Rajiv Gandhi college of engineering and research, wanadongri.BE 1ST YEAR
BASICS OF CIVIL ENGINEERING
UNIT III
ENVIRONMENT AND NATURAL RESOURCE MANAGEMENT1) Water supply
1.1 Importance and necessity of water supply schemes
Water supply scheme involves:
(a) Collection
(b) Conveyance
(c) Treatment
(d) Distribution of water
For every living being water, air, food, shelter etc are the primary needs of which the water has the greatest importance. It is truly said that the water is best of all things. Everywhere water is required for various purposes such as:
a) For drinking and cooking
b) For bathing and washing
c) Washing of clothes and utensils
d) For watering of lawns and gardens
e) For heating and air conditioning systemsf) For growing of crops
g) Fire fighting
h) Steam power and various industrial processes
i) Construction works
j) Washing of vehicles
k) Street washing
l) Recreation in swimming pools fountains and cascades etc.
Without food human can survive for a number of days, but water is such an essential element without it he cannot. In the ancient times humans required water for drinking, bating, cooking etc. but with the advancement of civilization the utility of water enormously increased and now such a stage has come that without well organized public water supply scheme, it is impossible to run the present civic life and develop the towns.
In ancient times the water was collected from surface sources like rivers, lakes and ponds.etc. The original small water source become insufficient and large water sources become inevitable. The large water source may be far away from the township and the water may not be safe for dinking. The role of water supply scheme, i.e. collection, conveyance treatment and distribution of water comes in handy here. For every town or a city, an administrative body, either the municipality or corporation has been established to look after the public health and to supply potable water to consumers after proper treatment.1.2: Salient features/essentials of water supply scheme:
1) Population forecast: Every scheme should be such that it may run satisfactorily at least for three decades. So, the probable population of a town or a city should be ascertained for the future decades.
2) Assessment of water demand: Depending upon the probable population, the total water requirement for the town or city should be estimated considering the domestic demand, industrial and fire demand etc.
3) Record of industry: The nature and the number of the industries in the town or a city should be recorded because the industries require much water for running the maintenance. This record should also be updated from time to time.
4) Record of public places: The nature and number of public places like markets, cinema halls, auditoriums, parks, swimming pools, schools, colleges etc. Should be recorded for the provision of additional water requirement.
5) Sources of water: The cost of water supply scheme depends on the selection of site for the sources of water. So the source of water should be such that the cost of conveyance and treatment of water may be reasonable.
6) Quality of water: There should not be too turbid and there should be no or minimum sources of contamination to avoid any excessive treatment.
7) Over-head Reservoir: The water after treatment is generally stored in the overhear reservoirs from where it is supplied to the consumers. The location of a reservoir should be such that the water can flow to the network of distribution system.
1.3 Importance and Reliability of Water Works
Water is good carrier of disease germs and may be responsible for water-borne diseases. Therefore, the water which is supplied to the public should be wholesome and must be free from any pathogens, poisonous substances and excessive amount of mineral and organic matter. The water-borne diseases are cholera, typhoid, jaundice, dysentery etc. therefore it is very important that water works must remove all the impurities and bacteria from water and make it wholesome.
The following is the
a) Water should be taken from the permanent (never failing) surface of ground source.b) Source of water should be large impounding reservoirs, from where it can flow under the gravity to the city.
c) If reservoir is at low level water can be pumped to the city.
d) Water should be taken from the tube-wells.
The reliability of water works depends upon the design, construction and maintenance of works for collection and distributing the water.
1.4 Duties of Water Works Engineer
a) He must be well conversant with the planning, designing, construction, maintenance and operation of water works.
b) He must be capable of designing the water works scheme in the best possible way with maximum economy and efficiency to remove the impurities and bacteria.
c) He must be capable of operating water works scheme without fail and should supply the safe palatable water to the public in the required pressure at various points.
d) He should protect the sources of water as well as treat the water from contamination or any type of pollution.
e) He should have sound knowledge of laboratory tests to check the water samples for the presence of bacterias.
f) He should be able to alter the purification method depending on the type o impurities and bacterias present in water.
2) SOURCESFOLLOWING ARE THE SOURCES OF WATER:
1) Surface sources:
a) Rivers, streams
b) Lakes
c) Ponds
d) Impounded reservoirs.
2) Underground sources(sub-surface):
a) Springs
b) Wells
1) Artesian well
2) Dug/draw well
3) Tube well
c) Infiltration galleries.Surface sources:NATURAL PONDS AND LAKES
In mountains at some places natural basins are formed with impervious bed by springs and streams are known as lakes. The quality of water in the natural ponds and lakes depends upon the basins capacity, catchment area, annual rainfall, porosity of ground etc. But lakes and ponds situated at higher altitudes contain almost pure water which can be used without any treatment. But ponds formed due to construction of houses, road, and railways contains large amount of impurities and therefore cannot be used for water supply purposes.STREAMS AND RIVERS
Rivers and streams are the main source of surface source of water. In summer the quality of river water is better than monsoon because in rainy season the run-off water also carries with clay, sand, silt etc which make the water turbid. So river and stream water require special treatments. Some rivers are snow fed and perennial and have water throughout the year and therefore they do not require any arrangements to hold the water. But some rivers dry up wholly or partially in summer. So they require special arrangements to meet the water demand during hot weather. Mostly all the cities are situated near the rivers discharge their used water of sewage in the rivers, therefore much care should be taken while drawing water from the river.IMPOUNDING RESERVOIRS:In some rivers the flow becomes very small and cannot meet the requirements of hot weather. In such cases, the water can be stored by constructing a bund, a weir or a dam across the river at such places where minimum area of land is submerged in the water and max. Quantity of water to be stored. In lakes and reservoirs, suspended impurities settle down in the bottom, but in their beds algae, weeds, vegetable and organic growth takes place which produce bad smell, taste and colour in water. Therefore this water should be used after purification. When water is stored for long time in reservoirs it should be aerated.SUBSURFACE SOURCES:INFILTRATION GALLERIES:
INFILTRATION WELLS:In order to obtain large quantity of water, the infiltration wells are sunk in series in the blanks of river. The wells are closed at top and open at bottom. They are constructed by brick masonry with open joints as shown in fig.
Infiltration Well Jack WellFor the purpose of inspection of well, the manholes are provided in the top cover. The water filtrates through the bottom of such wells and as it has to pass through sand bed, it gets purified to some extent. The infiltration well in turn is connected by porous. pipes to collecting sump called jack well and there water is pumped to purification plant for treatmentSPRINGS:
Sometimes ground water reappears at the ground surface in the form of springs. Springs generally supply small springs. Springs generally supply small quantity of water and hence suitable for the hill towns. Some springs discharge hot water due to presence of sulphur and useful only for the curve of certain skin disease patients.
Types of springs:
1. Gravity Springs: When the surface of the earth drops sharply the water bearing stratum is exposed to atmosphere and gravity springs are formed as shown in fig.
Gravity Spring
2. Surface Spring: This is formed when an impervious stratum which is supporting the ground water reservoir becomes out crops as shown in fig.
Surface Spring
3. Artesian Spring: When the ground water rises through a fissure in the upper impervious stratum as shown in fig.
Artesian springWhen the water-bearing stratum has too much hydraulic gradient and is closed between two imperious stratum, the formation of Artesian spring from deep seated spring.
Artesian springWELLS:
A well is defined as an artificial hole or pit made in the ground for the purpose of tapping water. In India 75 to 85% of Indian population has to depend on wells for its water supply.
The three factors which form the basis of theory of wells are
1. Geological conditions of the earths surface
2. Porosity of various layers
3. Quantity of water, which is absorbed and stored in different layers.
The following are different types of wells
1. Shallow wells
2. Deep wells
3. Tube wells
4. Artesian wells
(a) Shallow Wells:Shallow wells are constructed in the uppermost layer of the earths surface. The diameter of well varies from 2 to 6 m and a maximum depth of 7m. Shallow wells may be lined or unlined from inside. Fig. shows a shallow well with lining (steining). These wells are also called draw wells or gravity wells or open wells or drag wells or percolation wells.
