chapter-3 hydrogeology and aquifer parameters 3.1...

31

CHAPTER-3

HYDROGEOLOGY AND AQUIFER PARAMETERS

3.1 General Introduction

This chapter deals in detail with the Hydrogeology, groundwater occurrence, Well

inventory, and future scope of groundwater development in the study area. The quality of

water is of vital concern for humankind, since it is directly linked with human welfare. It

is now generally recognized that the quality of groundwater available in an area is as

important as the quantity. Groundwater quality data gives important clues to the geologic

history of rocks and indications of groundwater recharge, discharge, movement and

storage (Walton, 1970). Good quality groundwater generally is clear and colorless

although changes may be occur due to water logging, over draft from areas adjoining

saline water resources, recycling of water applied for irrigation and seepage of industrial

wastes. Hydrogeochemical studies explain the relationship of water chemistry to aquifer

lithology (Sastri, 1976). Such relations not only explain the origin and distribution of the

dissolved constituents but also elucidate the factors controlling the groundwater

chemistry (Rangarajan and Balasubramanyam, 1990).

Water resources are increasingly in demand in order to help agricultural and

industrial development, to create income and wealth in rural areas, to reduce poverty

among rural people, and to contribute to the sustainability of natural resources and the

environment. As urban demand grows, agricultural water allocations are increasingly

viewed as a reservoir from which water can be transferred to towns, although wastewater

from cities can sometimes be recycled to provide some sort of offset (World Bank, 2005).

Research has shown that chemical composition of groundwater (Foster 1995; Moor et al.,

2006) has marked impact on well being of human beings.

It is not necessary that a person falls ill soon after drinking contaminated water;

rather it needs years before adverse affects appear. About one-third of solar flux absorbed

32

by the earth‟s surface is used to drive the hydrological cycle – massive evaporation from

the oceans, cloud formation and precipitation. Precipitation provides us with supply and

reserves of fresh-water. Water to reach the groundwater reservoir has to pass through

atmosphere, soil and weathered/fractured rock. In this journey, it comes in contact with

several organic and in organic substances. During its slow movement through the

different layers below the ground the percolating water reacts with number of minerals;

organic and inorganic and carries them along with it in dissolved state at the same time

groundwater gets rid of most of the microorganisms and other suspended matter through

the natural filtration process and it is generally devoid of biological contamination.

Watershed approach has been the single most important landmark in the direction

of bringing in visible benefits in rural areas and attracting people‟s participation in

watershed programmes (Singh J, et. al., 2005). Intensive use of natural resources and

increased human activities are posing great threat to groundwater quality (Foster 1995).

Dissolved minerals determine the usefulness of the groundwater for various purposes.

Presence of some substances beyond certain limits may make it unsuitable for irrigation,

domestic or industrial uses. Corrosion or incrustation of tube well screens is another

hazard related to quality of groundwater. Therefore, before using the groundwater for any

of the purposes it is essential to find out possible hazardous substances, it may contain.

Water quality analysis brings out the concentrations of hazardous elements, based on

which a water source can be accepted or rejected for domestic, irrigation or industrial

purposes.

It also forms basis for groundwater treatment plan, if required. Some organic

compounds, or groups of compounds, are known to either toxic, or carcinogenic (cancer

producing) or to produce odors and tastes. Most of the toxic substances are pesticides

(including herbicides, fungicides and insecticides) which are applied in very large

quantities in some parts of the world. Chemical substances can be found either in

suspension or in solution. As mentioned earlier groundwater gets rid of suspended

particles through natural filtration mechanism. Substances carried in solution determine

the suitability of water for various purposes.

33

3.1.1 Previous Work

The reconnoiter surveys were conducted from time to time by Central Groundwater

Board and State Groundwater Department for different purposes. Very few geologists

have done extensive work on different aspects of geology in the area. Over the years, the

State Groundwater Department has been engaged in the area in various groundwater

resources developmental activities such as systematic hydrogeological mapping, well

inventory, hydrological and geophysical studies followed by exploratory-production

drilling and water resource management.

