discharge from the existing well whose groundwater

quality is

to be improved.

Estimation of volume of water required for dissolution.

Estimation of annual groundwater storage capacity of aquifer

Estimation of annual replenishment by rainfall

Identification of source for dissolution through artificial recharge

Estimation of net quantity of water required for dissolution

Calculation of number of recharge wells required

Determination of location of recharge wells

Figure 9.2 Flow chart showing design methodology

9.6.5 Assumptions in the design of artificial recharge system

1. The discharge through subsurface flow obeys Thiem’s

equation.

2. The velocity of subsurface water flow obeys Darcy’s law.

3. The well losses are ignored.

4. The artificial recharge system is within recharge boundary or

cone of influence

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9.6.6 Data to be collected

1. Specific yield of the aquifer ( Sy) in %

2. Infiltration rate of the substratum (Ir) in %

3. Hydraulic conductivity of the each stratum (K) in m/day

4. Depth of groundwater table (GWT) in m

5. Normal fluctuation of GWT before and after rains (gwt) in m

6. Depth of pumping water level (PWL) in m

7. Overall thickness of unconfined aquifer (huo) in m

8. Depth of the well(Dw) in m

9. Radius of proposed / existing dry well (rw) in m

10. Radius of influence circle of well (ro) in m

11. TDS content of the water sample from the selected well (TDS)mg/l

12. Allowable TDS content in drinking water (Per TDS) in mg / l

9.6.7 Design steps

Step 1 Estimation of annual discharge from the existing well for which

the groundwater quality is to be improved

Darcy’s Law and the fundamental equations governing

groundwater movement are important in finding groundwater flow into wells.

With the help of pumping tests, the storage coefficients and the

transmissivities of aquifers can be determined. Well flow equations have been

developed for steady and unsteady flows in various types of aquifers and for

several boundary conditions. For practical applications most of the solutions

have been reduced to convenient mathematical forms. (Todd 2001)

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When a well is pumped, water is withdrawn from the aquifer

surrounding the well and the water table or piezometric surface, depending on

the type of aquifer is lowered. The drawdown at a given point is the distance

to which the water level is lowered. A drawdown curve shows the drag down

of water level with the distance from the well. In three dimensions the draw

down curve describes a conic shape known as the cone of depression. Also,

the outer of the cone of depression defines the area of influence of the well.

An expression for the steady radial flow to a well in an unconfined aquifer

can be derived from Dupit’s assumptions. The flow direction and the cone of

depression in an unconfined aquifer as shown in Figure 9.3. For a well

completely penetrating into the aquifer, the discharge rate Qwelly is as given

Equation (9.1).

Qwelly = K (ho2 – hw

2) / ln ( ro/ rw) (9.1)

where, K - hydraulic conductivity in m/day,

hw - distance between pumping water level and impermeable

stratum in m,

ho - distance between groundwater table and impermeable stratum

in m,

ro - radius of influence circle in m,

rw - radius of well in m.

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Figure 9.3 Radial flows into a pumping well penetrating into

unconfined aquifer

As there is no artesian well in the study area, it is evident that the

whole subsurface of study area consists of unconfined aquifer.

Step 2 Estimation of volume of water required for dissolution

TDS content of the groundwater from the existing bore/open well

= TDS

Permissible TDS content as per IS: 10500 in the groundwater

= Per TDS

Multiplication factor (FQf) required for the determination of

dissolution quantity of water (Qdis),

FQf = TDS / Per TDS

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The average rainfall recorded at rain gauge station of the study area

during premonsoon season of the year 2007 is 684 mm and during postmonsoon

season is 564 mm. The average TDS content at the rain gauge stations is 1148

mg/L in premonsoon season and 1753 mg/L in postmonsoon season. The TDS

content is 1.53 times higher in postmonsoon season and the rainfall is 1.2 times

higher in premonsoon season. Hence it may be taken that 1.2 times increase in

rainfall has shown difference in postmonsoon TDS by 64%.

Hence, a factor of safety of 1.5 may be assumed to find volume of

water required for dissolution.

Allowing a factor of safety of 1.5,

Safe FQf = FQf x 1.5

Quantity of water required (Q dis) for dissolution is given in

Equation (9.2)

Q dis = Qwelly x Safe FQf (9.2)

Step 3 Estimation of annual groundwater storage capacity

Annual groundwater storage (Qy) = Area of pheratic aquifer (Aq) x

Normal fluctuation of groundwater table before and after rains (gwt) x

specific yield (Sy)

Qy = Aq x gwt x Sy /100 (9.3)

Step 4 Estimation of annual replenishment by rainfall

Quantity of annual groundwater replenishment by normal rainfall

(Qrf) is,

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Qrf = Area of pheratic aquifer (Aq) x Infiltration rate (Ir) x Normal

rain fall (Nrf)

Qrf = Aq x Ir/100 x Nrf /1000 (9.4)

Step 5 Identification of source for dissolution through artificial

recharge

Case (i) If the quantity of normal rainfall required for annual

groundwater replenishment is less than annual groundwater storage capacity

of the aquifer then the quantity of water infiltrating after surface runoff due to

normal rainfall is not sufficient for dissolution through artificial recharge.

Then the amount of water required for dissolution through recharge

can be collected from roof top over an area mentioned in Table 9.1 as

supplement quantity (Q sup).

i.e. If Qrf < Qy, then Q sup is required.