Shallow Well
Quantity of water available from shallow wells is limited as their source of supply is uppermost layer of earth only and sometimes may even dry up in summer. Hence they are not suitable for public water supply schemes. The quantity of water obtained from shallow wells is better than the river water but requires purification. The shallow wells should be constructed away from septic tanks, soak pits etc because of the contamination of effluent.
The shallow wells are used as the source of water supply for small villages, undeveloped municipal towns, isolated buildings etc because of limited supply and bad quality of water.(b) Deep Wells :
The Deep wells obtain their quota of water from an aquifer below the impervious layer as shown in fig No. The theory of deep well is based on the travel of water from the outcrop to the site of deep well. The outcrop is the place where aquifer is exposed to the atmosphere. The rain water entered at outcrop and gets thoroughly purified when it reaches to the site of deep well. But it dissolves certain salts and therefore become hard. In such cases, some treatment would be necessary to remove the hardness of water.
Deep WellThe depth of deep well should be decided in such a way that the location of out crop is not very near to the site of well. The water available at a pressure greater atmospheric pressure, therefore deep wells are also referred to as a pressure wells.3) DRINKING WATER REQUIRMENTS
Absolutely pure water is never found in nature. Absolutely pure water is that water which only contains two parts of Hydrogen and one part of Oxygen by volume and nothing else. But the water found in nature contains number of impurities in varying amounts. While falling in the form of rains the water absorbs number of gases, dust and organic and inorganic impurities. This water when moves on ground further carries the silts and other impurities. Therefore the runoff water has large no of impurities. These impurities make the water unsuitable for the drinking. Therefore such impurities must be removed from the water as well as while removing such impurities the essential elements and bacterias that naturally present in water and mostly useful for the human health must not be removed.Therefore the drinking water has the following requirements
a) It should be free from the bacterias that causes the diseases.
b) It should be colourless
c) It should be odourless
d) It should be tasty and cool
e) It should be free from the silts
f) It should be free from any objectionable matter
g) It should have dissolved oxygen and free carbonic acid so that it may remain fresh
h) It should not corrode pipes
The water supplied to the community should be strictly according to the standards laid down from time to time.
4) IMPURITIES IN WATER AND THEIR EFFECT
Impurities in water can be listed as follows:
a) Suspended impurities
b) Colloidal Impurities
c) Dissolved impurities
(a) Suspended Impurities: These impurities are the suspension of solid particles that are large enough to be removed by filtration or surface and heavier ones settle down. The suspended particles which have same specific gravity as that of water are mixed in the water. Suspended impurities include clay, algae, fungi, organic and inorganic matter and mineral matter etc.
These all impurities are macroscopic and cause turbidity in water. The concentration of suspended matter in water is measured by its turbidity.
Examples: sand clay and other inorganic soils, algae, bacterias.(b) Colloidal Impurities: It is very finely divided dispersion of particles in water. These particles are so small that these particles cannot be removed by ordinary filters and are not visible to the naked eye. As a matter of fact all the colloidal impurities are electrically charged and remain in continuous motion. The electric charge is due to presence of absorbed ions on the surface of the solid. Acid or neutral materials such as silica, glass and most organic particles acquire negative charge in neutral water, where as basic materials such as metallic oxides AL2O3 and. Fe2O3 are positively charged. These electric charges on the surfaces of particles are large enough in comparison with their mass to cause the particles to repel one another when they move within the sphere of action of each others charge. Due to this repelling action all colloidal particles remain in motion and do not settle. That is why there removal is very difficult. These colloidal impurities are generally associated with organic matter containing bacterias and are the chief source of epidemics.
Most of the colour of water is due to colloidal impurities their quantity is determined by the colour tests. The size of colloidal particles is in between (1=1 micron=0.001mm) to (1=1 milli micron =0.000001mm) or (10-3 mm to 10-6mm).
Examples: Silica, clay, iron oxide Fe2O3 , aluminum AL2O3 , manganese oxide MnO2 ,Vegetable and organic waste.
(c) Dissolved Impurities: Some impurities are dissolved in water when it moves over the rocks, soil etc. solids, liquids; gases are dissolved in natural waters. These dissolved impurities may contain organic compounds, inorganic salts and gases etc. The concentration of local dissolved solids is usually expressed in p.p.m and is obtained by weighing the residue after evaporation of the water sample from a filtered sample.Examples: calcium, magnesium, sodium, potassium, iron, salts, gases like hydrogen.
Effects of the impurities
IMPURITYCONSTITUENTSEFFECTS
Suspended Impuritiesa) Bacteria
b)Algae, Protozoa
c)SiltsSome cause diseases
Odour, Colour, Turbidity
Murkiness or Turbidity
Dissolved Impuritiesa)Salts
1)Calcium & MagnesiumBicarbonateAlkalinity
Alkalinity & Hardness
Hardness
Hardness Corrosion
Carbonate
Sulphate
Chloride
2)sodiumBicarbonateAlkalinity, Softening effect
Alkalinity, Softening effect
Foaming in Boilers
Dental Flurosis or mottled enamel
Taste
Carbonate
Sulphate
Fluoride
Chloride
b) Metals and Compounds
Taste, red colour, corrosiveness, hardness
Black or brown colour
Cumulative poisoning
Toxicity , poisoning
Toxic effect on heart and nerves
Toxic & illness
Fatal
Affect central nervous system
Highly toxic to animals
Discoloration of skin & eyes
Blue baby conditions, infant poisoning, colour, acidity
Iron oxide
Manganese
Lead
Arsenic
Barium
Cadmium
Cyanide
Boron
Selenium
Silver
nitrates
( c ) Vegetable Dyes
( d ) gasesOxygenCorrosiveness to metals
Acidity, corrosiveness
Odour, acidity, corrosiveness
Carbon Dioxide
Hydrogen Sulphide
6) TREATMENT OF WATER (Purification of Water) GENERAL INTRODUCTION
Water available in various sources contains various types of impurities and cannot be directly used by the public for various purposes, before removing the impurities. For potability water should be free from unpleasant tastes, odours and must have sparkling appearance. The water must be free from disease-spreading germs. The amount and type of treatment process will depend on the quality of raw water and the standards of quality of raw water and the standards of quality to be required after treatment as per the table no.
The surface sources generally contains large amount of impurities therefore they requires sedimentation, filtration and chlorination as treatment. If the water contains algae or other micro organisms, pre chlorination has to be done tastes and odours , dissolved gases like CO2, H2S are removed by aeration. During the flood season, the turbidity of the surface water may be high and flocculation may become necessary to remove turbidity.
Ground water which is usually clear may require only disinfection and chemical treatment for the removal of pathogens, Iron removal, Softening etc. Sometimes ground water contains dissolved gases like hydrogen sulphide (H2S) carbon dioxide (CO2), which gives very bad odour and requires its removal by aeration.
PURIFICATION OF WATER
Object: The water from sources may have some characteristics which are unsuitable for human consumption, industrial use, commercial use etc. the following are some of those characteristics:
a) Turbidity
b) It may contain colour
c) It may contain acids, salts and gases which have corrosive action and may impart hardness of water.
d) It may contain bacteria which may cause water borne diseases.
Therefore the object of purification of water is to remove those impurities and make the water suitable for domestic, industrial, commercial uses. Underground water may be free from the above impurities but sometimes it may possess the property of hardness which should be removed.
PRIMARY TREATMENT OF WATER(TREATMENT UNIT FLOW DIAGRAM)
Water treatment includes many operations like Aeration, Flocculation, Sedimentation, Filtration, Softening, Chlorination and demineralization. Depending upon the quality of raw water and the quality of water desired. Several combinations of the above processes may be adopted as shown in the flow diagram above processes may be adopted as shown in the flow diagram
One complete water treatment plant requires the following process starting from the source of water up to the distribution zone in order of sequenceSEQUENCE OF UNITS:
1) Intake point
2) Pump house
3) Plain sedimentation tank
4) Coagulation tank
5) Filtration unit
6) Chlorination unit
7) Water softening plant
8) Overhead reservoir
The following points should be kept in mind while giving layout of any treatment plant.
1. The W.T.P. should be located as near to the town so as to avoid the contamination.
2. All the units of plant should be located in order of sequence and flow from one unit to
other by gravity.