3.1.2 Hydrogeology of the study area

Entire study area is underlain by rocks of archaean metamorphic complex. About

70% of the area is underlain by Hornblende-Biotite Gneiss and remaining area covered

with the Charnockite/Gneissic Charnockites. Intrusives of pegmatites and quartz veins

are also common in the northeastern parts of the study area. These geological units have

undergone continue weathering up to 2 to 12m depth. The weathered zone and the

secondary porosity facilitate groundwater recharge at some places. Major part of the

study area covered with alluvial fills and dissected plateau having high recharge values.

Groundwater occurs in all the geological formation from archaean crystalline rock to

recent alluvium, it is in phreatic condition in alluvium and weathered crystalline and in

semi confined to confined condition in the deep fractured rocks. Based on

Hydrogeological information the study area can be divided into two units Valley

fills/Alluvium and Crystallines. Valley fills are noticed along the valley portion and along

the streams. Rainfall is the main source of groundwater recharge in the area. The water

level ranges from 2.2 to 11.8m bgl (pre monsoon) and 1.2 to 4.6m bgl (post monsoon).

34

3.1.3 Well Inventory

In order to monitor groundwater level for pre monsoon and post monsoon periods,

42 monitoring wells (Open Wells and bore wells) were established in the study area

(Figure 3.1 & Table 3.1). The well inventory includes, depth to water level (bgl), total

depth, type of well, well diameter, purpose of well, well history, water sampling for

chemical analysis in laboratory, geo co-ordinates, insitu EC and pH.

Figure 3.1 Location map of observation wells in the study area.

35

Table 3.1 Well inventory data, reduced levels and groundwater levels of observation wells (June 2010, November 2010).

Well

ID Location/Owner name Well Type Well Dia (m) MP (m) TD (m) RL (m)

WL bgl (m)

Pre

WL bgl (m)

Post

P 1 Pudunagaram, Public Well DW 2.50 0.8 11.5 119.53 7.09 2.93

P 2 Vadavannur, Chidambaram DW 2.80 0.75 12.6 121.012 11.87 4.63

P 3 Vadavannur, Narayanan DW 1.50 0.55 8.1 120.651 6.00 4.32

P 4 Vadavannur, Prashanth DW 2.30 0.7 9.7 119.845 6.75 3.52

P 5 Vadavannur Junction, Ananthakrishnan DW 2.00 0.75 6 118.653 3.91 2.93

P 6 Main road Vadavannur, Mani DW 2.00 0.7 6.8 118.756 3.10 2.08

P 7 Pudunagaram Village, Venugopalan DW 2.80 0.75 9.8 119.9 5.84 3.7

P 8 Pudunagaram main road, Gangadharan DW 1.60 0.7 11.35 118.456 8.64 4.01

P 9 Pudunagaram ward no:5, Majeed DW 2.50 0.85 10.55 119.021 6.10 3.2

P 10 Peruvambu panchyat, Dhashayani DW 1.50 0.7 7.7 117.524 5.31 3.15

P 11 Peruvambu ward no:12, Chinnammu DW 1.60 0.7 6.2 114.021 5.18 3.08

P 12 Kodavayur, Abdul Rasheed DW 2.80 0.7 7.5 110.012 3.00 1.38

P 13 Kodavayur, Sakeer Husain DW 1.20 0.75 9.65 98.658 6.66 3.46

P 14 Kakayur village, Abdul Kalam BW 0.15 0.1 60.9 92.031 - 17.781

P 15 Main stream STREAM 14.85 length 1.00 - 80.124 4.25 -

P 16 Vamballur Junction, Mukundhan DW 1.85 0.7 8.4 78.455 4.95 3.91

P 17 Kodavayur,ward no:10, Mohanan DW 1.50 0.75 7.2 97.864 2.83 2.16

P 18 DRW 04 GWD CANAL 9.40 length 0.90 - 97.986 - -

P 19 Kakkayur HP 0.13 0.50 45.7 84.05 - -

P 20 Vakkod, Swaminadhe DW 1.20 0.5 4.65 98.561 3.12 3.5

P 21 Pallasani , Krishnan R DW 0.90 0.75 5.2 102.053 4.72 1.76

36

Table 3.1 Cont. Table 3.1 Well inventory data, reduced levels and groundwater levels of observation wells (June 2010, November 2010).

