UNESCO-NIGERIA TECHNICAL & VOCATIONAL EDUCATION

REVITALISATION PROJECT-PHASE II

YEAR I- SE MESTER I THEORY

Version 1: December 2008

NATIONAL DIPLOMA IN

CIVIL ENGINEERING TECHNOLOGY

INTRODUCTORY HYDROLOGY

COURSE CODE: CEC102

TABLE OF CONTENT

WEEK 1

1.0 INTRODUCTION

1.1 Define Hydrology

1.2 Brief history of hydrology

1.3 Hydrologic Cycle

1.4 Hydrology as applied in engineering

WEEK 2

1.5 The importance of the cycle in water resources

development.

1.6 Distinguishing between weather and climate

1.7 Pattern of circulation

WEEK 3 2.0 EVAPORATION

2.1 Definition

2.2 Measurement of evaporation

2.2.1 Evaporation tank or pan

WEEK 4 3.0 EARTH

3.1 Latitude

3.2 Longitude

3.3 Earth rotation

3.4

4.1 Humidity Earth revolution

WEEK 5 4.0 CLIMATE

4.2 Rainfall

4.3 Pressure

4.4 Temperature

4.5 Wind

WEEK 6 5.0 PRECIPITATION

5.1 Formation of precipitation

.5.2 Mechanism of precipitation

5.3 Cyclonic or frontal precipitation

5.4 Orographic precipitation

5.5 Convective precipitation

WEEK 7 5.6 Classification of precipitation

5.7 Forms of precipitation

5.8 Measurement of precipitation

5.9 The self-recording and non- rain gauge

5.9.1 The self recording gauge

WEEK 8 6.0 GAUGING A CATCHMENT

6.1 Sources of errors in reading Theissen

instrument

6.2 Factors to be considered in locating

gauges

6.3 Gauge networks

WEEK 9.0 7,0 MEASUREMENT OF PRECIPITATION

7.1 Mean areal depth of precipitation

7.2 Interpretation of rainfall data

7.3 Determining rainfall patterns

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WEEK 10 8.0 CONCEPT OF EVAPORATION AND

TRANSPIRATION

8.1 Importance of evaporation and

transpiration

8.2 Factors affecting transpiration

WEEK 11 9,0 MEASUREMENT OF PARAMETERS

9.1 Measurement of transpiration

9.2 Factors affecting transpiration

WEEK 12 10.0 RUN-OFF

10.1 Definition

10.2 Factors affecting run-off

10.3 Sources and components of runoff

WEEK 13 10.4 Estimating of runoff

10.5 Catchment characteristics and their

effects on runoff

WEEK 14 11.0INFILTRATION

11.1 Definition

11.2 Factors affecting infiltration

WEEK 15 11.3 Measuring infiltration

11.4Infitraion capacity

11.5 Surface cover conditions

WEEK ONE

1.0 INTRODUCTION

1.1 Definition of hydrology

It is defined as the science that deals with the origin, distribution and properties of

water on the earth including that in the atmosphere in the form of water vapour, on

the surface as water, snow or ice and beneath the surface as ground water.

The fact that hydrology has in the past been defined as science of water, made that

usage to restrict it to the study of water as it occurs on, over, and under the earth's

surface. But in recent years two trends in particular have resulted in important

modifications to this generalized view. The first trend has been the development of

the system concept and the resulting improved understanding of the hydrological

cycle on a more sophisticated and higher conceptual level. Thus not only may we

recognize the that the physical processes, which together constitute physical

hydrology, can be investigated and explained by modern systems analysis

techniques but also that these physical processes and subsystems can be simulated

mathematically. Numerous mathematical and statistical techniques are becoming

available to the hydrologist and the system concept has opened up new possibilities

in the fields of theoretical hydrology, e.g. systems hydrology, stochastic hydrology

and so on.

