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UNIVERSITI TUNKU ABDUL RAHMAN
FACULTY OF ENGINEERING AND GREEN TECHNOLOGY (FEGT)
ENVIRONMENTAL ENGINEERING
UGNA2052 Water Resour ce
Group Assignment
Year 2 Trimester 2
Name : Lee Pei Ing, Tan Yi Mi
Student ID : 11AGB00069, 11AGB01150
Title : Hydrology
Lecturer : Ms.Ho Y.C.
Date of Submission : 5thAugust 2012
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Contents1.0 Abstract ................................................................................................................ 3
2.0 Introduction .......................................................................................................... 3
3.0 Distribution and Water Resource.......................................................................... 4
4.0 Hydraulic Cycle .......4
5.0 Hydraulic Event .................................................................................................. 15
6.0 Environmental sustainability ............................................................................... 17
7.0 Conclusion ......................................................................................................... 20
8.0 References ......................................................................................................... 20
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1.0 Abstract
Hydrology in simple term is the study of water. In this assignment we will discuss
about distribution of water, hydrologic cycle (precipitation, evaporation, infiltration and runoff),
hydraulic event which include flood and drought and environmental sustainability of water.We will briefly explain distribution of water within the earth in term of percentage. Then we
will discuss about cycle of water within the earth in hydrologic cycle which include
precipitation, evaporation, infiltration and runoff. In hydraulic event we will talk about
definition and method to manage and prevent flood and drought. Lastly we will talk about
environmental sustainability of water which mainly focus of management, control and
prevent of pollution of water nowadays.
2.0 Introduction
Water is one of the most essential requisites that nature provides to sustain life for
every living organism on Earth and it is the most common substance on the surface of the
Earth, with the ocean containing 70 percent of the planet. Although there is plenty of water
on earth, it is neither evenly distributed nor evenly accessible. Moreover there is an
increasing evidence of the contaminants discarded by human activities showing up the water
supplies. Thus, hydrologists, people who are expert in the field of hydrology, play a vital role
in finding solutions to water problems.
What is hydrology? Literally, hydrology is the science or study of (logy from Latin
logia) water (hydro from Greek hudor) (Davie, 2008).However, modern hydrology is
concerned with the distribution of water on the surface of the earth and its movements over
and beneath the surface, and through the atmosphere. It is the science that treats the water
of the Earth, their occurrence, circulation and distribution, their chemical and physical
properties, and their reaction with their environment, including their relation to living things.
The domain of hydrology embraces the full life history water on the Earth (Maidment, 1993).
Hydrologist seeks to apply hydrologic knowledge to solve problems and make life
better for people. They are concerned with three issues: water use which is meant of
withdrawal of water from lakes, rivers, and aquifers for water supply; water control which is
meant by controlling of hydrologic extremes, and the erosion and sediment transport which
occur during floods; and pollution control which is the prevention of the spread of pollutants
or contaminants in natural water bodies, and the cleanup of existing pollution (Maidment,
1993).
As a branch of scientific and engineering discipline, the knowledge of hydrology isnot only fundamental to hydrologists but also to other water and environmental professionals
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(engineers, scientists and decision makers) in such tasks as the design and operation of
water resources, wastewater treatment, irrigation, flood risk management, navigation,
pollution control, hydropower, ecosystem modeling, etc (Han, 2010).
3.0 Distribution and Water Resource
On the surface area of earth only 29% is
occupied by land and the remaining 71% is covered
by seas and ocean. There seas and oceans hold 97%
of earths total water while 2% is kept frozen in ice
caps. The very deep ground water accounts for
0.31%. Thus, 99.31% of water on earth is of no
practical use to the people. The only remaining 0.69%
represents of fresh water resource with which the
man has to deal. At any instant rivers and lakes hold only 3% of this fresh water, i.e. 0.0093%
of the total water. It appears quite surprising that this most important water resource of the
human beings which is in the order of only 0.0093% of total earths water. (Saikia, 2009)
The Oldest Civilizations India, China, Egypt, Mesopotamia all begin beside the river.
Water bodies such as river, ocean will provide food, transport, water and etc. If water
resource is systematically managed and exploited, water will bring huge benefit and
convenient to human and social. On the other hand, water can be the most bitter enemy of
the people in the form of flood and erosion to bring about disaster and devastation that
causes great destruction, catastrophes to the society if it is not properly managed and
controlled.
4.0 Hydrologic Cycle
The water cycle, which is known as the hydrologic cycle, describes the movement of
water between the various stores of water that exist on the earth. It recycles the earths
valuable water supply powered by the suns energy and driven by gravity. The sun, which
drives the water cycle, radiates solar energy on the oceans and land. Thus, by this process,
water keeps changing states between liquid, vapor and ice in the blink of an eye and over
millions of years.