3. All the units are arranged in such a way that minimum area is required so as to reduce
the cost of construction.
4. Sufficient area should be reserved for the future expansion
5. Staff quarters and office should be provided near the treatment plants so that the
operators can watch the plants easily.
6. The site of treatment plant should be very neat and give very good aesthetic appearance.Functions of units:1) Intake point: The function of this unit is to collect water in the intake well so that the water can be supplied throughout the year.2) Pump House: The function of this unit is to draw the water from the intake well and to supply same to the treatment plat.
3) Plain Sedimentation Tank: The function of this unit is to remove the heavier suspended particles in water. In this tank the water is detained for some period or allowed to flow at very low velocity so that the heavier suspended particles are settle down at the bottom of the of sedimentation tank but some lighter particles still remain in suspension.
4) Coagulation Tank: the function of this unit is to remove the lighter suspended particles by the application of some coagulants. In this tank some recommended coagulants is mixed with water and the water is allowed to flow at very low velocity through the coagulation tank. The coagulants make the liter particles to gain the settle able size and ultimately settle down at the bottom of the tank but some finer colloidal particles still remain in the suspension.
Sedimentation with Coagulation5) Filtration Unit: The function of this unit is to remove the finer colloidal particles and some bacteria for filtering media of sand and gravel but some bacteria still remain in the water.
6) Chlorination unit: the function of this unit is to destroy the bacteria by application of chlorine.
7) Water Softening Tank: the function of this unit is to remove the hardness of water to make it fit for commercial purpose. This unit is not always necessary.
8) Overhead Reservoir: The function of this unit is to store purified water after the treatment is complete. The water from the reservoir is supplied to the consumers by gravity.7) DISINFECTION OF WATERNECESSITY OF DISINFECTION: The processes of destroying harmful bacteria from water and to make it safe for drinking is known as disinfection. The substances used for disinfection used for disinfectants. The common disinfectants are lime, iodine and bromine, ozone, potassium permanganate, silver; chlorine etc. chlorine is the most important disinfectant which has a wonderful power for killing bacteria in short span of time with a minimum amount of expenditure. So this chemical is used in most developing countries.
The processes of destroying all the bacteria (either harmful or harmless) are known as sterilization. But in a water supply scheme, we require only the removal of harmful bacterias (i.e. pathogenic bacteria) which may cause water borne diseases like cholera, dysentery, typhoid etc.REQUIREMENTS OF GOOD DISINFECTANTS
1. They should destroy all the harmful pathogens and make it safe for use,.
2. They should not take more time in killing bacteria
3. They should be economical and easily available
4. They should not require high skill for their application
5. After treatment the water should not become toxic and objectionable to the user.
6. The concentration should be determined by simply and quickly.METHODS OF DISINFECTION:
a) Disinfection by boiling
b) By ultra-violet rays
c) By iodine and bromine
d) By excess lime
e) By ozone
f) By potassium permanganate
g) By silver
h) By chlorine
Disinfection by Boiling: When water is boiled to the boiling temperature ( 100oc ) the bacteria is completely removed. It should be boiled at least for 10-15 minutes. Boiling also removes some of the dissolved salts. It is the most effective method of disinfection. But this is not suitable for large scale. It is suitable for domestic purpose, i.e. to boil water before its use as drinking water. In case of an epidemic, the consumers should always boil water to check the water borne diseases.Disinfection by ultraviolet rays: When mercury enclosed in a quarts bulb an electric current is passed through it, the ultra violet rays are emitted. These rays are found to be very powerful in killing all type of bacteria. In this method the water is allowed to flow under the bulb for several times. The depth of flow should not exceed 10-15 cm. this method does not impart any taste or colour to the water or there is no possibility of overdosing. It is costly processes and suitable for small water supply installations like factories, institutions, training camp, etc.
Disinfection by iodine and bromine: the iodine and bromine also have property of killing bacteria. Dose of iodine and bromine should be 8-10 ppm. These chemicals are available in the form of small pellets. The water is stored in a suitable container and required number of pellets are dropped in the water and left for 5 minutes. Water becomes safe for drinking. This method is suitable for small water supply installations like industries, military or survey camps.Disinfection by excess lime: naturally lime is added to the water is to remove some salts but when excess lime is added to the water it is found to be act as a disinfectant. The excesses lime increases the pH value of water i.e. increases the alkalinity of water which is detrimental to bacteria because bacteria cannot resist the alkalinity of water. It is found that pH value 9-10 can remove bacteria to the extent of 99% but after treatment the residual lime should be removed by the method of re carbonation.
Disinfection by ozone: in atmosphere the molecules of oxygen contains two items (O2 ) but it changes to three when electric current of high voltage is passed through the stream of air in chamber. This triatomic oxygen is known as ozone (O 3 ).the ozone easily breaks into oxygen ( O2 ) and nascent atom ( O ). This third atom is very powerful in killing bacteria. The dose of ozone varies from2-5 ppm and contact period varies from 5-10 mins. If after treatment some residual ozone is present in water, it is automatically removed. Since ozone is unstable in nature, there is no possibility any danger to the consumers. It is costly method. Disinfection by potassium permanganate: potassium permanganate is a powerful oxidizing agent. It oxidizes the organic matter present in water and hence the bacteria get killed. this mostly used for disinfecting water of wells in village, swimming pools, ponds etc. not suitable for large scale. Dose of chemical is about2-3 ppm and contact period is 2-3 hrs.
Disinfection by chlorine: Chlorine has got the wonderful power of destroying bacteria. It is best among all the other disinfectants used for the disinfection of water. It kills bacteria very fast and its effect effect lasts for such a long time that it even acts in the distribution systems. It is cheap and reliable. If some residual chlorine exists in water it does not cause any harm to the consumers.8) STANDARDS OF PURIFIED WATER
The physical, chemical, bacteriological standards for water quality as suggested by the following agencies:
1) Indian Council of Medical Research (I.C.M.R) committee
2) World Health Organization (W.H.O)
3) United States Public Health Society (U.S.P.H.S)
4) American Water Works Association (A.W.W.A)
The manual on water supply and treatment prepared by the central public health and environmental engineering Organization, under the Ministry of Urban Development (MUD) India lays down the following standards of water.
S.NCHARECTERISTICSACCEPTIBLECAUSE OF REJECTION
1Turbidity ( J.T.U scale)2.510
2Colour (platinum cobalt scale)5.02.5
3Taste and OdourunobjectionableUnobjectionable
4Total Dissolved Solids(mg/l)5001500
5Hardness ( as CaCO3) (mg/l)200600
6Chlorides ( as Cl) (mg/l)2001000
7Fluorides ( as F) (mg/l)1.01.5
8Sulphates ( as SO4) (mg/l)200400
9Nitrates ( as NO3) (mg/l)4545
10Calcium ( as Ca) (mg/l)75200
11Magnesium ( as Mg) (mg/l)30150
12Iron ( as Fe) (mg/l)0.11.0
13Manganese ( as Mn) (mg/l)0.050.5
14Copper (as Cu) (mg/l)0.051.5
15Zinc (as Zn) (mg/l)5.015.0
Toxic materials
16Arsenic ( as As) (mg/l)0.050.05
17Cadmium (as Cd) (mg/l)0.010.01
18Chromium (as Hexavalent Cr) (mg/l)0.050.05
19Cynides ( as Cn) (mg/l)0.050.05
20Lead (as Pb) (mg/l)0.10.01
21Mercury (total Hg) (mg/l)0.0010.001
Radio Activity
22Gross Alpha Activity3 pci/l3 pci/l
23Gross Beta Activity30 pci/l30 pci/l
24Pci= pico curie
The figures indicated under acceptable column are the limits up to which the water is generally acceptable for consumers. Cause of rejection column shows the limit of tolerance if the supply contains the impurities exceeds the limit the water is not safe for drinking and must be rejected. WASTE MANAGEMENT
(Collection & disposal methods of liquid, solid and gaseous wastes)SANITARY ENGINEERING: It is the branch of public health engineering which deals with the preservation and maintenance of health of the individual and the community, by preventing communicable diseases. It consists of scientific and methodical collection, conveyance, treatment and disposal of waste matter so that public health can be protected from the offensive and injurious substances. Sanitation is the prevention of sporadic outbreak of disease, and can be achieved by either controlling or eliminating such environmental factors that contributes into the some form or the other to the transmission of diseases.