Case (ii) If the quantity of normal rainfall required for annual

groundwater replenishment is greater than the annual groundwater storage

capacity of the aquifer, then the quantity of water available from surface

runoff due to normal rainfall can be collected or diverted to artificial recharge

well for dissolution purpose.

i.e. If Qrf > Qy, then Q sup is not required

Additional water available (Q add) from rainfall for dissolution

after replenishing aquifer

Q add = Qrf - Qy

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Step 6 Estimation of net quantity of water (Q net) required for

dissolution through artificial recharge

If the selected well is of Case (i)

Net quantity of water required = Quantity of water required for dissolution +

Quantity of water required for replenishment

Q net = Q dis + Qy (9.5)

If the selected well is of Case (ii)

Net quantity of water required = Quantity of water required for dissolution-

Water available after the replenishment of

groundwater storage.

Q net = Q dis - Q add (9.6)

Step 7 Number of recharge wells required

Recharge well may be defined as a well that admits water from the

surface to fresh water aquifers. The flow in the recharge well is the reverse of

a pumping well, but it construction may or may not be the same. If water is

admitted into a well, a cone of recharge will be formed that is similar in shape

but is the reverse of cone of depression surrounding a pumping well. It is

considered that the rainfall water is admitted for recharge into recharge well at

ground level.The total depth of recharge well is taken as the depth of water in

recharge well (hw1) for calculation purpose. The equation for the curve can

be derived in a similar manner to that for a pumping well.

The Radial flow from recharge well penetrating into unconfined

aquifer is shown in Figure 9.4. For an unconfined aquifer with water being

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recharged into a completely penetrating well at a rate QR, the approximate

steady-state expression is given in Equation (9.7).

Q rw = K (hw12 – H

2) / ln (ro/ rw) (9.7)

where, K - hydraulic conductivity in m/day,

hw1 - distance between pumping water level and impermeable

stratum in m,

ho - distance between groundwater table and impermeable

stratum in m,

ro - radius of influence circle in m,

rw - radius of recharge well in m.

Figure 9.4 Radial flow from recharge well penetrating into unconfined

aquifer

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No recharge wells required (Nw) = Net quantity of water required forrecharge /

Discharge through one recharge well

Nw = Q net / Q rw (9.8)

9.7 LOCATION OF RECHARGE WELLS

The recharge wells may be located in the groundwater flow

directions. The flow lines and equipotential lines are mapped in two

dimensions to form a flow net. The groundwater flow direction in an area may

be found out from constructing flow nets for that location. A typical flow net

diagram is shown in Figure 9.5.

Figure 9.5 Flow net formed by flow and equipotential lines

9.8 WATER TABLE CONTOURS

The groundwater flow lines can be drawn from equipotential lines

of water table. The water table during premonsoon season is shown in Figure

9.6 and the water table during postmonsoon season is shown in Figure 9.7.

The groundwater flow is always towards the lower water table. By comparing

the adjacent water table contours, the groundwater flow direction can be

determined. The location of artificial recharge wells can be found out from the

water table contour diagrams.

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Figure 9.6 Water table contour during premonsoon season

Figure 9.7 Water table contour during postmonsoon season

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9.9 SUMMARY AND APPLICATION OF ARTIFICIAL

RECHARGE IN GROUNDWATER QUALITY

The groundwater quality of the study area was found good during

premonsoon season when compared with the groundwater quality of

postmonsoon season. It has been discussed that the reason for this

groundwater quality variation is primarily due to dissolution in groundwater

due to rainfall infiltrations. Hence, an attempt is proposed in this work to

improve the groundwater quality by the process of dissolution using artificial

recharge. The various aspects of artificial recharge such as recharge potential,

recharge method, design of recharge wells and location of recharge wells are

carried out in this work.

The whole study area contains potential artificial recharge zones of

moderate to very good categories. It shows that the artificial recharge system

can be implemented in any part of the study area. The direct sub surface

technique of recharge using recharge wells is suggested in this work as a

recharge method for the study area.

The artificial recharge wells are acting in a reciprocal fashion to

that of a pumping well. The concept applied to measure the discharge from a

pumping well is used here in reciprocal fashion by calculating the amount of

water to be pumped in for dissolution of groundwater.

The TDS content in the groundwater is estimated using ANN

model for a proposed new well or TDS content is determined by standard

tests for an existing well. The expression derived after Thiem’s equation and

Dupit’s assumptions are used here for the determination of discharge in the

well. The rate to which the TDS is to be reduced is determined from dividing

TDS content at the well with permissible TDS content. The amount of

volume required for dissolution is determined from multiplying calculated

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annual discharge of the well and rate to which TDS is to be reduced. The

number of artificial recharge wells required is calculated from the amount of

water that can be driven into aquifer from recharge well from its dimensions

and hydrological conditions.

The amount of water required for dissolution may be received from

roof top rain water harvesting. The roof top area over which rain water is to

be collected may be known from the data provided by artificial recharge

guidelines. A design program “ARD PRO 1.0” in C language has been

developed to carry out the design of artificial recharge wells. This program

helps to execute the design quickly. Thus designed artificial wells are

located around the well whose groundwater quality is to be improved. The

location for the recharge wells are fixed from the flow nets developed with

the help of hydraulic gradient, flow directions and water level contours.