Chart 3.1 Distribution of global water
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Water on Earth can be
stored in any one of the following
major reservoirs: atmosphere,
oceans, lakes, rivers, soils,
glaciers, snowfields,
and groundwater. Water moves
from one reservoir to another by
several physical processes such
as evaporation, precipitation,
infiltration, transpiration, and
runoff (Hubbart & Pidwirny, 2010).
These physical processes
plus the storage of water form a continuum of water movement. Complex pathways include
the passage of water from the gaseous envelope around the planet called the atmosphere,
through the bodies of water on the surface of earth such as the oceans, glaciers and lakes,
and at the same time (or more slowly) passing through the soil and rock layers underground.
Later, the water is returned to the atmosphere. A fundamental characteristic of the
hydrologic cycle is that it has no beginning and it has no end (National Oceanic and
Atmospheric Adminstration). An individual molecule of water can take a few days to
thousands of years to complete the hydrologic cycle from ocean to atmosphere to land to
ocean again as it can be trapped in ice for a long time (Rosenberg, The Hydrologic Cycle,
2012).
4.1 Precipitation
Precipitation is the process of releasing water from the atmosphere to the surface of
the earth and is the major input of water to a river catchment area (Davie, 2008). The water
released from the atmosphere can occur as snow, hail, sleet and rainfall.
Formation of precipitation
Precipitation is produced whenever moist air rises sufficiently to produce saturation,
condensation, and the growth of the precipitation particles. Precipitation formation processes
may be classified into two categories. Precipitation that is formed in temperatures entirely
above freezing is called warm precipitation; cold precipitation involves ice at some stage of
the process. Historically, the cold rain processes were closely examined first because it was
believed that this was the main process that leads to the formation of rain (Chuey & Nelson,2012).
Figure 4.1 The hydrologic cycle showing the movementof water through the cycle.
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Nearly all precipitation begins with condensation of water vapour about small
(diameters between 0.001 to 10 m) particles in the air called cloud condensation nuclei,
which are also called aerosols. Sea-salt particles left behind when sea spray evaporates are
particularly effective nuclei. Saturation of air occurs when rising air currents cool without loss
of heat by expansion. As the ability of cold air to hold the water vapour is poorer than warm
air, cooling of a moist air mass by lifting is an efficient mechanism for producing saturation
and condensation (Davie, 2008).
The condensation processes are efficient in producing only cloud drops that are too
small (diameters between 10 and 500m) to have an appreciable fall velocity relative to the
air. In order to produce precipitation particles that are heavy enough to fall to the surface, a
cloud drop with a radius of 0.001 cm must increase its radius by a factor of 10 and its volume
by a factor of 1,000 (Anthes, 2012).
Warm precipitation usually occurs in the warm, humid tropical regions, and the
clouds are with temperatures above freezing. In this type of cloud conditions, the growth of
the water droplets occurs by coalescence, which is simply the merging of water drops that
collide. This merging is facilitated when an electric field is present. Laboratory experiments
show that drops will bounce off one another in the absence of an electric field (Anthes, 2012).
On the other hand, the formation of cold precipitation in middle latitudes usually
involves ice. Because the vapour pressure at saturation is less over ice than over water, ice
crystals will grow at the expense of water drops when both exist together in a super-cooled
cloud (which contains liquid drops at temperatures below freezing).
Although most cold precipitation begins as snow at altitudes above the freezing, the
form of the precipitation reaching the surface depends on the temperature structure of the
atmospheric layers through which the precipitation falls. If the temperature near the ground
is warm enough, the snow has time to melt and reaches the ground as rain while a warm
layer aloft and a subfreezing layer at the surface may produce sleet. Hail occurs when
alternating strong updrafts and downdrafts cause ice crystals to pass repeatedly through
layers that contain super-cooled water. The frequent passage through these layers allowsthe water to freeze around the growing hailstone and to accumulate in one layer after
another (Anthes, 2012).
Types of Precipitation
The formation of precipitation also requires vertical transport of air masses. There are
three major categories of precipitation classified by the mechanism of air mass lifting.
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1. Convective precipitation: Heated air near the ground expands and absorbs
more water moisture. Because of the low temperature, the warmer moisture-
laden air moves up and gets condensed, thus producing precipitation. Convective
precipitation spans from light shows to thunderstorms with extremely high
intensity.