Well

ID Location/Owner name Well Type Well Dia (m) MP (m) TD (m) RL (m)

WL bgl (m)

Pre

WL bgl (m)

Post

P 22 Pulaparambu junction, Public Well DW 2.60 0.80 8 104.159 7.01 3.25

P 23 Pallasani, Noormuhammed BW 0.15 0.8 91.4 126.25 - 3.58

P 24 Vadavannur, Ramankutty DW 1.50 0.4 5.85 113.35 3.04 1.88

P 25 Vadavannur, Saludheen DW 1.40 0.65 7.7 116.534 3.93 -

P 26 Tamarapadam, Ramachadran BW 0.15 0.75 53.3 115.021 - 1.9

P 27 Karippode, Manikandan DW 1.50 0.96 7.5 119.162 8.01 2.72

P 28 Karippode, Mohandas DW 1.80 0.75 6.7 116.12 5.98 1.9

P 29 Podikal pad, Public Well DW 2.20 0.65 5.7 107.046 4.15 2.81

P 30 Pudungaram, Public Well DW 1.30 0.65 8.1 116.021 4.48 2.45

P31 Tattamangalam, Chandran.v DW 1.40 0.85 8.3 122.02 2.20 1.23

P32 Arampadam , Lalitha.k DW 1.70 0.8 8.6 109.12 3.62 2.02

P33 Vadavannur, Salva kumar.k DW 1.10 0.57 7.6 117.05 6.25 4.35

P34 Tattamangalam, Devrajan BW 0.15 0.60 76.2 128.06 - 4.98

P35 Vadavannur , Mustaffa DW 3.20 0.88 13 120.25 6.61 3.44

P36 Kodavayur, Public Well DW 3.30 0.72 22.8 104.07 3.12 2.02

P37 Kannamkode, Public Well BW 0.15 0.55 109.7 98.04 - 17.66

P38 Kannankode, Thanga prakash DW 2.50 0.2 3.25 85.07 2.31 1.57

P39 Pallsani, Muralidhran DW 3.25 0.65 9.5 93.02 2.57 2.3

P40 Thenkurussi Village BW 0.15 0.47 121.9 86.45 - -

P41 Thekkampuram, Public Well BW 0.15 1.54 92.3 83.05 - 2.38

P42 Kodavayur, Public Well DW 2.90 0.73 80.5 98.658 4.95 3.13

37

Groundwater level in the study area varies from 2.2 to 11.87m (bgl) in pre-

monsoon periods and 1.23 to 4.63 m (bgl) in post monsoon periods. The depth to water

level maps (pre and post monsoons) and fluctuation map are shown in below paragraphs.

Figure 3.2a Contour map showing water level (in meters, bgl) for pre-monsoon.

In the pre monsoon season, deeper groundwater level of 11.87m (bgl) noted in P2,

P8, P27 and P33 wells in the eastern part of the study area. The excessive withdrawal of

groundwater for agriculture and other purposes caused the decline of water levels.

Western part of the study area is noted with shallow groundwater levels 2.2m (bgl), this

could be due to less groundwater exploitation (Figure 3.2a).

In the post monsoon season deeper groundwater levels of 4.2 m (bgl) noted in P2,

P3, P8, P9,P33 wells in the eastern part and P13,P14,P15,P16,P20,P40,P41 wells in the

western part of the study area and shallow groundwater levels observed in middle portion

of the area.(Figure 3.2b).

38

Figure 3.2b Contour map showing water level (in meters, bgl) for post monsoon.

Figure 3.3 Groundwater level fluctuations of pre- and post-monsoon seasons.

39

The groundwater level fluctuation map (Figure 3.3) of pre and post monsoon

indicates, that eastern part and southwestern parts of the study area show the patches of

maximum fluctuation up to 7.2m (bgl). The water level was raised to 4.2 m (bgl) in post-

monsoon from 11.87 m (bgl) in pre-monsoon.

3.2 AQUIFER PARAMETERS

3.2.1. Pumping test

3.2.1(i) Introduction

To know the groundwater saturation and sustainability 4 Pumping tests were

conducted and are discussed at length in the ensuing paragraphs. Aquifer studies provide

essential information for water-resource management and form an essential tool to assess

and document the potential influences on local wells and to understand the local aquifer

characteristics. Hydraulic properties of aquifer are its hydraulic conductivity and

Storativity. Other parameters like transmissivity, leakage, etc., are derived parameters.

