PRINCIPLES OF HYDROLOGY
CHAPTER 1
INTRODUCTION
______________________________________________________________________________
1.1 Background
According to the committee of the US National Research Council defined hydrologic Science to
include (1) the physical and chemical processes in the cycling of continental water at all scales as well as
those biological processes that significantly interact with the hydrologic cycle, (2) the spatial and
temporal characteristics of the global water balance in all compartments of the Earth system. However,
this definition other scholars argue that it is not focused enough to give hydrology the unique identity
that can distinguish it from other water related sciences. Dooge J.C.I. states that “The business of
hydrology is to solve the water balance equation”, and quantitatively, the hydrological perspective is
reflected in the water balance equation. Therefore, hydrology can be defined as the science that seeks
to explain the water balance dynamics for any defined spatial (from a point to global) and temporal
scale (from seconds to years) and their relationships with the physical and chemical transport of matter
through the hydrologic cycle and with ecology (IAHS News letter, 1991).
Since the scientific study of the components of the hydrologic cycle are being carried out by the other
water related sciences it is left to the hydrologist to integrate the findings of the other sciences to
explain the dynamics of the water balance of an area over any defined time period and establish their
relationships to the physical and biological environments. According to Williams (Engineering
Hydraulics, ed. By H. Rouse, 1950, pp. 229 “Hydrology is peculiar among the natural sciences in its
dependence upon the findings of other allied sciences. These sciences are meteorology, climatology,
physical geography, agronomy and geology and soil science, hydraulics, oceanography and limnology.
The hydrologist must have a working knowledge of them all”
Therefore it can be seen that the classification of hydrological studies according to climatic regions,
tropical, temperate, polar, arid, humid), surface characteristics (urban, farmland, forest, lakes) and
geology (Karst) follows naturally from the definition as they all influence the water balance
characteristics of a defined area. The unnatural classification of hydrological studies according to
observation techniques (isotope hydrology, satellite hydrology), phenomenon (flood hydrology, drought
1
,hydrology) methodology (Stochastic hydrology, deterministic hydrology) and the major domain in which
water moves (surface water hydrology, groundwater hydrology) can also clearly be seen.
1.2 The development of hydrology
Hydrology is one of the newest of the natural sciences although history dates back as early as 1000 B.C.
when philosphers like Homer, Plato and Aristotle, speculated on the concept of the hydrological cycle.
Many of these philosophical concepts proved erroneous. The forerunner of the modern concept of
hydrological cycle was Marcus Vitruvious who was contemporary to Christ and who stated that, the
groundwater is far the most part derived from rain and snow by infiltration through the surface.
In a broader sense, the various periods of development of hydrology according to Chow (1964) may be
classified as follows:
(a) The period of speculation (Ancient) before 1400 A.D.
(b) Period of observation 1400- 1600
(c) Period of measurement 1600-1700
(d) Period of experimentation 1700 - 1800
(e) Period of mordenization 1800 - 1900
(f) Period of empiricism 1900 - 1930
(g) Period of rationalization 1930 - 1950
(h) Period of theorization 1950 - to date
(i) Period of computerization 1970 - to date
Prominent contributors during the 15 th Century include Leonard Da Vinci and Palissy; in the 17th
Century, Perrault, Mariotte and Halley whose concepts on flow and flow measurement are valid to this
age. Bernoulli, Pitot and Chezy in the 18 th Century made new discoveries in the understanding of
hydraulic principles which greatly accelerated the beginning of hydrological studies on a quantitative
basis.
In the field of groundwater, Poisuille (1856), Dupuit (1863) and Thiem (1906) for the first time applied
the knowledge of geology to the solution of hydrological problems. In the field of surface water,
outstanding contributions were for Humphrey and Abbot (1855), Carter (1869), and Manning (1889)
whose formulae helped in the systematic stream gauging. During the 1930's, the development of
quantitative hydrology was substantial but still immature as it was largely empirical with the physical
2
,basis for determination of most hydrological quantities having not yet been established. As a result,
solutions of practical hydrological problems were soon found to be unsatisfactory and many
governmental agencies and technical societies increased their effort towards a systematic advancement
of the science in hydrology. During the period of rationalization, Sherman (1932) made a distinct
advance by demonstrating the use of unit hydrograph in the determination of the runoff hydrograph, by
translating the rainfall excess into surface runoff. Horton in 1933 was the first to recognize the ability of
the drainage basin to absorb and detain water and proposed the theory of infiltration capacity. The non-
equilibrium theory introduced by Theis (1939) revolutionalized the whole concept of hydraulics of wells.