2. Orographic precipitation: lifting
occurs when air is forced to rise
due to the physical presence of
elevated land such as mountain
ranges. This type of lifting often
causes rainfall on the windward
slope. The rainfall amount of
orographic precipitation is usually
the highest in the mountainous part of the
river basin.
3. Frontal precipitation: The uneven heating of the earths surface by the sun
results high and low pressure regions and air masses move from high pressure
regions to low pressure regions. If warm air replaces colder air, the front is called
a warm front. If cold air displaces warm air, its front is called a cold front (Han,
2010).
Interception
Interception is the process of interrupting the movement of water in the chain of
transportation events leading to streams. The interception can take place by vegetal cover or
depression storage in puddles and in land formations such as rills and furrows. The three
main components of interception by vegetation are throughfall, stemflow, and interception
loss (Maidment, 1993).
Throughfall is the water that falls to the ground either directly, through gaps in thecanopy, or indirectly, having dripped off leaves, stems or branches while stemflow is the
rainfall that is intercepted by stems and branches and flows down the tree trunk in to the soil.
When the water sits on the canopy, prior to indirect throughfall or stemflow, it is available for
evaporation, referred to as interception loss (Davie, 2008).
Measurements of precipitations
Average annual precipitation is a vital piece of climatic data - one that is recorded
through a variety of methods (Rosenberg, 2012). Precipitation is measured in units over a
given time period. For hydrological analysis, it is important to know how much precipitation
Figure 4.2 Orographic Precipitation
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has fallen and when this occurred. The usual expression of precipitation is as a vertical
depth of liquid water. Rainfall is measured by millimetres or inches depth, rather than by
volume such as litres or cubic metres (Davie, 2008).
The instrument for measuring rainfall is called a rain gauge. A rain gauge measures
the volume of water that falls onto a horizontal surface delineated by the rain gauge rim.
There are three main types of rain gauges: the standard rain gauge, the weighing
precipitation rain gauge and the tipping bucket rain gauge.
The standard rain gauge, developed around the start of the 20th century, consists of
a funnel attached to a graduated cylinder that fits into a larger container which may
accommodate any excess flowing. When measurements are taken, the rainwater collected
in the cylinder will be measured and then the excess will be put in another cylinder and
measured (Pidwirny, Precipitation Types and Measurement, 2012).
The tipping bucket rain gauge consists of a large copper cylinder set into the ground.
At the top of the cylinder is a funnel that collects and channels the precipitation. The
precipitation falls onto one of two small buckets or levers which are balanced in same
manner as a scale. The top bucket is held in place by a magnet until it has filled to the
calibrated amount (usually approximately 0.001 inches of rain). When the bucket has filled to
this amount, the magnet will release its hold, causing the bucket to tip. The water then
empties down a drainage hole and raises the other to sit underneath the funnel. When the
bucket tips, it triggers a reed switch (or sensor), sending a message to the display or
weather station.
A weighing-type precipitation gauge consists of a storage bin, which is weighed to
record the mass. Certain models measure the mass using a pen on a rotating drum, or by
using a vibrating wire attached to a data logger. It is the storage space drum that collects
any type of precipitation. The pen that positioned below the drum shows its weight. It does
not underestimate intense rain, and it can measure other forms of precipitation, including
rain, hail and snow. These gauges are, however, more expensive and require more
maintenance than tipping bucket gauges. The weighing-type recording gauge may alsocontain a device to measure the quantity of chemicals contained in the location's
atmosphere. This is extremely helpful for scientists studying the effects of greenhouse gases
released into the atmosphere and their effects on the levels of the acid rain.
Water depth is not the only rainfall measure of interest in hydrology; also of
importance is the rainfall intensity and storm duration. These are simple to obtain from an
analysis of rainfall record using frequency analysis. The rainfall needs to be recorded at
short time interval to provide meaningful data (Davie, 2008).
4.2 Evaporation
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Evaporation is the process which liquid water being transfer into a gaseous state and
diffuses into the atmosphere. Typically, solar radiation and other factors such as air
temperature, vapour pressure, wind, and atmospheric pressure affect the amount of natural
evaporation that takes place in any geographic area. In terms of water, evaporation requires
that the humidity of the atmosphere be less than the evaporating surface (at 100%
relative humidity there is no more evaporation). The evaporation process requires an input
of energy from the environment. For example, the evaporation of one gram of water requires
600 calories of heat energy (Pidwirny, Evaporation, 2007). The reverse process, a
transformation from gas to liquid, is referred to as condensation. Condensation releases
energy to the environment. The evaporation above a land surface occurs in two ways
either as actual evaporation from soil matrix or transpiration from plants (Davie, 2008).
