hydrology assignment.docx

7/27/2019 hydrology assignment.docx

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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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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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