Hydraulic conductivity (K) is defined as the rate of flow through unit area of an aquifer

under unit hydraulic gradient at prevailing kinematic viscosity. Its dimensions are L't.

Storativity is the volume of water that an aquifer can release from storage over a unit

decline of head (or take into storage over a unit rise in head) per unit surface area. It is

dimensionless. Transmissivity is an important derived parameter defined as the rate of

flow through unit width of an aquifer under unit hydraulic gradient at prevailing

kinematic viscosity. Its dimensions are L2/t.

Since, there is a large variation in vertical characteristics of the aquifer and flow

to a well occurs through entire thickness of the aquifer transmissivity is more appropriate

representation of flow characteristics around a well. It is determined using various steady

and unsteady flow equations. Thiem (1906) derived his steady state equation from

Darcy's law and used for determining transmissivity until Theim developed unsteady

flow equations in 1935 (Theis, 1935). This equation was modified by many other workers

to suit different conditions or to simplify the computations. Notable authors are

Papadopulos (1967), Walton (1962), Boulton (1963) and others. Knowledge of hydraulic

40

properties of aquifer and associated rock properties of formations is essential in any

scheme of groundwater resource assessment. Pumping tests are an accepted means of

acquiring data on hydraulic properties. In crystalline (hard) rocks, the development of

porosity and permeability is due to fracturing and weathering. Weathering and fracturing

are denser near the surface and hence the permeability of hard rocks generally decreases

with depth. An aquifer test is designed to impose a hydraulic stress on the aquifer in such

a way that measurements of response will fit in a theoretical model of aquifer response.

However, in hard rocks the data obtained from pumping test need to be interpreted with a

degree of caution as the system is highly an isotropic and heterogeneous. In a carefully

controlled pumping test, the following information can be obtained such as transmissivity

(hydraulic conductivity), storage coefficient (specific yield in unconfined aquifer),

leakage factor (of semi-confined aquifers), drainage factor (of semi-unconfined aquifers)

and hydraulic resistance (of confining layers). In addition, distance, direction, nature of

barrier (no-flow) or recharge boundaries, lateral gradation, thickening, pinching and

interconnection of aquifers. From these parameters, effects of current and projected

pumping on the water levels on surrounding wells for one-year period can be assessed if

rate of rise or decline in water levels is monitored continuously. The study can indicate if

water quality changes are likely to occur because of future pumping demands. Thorough

understanding of the Hydrogeological regime helps in interpreting the pumping test data.

In this study, the objective was to assess the aquifer parameters such as transmissivity,

Hydraulic conductivity and Storativity.

3.2.1(ii). Methodology adopted for the pumping test

Initially pre-pumping water level data was collected for several hours from each

of the tested wells. As continuous pumping for a long duration was needed diesel

generator of 30 KV capacities along with a standby generator of 10 KV capacities were

used as source of power for the pump used.

Pumping tests were carried out in the wells by prior informing the well owner for

not to run for 24 hours before pumping test start. The depth to water level and changes in

water levels with time (drawdown) during the test were- made with an accuracy of 1/2

41

cm using steel tapes and electronic drop line indicators. The electronic drop-line

indicators used in the study worked well and gave excellent results. For each log cycle of

time, at least 10 measurements were made although in the first log cycle. The pumped

water was released at least 100m away to avoid the insitu seepage of surface water to the

well. Residual water level readings were noted down during recovery of wells. Majority

of the wells were found 80 to 95 % of recovery within 8 to 12 hours. The pumping test

data was interpreted by THEIS time Vs draw down method. pH and EC were also noted

during pumping test, but no significant variations were observed in ph & EC.

3.2.1(iii). Pumping test data analysis

Analysis of the pumping test data is a crucial phase in the determination of aquifer

parameters. Obtaining reliable values depends largely on the accuracy of the analysis. It

comprises calculations and representations of the data on graphs from which aquifer

types and flow conditions are understood. There are several methods and formulae for

analysing the pumping test data in various aquifer conditions. Most of these are meant for

analysing the pumping test data from bore wells with some modification, depending on

the aquifer conditions and assumptions many hydrogeologists have successfully applied

the same methods and formulae for large diameter wells in water table conditions.