Evapotranspiration
Transpiration is the term used to describe the transport of water through an actual,
vegetated plant into the atmosphere (Burba, 2010). Transpiration may also refer to the rate
of the water vapour transport through the whole vegetative canopy. Transpiration from a
plant occurs as part of photosynthesis and respiration. The rate of transpiration can be
affected by the temperature, solar radiation, relative humidity, wind and air movement, soil
moisture availability, and types of plant.
Evapotranspiration is the combined effect of both direct evaporation from soil orwater and transpiration of plants. This term also recognises the fact that much of the Earths
surface is a mixture of vegetation cover and bare soil. Evapotranspiration is important to the
hydrologic cycle because it represents a considerable amount of moisture lost from a
watershed. As precipitation falls and soaks into the soil, a plant absorbs it and then
transpires it through its leaves, stem, flowers, and/or roots. When this is combined with the
evaporation of moisture that was not directly absorbed by the soil, a significant amount of
water vapour is returned to the atmosphere. Through evapotranspiration and the hydrologic
cycle, forests or other heavily wooded areas typically reduce a locations water yield.
4.3 Infiltration
Infiltration is the process when water that penetrates into the surface of soil from
rainfall, snowmelt or irrigation. The maximum rate at which a given soil in a given condition
can absorb water is known as the infiltration capacity.
Infiltration rate is of great interest to hydrologists, agriculturalists, irrigation engineers,
etc. as it influences many hydrological processes, such as surface runoff, soil moisture,
evapotranspiration, ground water recharge and spring flow rates. The knowledge of
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infiltration properties can help agriculturists in adopting proper irrigation methods and
irrigation schedule. Infiltration is one of the most important processes responsible for
modifying precipitation and converting it to runoff and additions to soil moisture storage. The
infiltration process and other hydrological processes are inter-related through a common
dependence on soil moisture conditions (Han, 2010).
Movement of water into the soil is controlled by gravity, capillary action, and soil
porosity. Of these factors soil porosity is most important. A soil's porosity is controlled by its
texture, structure, and organic content. Coarse-textured soils have larger pores and fissures
than fine-grained soils and therefore allow for more water flow. Pores and fissures found in
soils can be made larger through a number of factors that enhance internal soil structure.
The amount of decayed organic matter found at the soil surface can also enhance infiltration.
Organic matter is generally more porous than mineral soil particles and can hold much
greater quantities of water (Pidwirny, 2006).
There are several factors affecting the infiltration capacity:
1. The precipitation:Precipitation that infiltrates into the ground often seeps into
streambeds over an extended period of time, thus a stream will often continue to
flow when it hasn't rained for a long time and where there is no direct runoff from
recent precipitation. Moreover, raindrop impact breaks large soil clumps into
smaller particles. These particles then clog soil surface pores reducing the
movement of water into the soil (Pidwirny, 2012).
2. Soil characteristics:Some soils, such as clays, absorb less water at a slower
rate than sandy soils. Soils absorbing less water result in more runoff overland
into streams.
3. Soil saturation:Dry soil absorbs water more readily than a wet soil. Like a wet
sponge, soil already saturated from previous rainfall can't absorb much more
water, thus if rainfall intensity is greater than the infiltration rate, water will
accumulate on the surface and runoff will begin.
4. Land cover:Some land covers have a great impact on infiltration and rainfallrunoff. Vegetation can slow the movement of runoff, allowing more time for it to
seep into the ground. Impervious surfaces, such as parking lots, roads, and
developments, act as a "fast lane" for rainfall - right into storm drains that drain
directly into streams. Agriculture and the tillage of land also changes the
infiltration patterns of a landscape. Water that, in natural conditions, infiltrated
directly into soil now runs off into streams (U.S. Geological Survey, 2012).
5. Slope of the land:Water falling on steeply-sloped land runs off more quickly
and infiltrates less than water falling on flat land.
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6. Evapotranspiration:Some infiltration stays near the land surface, which is
where plants put down their roots. Plants need this shallow ground water to grow,
and, by the process of evapotranspiration, water is moved back into the
atmosphere (U.S. Geological Survey, 2012).
Once water has
infiltrated through the
subsurface soil, it forms an
unsaturated zone and
saturated zone. In the
unsaturated zone, the
voidsthat is, the spaces
between grains of gravel,
sand, silt, clay, and cracks
within rockscontain both air
and water. Although a lot of
water can be present in the
unsaturated zone, this water cannot be pumped by wells because it is held too tightly by
capillary forces. The upper part of the unsaturated zone is the soil-water zone. The soil zone
is crisscrossed by roots, openings left by decayed roots, and animal and worm burrows,which allow the precipitation to infiltrate into the soil zone. Plants use the water here in life in
life functions and leaf transpirations, and the water in this zone can evaporate directly to the
atmosphere.