If the waste water created and given out by the human and animal life, and also by industries etc, is allowed to accumulate, it will get decompose and will contaminate or pollute air, water and food. Hence sanitary disposal of waste, either in solid form or in liquid form, is most essential. The sanitary sewage includes excreta (i.e. waste matter eliminated from the boy), domestic sewage (i.e. used water form the home community which includes toilet, bath, laundry, and Lavatory and kitchen-sink wastes) and industrial waste. The improper disposal of human excreta and sewage is the major factor threatening the health and comfort of individuals where satisfactory sewage system is not available.IMPORTANT TERMS AND DEFINATIONS:
1) Refuse: is a general term used to indicate what is rejected or let out as worthless. It may be liquid, semisolid or solid form and may be divided into six catagories: a) garbage b) rubbish c) sullage d) sewage e) subsoil water f) storm water.2) Garbage: Dry refuse such as papers, decayed fruits, vegetables, grass and leaves, and sweeping from streets, markets and other public places. Thus garbage contains large amount of organic and putrefying matter.
3) sullage: sullage is a term used to indicate waste water from bathrooms kitchens, washing places and wash basins etc. It does not create any bad smell because the organic matter in it is either absent or in very negligible amount.
5) Sewage: sewage indicates the liquid waste from community. It includes sullage , discharge from latrines, urinals, stables, industrial waste and also ground surface and storm water. It is extremely putrescible: its decomposition produces large quantities of malodorous gases and it may contain numerous pathogenic or disease producing bacteria.6) Sub-soil water: it is the ground water that finds its entry into sewers through leaks.
7) Storm water: it indicates the rain water of the locality
8) Sanitary sewage: sanitary sewage or the domestic sewage indicates sewage mainly derived from the residential building and industrial establishments. It is extremely foul in nature. Sanitary sewage may be classified as a) domestic sewage and b) industrial sewage.
9) Domestic sewage: it is the sewage obtained from the lavatory basins, urinal and water closets of residential buildings office buildings, theaters and other institutions. Since it contains human excreta and urine, it is extremely foul in nature.10) Industrial sewage: It s wastewater obtained from the industrial and commercial establishments. Is may contain objectionable organic compounds that may not be amenable to conventional treatment processes.
11) Night soil: It is a term used to indicate the human excreta.
12) Sewer: it is an underground conduit or drain through which sewage is carried to a point of discharge or disposal.
Sources of Wastes: Solid waste- vegetable waste, kitchen waste, household waste etc.
E-waste- discarded electronic devices like computer, TV, music systems etc.
Liquid waste- water used for different industries e.g. tanneries, distilleries, thermal power plants
Gaseous waste:
Plastic waste- plastic bags, bottles, bucket etc.
Metal waste- unused metal sheet, metal scraps etc.
Nuclear waste- unused materials from nuclear power plants
For the disposal of waste products of a town two works are required:
1) Collection works
2) Disposal works
The disposal works mainly consists of treatment works which are essential to neither treat the waste water and dispose it off on such a way that it may not cause any harm to the health of public nor pollute the nearby water sources and environment. The collection works are the works which are done to collect the waste products. In olden days it was done by the conservancy method, but in modern cities it is done by water carriage method. The water carriage system has so many systems as separate, combined or partially separate in which the sewage or storm water can be collected. METHODS OF COLLECTION
The sanitation of a town or city is done by two methods which are:
1) Conservancy system
2) Water carriage System.
CONSERVANCY SYSTEM
This is an old system in which various types of wastes, such as night soil, garbage etc. are collected separately in vessels or deposited in pools or pits and then removed periodically at least once in 24hrs. On account of this method of handling independently the different type of refuse from place the term conservancy system has been derived. The system is also known as the dry system. The following are the methods of collection of various types of waste in the system.
1) Night soil: night soils or human excreta in latrines, privies or cesspools etc . is collected separately in pans or pails and carried on heads of sweepers to a central place from where it is transported in bullock carts or motor vans to a place away from the town for final disposal. Normally it is buried into ground, in trenches, to give excellent manure in one or two years.2) Garbage: garbage is collected separately, in dust bins and conveyed on head, carts or motor vans once or twice a day. It may consist of waste matter of both non combustible as well as combustible type the two are therefore sorted out. Garbage disposal method includes the open ump, hog fiddling, and incineration, dumping into sanitary field, fermentation or biological digestion.
Incineration, if properly controlled, is satisfactory for burning combustible diffuse.
3) Refuse: sullage and storm water. Sullage and storm water are collected and conveyed separately in closed or open gutters. The liquid and semi liquid mass of filth which frequently overflow the receptacles in privies is swept away by the sweepers to drain from the privies, which carry it to drains carrying sullage and storm water , along the public lanes or streets.
In India, the conservancy system is still on vogue in all the villages and small towns. Only a few cities have the water carriage systems. Disadvantages of conservancy system: 1) Hygiene and sanitary aspect: the conservancy system is highly unhygienic and cause insanitary conditions since the excreta start decomposing within few hrs of its production. Even if it is assumed that cleaning will take place twice in a day, the excreta remaining in the privies will emit bad smell and will give rise to fly nuscence.
2) Transportation aspect: transportation of night soil takes place in open carts through streets and other crowded localities this is highly undesirable.
3) Labor aspect: the working of the system depends entirely on the mercy of labors (sweepers). If they go on strike even for one day for any reason what so ever, the privies can not be used because of foul smell. Te whole locality will smell very badly.
4) Building design aspect: The lavatories or privies are to be located outside the house and slightly away from the main building the compact design is therefore is not possible.
5) Conditions of drains: insanitation may be there due to carriage of sullage through open drains laid in the streets.
6) Human aspects: in the present day world, when man has progressed much, it is highly humiliating to ask human beings to transport night soil in pails on their heads.
7) Risk of epidemic: due to improper or careless disposal of night soil, there are more chances of outbreak of epidemic.
8) Pollution problems: Liquid waste from lavatories etc., during their washing may soak in the ground, thus contaminating the soil. If the ground water is a t a shallow depth, it may also be polluted due to percolation of waste water.
9) Cost consideration: though t system is quit cheap in the beginning its maintenance and establishment cost are very high.
10) Disposal land requirements: the system requires considerable land for the disposal of sewage.
WATER CARRIAGE SYSTEM
In this system, the collection, conveyance and disposal of various types of waste are carried out with the help of water. Thus water is used as medium to convey the waste from its point of production to the pint of its treatment or a final disposal. Sufficient quantity of water is required to be mix with the waste so that dilution ratio is so great that the mixture may flow just like water.
In this system, specially designed latrines called water closet (w.c) are used which are flushed with 5-10 liters of water after its used by every person the human excreta is thus flushed away and lead to suitable design and maintain sewer. The waste from kitchens, baths, wash basins etc. re also laid to the sewers the sewers are the underground closed pipes which are laid on suitable longitudinal gradient slow that flow takes under gravity and proper flow velocity is maintained to keep the sewer clean. The sewers laid the sewerage so collected to suitable site where it is treated suitably and then is disposed off by irrigation or by dilution.
It should be noted that the garbage is collected separately and conveyed in same manner as in case if conservancy system. If garbage is permitted in the sewers, they may be clogged.
This system requires large initial cost of installation and it requires large quantity of water also to create efficient flow conditions. If the financial conditions of people are poor, it may be difficult to adopt this system. However this is the most efficient and hygienic system of sewerage disposal, and may be adopted in stages if sufficient funds are not available in the beginning.
ADVANTAGES OF WATER CARRIGE SYSTEM
This is the most modern system of drainage with the following advantages.
1) Huygens and sanitary aspect: the system is very hygienic since the night soil and other waste water is conveyed through closed conduits which are not directly exposed to the atmosphere. There is no bad smell because of continuous flow.
2) Epidemic aspect: there are no chances of outbreak of epidemic because flies and other insects do not have direct access to the sewage.