Large diameter dug wells are the main source of water supply in many areas in

the world. They are particularly useful in shallow aquifer conditions with low

transmissivity. They are mainly used for domestic and agricultural supply. Since they are

common and widely prevalent it becomes imperative to make use of these wells to

determine the aquifer characters in these areas. This situation becomes more relevant in

the case of hard rock terrains.

In 1981, Herbert and Kitching stated, "There is no accurate method which will

allow the calculation of Transmissivity from recovery data obtained from partially

penetrating large diameter wells" and situation is not much different even today.

42

Figure 3.4 Pumping test locations in the study area.

In the present study, pumping tests were conducted at four, wells (Figure 3.4).

Three of them are located in the Hornblende-Biotite Gneiss and rest of the one located in

charnockites. Aquifer characteristics have been determined from the data collected and

the results are analyzed and interpreted. Keeping in view the hydrogeological conditions,

Theis method is used to determine the aquifer parameters.

43

Pumping test 1 is carried out in observation well no P12. The values of Hydrogeological

parameters obtained in PT1 are as Hydraulic conductivity: 8.216 m/d, Transmissivity:

38.53 m2/d and Storativity(s) 0.204. The details of the pumping well are as follow.

Location Well No. P12

Initial WL (m) 1.49 m

Discharge Rate 25 Lit/ 6.22 sec

HP of Pump 3 HP

Well Diameter 2.9 m

Total Depth 6.18 m

Running Hour/ Day 10 minutes

Purpose Domestic


parameters obtained in PT2 are as Hydraulic conductivity: 176 m/d, Transmissivity: 241

m2/d and Storativity (s) 0.0588. The details of the pumping well are as follow.


Initial WL 3.43 m


HP of Pump 3 HP

Well Diameter 1.27 m

Total Depth 4.8 m

Running Hours/ Day 20 minutes

Purpose Domestic

44


parameters obtained in PT3 are as Hydraulic conductivity: 29.6 m/d, Transmissivity: 61

m2/d and Storativity (S) 0.268. The details of the pumping well are as follow.


parameters obtained in PT4 are as Hydraulic conductivity: 18.9 m/d, Transmissivity: 51.3

m2/d and Storativity (S) = 0.09. The details of the pumping well are as follow.


Initial WL (m) 4.51


HP of Pump 3

Well Diameter 1.06 m

Total Depth 7.22 m

Running Hours / Day 30 minutes

Purpose Domestic

Location Well No.P38

Initial WL (m) 1.19


HP of Pump 3

Well Diameter 2.5 m

Total Depth 3.25 m

Running Hours /Day 10 minutes

Purpose Domestic

46

Figure 3.5 Graphical representation of pumping test data.

47

The pumping tests at four locations depicts that the hydraulic conductivity in

the middle portion is 8.2 m/d to as high as 176 m/d in the downstream. Similarly,

Transmissivity was noted to gradualy increase from middle to downstream of the study

area. Transmissivity in the middle portion is 38.53m2/d to 61m

2/d in the downstream of

the study area.

3.2.2. INFILTRATION TEST

3.2.2(i). Introduction

Infiltration rate is the physical property of soil, which determines the velocity of

downward movement of surface water in to the ground. The infiltration rate of soil is

dependent on soil matrix i.e. soil grain size, texture, loose of compactness,

interconnectivity of pore spaces, moisture, slope or topography temperature etc. It is

usually measured by the depth (in m) of the water layer that can enter the soil in one

hour. In dry soil, water infiltrates rapidly called the initial infiltration rate. As more

water replaces the air in the pores, the water from the soil surface infiltrates more slowly

and eventually reaches a steady rate known as the basic Infiltration rate. The infiltration

rate helps in estimating groundwater recharge with respect to rainfall.

3.2.2(ii).Methodology and Field Observation

A double ring „Infiltrometer‟ with 60 cm and 30 cm diameter of outer and inner

rings respectively with height of 30cm for both the rings was used to carry out the

infiltration tests. The lateral spread of water from outer ring will reduce the error by

allowing vertical downward movement of inner ring water, constant water level is

maintained in outer ring and every precaution had been taken to minimize the error.

