eChapters

14.1 Introduction

Groundwater is an important source of water for irrigation. It is the most abundant fresh water resource of the earth. Underground water reservoirs contain large stock of fresh water resources. Total quantity of groundwater within 800 m distance below the ground surface is more than 30 times the total water in all fresh water lakes, more than 60 times the total water in soil and other unsaturated rock materials, more than 300 times the water vapour in the atmosphere and 3000 times the average volume of all rivers and rivulets in the world (Lenka, 2001). But the distribution of groundwater is not uniform. At some places, it lies below a few metres whereas at other places, it is a thousand metres or more below the ground surface. In some places, there is abundant groundwater potential whereas at other places there is meager potential.

Groundwater is the water reaching the groundwater reservoir from the infiltrated water of precipitation which constitutes an important component of the hydrologic cycle. It is only the part of the subterranean water that occurs in the saturated pores of the containing rock materials underlain by water held in a zone of aeration. It should not be confused that all the water present in soil below the ground surface is groundwater.

ABSTRACT

The over extraction of water from the coastal environment, results in reduction of groundwater resources which has reflected in lowering of water level. In general, the depletion of water level enhances the landward migration of saltwater wedge. Pondicherry is one such region with recent alluvium as the major litho unit. A study has been attempted to calculate the extraction of water and to estimate the amount of recharge into this alluvial aquifer. The monthly water level fluctuation was observed for the study period in eighteen locations (20002002). The highest water level observed during 2000 was taken as the initial water level for the study and the subsequent decline in water level up to 2001 was monitored monthly until the rising trend was noted. This was taken as the fall in water level due to extraction. Keeping this as the initial value increasing trend was studied until there was a notice of decline in water level. This was taken as the rise in water level due to recharge. The spatial representation of these data in the above said eighteen locations were carried out by using GIS and the area occupied by different water level contours were calculated and the amount of water withdrawn was estimated. The maximum recharge was noted in the central and the northern part of the study area when compared to the other regions. Similarly, the maximum discharge was noted in the northern and the southern part of the study area.

Keywords: Rainfall, Recharge, Groundwater Budget, GIS.

Introduction

Large scale exploitation of groundwater using modern deep well boring technology and powerful pumps is the order of the day in India and elsewhere. Increase in agriculture area and year around cultivation of water intensive crops, frequently failing monsoons (Fig.5.1) all have led to drying up of surface water and increased dependence on groundwater.

Thus, given the scenario of over exploitation of the available groundwater, it is essential that proper storage and management of available groundwater resources be identified.

Introduction

The science of hydrogeology is defined as hydrology with emphasis on geology. This chapter is to refresh your geology knowledge. The key words are highlighted to assist a quick review.

The Crust and its Composition

The thin outermost layer of the earth is called the crust and ranges in thickness from about 8 km under the oceans to about 25 km on land. It extends under both oceans and continents, and forms the source for all the soils, vegetation, and gases in the atmosphere.

The crust is primarily composed of two elements: silicon and oxygen which account for 75% of the earth’s crust. Note that these are the two elements found in quartz (e.g., sand), which suggests this is the most common of all minerals.

Hydraulics of wells means the laws that are applicable to understand the flow of water through the formation and certain aquifer properties that determine the discharge of a well. Darcy’s law is used in studying groundwater flow though Darcy’s law is not valid under certain cases.

8.1  Water Bearing Formation

The earth’s crust is called the lithosphere which consists of hard rocks and disintegrated rock materials. The outer parts of the earth’s crust are porous and containing partially and fully filled up with water. The surface strata of the earth is partially filled with water and is called as zone of aeration and the zone below this which is completely filled with water is called the zone of saturation. The zone of aeration is divided into (i) the soil water zone (ii) the intermediate zone and (iii) the capillary fringe (Fig.8.1).

Q. 1 The development of a tube well should be started from :-
(A) Middle of screen      (B) Top of screen
(C) Bottom of screen     (D) Bottom of casing pipe

Introduction

Groundwater investigation has a long history. In the past a waterman in the village would walk around the investigation area with a Y shaped wooden fork and identify the location for digging the wells. Certain trees and organic landforms like termite mounds were considered as indicators. The native intelligence of local topography should have played a role in identifying potential location. Successful or otherwise the method can be said to lack scientific objectivity. The optimal groundwater surveying method is no doubt drilling. This method ensures that all necessary information is being brought up from the geological formations. However, in order to obtain a desired degree of information from the subsurface of an area, drilling alone is normally not a feasible alternative.