3) Pollution aspect: the liquid waste etc. is directly conveyed through the sewers, and therefore there are no changes of the waste Water being soaked in the ground thus contaminating the soil. The waste water dies not percolate down to join the ground water. There are no chances of pollution of water of well in individual houses if any.
4) Compactness in design: since the latrines are flushed after every use, excreta do not remain and there are no foul smells. The latrines can therefore be attached to the bedrooms and living. This permits a compact design. The lavatories can be accommodated in any part of the house.
5) Labour aspect: the labour required for the operation and maintenance is extremely small. In fact, the functioning of the system is practically automatic; except for the operation of certain pumps etc. there is no labour problem. In the individual houses, the latrines/lavatories can be conveniently cleaned by occupants themselves.
6) Treatment aspect: the system permits the use of modern methods of treatment of the sewage collected through the sewers. The treated waste water and sewage can be safely disposed of without any risk.7) Land disposal requirements: because of treatment facilities the land required for the disposal of the treated waste water is very much smaller than that required for the conservancy system.
8) Cost consideration: though the initial cost of installation of the system are very high, the running costs are very small manual labour is very much reduced.
Management of Solid Waste
For waste management we stress on three Rs-Reduce, reuse and recycle before destruction and safe storage of wastes.
(i) Reduction in use of raw materials: Reduction in the use of raw materials correspondingly decreases the production of waste. Reduced demand for any metallic product decreases its mining, hence less production of waste.
(ii) Reuse of waste materials: The refillable containers and plastic bags which are discarded after use should be reused. In Villages casseroles and silos are made from waste paper and rubber rings from discarded cycle tubes. Such practices reduce waste generation
(iii) Recycling of materials: Recycling is the reprocessing of discarded materials into new useful products.
Formation of some old type products e.g., old aluminum cans and glass bottles are melted and recast into new cans and bottles.
Formation of new products: Preparation of cellulose insulation from paper, preparation of fuel pellets from kitchen waste. Preparation of automobiles and construction materials from steel cans.
The process of reducing, reusing and recycling saves money, energy, raw materials, land space and also reduces pollution. Recycling of paper will reduce cutting of trees for making fresh paper. Reuse of metals will reduce mining and melting of ores for recovery of metals from ores and prevent pollution.
(iv) Waste disposal:
For discarding wastes the following disposal methods can be adopted:
Sanitary landfill: In a sanitary landfill, garbage is spread out in thin layers, compacted and covered with clay or plastic foam. In the modern landfills the bottom is covered with an impermeable liner, usually several layers of clay, thick plastic and sand. The liner protects the ground water from being contaminated due to percolation of leach ate. Leach ate from bottom is pumped and sent for treatment. When landfill is full it is covered with clay, sand, gravel and top soil to prevent seepage of water. Several wells are drilled near the landfill site to monitor if any leakage is contaminating ground water. Methane produced by anaerobic decomposition is collected and burnt to produce electricity or heat.
Composting: Due to shortage of space for landfill in bigger cities, the biodegradable yard waste (kept separate from the municipal waste) is allowed to degrade or decompose in an oxygen rich medium. A good quality nutrient rich and environmental friendly manure is formed which improves the soil conditions and fertility. Wormy technology, using earthworms can further help in converting solid organic waste into good quality compost.Incineration: Solid wastes can be brunt in large amounts at high temperature (around 1800C) in incinerator. Incinerator is a high temperature furnace used for burning solid wastes. Earlier incinerators used to be made of simple brick lining, but the modern ones are rotary. Kiln incinerators having a long inclined passage through which the waste is constantly moved. There is about 75% reduction in waste mass and 90% reduction in volume. The incinerators in which the waste to be burnt is not segregated are known as mass burn incinerators. There are special incinerators where potentially harmful or hazardous.Air Pollution
Air is defined as the elastic, invisible and tasteless mixture of gases that surrounds the earth. Air pollution is an environmental evil. Under ideal condition, the air that we inhale has a qualitative and quantitative balance that maintains the well being of a man. When the balance among the air components is distributed, air is said to be polluted. Some specific definition of air pollution is given below.
According to Indian standards institution, air pollution is the presence of ambient atmosphere of substances, generally resulting from the activity of man, insufficient concentration, present for a sufficient time and under circumstances with interfere significantly with the comfort, health or welfare of persons or with the full use of enjoyment of property.
Air pollution is an increasing problem in all countries where urban growth and population increasing are accompanied by rapid and extensive industrial development and extensive use of automobiles. Air pollution is attributed as the price of industrialization. Air pollution can impare health and sometimes cause death. It can cause respiratory problems and eye irritation. it also affects plants , animals and buildings.
Causes of air pollution:
As defined earlies, air pollution is any atmospheric condition certain substances are present in such concentrations that they produce undesirable effects on man and his environment. Following are the main causes of the air pollution
1) High rate of population growth: consequent to high population density, there is higher rate of fuel consumption.
2) Rapid industrialization: this is one of the major causes. The smokes from the factories, coke, oven and furnaces, steam engine; exhaust fumes from power plants etc; chemical fumes from oil refineries, zinc refineries, chemical industries, metallurgical plants, iron and steel plants, incineration plants etc. are the common sources of atmospheric pollution. Industrial pollution is most is most complex, because of the large no. of chemicals emitted by it in the atmosphere and the modifications with these emitted pollutants can undergo by reactions with one another in presence or absence of sunlight. Some, critics comment on air pollution as the price of industrialization.
3) Transportation facilities: intensive increase in transportation services such as motor vehicles, rails-trains, and aero planes etc., through the world is another major contributing factor to air pollution. The exhaust fumes form the automobiles pollutes the atmosphere considerably in the urban area. Air pollution caused by automobile is sometimes described as disease of wealth.
4) Radioactive substances: evolution of radioactive gases and suspended radioactive dust from atomic explosions and accidental discharges from nuclear reactors are very dangerous sources of air pollution.
5) Natural causes: the natural sources which cause air pollution including organic compounds from vegetation, ground also, salt spray from ocean, cosmic dust and evolution of nitrogen sulphide from natural source. These natural sources are beyond the control of man.
COMPOSITION OF ATMOSPHERIC AIRClean dry air contains 78.09% nitrogen and 20.94% oxygen. The remaining 0.97% contains the gases mixture of carbon dioxide, helium, argon, neon, krypton, nitrous oxide etc. including very small amounts of some other organic and inorganic gases whose content varies with the time and place.
Classification and sources of air pollutants
1. Categories of air pollution: Air pollution exists in three distinct categories.
1) Personal air pollution
2) Occupational air pollution
3) Community air pollution
1) Personal air pollution: this represents the exposure of individuals to the dust, fumes and gases. The common example of this is when a person indulges in smoking of cigarette, cigar or pipe
2) Occupational air pollution: this represents the exposure of individual to the aerosols, vapors and gases in harmful concentrations, in their working and occupational environment.
3) Community air pollution: it represents the pollution from various sources and factors which cause adverse social, economic and health effects. Apart from affecting individuals the community air pollution exerts a significant impact on mans total environment including plants, animals, property and weather.
2. Sources of air pollution: there are two main sources of air pollution
1) Natural sources
2) Man made source or anthropogenic air pollution sources.
(i) Natural air pollution sources: the natural air pollution sources consist of the following:
a) Wind blow dust 2) salt particles from sea water 3) dust of meteoric region 4) micro organism like (bacteria, spores, pollen) 5) gases and odours from swamps & marshes 6) fog 7) volcanic ash and gases ( hydrogen fluoride & hydrogen sulphide ) 8) oxides of nitrogen from electric storm.
(ii) Manmade sources: The table shows the main source of air pollution due to mans activities.CLASSAEROSOLSGASES AND VAPOURS
COMBUSTION PROCESS
(domestic gas burning, thermal power plants, automobiles, aero planes, railways, refuse incineration)Dust, fume , smokeSO2 , NO2 , CO2 organic vapors, odours
CHEMICAL PROCESS
(paper mills, cement plants, fertilizers, other chemical plants)Dust , fume, mistProcess dependent
(SO2,CO2,NH3,NO2 organic vapors, odours)
PETOLEUM OPERATIONSDust, mistSO@,NH3,CO,H2S,hydrocarbons
METALLURGICAL PROCESS
(Aluminum industries, steel plants/ mills, smelter, non ferrous industries)Dust , fumeSO2,CO,fluorides,organic vapors)
FOOD & FOOD OPERATIONSDust, mistOdorous materials
AGRICULTURAL ACTIVITIES
a) Crop spraying
b) Field burningDust ,mistOrganic phosphates, chlorinated hydrocarbons, arsenic, lead.