With the classical theory of Einstein (1950), bed load formulation for sediment production, the physics
of erosion and transport of solids by fluids were fairly well understood. His works on suspended solids
(1972) and high sediment rate in alluvial rivers (1972) further gave insight to the role of precipitation
falling on solid ground, partly evaporating, partly infiltrating and partly appearing as surface runoff and it
is this last part of the precipitation which contributes mostly to river flow carrying suspended sediment
with it. While discussing the river ecology and man (1972), he considered sediments of sizes all the way
from boulders, down to the most minute clay particles including gels. According to Einstein, it is
imperative that every student of river ecology familiarise himself thoroughly with the rules and laws of
river hydraulics of which motion of its sediment (be it a river, a lake or an ocean) is an important factor.
Among the contributions made in the recent past, mention should be made of the pioneering work of
Linsley (1949) on the application of principles of hydrology to small and large watersheds, using the
concept of unit hydrograph and that of Horton’s infiltration theory. Together with Crawford (1966), he
developed the classical ‘Stanford Watershed Model Mark IV’ with as many as 39 hydrological variables,
many of which could be used for a rigorous analysis of a conceptual model. His method of multiple
regression analysis by way of co-axial graphical correlation technique is widely used to correlate annual
or seasonal precipitation with the physiographic parameters of the drainage basin.
Corey and Corey (1965) studied the non-steady drainage of partially saturated soils. They introduced
both theoretical and experimental works on unsteady drainage of similar and dissimilar media making
use of a complicated partial differential equation of the second order, with moisture-dependent
diffusivity and permeability coefficients. The capillary force and effective permeability at various points
would depend upon whether we work on drainage or imbibition cycle. The process of drainage and
imbibition constitute a hysteresis loop and involves pressure reversals. The study has direct bearing on
the infiltration process in hydrology and explains the retention and release of moisture during the
drainage cycle.
To determine the effect of man-made changes on the drainage basins the use of synthesized
hydrographs are in vogue which facilitates the estimation of streamflow records, calculation of runoff
from ungauged stations and the calculation of extreme flood discharges from either measured of
hypothetical precipitation storms. Donald (1968) presented a greatly simplified empirical method which
3
, proves valuable as an interim procedure for hydrologic analysis. The important assumption of this
method is that the discharge hydrograph comprises of two major components, that is formed by storm
runoff and the other formed by groundwater storage, usually called the base flow. The concept of a 24-
hour unit hydrograph is introduced and the daily runoff values are synthesized using precipitation excess
on a daily basis. As base flow recession curves may change with seasons the depletion curves may be
varied in nature.
Fleming (1974, 1975) discussed an application of systems analysis to water resources problems, citing
the advantages of computer simulation and systems analysis approach in accounting for the interacting
processes affecting hydrologic response of physical watershed and the integration of this response to
assess and evaluate the water resource.
Yevjevich (1972) introduced the application of probability theory and mathematical Statistics to
hydrology. He stresses that since most hydrological processes in nature are governed by the laws of
chance, the use of probability theory and mathematical statistics is unavoidable in the extraction of
information from hydrologic data..
The computer era (from 1950's to date) has revolutionalized the study of hydrology and the solving of
hydrology and water related problems. The computer erra has also enabled modelers to develop many
different kinds of models and information management systems and Decision support systems (DSS), in
order to provide solutions to water related problems. The application of GIS coupled with hydrological
models in hydrology has also helped in the advancement of the science of hydrology.
One of the major factor of an information management system is the ability to store, analyse and
retrieve data. A GIS is a computerized mapping tool that provides flexibility, accuracy and ease of
updating capabilities over conventional methods. GIS provides a cataloging of data found in tabular
format. The data called attributes, describe the mapped information (Reese and others 1993). A number
of GIS packages are available such as, IDRIS, ARC/INFO, ARC/VIEW, etc. Geographical Information
Systems (GIS), identified by many scientists and managers as a powerful decision support tool.
Important characteristics of a Decision Support System (DSS) for sustainable water resources
management include flexibility for tackling various 'what-if?' scenarios, the facilitation of problem
identification and solving by analytical tools enabling the end-user to manage, analyse and present
information, and interaction and ease of use to involve the stakeholders into the management process
themselves [Simonovic and Bender 1996]. Integrated water resources management comprises
numerous complex and unstructured management problems including a geographical component.
