Rezaul Karim

Environmental Science and Technology

Jessore Science and Technology University

Hydrology: Chapter 1 Introduction

Introduction

hydrology defined;

a brief history;

the hydrologic cycle;

hydrologic equation / the hydrologic budget;

common units of measurement;

hydrological data;

scope of hydrology;

application of hydrology to environmental problems;

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Recommended references

Tim Davie (2002) Fundamentals of hydrology, Routledge

Fundamentals of Physical Geography, 2nd ed. Routledge

270 Madison Avenue, New York, NY 10016

Viessman, W., Jr., and G.L. Lewis, 2003. Introduction to

Hydrology, 5th Edition. Harper Collins College Publishers,

New York, NY.

Raghunath, H. M. (2006) Hydrology: principles, analysis and

design. 2nd ed. New age international (p) limited, publishers

4835/24, ansari road, daryaganj, new delhi - 110002

Chaw, David and Larry, Applied Hydrology

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Hydrology

The word hydrology combines the Greek word Hudor

which means water and the logy designates a study

of.

It is also origins in the new Latin word hydrologia.

Most specifically, the general word hydrology refers to the

scientific study of water and its properties, distribution,

and effects on Earths surface, soil and atmosphere.

The study of water can mean different things to different

professions. E.g. Chemist, ground water hydrologist,

hydrologic engineer, planners, environmentalists, water

managers, and meteorologists and so on.

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Defination

Hydrology is an earth science.

It encompasses the occurrence, distribution, movement

and properties of the waters of the earth.

Water and environmental issues are inextricably linked'

and it is important to clear understand how water is

affected by and how water affects ecosystem

manipulations.

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Importance of Water

Water is the most common substance on the surface of the earth, with the oceans covering over 70 per cent of the planet. Water is one of the few substances that can be found in all three states (i.e. gas, liquid and solid) within the earths climatic range.

The chemical properties of water are equally important for our everyday existence. Water is one of the best solvents naturally occurring on the planet. This makes water vital for cleanliness.

The capability of water to support life goes beyond bodies of water; the human body is composed of around 60 per cent water.

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Other importance

In places such as Norway, parts of the USA and New Zealand energy generation for domestic and industrial consumption is through hydro-electric schemes, arnessing the combination of water and gravity in a (by and large) sustainable manner.

Water plays a large part in the spiritual lives of millions of people. In Christianity baptism with water is a powerful symbol of cleansing

and God offers streams of living water to those who believe (John 7:38).

In Islam there is washing with water before entering a mosque for prayer.

In Hinduism bathing in the sacred Ganges provides a religious cleansing.

Many other religions give water an important role in sacred texts and rituals.

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Water regulates the Earths temperature. It also regulates

the temperature of the human body, carries nutrients and

oxygen to cells, cushions joints, protects organs and

tissues, and removes wastes.

75% of a living tree is water.

Human brains are 75% water.

Human bones are 25% water.

Human blood is 83% water.

A person can live about a month without food, but only

about a week without water.

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Worlds water resources Item Area Land

(106 km3)

Volume

(km3)

Percent of

total water

Percent of fresh

water

Oceans 361.3 1,338,000,000 96.5

Groundwater

Fresh 134.8 10,530,000 0.76 30.1

Saline I 34.8 12,870,000 0.93

Soil Moisture 82.0 16.500 0.0012 0.05

Polar ice 16.0 24,023,500 1,7 68.6

Other ice and

snow

0.3 340,600 0.025 1.0

Lakes

Fresh 1.2 91,000 0.007 0.26

Saline 0.8 85,400 0.006

Marshes 2.7 11,470 0.0008 0.03

Rivers 148.8 2,120 0.0002 0.006

Biological water 510.0 1,1 2 0 0.0001 0.003

Atmospheric

water

510.0 12,900 0.001 0.04

Total water 5 10.0 1,385,984,610 100

Fresh water 148.8 35,029,210 2.5 100

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A brief history of development hydrology

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Major aspects of hydrology

The main jobs of a hydrologist are collection and analysis of data, and making predictions out of this analysis.

Collection of data

The hydrologic data comprises rainfall data, snowfall and snowmelt data, runoff data, topographic maps and groundwater data

Analysis of data

Analysis of data includes checking it for consistency and homogeneity as well as its various statistical parameters.

Prediction

Prediction means findings design values and maximum possible floods and drought. Various approaches for prediction of hydrologic values

Statistical approach

Physical approach and

Deterministic approach

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Hydrological data For the analysis and design of any hydrologic project adequate data and

length of records are necessary.

A hydrologist is often posed with lack of adequate data. The basic hydrological data required are: Climatological data

Hydro-meteorological data like temperature, wind velocity, humidity, etc.

Precipitation records

Stream-flow records

Seasonal fluctuation of ground water table or piezometric heads

Evaporation data

Cropping pattern, crops and their consumptive use

Water quality data of surface streams and ground water

Geomorphologic studies of the basin, like area, shape and slope of the basin, mean and median elevation, mean temperature (as well as highest and lowest temperature recorded) and other physiographic characteristics of the basin; stream density and drainage density; tanks and reservoirs

Hydrometeorological characteristics of basin:

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Hydrometeorological characteristics of

basin:

(i) long term precipitation, space average over the basin using isohyets and Several other methods

(ii) Depth-area-duration (DAD) curves for critical storms (station equipped with Self-recording rain gauges).

(iii) Isohyetal mapsIsohyets may be drawn for long-term average, annual and Monthly precipitation for individual years and months

(iv) Cropping patterncrops and their seasons

(v) Daily, monthly and annual evaporation from water surfaces in the basin

(vi) Water balance studies of the basin

(vii) Chronic problems in the basin due to a flood-menacing river (like Tapti or Tapi in central India) or silt menacing river (like Tungabhadra in Karnataka)

(vii) Soil conservation and methods of flood control

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Scope of hydrology

The study of hydrology helps us to know

the maximum probable flood that may occur at a given site and its frequency; this is required for the safe design of drains and culverts, dams and reservoirs, channels and other flood control structures.

The water yield from a basinits occurrence, quantity and frequency, etc; this is necessary for the design of dams, municipal water supply, water power, river navigation, etc.

the ground water development for which a knowledge of the hydrogeology of the area, i.e., of the formation soil, recharge facilities like streams and reservoirs, rainfall pattern, climate, cropping pattern, etc. are required.

The maximum intensity of storm and its frequency for the design of a drainage project in the area.

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Application of hydrology to

environmental problems It is true that humans cannot exist without water; it is also true that water,

mismanaged, or during times of deficiency (droughts), or times of surplus (floods), can be life threatening.

Furthermore, there is no aspect of environmental concern that does not relate in some way to water. Land, air, and water are all interrelated as are water and all life forms.

Accordingly, the spectrum of issues requiring an understanding of hydrologic processes is almost unlimited.

As water becomes scarcer and as competition for its use expands, the need for improved water management will grow.

And to provide water for the world's expanding population, new industrial developments food production, recreational demands, and for the preservation and protection of natural systems and other purposes, it will become increasingly important for us to achieve a thorough understanding of the underlying hydrologic processes with which we must contend.

This is the challenge to hydrologists water resources engineers; planners, policymakers, lawyers, Economists, and others who must strive to see that future allocations of water are Sufficient to meet the needs of human and natural systems.

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