The second trend has been that towards relevance, i.e. the extent to which

disciplines, including hydrology are applicable in solving the problems of the

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society. Within hydrology, the quest for relevance has resulted in the growth of

interest in man's impact on hydrological conditions, e.g. urban hydrology, the

hydrology of vegetation and land-use manipulation and the long over due

recognition of major omissions such as water quality which has in the past been

virtually excluded as a parameter of water science in favour of almost total attention

to quantitative aspects.

The scope of hydrology is thus wider now than it has been. Discussion of the

principles of hydrology, however, involves a much more restricted field of study.

Principles are concerned with the basic physical processes, i.e. with an accurate

knowledge and understanding of the occurrence, distribution, and movement of

water over, on, and under the surface of the earth, and with the recognition that

water is an element in the physical environment, just as soil, vegetation, climate

e.t.c.

1.2 Brief history of hydrology

That water is essential to life and that its availability and distribution are closely

associated with the development of human society seems so obvious as to be a

fundamental truism. This being so it was almost inevitable that the development of

water resources preceded any real understanding of their origin and formation.

Aristotle (384-3220 explained the mechanics of precipitation, Vitruvius, three

centuries later, believed in the pluvial origin of springs, da Vinci (1452-1619) had

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somewhat confused ideas about the hydrological cycle but a much better

understanding of the principles of flow in open channels than either his

predecessors or contemporaries.

It was not until near the end of the seventeenth century, however, that plausible

theories about the hydrological cycle, based on experimental evidence, were

advanced.

After a period of modest consolidation during the eighteenth century there was a

remarkably rapid growth of knowledge in hydrology during the nineteenth century,

which saw the beginning of systematic river flow measurement.

The nineteenth century also saw the publication of the first text book in hydrology.

This was Nathaniel Beardmore's Manual of Hydrology published in 1862 which

was itself a revision of an earlier work, Hydraulic Tables, of 1850. In 1904, Daniel

W.Mead, of the University of Wisconsin, published his notes on Hydrology as the

first American text and in fact his later texts are still widely used today.

1.3 Hydrologic cycle

It is the cycle movement of H2O from the sea to the atmosphere and thence by

precipitation to the earth where it collects in streams and runs back to the sea is

referred to as Hydrological Cycle. Such a cycle order of events does occur but it is

not so simple as that.

• The cycle may short circuit at several stages e.g. the ppt may fall directly into the

sea, lakes or rivers. 8

• There is no uniformity in the time a cycle takes place.

• The intensity and frequency of the cycle depends on geography and climate, since

it operates as a result of solar radiation.

The three main phases of hydrologic cycle are:

(i) Evaporation and transpiration

(ii) Precipitation – that part occurring over land areas being of greatest interest

(iii) Run Off (Both surface and underground)

Water in the sea evaporates under solar radiation, and clouds of H2O vapour move

over land areas. Precipitation occurs as snow, heat, rain and condensate in the form

of dew, over land and sea. Rain falling over land surfaces may be intercepted by

vegetation and evaporate back to the atmosphere. Some of it infiltrates into the soil

and moves down or percolates into the saturated ground zone beneath the water

table, the H2O in this zone flows slowly through a guiter to river channels or

sometimes directly to the sea. The H2O that infiltrates also feeds the surface plant

life and some gets drawn up into this vegetation where transpiration takes place

from leafy plant surface.

The H2O remaining on the surface partially evaporates back to vapour, but the bulk

of the coalesces into streamlets and runs as surface runoff to the river channels. The

river and lake surfaces also evaporate, so the remaining H2O that has not infiltrates

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or evapourated arrives back at the sea via the river channels. Finally the

groundwater moving much more slowly, either emerges into the stream channels or

arrives at the coasthine and seeps into the sea, and the whole cycle starts again

Wind

Evaporation from

Falling Rain

Solar

Radiation Falling Rain Falling Rain

Transpiration

Run-Off

Evaporation

Sea Lake Storage Percolation

10 Infiltration

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