After the water has infiltrated through the unsaturated zone and the aquifer, it
reaches the water table and become groundwater. The water table is the boundary between
the unsaturated zone and saturated zone. In this area, no fluid pressure is present. An
aquifer is a layer of unconsolidated or consolidated rock that is able to transmit and store
enough water for extraction. All aquifers have an impermeable layer, which are called
aquifuge (refers to a totally impermeable rock formation) beneath them that stops
the groundwater from infiltrating further. There are two forms of aquifers that can be seen:
confined and unconfined aquifers. Confined aquifers have lower boundaries (aquitard)
above and below it that constricts the flow of water into a confined area. An aquitard is a
geological formation that transmits water at a much slower rate than the aquifer. Unconfined
aquifers have no boundaries above them and therefore water table is free to rise and fall
dependent on the amount of water contained in the aquifer (Davie, 2008).
Figure 4.3 The Water Cycle: Groundwater Storage.Source USGS
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Aquifers are natural filters that trap sediment and other particles such as bacteria and
provide natural purification of the ground water flowing through them. Clay particles and
other mineral surfaces in an aquifer also can trap dissolved substances or at least slow them
down so they don't move as fast as water percolating through the aquifer.
Groundwater can move through aquifers until it reaches an opening to the surface. In
a seep, the water reaches the surface over a large area. In a spring, water flows from the
earth at a small point. Because of the pressure of the water above it, water in confined
aquifers is generally under high pressure and can result in the production of an artesian
spring. Springs and seeps will only continue to flow as long as the water table is higher than
they are. Because of movement of water, the location of the recharge zone may be far from
the location of seeps and springs (Pidwirny, 2006).
Aquifers have historically been extremely important for humans who have used the
water for watering livestock, irrigating crops, powering mills, and as a source of municipal
water. If rates of removal of water for human use exceed the very slow, natural rate of
recharge, then the total amount of water in the aquifer is reduced which results in a lowering
of the water table. Lower water tables require deeper wells which greatly increase the cost of
pumping water from aquifers and further deplete water from the already slow, natural rate of
recharge (Pidwirny, 2006).
4.4 Runoff
Runoff is the downward movement of surface water under gravity in channels
ranging from small rills to large rivers. The runoff can be majorly divided into three types:
overland flow, throughflow and groundwater flow.
Types of Runoff
Overland flow (surface runoff) is the water which exits the watershed and runs across
the surface of the land reaching the stream without entering the soil. If the amount of water
falling on the ground is greater than the infiltration rate of the surface, overland flow willoccur. Channel flows of this sort can be perennial, flowing all the time, or they can be
ephemeral, flowing intermittently after periods of rainfall or snowmelt. Such surface waters
provide the majority of the water utilized by humans (Encyclopedia Britannica, 2012).
A continuous record of one of the surface flow (stream flow) is called hydrograph. In
the hydrographs, there are several peaks between periods of steady, much lower flows. The
hydrograph flow is referred to as peakflow, stormflow or even quickflow. Thery are the water
in the stream during and immediately after a significant rainfall event. The steady periods
between peaks are referred to as baseflow or sometimes lowflow. The shape of the
hydrograph, and in particular the shape of the stormflow peak, is influence by the storm
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characteristics (such as rainfall intensities and duration) and many physical characteristics of
the upstream catchment (Davie, 2008).
Throughflow (subsurface runoff) occurs in the shallow subsurface, predominantly,
although not always, in the unsaturated zone. Once water infiltrates the soil surface it
continues to move, either through the soil matrix or along preferential flow paths.
Groundwater flow is in the deeper saturated zone. Ground water flows from zones
where the water table is highest toward areas where it is lowest. In general, the water table
is higher beneath a hill than it is beneath an adjacent valley. Ground water flows from areas
of high water pressure toward areas of low pressure. The water pressure at any point is
proportional to the weight of water above that point. Ground water beneath a hill is under
greater pressure than water beneath the valley because the water table is higher beneath
the hill. Thus, the water pressure beneath the hill forces the water upward beneath the valley.
Because ground water flows from high places to low ones, the water table becomes flatter
during a dry season (Thompson & Turk, 1997).
Factors Affecting Runoffs
Runoffs are mainly influenced by following two factors climatic factors and
physiographical factors (Saikia, 2009).
Climate factors:
1. Types of Precipitation: It has great effect on the surface runoff. The surfacerunoff is quick and immediate if the precipitation falls as a rainfall depending upon
rainfall intensity while precipitation in the form of snow does not result in surface
runoff.