Resolving ill-structured problems, however, can be achieved by desegregating them into a series of
structured components, each of which tackled with its unique set of tools [Reitsma 1996], and
integrated into a comprehensive framework system. That means, Geographical Information Systems
4
CHAPTER 1
INTRODUCTION
______________________________________________________________________________
1.1 Background
According to the committee of the US National Research Council defined hydrologic Science to
include (1) the physical and chemical processes in the cycling of continental water at all scales as well as
those biological processes that significantly interact with the hydrologic cycle, (2) the spatial and
temporal characteristics of the global water balance in all compartments of the Earth system. However,
this definition other scholars argue that it is not focused enough to give hydrology the unique identity
that can distinguish it from other water related sciences. Dooge J.C.I. states that “The business of
hydrology is to solve the water balance equation”, and quantitatively, the hydrological perspective is
reflected in the water balance equation. Therefore, hydrology can be defined as the science that seeks
to explain the water balance dynamics for any defined spatial (from a point to global) and temporal
scale (from seconds to years) and their relationships with the physical and chemical transport of matter
through the hydrologic cycle and with ecology (IAHS News letter, 1991).
Since the scientific study of the components of the hydrologic cycle are being carried out by the other
water related sciences it is left to the hydrologist to integrate the findings of the other sciences to
explain the dynamics of the water balance of an area over any defined time period and establish their
relationships to the physical and biological environments. According to Williams (Engineering
Hydraulics, ed. By H. Rouse, 1950, pp. 229 “Hydrology is peculiar among the natural sciences in its
dependence upon the findings of other allied sciences. These sciences are meteorology, climatology,
physical geography, agronomy and geology and soil science, hydraulics, oceanography and limnology.
The hydrologist must have a working knowledge of them all”
Therefore it can be seen that the classification of hydrological studies according to climatic regions,
tropical, temperate, polar, arid, humid), surface characteristics (urban, farmland, forest, lakes) and
geology (Karst) follows naturally from the definition as they all influence the water balance
characteristics of a defined area. The unnatural classification of hydrological studies according to
observation techniques (isotope hydrology, satellite hydrology), phenomenon (flood hydrology, drought
1
,hydrology) methodology (Stochastic hydrology, deterministic hydrology) and the major domain in which
water moves (surface water hydrology, groundwater hydrology) can also clearly be seen.
1.2 The development of hydrology
Hydrology is one of the newest of the natural sciences although history dates back as early as 1000 B.C.
when philosphers like Homer, Plato and Aristotle, speculated on the concept of the hydrological cycle.
Many of these philosophical concepts proved erroneous. The forerunner of the modern concept of
hydrological cycle was Marcus Vitruvious who was contemporary to Christ and who stated that, the
groundwater is far the most part derived from rain and snow by infiltration through the surface.
In a broader sense, the various periods of development of hydrology according to Chow (1964) may be
classified as follows:
(a) The period of speculation (Ancient) before 1400 A.D.
(b) Period of observation 1400- 1600
(c) Period of measurement 1600-1700
(d) Period of experimentation 1700 - 1800
(e) Period of mordenization 1800 - 1900
(f) Period of empiricism 1900 - 1930
(g) Period of rationalization 1930 - 1950
(h) Period of theorization 1950 - to date
(i) Period of computerization 1970 - to date
Prominent contributors during the 15 th Century include Leonard Da Vinci and Palissy; in the 17th
Century, Perrault, Mariotte and Halley whose concepts on flow and flow measurement are valid to this
age. Bernoulli, Pitot and Chezy in the 18 th Century made new discoveries in the understanding of
hydraulic principles which greatly accelerated the beginning of hydrological studies on a quantitative
basis.
In the field of groundwater, Poisuille (1856), Dupuit (1863) and Thiem (1906) for the first time applied
the knowledge of geology to the solution of hydrological problems. In the field of surface water,
outstanding contributions were for Humphrey and Abbot (1855), Carter (1869), and Manning (1889)
whose formulae helped in the systematic stream gauging. During the 1930's, the development of
quantitative hydrology was substantial but still immature as it was largely empirical with the physical
2
,basis for determination of most hydrological quantities having not yet been established. As a result,
solutions of practical hydrological problems were soon found to be unsatisfactory and many
governmental agencies and technical societies increased their effort towards a systematic advancement
of the science in hydrology. During the period of rationalization, Sherman (1932) made a distinct
advance by demonstrating the use of unit hydrograph in the determination of the runoff hydrograph, by
translating the rainfall excess into surface runoff. Horton in 1933 was the first to recognize the ability of
the drainage basin to absorb and detain water and proposed the theory of infiltration capacity. The non-
equilibrium theory introduced by Theis (1939) revolutionalized the whole concept of hydraulics of wells.