NEUCLEAR ENERGY PROGRAMMES
a) Fuel preparation
b) Ore preparation
c) Nuclear device explosion/testingdustFluorides iodine-131 &a argon 41, radioactive gases ( Sr.90, Cs-137,C-14 etc)
MINERAL PROCESSINGDust , fumesProcess dependants
(SO2,CI,fluorides,organic vapors)
3. Classification of the pollutants: Air Pollution can be classified under three heads:a) Natural contaminants : natural fog, pollen grains, bacteria , product of volcanic eruptions)
b) Aerosols (particulates): dust, smoke, mist, fog, fume
c) Other contaminants: gases vapors and compounds.
4. Primary and secondary pollutants:
Are those which are emitted directly from the identifiable source. The atmosphere contains hundreds of air pollutants from natural or anthropogenic sources. Some important primary pollutants are:
1) Particulate matter: a) coarse particles (>100 ) b) fine aerosols of metals,
carbon, tar, resin, pollen, bacteria.
2) Sulphur oxides and compounds
3) Nitrogen oxides
4) Carbon monoxides
5) Hydrocarbons 6) Halogen compounds 7) Organic compounds
8) Radioactive compounds
9) Photochemical oxidents.
b) Secondary pollutants Are those which are formed in the atmosphere as result of incineration between two or more primary pollutants or by reaction with normal atmospheric constituents, with or without photocavitation. These are therefore chemical substances which are often more harmful than organic basic chemicals that produce them.
1) Sulphuric acid H2SO4 or acid mist
2) Ozone O3
3) Formaldehyde
4) Peroxy-acetyl-nitrate (PAN)
5) Photochemical smog.
5. Stationary and mobile sources of air pollution:
a) stationary sources are asphaltic plants,boilers, heating installations,cement and steel plants,fertilizers plants, mineral and acid plants,paper pulp plants, power plants,incinerators and sewage treatment plants
b) mobile sources are automobiles moving on the roads emitting highly toxic gases
EFFECTS OF AIR POLLUTION:
A) EFFECTS OF AIR POLLUTION ON ANIMALS:
The effects of air pollution on animals takes in two steps:
a) Accumulation of air pollution in vagitation, plants and forageb) Subsequent poisoning of the animals when they eat the contaminated vegetationImportant contaminants that affects the live stock:
a) Fluorine
b) Arsenic
c) Lead
These pollutants originate either from the industries situated nearby, or from dusting and spraying. Out of the contaminants,fluorine contamination is most prominent since cattele and sheep are found more susceptible to it. Symtoms of advanced fluorosis includes lack of apetite ,general ill health due to malnutrition,lowered fertility, reduced milk production and growth retardation. Arsenic in dusts or sprays on plants can cause to the poisoning of cattle leading to salivation, thirst, vomiting, uneasiness, feeble and irregular pulse and respiration. Lead contamination of atmosphere takes place on account of various industries such as smellers, coke ovens, and other coal based industries. Prostration, staggering inability to rise are the prominent symptoms of lead poisoning. There is a complete loss of apetite , paralysis of digestive tract and diarrhea.
EFFECT OF AIR POLLUTANTS ON HUMAN HEALTH:
The inhalation of the polluted air has makes adverse effect on the health of human beings. These adverse effects may be devided into two classes viz, acute effets and chronic effects. The acute effects are reveled immidietly after short term exposure to the air pollutants of high concentrations. While chronic effects become evidently only after continuous exposure to low level air pollution. Following is the list of health hazards caused by air pollution.
1) Ear nose and throat irritation
2) Irritation of respiratory tract
3) Odour nusance due to hydrogen sulphide, ammonia, mecaptants, etc. even at low concentrations.
4) Chronic pulmonary diseases such as bronchitis, asthama, etc., are aggravated by high concentration of sulpher dioxide SO2,nitrogen dioxide NO2,particulate matter and photochemical smog.
5) Pollens causes asthma
6) Carcinogens causes cancer
7) Dust particles cause respiratory diseases, silicosis is caused by silica dust of cement factories, and asbestosis is caused by asbestos plant.
8) Lead poisoning is caused by entry lead into lungs
9) Hydrogen fluoride causes bone fluorosis and mottling teath.10) Carbon monoxide CO may causes death by asphyxiation. It also increases Stress on persons suffering from the cardiovascular and pulmonary
diseases.
11) Air pollution is general cause in mortality rate and morbidity rate
12) Radioactive radiations may cause cancer, shortening of life spans, genetic
defects.
EFFECTS OF AIR POLLUTION ON VEGITATION
AIR POLLUTION HAS LONG TERM AND ADVERSE EFFECTS ON PLANTS:
The most oblivious damage caused by air pollutants to plants and vegetation occur is the leaf structure. The stomata of the leaves get clogged thereby reducing the intake of co2 and thus affecting the photosynthesis. The adverse effects range from reduction in growth rate to death of plants.
METHODS TO CONTROL THE AIR POLLUTION
Following are the methods to control the air pollution
1) Setting chamber
2) Cyclone separator
3) Bag filters1) SETTING CHAMBER TO CONTROL AIR POLLUTION: Gravitational setting chambers are generally used to collect the large particles of size greater than 50microns. A stream of dust laden gas is passed into the setting chamber where the velocity of the gas suddenly reduced. As a result the dust particles settle down and collected through a hopper at the bottom. There are various types of settling chambers. Horizontal setting chamber is most commonly used. To increase the efficiency one can install the series of setting chamber into parallel.
2) CYCLONE SEPARATOR TO CONTROL AIR POLLUTION: Cyclone separators utilize centrifugal force to separate the particulate matters from the carrier gas. The particle laden gas receives a rotating motion as it enters the cyclone cylinders. A centrifugal force is developed due to the vortex formed which throws the particles towards the wall. These particles get collected in the conical bottom of cyclone cylinder. The spinning gas streams spirals downwards to the bottom of the cone. At this point the flow reverses to form an inner vortex and finally leaves the cylinder through the outlet pipe situated at the top. High efficiency cyclones are designed. A series of cyclones called the multicyclones used in the industries to increase the efficiency of collection.
3) BAG FILTERS TO CONTROL AIR POLLUTION: Bag filters are the devices by which the gas is purified through various filtering cloths (cotton, wool, chemical fibers, fiber glass etc.) or fabric filter (filters made of granular materials like ceramics porous plastics etc.). A typical bag house contains a tubular bag or an envelope mounted in such a manner that the particle laden gas passing through the filters bags gets deposited on the inside surface of the bags which are dusted by shaking in intervals. The dust is collected in the hopper at the bottom. The collection of the dust particles or the surface of filters takes place due to several physical phenomenons. They are inertial impaction (suspended particles in a stream flow lend to retain the direction when the direction of gas flow changes), direct interception (for particles having low inertia, the collection mechanism is interception) and diffusion (particles in semi micron range do not move by stream flow but more by diffusion where particles in zigzag Brownian motion which causes them to impinge and adhere to the surface of fabrics).Bag filters have high efficiency but the filters are required to be clean and changed in regular intervals. Many filters made up of clothes and plastics cannot work at high temperatures. These filters are normally more expensive and require frequent maintenance. Jet type of bag filters is the most common bag filter in use.diagrams
WATER RESOURCE ENGINEERING
HYDRAULIC STRUCTURES OF STORAGE: The structures built up for the storage of water which can be used in future are known as hydraulic structures of storage. Following are the type of structures used for the storage of water:1) Dams
2) Bunds
3) Reservoirs
4) Storage Tanks
DAMS: A dam is a barrier constructed across a river or a natural stream to create a reservoir for impounding water or to facilitate diversion of water from the river or to retain debris flowing in the river along with water. The excess water is released in the river and useful water is transferred through canals. Dams may be classified in different ways on the basis of their function, hydraulic design, and material of construction, structural design and size:
A) Classification based on function:
a) Storage or Impounding Dam
B) Detention DamC) Detention DamD) Diversion DamE) Coffer dam
B) Classification Based On the Hydraulic Designa) Over Flow or over fall DamB) Non Over Flow DamC) Classification Based On Structural Behavior
A) Gravity DamB) Earth Dam
C) Arch Dam
Gravity dam: In the construction of a gravity dam the rigid materials such as concrete is mainly used to resist the force exerted upon it by its own weight and the water stored behind the dam on upstream side. Gravity dams are relatively more strong and stable then other type of dams because the concrete is used as a major construction material. If the reservoir gets over flooded the overflow spillway crest is provided. The construction of the dam can be done to the suitable heights as there is no limitation or restriction for height. Maintenance cost is very less for gravity dams. These dams gives enough warning times before the complete failure. Life of gravity dams is more (up to 100 yrs) as compared to other dams.