2. Rainfall Intensity: Runoff is directly proportional to the intensity of precipitation.
If the rainfall intensity is greater than infiltration rate of soil then surface runoff
starts immediately after rainfall. While in case of low rainfall intensity runoff starts
later.
3. Duration of Rainfall: It is directly related to the volume of runoff because
infiltration rate of soil decreases with duration of rainfall. Therefore medium
intensity rainfall even results in considerable amount of runoff if duration is longer.
If the duration of rainfall is quite small, surface runoff may not occur due to
infiltration and interception
4. Arial Rainfall Distribution: Runoff from a watershed depends very much on the
distribution of rainfall. It is also expressed as distribution coefficient mean ratio
of maximum rainfall at a point to the mean rainfall of watershed. Therefore, near
outlet of watershed runoff will be more.
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5. Direction of Prevailing Wind:If the direction of prevailing wind is same as
drainage system, it results in low peak. A storm moving in the direction of stream
slope produce a higher peak in shorter period of time than a storm moving in
opposite direction.
6. Other Climate Factor: Other climatic or meteorological conditions such as
temperature wind velocity, relative humidity, pressure, radiation, annual rainfall
etc. will also affect the water losses from watershed area (Saikia, 2009).
Physical factors:
1. Size of Watershed:A large watershed takes longer time for draining the runoff to
outlet than smaller watershed and vise-versa.
2. Shape of Watershed: Runoff is greatly affected by shape of watershed. Shape
of watershed is generally expressed by the term form factor and compactness
coefficient.
3. Slope of Watershed: It has complex effect. It controls the time of overland flow
and time of concentration of rainfall. E.g. sloppy watershed results in greater
runoff due to greater runoff velocity and vice-versa. Thus, change of runoff runoff
takes place due to rise and fall of surface level, such as elevation.
4. Orientation of Watershed: If the basin is oriented most of the time towards the
sunrays temperature increases due to heat received from the sun. Increased
temperature accelerates the rate of evaporation, which affects the surface runoff
due to rain. The north or south orientation, affects the time of melting of collected
snow.
5. Land Use: Land use and land management practices have great effect on the
runoff yield. E.g. an area with forest cover or thick layer of mulch of leaves and
grasses contribute less runoff because water is absorbed more into soil. In non-
forested areas, interception, infiltration, evaporation, evaporation is less so runoff
is more.
6. Soil moisture: Magnitude of runoff yield depends upon the initial moisture
present in soil at the time of rainfall. If the rain occurs after along dry spell then
infiltration rate is more, hence it contributes less runoff.
7. Soil type: In filtration rate vary with type of soil. So runoff is great affected by soil
type. Sandy soil has high infiltration producing less runoff. Clay soil tends to
produce high runoff as infiltration is less.
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8. Topographic characteristics: It includes those topographic features which
affects the runoff. Undulate land has greater runoff than flat land because runoff
water gets additional energy due to slope and little time to infill rate.
9. Drainage Density: It is defined as the ratio of the total channel length (L) in the
watershed to total watershed area (A). Greater drainage density gives more
runoff (Saikia, 2009).
10. Other physical factors: Other physical factors such as upstream reservoirs and
lakes, groundwater storage can also affect the runoff.
5.0 Hydraulic Event
Flood is defined as abnormal high stage of flow which overtops the natural artificial
river bank in any reach
and causes immense loss
of crops, property, human
lives and lines of
communication. Flood will
cause huge economy lose.
It is a natural event that
results from excess runoff
generated from a drainagebasin due to severe
combination of critical
hydrologic and
meteorological conditions
over the region. To avoid
huge economy lose due to flood, proper measurement or estimation is very much essential
for its control and design of different hydraulic structure. (Saikia, 2009) Some of the existing
method of estimating flood such as Flood frequency analysis.