There are a number of efficient and inexpensive geophysical surveying methods available to the hydrogeologist. It is worth noting at this point that these are, without exception, indirect methods. This implies that no method measures directly what we are actually looking for. With geophysical surveys, the target features are therefore invariably associated features. This implies that unless we understand the water context of these features, our geophysical surveys will be less than meaningful.

Objective methods of investigating groundwater are discussed in this chapter.

Groundwater is a precious renewable resource which gets replenishment from the precipitation. Total water resources of the world are estimated at 1.37 x 10⁸ million ha-m. Of these, about 97.2% is salt water, mainly in oceans, and only 2.8% is available as fresh water. And, out of this 2.8%, about 2.2% is available as surface water (2.1% is fresh water in glaciers and icecaps, 0.1% is available in lakes and reservoirs, 0.0001% in streams) and 0.6% is available as groundwater. Only 50% of groundwater resource is economically extracted with available technology. Presently, 1.3 x 10⁴ million ha-m fresh water in reservoirs and 41.1x10⁴ million ha-m groundwater is theoretically available to provide usable water for drinking, domestic use, irrigation, etc., to mankind. Groundwater is the largest source of fresh water excluding the polar icecaps and glaciers. The amount of groundwater within 800 m from the ground surface is over 30 times the amount in all fresh water lakes and reservoirs, and about 3000 times the amount in stream channels, at any one time.

Introduction

Fresh water, a renewable but not an infinite resource, is becoming increasingly scarce. The amount available for use to the world today is almost the same as it was 4500 years ago but global demand has been increasing exponentially. Since 1950, the renewable supply per person has fallen 58 percent as world population has swelled from 2.5 billion to 6 billion. Moreover, unlike oil and most other strategic resources, fresh water has no substitute in most of its uses. It is essential for growing food, manufacturing goods, and safeguarding human health.

According to a World Policy Forum report, the largest and most combustible imbalance between population and available water supplies will be in Asia, where crop production depends heavily on irrigation. Asia today has roughly 60 percent of the world’s people but only 36 percent of the world’s renewable fresh water. China, India, Iran, and Pakistan are among the countries where a significant share of the irrigated land is now jeopardized by groundwater depletion, scarce river water, a fertility-sapping buildup of salts in the soil, or some combination of these factors. Groundwater depletion alone places 10 to 20 percent of grain production in both China and India at risk.

Introduction

All models are but approximations of reality. When we approximate there is always room for uncertainty. The preference of a particular model over the other is the relative degree of uncertainty acceptable to the objective and budget of the study. With the advent of computers, hosts of modeling software promising a lot to the researcher have arrived on the horizon. It is not in the scope of the book to enumerate all the techniques of hydrogeological modeling. Physical modeling using sand tanks was the earliest attempted modeling technique, about 107 years ago. Most recent and significant modeling technique practiced by many in groundwater potential identification is Geographic Information System (GIS) based modeling. After a brief treatment of physical models, concepts of mathematical models and GIS modeling are elaborated. The modeling techniques have involved mathematics and or software specific instructions. Hence it is recommended that relevant text books for individual techniques be referred. This chapter deals more on modeling concepts.

Key words : Groundwater Modelling, GIS, PMWIN, ArcInfo Interface Con2grid, Interface Programme, ArcMacro Language.

Introduction

Groundwater is an important source of irrigation in India and has played a major role in increasing the food production. About 50 per cent of total irrigated area in the country is dependent on groundwater (Central Water Commission (CWC), 2000). Productivity of groundwater is normally more than the surface water due to the fact that it is available at the point of use, requires minimum conveyance infrastructure, is available on demand and maximizes the application efficiency. However, in past few years, excessive and unplanned groundwater pumping in certain parts of the country has resulted in depletion of groundwater resources. Water table in these region is going down day by day and making it beyond the reach of poor farmers. Therefore, keeping the water table in the desirable range is a major concern. This can be achieved by adopting proper pumping rate and pumping schedule. Groundwater modelling has successfully been used for deciding the pumping rate and pumping schedule. Groundwater modelling refers to simulation of groundwater behaviour under varying pumping and recharge conditions. A groundwater model is simply a set of equations, which describe the physical processes active in the aquifer subjected to certain assumptions. While the model itself obviously lacks the detailed reality of the groundwater systems, the behaviour of the validated model approximates that of the aquifer.