Components forces in gravity dam
Plan of damEarth/Embankment dam: The main construction material for these types of dam is clays, gravel, sand, silt. It resists the forces exerted upon it mainly by its shear strength. These dams are relatively less strong and stable. Earth dams cannot be used as a overflow dams. The height of these dams is restricted to its stability of slopes. Earth dams require frequent maintenance. These dams generally fails suddenly without showing any signs of failure. Life of these dams is less.
An embankment dam is a massive artificial water barrier. It is typically created by the emplacement and compaction of a complex semi-plastic mound of various compositions of soil, sand, clay and/or rock. It has a semi-permanent waterproof natural covering for its surface, and a dense, waterproof core. This makes such a dam impervious to surface or seepage erosion. The force of the impoundment creates a downward thrust upon the mass of the dam, greatly increasing the weight of the dam on its foundation. This added force effectively seals and makes waterproof the underlying foundation of the dam, at the interface between the dam and its stream bed. Such a dam is composed of fragmented independent material particles. The friction and interaction of particles binds the particles together into a stable mass rather than by the use of a cementing substance
Typical Section of an Earthen DamTypes of an earthen dam:
1. Rock fill type earthen dam.2. Concrete face earthen dams.3. Earth fills dams.
Rock fills dams: A rock fill dam is built of rock fragments and boulders of large size. An impervious membrane is placed on the rock fill on the upstream side to reduce the seepage through the dam. The membrane is usually made of cement concrete or asphaltic concrete. In early rock fill dams, steel and timber membrane were also used, but now they are obsolete. A dry rubble cushion
is placed between the rock fill and the membrane for the distribution of water load and for providing a support to the membrane. Sometimes, the rock fill dams have an impervious earth core in the middle to check the seepage instead of an impervious upstream membrane. The earth core is placed against a dumped rock fill. It is necessary to provide adequate filters between the earth core and the rock fill on the upstream and downstream sides of the core so that the soil particles are not carried by water and piping does not occur. The side slopes of rock fill are usually kept equal to the angle of repose of rock, which is usually taken as 1.4:1 (or 1.3:1). Rock fill dams require foundation stronger than those for earth dams. However, the foundation requirements are usually less stringent than those for gravity dams. Rock fill dams are quite economical when a large quantity of rock is easily available near the site.
Concrete face earthen dams.
A concrete-face rock-fill dam (CFRD) is a rock-fill dam with concrete slabs on its upstream face. This design offers the concrete slab as an impervious wall to prevent leakage and also a structure without concern for uplift pressure. In addition, the CFRD design is flexible for topography, faster to construct and less costly than earth-fill dams.
Earth dams: An earth dam is made of earth (or soil). It resists the forces exerted upon it mainly due to shear strength of the soil. Although the weight of the earth dam also helps in resisting the forces, the structural behavior of an earth dam is entirely different from that of a gravity dam. The earth dams are usually built in wide valleys having flat slopes at flanks (abutments). The foundation requirements are less stringent than those of gravity dams, and hence they can be built at the sites where the foundations are less strong. They can be built on all types of foundations. However, the height of the dam will depend upon the strength of the foundation.SPILLWAYS
INTRODUCTION
Spillways are provided for storage and detention dams to release surplus floodwater, which can not be contained in the allotted storage space. In diversion works, like weirs and barrages, spillways bypass the flow exceeding that which is released in to the system like irrigation canals, power canals, feeder canals, link canals etc. Ordinarily, the excess flow is drawn from the top of the pool created by the dam
and conveyed through an artificial waterway i.e. spillway, back into the same river or to some other drainage Channel. TYPES OF SPILLWAYS
Spillways may be broadly categorized as service spillway and emergency type spillway. The service spillways are those which are in constant use in every flood when the reservoir level exceeds the crest level of the spillway. An emergency spillway, also known as auxiliary spillway, is one which is rarely used and come into operation during extraordinary flood when the actual flood discharge exceeds the
design capacity of the service spillway. Various types of service spillways in common
use are briefly described below:
Vertical Drop type Spillway
A vertical drop or free over fall type spillway is one in which the flow drops freely from the acres of the dam. This type is suited in a thin arch or a deck overflow type dam. Flows may be freely discharging, or they may be supported along a narrow section of the crest. Occasionally, the crest is extended in the form of an overhanging lip to direct small discharges away from the face of the overflow section. In free over fall spillways, the underside of the nappe is ventilated sufficiently to prevent a pulsating, fluctuating jet. Where no artificial protection is provided at the base of the over fall, scour will occur in most streambeds and will form a deep plunge pool. The volume and depth of the hole are related to the range of discharges, the height of the drop, and the depth of tailwater. The erosion-resistant properties of the streambed material including bedrock have little influence on the size of the hole, the only effect being the time necessary to scour the hole to its full depth. Such spillway can be provided only in case of low height dams on hard bed. In high dams these are not to
be adopted, as it will subject the foundation to heavy scour and cause vibration
leading to failure of the dam.
Ogee (overflow) Spillways
The ogee spillway as shown in Fig.3 (a) and Fig.3 (b) has a control weir, which is ogee or S-shaped in profile. Ordinarily, the upper curve of the ogee spillway is made to conform closely to the profile of the lower nappe of a ventilated sheet falling from a sharp-crested weir. Flow over the crest is made to adhere to the face of the profile by preventing access of air to the under side of the sheet. For discharges at designed head, the flow glides over the crest with no interference from the boundary
surface and attains near-maximum discharge efficiency. The profile below the upper curve of the ogee is continued tangent along a slope to support the sheet on the face of the overflow and flow onto the apron of a stilling basin or into the spillway discharge channel. This type of spillway is commonly used in high dams and it is suitable to handle large flood flow s. .
Chute (Open Channel or Trough) Spillways
A spillway, whose discharge is conveyed from the reservoir to the downstream river level through an open channel, placed either along a dam abutment or through a saddle, might be called a chute, open channel, or trough type spillway. These designations can apply regardless of the control device used to regulate the flow. Thus, a spillway having a chute-type discharge channel, though controlled by an
overflow crest, a gated orifice, a side channels crest, or some other control device might still be called a chute spillway. However, the name is most often applied when the spillway control is placed normal or nearly normal to the axis of an open channel, and where the streamlines of flow both above and below the control crest follow the direction of the channel axis. The chute spillway has been used with earthfill dams more often than has any other type. Chute spillways ordinarily consist of an entrance
channel, a control structure, a discharge channel, a terminal structure, and an outlet
channel.
Conduit and Tunnel Spillways
Where a closed channel is used to convey the discharge around or under a dam, the spillway is often called a tunnel or conduit spillway, as appropriate. The closed channel may take the form of a vertical or inclined shaft, a horizontal tunnel through earth or rock, or a conduit constructed in open cut and backfilled with earth materials.Most forms of control structures, including overflow crests, vertical or inclined orifice entrances, drop inlet entrances, and side channel crests, can be used with conduit and
tunnel spillways. Tunnel spillways may present advantages for dam sited in narrow canyons with steep abutments or at sites where there is danger to open channels from snow or rockslides. Conduit spillways may be appropriate at dam sites in wide valleys, where the abutments rise gradually and are at a considerable distance from the stream channel. Use of a conduit will permit the spillway to be located under the dam near the streambed.