Flood frequency analysis is a form of risk analysis, yet a risk analysis of the activity of
itself is rarely undertaken. Flood frequency analysis has 3 main characteristic which are (1) a
proliferation of mathematical models, lacking theoretical hydrologic justification, but used to
extrapolate the return periods of floods beyond the gauged record; (2) official mandating of
particular models, which has resulted in (3) research focused on increasingly reductionist
and statistically sophisticated procedures for parameter fitting to these models from the
limited gauged data. By this type of method, even over modest timescales such as 100
years, which offer the best promise for testing alternative models of extreme flood behaviour
Figure 5.1 Flood in Sungai Lembing, Pahang
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across a wider range of basins. Flood frequency analysis able to accurate estimate the flood
magnitude and used widely for design purposes: the power law model produces far more
conservative estimates of return period of large floods compared to conventional models,
and deserves closer study. (R.Kidson, K.S.Richards, 2005)
Drought is a condition of moisture deficit sufficient to have an adverse effect on
vegetation, animals, and man over a sizeable area. -- (Warwick, R.A., 1975, Drought hazard
in the United States: A research assessment: Boulder, Colorado, University of Colorado)
Compare to flood droughts may not be as quick and suddenly but drought are long period
and more devastating. Drought are long periods in which a region experiences an
abnormally low level of rainfall, or no rain at all. This is the most serious physical hazard to
agriculture in nearly every part of the world. It can cause soil to dry out, plant and crops to
die, and stream, lakes and river to dry up. At its worst, drought can result in widespread
famine and depth for thousands of people. (Gifford, 2005)
There are five recognized forms of drought, which are meteorological or
climatological drought, hydrological drought, agricultural drought, ecological drought an
socioeconomic drought. Meteorological drought is the amount of dryness and the duration of
the dry period. Atmospheric conditions that result in deficiencies of precipitation change from
area to area. Agricultural drought mainly effects food production and farming. Agricultural
drought and precipitation shortages bring soil water deficits, reduced ground water orreservoir levels, and so on. Deficient topsoil moisture at planting may stop germination,
leading to low plant populations. Hydrological drought is associated with the effects of
periods of precipitation shortages on water supply. Water in hydrologic storage systems
such as reservoirs and rivers are
often used for multiple purposes
such as flood control, irrigation,
recreation, navigation, hydropower,
and wildlife habitat. Competition forwater in these storage systems
escalates during drought and
conflicts between water users
increase significantly.
Socioeconomic drought occurs
when the demand for an economic
good exceeds supply as a result of
a weather-related shortfall in water
supply. The supply of many economic goods, such as water, forage, food grains, fish, and
Figure 5.2 Drought in Africa
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hydroelectric power, depends on weather. Due to variability of climate, water supply is
sufficient in some years but not satisfactory to meet human and environmental needs in
other years. The demand for economic goods is increasing as a result of increasing
population. Supply may also increase because of improved production efficiency and
technology. (David, Suketu, Roman, 1998)Same as flood, drought can control and manage
by indicate and measurement of drought. The Palmer Drought Severity Index is one of
several measuring systems for droughts. It uses temperature and rainfall data to indicate
which areas of a country are more likely to be affected by drought. The index uses 0 as
normal; drought is shown in term of negative numbers. For example, -2 is a moderate
drought, -3 is severe drought and -4 is an extreme drought. (Gifford, 2005)
6.0 Environmental sustainability
From evaluate the cycle of earths water, we known that the water is hard to neither
destroy nor create. The same water has been around on Earth for millions of years. But in
fact, nowadays lack of water supplies become a global crisis.
Even if water is a renewable resource but why we still face global water crisis. Low
precipitation in combination with a high evaporative will cause large proportion of water
become water vapor and store in atmosphere and relatively small amount of availability is
largely dictated by climate. Climate will affect the phase of water (gas, liquid, solid liquid
water present on earths surface therefore available water can be put to use is small.
Except interpret water scarcity in hydrological terms. Pollution also one of the factors
contributed to global water crisis. Pollution causes by industry activity, agriculture activity,
domestic waste which disposal to the water of bodies. Polluted water cant direct use by
human, moreover natural purification process-evaporation also cant treat those polluted
water. As the water molecule evaporated, pollutant will remain and sediment to the bottom of
bodies of water such as river, lake, ocean, etc. If untreated, pollutant cant degrade by
naturally and water cant use by human. Contaminated sediments are an ongoing source ofpollution. It will continually pollute other water come to those water bodies until they are
permanently removed. Those pollutants can be cleaned up or buried by clean materials. For
example, the US Army Corps of Engineers dredges roughly four million m 3per year in the
Great Lakes to maintain a navigable depth of water. The Corps of Engineers is now finding
that over half of the sediments are contaminated and must be disposed of as hazardous
waste. (Stauffer, 1998)
To keep earths water sustainable some management and prevention have to take.
Control of pollution can achieve by technology, management, policy, education, etc. Prevent
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is better than cure. We can mitigate pollution by let the social understood and know how
serious the problem we are facing. And what we can do in daily life to mitigate this problem.
Such as use water in possible way. The most critical task is making sure the problem is
much better understood worldwide. In technology field, we can develop technology and
facilities to conservation water. Such as modification of toilet flush system, make it use less
water while operation.