With the classical theory of Einstein (1950), bed load formulation for sediment production, the physics
of erosion and transport of solids by fluids were fairly well understood. His works on suspended solids
(1972) and high sediment rate in alluvial rivers (1972) further gave insight to the role of precipitation
falling on solid ground, partly evaporating, partly infiltrating and partly appearing as surface runoff and it
is this last part of the precipitation which contributes mostly to river flow carrying suspended sediment
with it. While discussing the river ecology and man (1972), he considered sediments of sizes all the way
from boulders, down to the most minute clay particles including gels. According to Einstein, it is
imperative that every student of river ecology familiarise himself thoroughly with the rules and laws of
river hydraulics of which motion of its sediment (be it a river, a lake or an ocean) is an important factor.
Among the contributions made in the recent past, mention should be made of the pioneering work of
Linsley (1949) on the application of principles of hydrology to small and large watersheds, using the
concept of unit hydrograph and that of Horton’s infiltration theory. Together with Crawford (1966), he
developed the classical ‘Stanford Watershed Model Mark IV’ with as many as 39 hydrological variables,
many of which could be used for a rigorous analysis of a conceptual model. His method of multiple
regression analysis by way of co-axial graphical correlation technique is widely used to correlate annual
or seasonal precipitation with the physiographic parameters of the drainage basin.
Corey and Corey (1965) studied the non-steady drainage of partially saturated soils. They introduced
both theoretical and experimental works on unsteady drainage of similar and dissimilar media making
use of a complicated partial differential equation of the second order, with moisture-dependent
diffusivity and permeability coefficients. The capillary force and effective permeability at various points
would depend upon whether we work on drainage or imbibition cycle. The process of drainage and
imbibition constitute a hysteresis loop and involves pressure reversals. The study has direct bearing on
the infiltration process in hydrology and explains the retention and release of moisture during the
drainage cycle.
To determine the effect of man-made changes on the drainage basins the use of synthesized
hydrographs are in vogue which facilitates the estimation of streamflow records, calculation of runoff
from ungauged stations and the calculation of extreme flood discharges from either measured of
hypothetical precipitation storms. Donald (1968) presented a greatly simplified empirical method which
3
, proves valuable as an interim procedure for hydrologic analysis. The important assumption of this
method is that the discharge hydrograph comprises of two major components, that is formed by storm
runoff and the other formed by groundwater storage, usually called the base flow. The concept of a 24-
hour unit hydrograph is introduced and the daily runoff values are synthesized using precipitation excess
on a daily basis. As base flow recession curves may change with seasons the depletion curves may be
varied in nature.
Fleming (1974, 1975) discussed an application of systems analysis to water resources problems, citing
the advantages of computer simulation and systems analysis approach in accounting for the interacting
processes affecting hydrologic response of physical watershed and the integration of this response to
assess and evaluate the water resource.
Yevjevich (1972) introduced the application of probability theory and mathematical Statistics to
hydrology. He stresses that since most hydrological processes in nature are governed by the laws of
chance, the use of probability theory and mathematical statistics is unavoidable in the extraction of
information from hydrologic data..
The computer era (from 1950's to date) has revolutionalized the study of hydrology and the solving of
hydrology and water related problems. The computer erra has also enabled modelers to develop many
different kinds of models and information management systems and Decision support systems (DSS), in
order to provide solutions to water related problems. The application of GIS coupled with hydrological
models in hydrology has also helped in the advancement of the science of hydrology.
One of the major factor of an information management system is the ability to store, analyse and
retrieve data. A GIS is a computerized mapping tool that provides flexibility, accuracy and ease of
updating capabilities over conventional methods. GIS provides a cataloging of data found in tabular
format. The data called attributes, describe the mapped information (Reese and others 1993). A number
of GIS packages are available such as, IDRIS, ARC/INFO, ARC/VIEW, etc. Geographical Information
Systems (GIS), identified by many scientists and managers as a powerful decision support tool.
Important characteristics of a Decision Support System (DSS) for sustainable water resources
management include flexibility for tackling various 'what-if?' scenarios, the facilitation of problem
identification and solving by analytical tools enabling the end-user to manage, analyse and present
information, and interaction and ease of use to involve the stakeholders into the management process
themselves [Simonovic and Bender 1996]. Integrated water resources management comprises
numerous complex and unstructured management problems including a geographical component.
Resolving ill-structured problems, however, can be achieved by desegregating them into a series of
structured components, each of which tackled with its unique set of tools [Reitsma 1996], and
integrated into a comprehensive framework system. That means, Geographical Information Systems
4