Drop Inlet (Shaft or Morning Glory) Spillways
A drop inlet or shaft spillway, as the name implies, is one in which the water enters over a horizontally positioned lip, drops through a vertical or sloping shaft, and then flows to the downstream river channel through a horizontal or near horizontal conduit or tunnel. The structure may be considered as being made up of three elements; namely, an overflow control weir, a vertical transition, and a closed
discharge channel. Where the inlet is funnel-shaped, this type of structure is often called a morning glory or glory hole spillway. Fig.5 illustrates a typical drop inlet spillway.
Showing Drop Inlet or Shaft Spillway
Discharge characteristics of the drop inlet spillway may vary with the range of head. The control will shift according to the relative discharge capacities of the weir, the transition, and the conduit or tunnel. For example, as the heads increase on a glory hole spillway, the control will shift from weir flow over the crest to orifice flow in the transition and then to full pipe flow in the downstream portion. A drop inlet spillway can be used advantageously at dam sites in narrow canyons where the abutments rise steeply or where a diversion tunnel or conduit is available for use as the downstream leg. Another advantage of this type of spillway is that near maximum capacity is attained at relatively low heads; This characteristic makes the spillway ideal for use where the maximum spillway outflow is to be
limited. This characteristic also may be considered disadvantageous, in that there is little increase in capacity beyond the designed heads, should a flood occur. This would not be a disadvantage if this type of spillway were used as a service spillway in conjunction with an auxiliary or emergency spillway.
Culvert Spillway
A culvert spillway is a special adaptation of the conduit or tunnel spillway. It is distinguished from the drop inlet and other conduit types in that its inlet opening is placed either vertically or inclined upstream or downstream, and its profile grade is made uniform or near uniform and of any slopes. The spillway inlet opening might be sharp edged or rounded, and the approach to the conduit might have flared or tapered sidewalls with a level or sloping floor. If it is desired that the conduit flow partly full
for all conditions of discharges, special precautions are taken to prevent the conduit from flowing full. Culvert spillways should not be used for high-head installations where large negative pressures can develop.
Siphon Spillways
A siphon spillway is a closed conduit system formed in the shap of an inverted U, positioned so that the inside of the bend of the upper passageway is at normal reservoir storage level. The initial discharges of the spillway as the reservoir level rises above normal are similar to flow over a weir. Siphon action takes place after the air in the bend over the crest has been exhausted. Continuous flow is maintained by the suction effect due to the gravity pull of the water in the lower leg of the siphon.
Siphon spillway is composed of five component parts.. These include an inlet, an upper leg, a throat or control section, a lower leg, and an outlet. A siphon-breaker air vent is also provided to control the siphon action of the spillway so that it will cease operation when the reservoir water surface is drawn down to normal level. Otherwise the siphon would continue to operate until air entered the inlet. The inlet is generally placed well below the normal reservoir water surface to prevent entrance of ice and
drift and to avoid the formation of vortices and draw downs, which might break the siphon action. The upper leg is formed as a bending convergent transition to join the inlet to a vertical throat section. The throat or control section is generally rectangular in cross section and is located at the crest of the upper bend of the siphon. The upper bend then continues to join a vertical or inclined tube, which forms the lower leg of the siphon. Fig.6 shows typical siphon spillway with different parts.
Siphon spillway indicating various parts
The principal advantage of a siphon spillway is its ability to pass full-capacity discharges with narrow limits of headwater rise. A further advantage is its positive and automatic operation without mechanical devices or moving parts. In addition to its higher cost, as compared with other types, the siphon spillway has a number of
disadvantages, including the following:
(a) The inability of the siphon spillway to pass ice and debris.
(b) The possibility of clogging the siphon passageways and siphon breaker vents with debris or leaves.
(c) The possibility of water freezing in the inlet legs and air vents before the reservoir rises to the crest level of the spillway, thus preventing flow through the siphon.
(d) The occurrence of sudden surges and stoppages of outflow as a result of the erratic make-and-break action of the siphon, thus causing radical fluctuations in the downstream river stage.
(e) The release of outflows in excess of reservoir inflows whenever the siphon operates, if a single siphon is used. Closer regulation which will more nearly balance outflow and inflow can be obtained by providing a series of smaller siphons, with their siphon breaker vents set to prime at gradually increasing reservoir heads.
(f) The more substantial foundation required resisting vibration disturbances, which are more pronounced than in other types of control structures.
Side Channel Spillway
In a side channel spillway, the waterfalls from the reservoir over a service spillway like ogee type spillway into a narrow channel excavated from the side hills towards the abutment of the dam. The flow in the side channel is at right angle to the direction of the incoming flow from the reservoir. The side channel is provided with a control section at its end to ensure that the flow in the side channel is at sub-critical stage and there is thorough mixing of the incoming super critical jet in the side channel trough portion. The water from the side channel usually enters a chute type spillway after the control section. Fig.7 illustrates a typical side channel type of spillway commonly used for earthen and rock fill type dams
(a) Plan and (b) Section of Side Channel Spillway
Stepped Spillway
In a stepped spillway, water falls over a series of steps from crest to the toe of the dam. It has the advantage over other spillways in that it acts also as an energy dissipator as the water comes down from the reservoir level to the tail water level. It is not suitable for high dams with large overflow since the nappe flow changes to skimming flow with very little dissipation of energy and the steps are subjected to cavitation damage.
Selection of Spillway Size and Type
In determining the best combination of storage and spillway capacity to accommodate the selected inflow design flood, all pertinent factors of hydrology, hydraulics, design, cost, and damage should be considered. In this connection and when applicable, consideration should be given to such factors as (a) the characteristics of the flood hydrographic; (b) the damages which would result if such a flood occurred without the dam; (c) the damages which would result if such a flood occurred with the dam in place; (d) the damages which would occur if the dam or spillway were breached; (e) effects of various dam and spillway combinations on the probable increase or decrease of damages above or below the dam (as indicated by reservoir back-water curves and tailwater curves); (f) relative costs of increasing the capacity of spillway ; and (g) use of combined outlet facilities to serve more than one function, such as control of releases and control or passage of floods. Service outlet releases may be permitted in passing part of the inflow design flood unless such outlets are considered to be unavailable in time of flood.Conveyance systemCANALS: The irrigation water is conveyed from the reservoir to form through an open channel of trapezoidal shape known as canal. The canal may be excavated or constructed in the embankment. Types of canals:
1) According to their alignment :
a) Contour canal: the canal generally follow a falling contour except for necessary longitudinal slope. Main canal is run as counter canal in the head reach. It can irrigate one side that is lower side.
b) Ridge canal: the canal is laid along a natural water shed is known as a ridge canal. These canals are usually takes off from the contour canals. It irrigates on both sides. Cross drainage works can be avoided and hence it is economical.
c) In this alignment the canal is aligned across contours. No cross drainage works required. These canals have steep bed slope and hence the lining is necessary.2) Their origin and capacity:
a) Main canal: main canal starts directly from the weir head works. No direct irrigation is usually carried from the main canal.
b) Branch canal: when main canal reaches the area where irrigation is to be done it is divided into the branches joining to the different parts of the area. The branch canal ends into a distributor.
c) Major distributor: these are the smaller channels taking off from the branch canal or sometimes from the main canals. The capacity of distributary canal varies from 0.3 to 6 m3/sec.
d) Minor distributor: these are small channels of capacity less than 3.3 m3/sec. taking off from the branch distributor they supply the water to water course for irrigation.e) Water course or field canals: from these canals water enters into the field of cultivators. These are small canals having capacity less than 0.05m3/sec.
3) Shape of canal:
Canals generally constructed in following three shapes:
a) Rectangular canal
b) Triangular canal
c) Trapezoidal canal
a) Rectangular section: rectangular channel will be most economical when:-
1) Width of the bed is equal to the twice of depth of section.2) Hydraulic mean depth is half of the depth of flow.
b) Trapezoidal section: the required condition of for the trapezoidal section to be more economical, which can be expressed as half of the top width must be equal to the one of the sloping side of channel.
c) Triangular section: the most efficient triangular section is half of a square with diagonal horizontal hydraulic mean depth.Rectangular canal