Treatment apply to pollutant also one of way to keep water sustainable. One of the
most common treatments is wastewater treatment. Some countries, like Singapore, are
trying to recycle wastewater to clean water or even drinking water. The rich East Asian
republic is a leader in developing advanced technology that cleanses waste water for other
uses, including drinking. According to the environmental protection hierarchy, reduce
pollution is better than treatment after pollution. Thus, improve understanding about
important of water and technical ways are always preceded.
Figure 6.1 NeWater factory in Singapore (convert
wastewater into drinking water
Some more, almost 70 percent of the worlds freshwater is used for agriculture.
(Walton, 2010) Thus, improving irrigation can help close supply and demand gaps.
Improvement of irrigation facility and technology can converse water and in the other hand
can increase yield of food. In the other hand, agricultural practices also let farmer know how
to use minimum amount of water to get highest yield of farm product.
Figure 6.2 Produce of NeWater
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Economy always the first consider of most of people. To promote and increase
efficiency of water conservation, wastewater treatment or other water protection related
project the first factor we have to consider is economy. According to experts from the
Organization for Economic Co-operation and Development (OECD), an international
economic forum of 31 of the worlds richest countries, raising prices will help lower waste
and pollution. (Walton, 2010)
As mention before, the
groundwater hold 0.31% of worlds
total water. Ground water are the
main source of human used water.
But most of water treatment
processes that apply in surface
water cant apply to groundwater.
Groundwater has several unique
characteristic that make
groundwater pollution a particular
challenge to clean up. Groundwater
is form when rainwater percolates
through the soil and into underground reserves called aquifers. Once in the aquifers,
groundwater can remain there for tens to thousands of years before eventually making its
way out and into streams, rivers, lakes and ocean. The long residence time means pollutants
are not flushed out, nor is there a lot of clean, incoming water to dilute the pollutants. Even
more, groundwater is not exposed to air or sunlight, which can help breakdown organic
compound, and because the contaminants are trapped underground, volatile compounds
cannot evaporate. Furthermore, aquifers have fewer of the microorganisms that break down
organic contaminants in surface water. Finally, contaminants can become trapped in
inaccessible nooks and crannies of the aquifer and adsorb to the surface of the rocks,creating a long-term source of pollution within the aquifer. For all these reasons, contaminant
in groundwater can be far more concentrated than in surface water and persist for much
longer. (Stauffer, 1998)
There are several option are available to treat contaminated aquifer which are (1)
provide in ground treatment, (2) provide aboveground treatment, (3) remove or isolate the
source of contamination, (4) abandon the source of supply.
Figure 1 Formation of Groudwater
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7.0 Conclusion
As we know, hydrologic cycle is a natural process drives by solar. Water can
automatically purify through phase transform of water. Odour, colour and others perimeter
can remove once water change it phase through evaporation, condensation or othersprocess. Water molecules are exists and cycle within the earth for millions of years. But
nowadays, high development of human science and technology lead development of
industry, manufacture factory, transportation bring pollution to water. Those pollutants cant
be treated and degraded by natural process anymore. In 21th era, the hydrologic studies
also focus on management, control and treatment technology to keep water sustainability
and bring benefit to human.
Water resources available in basin if properly managed, bring huge benefit in
development of the society. For example, properly managed water resource help our
hydraulic turbines to generate hydroelectricity, can nourish cropland and forest , control
devastation of flood and erosion, help floating our ships in shallow water by increase depth,
can preserve and increase wildlife and water growing lives like fishes, provides drinking
water, can convert a dry land into beautiful residential and flourished crops land, helps in
beautifying the surroundings and environment for recreation, control pollution and mosquito
growth. (Saikia, 2009) In term of human healthy, a clean and safe water resource and main
factor contributed to human health. All water related disease can prevent and interred by
proper manage of water quality and quantity. The huge benefit come with proper water
management can drive development of water related management, control and treatment
technology. Development and innovation of all water related management, control and
treatment technology will be the main focus of hydrologic studies in near future.
8.0 References
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Encyclopedia Britannica. (2012). runoff and Stream Discharge. Retrieved August 4, 2012,
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sciences/14215/Runoff-and-stream-discharge
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Pidwirny, M. (2007, March 12). Evaporation. Retrieved August 3, 2012, from The
Encyclopedia of Earth: http://www.eoearth.org/article/Evaporation
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R.Kidson, K.S.Richards. (2005, September). Flood frequency analysis: assumptions andalternatives. Retrieved 08 03, 2012, from SAGE journals:
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Saikia, D. &. (2009). Hydrology.PHI Learning Pvt. Ltd., 2009.
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Walton, B. (2010, March 3). California Farmers Can Save Water, Money, Says Pacific
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save-water-money-says-pacific-institute-report/
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