Readings were noted accurately at unit interval and then increased interval with time until

the equilibrium of infiltration rate achieved then stopped the test. Based on readings

infiltration rates were calculated in mm/day.

Total Four infiltration tests were performed in the study area. The locations of the

Infiltration tests can be seen in Figure 3.6.

48

Figure 3.6 Locations of Infiltration Test in the study area.

Table 3.2 Infiltration rates of the study area.

Test No

Location

Long

Lat

Infiltration Rate

in mm/hour

1 Near to P29 76.67227 10.67985 157.7

2 Between P15 & 16 76.62092 10.67035 81.8

3 South of P32 76.70268 10.6691 70

4 Near to P22 76.65158 10.63808 157.2

The infiltration rates vary from 70 to 157.7mm/day. The lowest infiltration rate

was noted in the upstream, where as high values were recorded in the middle portion to

downstream of the study area.

49

3.2.3 MOISTURE AND PERMEABILITY MEASUREMENTS

3.2.3(i) Introduction

Neutron soil moisture gauge has been used in hydrology for the measurement of

moisture content of soil. Compared to other methods, the radiometric method has several

advantages such as better reproducibility, quicker measurement and non-destructing

insitu measurement. The neutron technique for soil moisture measurement is based on the

effective slowing down of fast neutrons by the hydrogen present in water compared to

other elements present in the soil matrix. The isotopic fast neutron source kept in the soil

moisture gauge gives high-energy neutrons, which undergo collision with elements

present in the soil and water. During such collisions, the energy lost by a neutron varies

according to the mass number of the target atoms as well as the angle of collision. The

energy lost during a head on collision with an atom of hydrogen is highest due to lowest

mass number of hydrogen. The slow neutron density around the fast neutron source when

kept in moist soil, varies according to moisture content i.e. hydrogen concentration of the

soil. This slow neutron density is measured and correlated to the moisture content of the

soil.

3.2.3(ii) Methodology

The Neutron soil moisture probe consists of a fast neutron source near a slow

neutron detector with associated electronic circuitry. The neutron Amercium241–

Berilium source is used in the present (Troxler make, USA, model 4300) neutron

moisture probe. The Am 241-Be activity source used in the present gauge is 10milli

curie. The nuclear source yields about 17000 neutrons per second. The fast neutrons

emitted are thermalized or slowed by the hydrogen (water) in the material. The ideal

detector which can be used with moisture gauge should have high efficiency for slow

neutrons and should be insensitive to fast neutrons and gamma radiations. In the present

gauge Helium-4 detector is used.

For the measurement of moisture content with depth probe an access tube

(aluminum tube/ pvc tube) is inserted in the soil at the required place of measurement.

Normally a special drilling facility (slim hole of 2.5-3” dia) would be used to drill in the

soil for the insertion of the access tube in the soil. The soil moisture probe would be

50

inserted into the access tube up to the depth of interest. The response of the probe in the

soil is noted. From this response, the moisture content of the soil at the measurement

position is obtained from the calibration graph. The moisture content of the soil thus

indicated depends upon many field parameters as well as on the accuracy of calibration

and precision in the measurement.

3.2.3(iii) Field Measurements

Slim holes were drilled at selected sites in the watershed using DTH drilling

technique and using 3"drilling bit and 1.5" drilling rods (Figure 3.7). The holes were

made up to the depth of 25-30 feet. Immediately after the drilling, PVC pipes were

inserted in to the holes. The bottoms of the PVC pipes are closed in order to avoid water

entering the access tubes. A calibrated neutron probe was used to monitor moisture from

the ground surface to the access tube depth.

Figure 3.7 Slim holes location map of the study area.

76.62 76.63 76.64 76.65 76.66 76.67 76.68 76.69 76.7 76.71 10.64

10.65

10.66

10.67

10.68

10.69

P1

P2 P3

P4 P5

P6

P7

P8

P9

P10 P11

P12 P13

P14

P15 P16 P17

P19

P20

P21 P22

P23

P24 P25

P26

P27

P28

P29 P30

P31

P32

P33 P34

P35

P36 P37 P38

P39

P40 P41

P42 Pudunagaram

Pilappull

Karuppod

Vadavannur Tamarpadam Tachankad

Kakkayur

Vakkaod

Ettanur

Koduyayur

Slim holes

D2

D1

D3

D4

D5

D6

D7

Shallow BW Deeper BW

51

Depth moisture measurements taken at 4 slim hole sites for two time intervals in

20cm section up to maximum depth of 6m. Depths versus moisture data graphs are

shown in figure 3.8. The sites are located in rainfed land near the irrigated fields. And

soil samples were collected from the field near to the each slim hole location and

conducted permeability test through constant head and variable head methods using

laboratory permeameter.