Introduction

Water is one of the most complex natural resources demanding a comprehensive understanding of its inherent features in occurrence and distribution for an integrated planning aimed at optimum development for agriculture, health, industry, power, etc. The well being and development of our society is dependent on the availability of water. An increase in groundwater development and utilization for industries and urban water supply has created improper disposal of liquid waste. Defective well constructions, sewage and waste disposal in man made lakes within city, open quarries with water and failure to seal the abandoned wells in city area have provided possible openings for downward movement of polluted water into subsurface formations without undergoing the process of natural filtration.

Abstract

Water is an essential and vital component for our life support system. Drought and floods are the extreme events of rainfall and the vagaries of monsoon and hydrogeological framework in the country are highly variable from place to place. The water resources available in the country are also not uniformly distributed. The changing Landuse pattern and population growth and the resultant water resources development has lead to water stress at many places. In such areas, the extraction of excessive quantities of groundwater has resulted in the drying up of wells, damages of ecosystems, land subsidence, salt-water intrusion and other related problems. Agricultural, urban & industrial wastes are increasingly threatening the groundwater quality, which is likely to become a more serious issue in the coming years. Considering the seriousness of the groundwater contamination, Central Ground Water Board has carried out detailed studies in few hot spots in the state of Tamil Nadu. The issues related to the water resources contamination and the findings of the studies in parts of Tamil Nadu are summarized in this paper.

ABSTRACT

Over the past four decades groundwater has become a topic of discussion and investigation and as a result the knowledge of understanding groundwater conditions has radically improved. For the past quarter century, remote sensing has played a vital role to target the groundwater resources for the essential survival of horticulture and agriculture crops in drought-prone areas. GIS technology has made a rapid stride for the past one decade to amalgamate the data generated from various space-born platforms and the ground based surveys to facilitate the generation and use of various thematic information for groundwater resources assessment. The present study aims for the demarcation of various groundwater prospective zones in the West Doon Valley and its environs, falling in the SOI toposheet 53 F/15. The role of various parameters namely, Geomorphology, Geology, Lineaments, Drainage, Land Use, Water table and Slope has been integrated for delineating groundwater prospective zones. IRS IC LISS-III geocoded satellite image on 1:50,000 scale was used. Index overlay model has been applied for GIS analysis. The resultant map indicates five prospective zones, such as poor, low, moderate, high and very high groundwater prospective zones in the study area.

ABSTRACT

Identification and mapping of fractures/lineaments and hydrogeomorphic units is prerequisite for undertaking ground water exploration and development in any terrain. Remote sensing and GIS techniques have been used for ground water potential mapping in Theni District. The study area has been divided into various geomorphic units based on visual interpretation of LISS III and PAN merged data in false colour composite on 1:50,000 scale. Ground water potential of each of the geomorphic units was assessed and correlated with geology, structure and recharge factors prevailing in the Theni District.

Technical Term       Definition

Groundwater         Water present in the zone of saturation (below water table) is called groundwater

10.1 Introduction

During rain or heavy irrigation, a part of the rainfall or irrigated water moves below the effective root zone of the crop which moves further below and adds to the water table lying above the impermeable bed or hard rock which is called as  ground  water  reservoir. At  times  the  accumulated  surface  water  is  also recharged to the soil reservoir both naturally as well as artificially that add to the underlying ground water reservoir. This groundwater is an important source of water for irrigation as well as domestic uses. It is the most abundant fresh water resource of the earth. Underground water reservoirs contain large stock of fresh water resources. Total quantity of groundwater within 800 m distance below  the  ground  surface  is  more than  30  times  the  total  water  in  all fresh water lakes, more than 60 times the total water in soil and other unsaturated rock materials, more than 300 times the water vapour in the atmosphere and 3000 times the average volume of all rivers and rivulets in the world (Lenka, 2001). But the distribution of groundwater is not uniform.

1. Result demonstration

It is a method of motivating the people for adoption of a new practice by showing its distinctly superior result. The demonstrations are conducted in the farm or home of selected individuals and are utilized to educate and motivate groups of people in their neighborhood. This is a very effective method for the transfer of technology in a community.

Objectives

1. To show the advantages and applicability of a newly recommended practice in farmer’s own situation.