Table 3.3 Saturated Permeability values of soil

Nearest Well Slim hole no K(m/d) Site condition

Near P21 P2 0.0916 Rainfed land, silt clay soil

Near P16 P5 0.1416 Rainfed land, sandy soil



52

Figure 3.8 Depth versus moisture data graphs at the sites of slim holes.

53

3.2.3(iv). Field Observations

Depth moisture data for two time intervals (March 2012 and July 2012) indicate

increase in moisture content for the month of July 12 in comparison to March 12 data.

The difference in depth moisture data is used for estimating moisture influx during the

period March to July 2012. The moisture influx values up to the depth of 3m range from

18-111mm in the study area. This is due to change in texture and structure of the soils as

observed in rock cuttings collected at the time of drilling. The increase in moisture flux is

probably due to rainfall occurred during the period of March to July 2012. The saturated

permeability of shallow soil zone is evaluated using laboratory permeameter through

constant head and variable head methods. The results are presented in Table 3.3. The

values range from 0.09 m/d to 0.37 m/d. The high moisture flux in the study area is

probably due to high hydraulic conductivity of shallow soil.

3.3 Summary

The results of Hydrogeological and Aquifer parameter investigations carried out in the

study area of 42 km2 are summarized below.

Groundwater occurs in all the geological formation from archaean crystalline

rocks to recent alluvium soft rocks. The major hard rock aquifer is hornblende

biotite gneiss.

These geological units have undergone continuous weathering up to 2 to 12m

depth. The weathered zone and the secondary porosity facilitate the groundwater

recharge in the study area.

Groundwater level in the study area varies from 2.2 to 11.87m (bgl) in pre-

monsoon periods and 1.23 to 4.63 m (bgl) in post monsoon periods.

In the pre-monsoon season, deeper groundwater level of 11.87m (bgl) is noted in

the eastern part of the study area.

Western part of the study area is noted with shallow groundwater levels 2.2m

(bgl) this could be due to less groundwater exploitation.

54

Eastern part and southwestern parts of the study area showing the patches of

maximum fluctuation up to 7.2m (bgl). The water level was raised to 4.2 m (bgl)

in post-monsoon from 11.87 m (bgl) in pre-monsoon.

The excessive withdrawal of groundwater for agriculture and other purposes

caused the decline of water levels.

The pumping tests data obtained in four locations depicts that the hydraulic

conductivity in the middle portion is 8.2 m/d to as high as 176 m/d in the

downstream.

Transmissivity was noted gradual increase from middle to downstream of the

study area. Transmissivity in the middle portion is 38.53m2/d and 61m

2/d in the

downstream of the study area.

The infiltration rates vary from 70 to 157.7mm/day. The lowest infiltration rate

was noted in the upstream, where as high values were recorded in the middle

portion to downstream of the study area.

The moisture influx values up to the depth of 3 m range from 18-111mm in the

study area. This is due to change in texture and structure of the soils.

The increase in moisture flux is probably due to rainfall during the period of

march to july 2012.

The saturated permeability test values range from 0.09 m/d to 0.37 m/d.

The High moisture flux in the study area is probably due to high hydraulic

conductivity of shallow soils.

55

Plate 3.1 Well inventory in the study area.

Plate 3.2 Water level measurement of observation well by Water Level Indicator.

56

Plate 3.3 Double Ring Infiltrometer.

Plate 3.4 Measuring of Infiltration Rates in the Field.

57

Plate 3.5 Neutron moisture probe.

Plate 3.6 Measuring of moisture content of soil in the study area.

58

Plate 3.7 Soil sample collection in the study area.

Plate 3.8 Measuring Soil Permeability with Permeameter in the laboratory.

chapter-3 hydrogeology and aquifer parameters 3.1...

Documents