Classification and Principle of Leveling
Classification of leveling
1. Different leveling:
It is the operation of leveling to determine the elevations of points. Some distance a part or to establish bench marks.
2. Check leveling:
It is the operation of running levels for the purpose of checking the series of levels, which have been previously fixed. At the end of each day’s work, a line of level is run, returning to the starting point of that day with a view to check the work done on that day.
3. Profile leveling:
It is the operation in which the object is to determine the elevation of points at known distance apart along a given line, and thus to obtain the accurate out line of the surface of the ground. It is called the longitudinal leveling or sectioning.
4. Cross sectioning:
It is the operation of leveling to determine the surface undulation or outline of the ground transverse to the given line and on either side of it.
5. Reciprocal leveling:
It is then method of leveling in which the difference in elevation between two points, accurately determined by two sets of observation when it is not possible to set up the level midway between the two points.
6. Barometric leveling:
It is the method of leveling in which the altitudes of points are determined by means of a barometer, which measures atmospheric pressure.
7. Hypsometry:
It is the method of leveling in which the heights of mountains are found by observing the temperature at which water boils.
8. Trigonometric leveling:
It is then process of leveling in which the elevations of points are computed from the vertical, angles and horizontal distance measured in the field.
Steps in Leveling:
When the level is set up and correctly leveled, the lines of collimation will be horizontal. When the telescope is rotated about its vertical axis, it will revolve in a horizontal plane known as the plane of collimation. Therefore all staff readings taken with the telescope will be vertical measurements made downwards from this plane. There are two essentials steps in leveling.
1. To find the elevation or R.L. of the plane of collimation (H.I) of the level by taking a back sight on a bench mark.
2. To find the levitation of R.L. of any other point by taking a reading on the staff held at the point.
Height of Instrument (H. I.) = R.L. of the plane of collimation
= R.L. of B.M. + B.S.
R. L. of point = H.I.-F.S.
= H. I. – I.S.
It is the necessary that after every back side. [However many intermediate sight may be], there must be a foresight. Leveling should always commence from a permanent common bench mark and end on a permanent bench mark.
Principle of Leveling:
1. Simple leveling:
It is the simplest operation in leveling when it is required to find the difference in elevation between two points both of which are visible from a single position of the level. Suppose A and b are two such point and level is set up at 0, approximately mid way between. A and B but not necessary on the line joining them, after finding the reading on point A and point B, let the respective reading on A and B be 2.340 and 3.315 difference between them is 3.315-2.340=0.795 m.
2. Differential leveling:
This method is used in order to find out the difference in elevation between two points.
1. If they too apart.
2. If the difference in elevation between them is too great.
In such cases it is necessary to set up the level in several positions and to work in a series of stages. The method of simple leveling is employed each of the successive stages. The process is also known as compound continues leveling.
Methods of Determination of the Reduced Level of Point from the Staff Reading
1. Collimation Method:
It consist of finding the elevation of the plane of collimation ( H.I.) for every set up of the instrument, and then obtaining the reduced level of point with reference to the respective plane of collimation.
1. Elevation of plane of collimation for the first set of the level determined by adding back side to R.L. of B.M.
2. The R.L. of intermediate point and first change point are then obtained by starching the staff reading taken on respective point (IS & FS) from the elation of the plane collimation. [H.I.]
3. When the instrument is shifted to the second position a new plane collimation is set up. The elevation of this plane is obtained by adding B.S. taken on the C.P. From the second position of the level to the R.L. C.P. The R.L. of successive point and second C.P. are found by subtract these staff reading from the elevation of second plane of collimation Arithmetical check
Sum of B.S. – sum of F.S. = last R.L. – First R.L.
2. Rise and Fall Method:
It consists of determining the difference of elevation between consecutive points by comparing each point after the first that immediately preceding it. The difference between there staff reading indicates a rise fall according to the staff reading at the point. The R.L is then found adding the rise to, or subtracting the fall from the reduced level of preceding point.
Arithmetic check
Sum of B.S. – sum of F. S. = sum of rise – sum of fall = last R. L. – first R.L.
Booking the staff readings:
The following points may be kept in mind entering the readings in a level field book.
1. The reading should be entering in the respective columns and in order their observation.
2. The first page is always a back side and the last one is ways a foresight.
3. It a page finished with an IS reading, the reading is entered in the IS and FS columns on that page and brought forward to the next page.
4. The FS and BS of any change point are entered in the same horizontal line.
5. The RL of the line of the collimation is entered in the same horizontal line.
6. Bench marks and change points should be clearly described in the remark column.
Specimen pages of level field book: Collimation system
Station
Distance (cm)
Reading
RL of plane of collimation [HI]
Reduced level
Remarks
BS
IS
FS
A
B.M.
B
C
Arithmetic check
Sum of BS-Sum of FS= Last RL-1st -RI
Specimen pages of level field book: Rise & Fall System
Station
Distance(m)
Reading
Rise
Fall
Reduce level
Remarks
BS
IS
FS
B.M
A
B
C
Check :
BS-FS=Rise-fall=last RL -1st-Rl
Study of Contour
The purpose of topographic survey is to get the necessary data to produce a topographic map of the earth’s surface. This map will include contour lines, location of natural features, such as streams, gullies, and ditches and man-made features like bridges, culverts, roads, fences, etc. which are needful for detailed planning. The best practical method of presenting topography is by means of contour maps.
Contour or contour lines:
“A contour is an imaginary line of constant elevation on the surface of the ground”. Contours are represented on the map by contour lines. The contour and contour lines are often used inter-changeably.
Contour interval:
“The vertical distance between any two successive contours on a given map is called the contour interval”. Contour intervals usually vary from 25 to 250 cm in engineering work. In rough country, the vertical distance between contours is kept greater while in flat areas 25 to 50 cm contour intervals are used.
Characteristic of Contour Lines:
1] All points on a contour line have same elevation
2] Contour line close to each other on s plan view; represent very steep ground. Contour lines for apart indicate relatively flat land
3] On uniform slopes the contour lines are spaced uniformly .along plane surfaces these lines are straight and parallel to one another.
4] Contour lines Crosse ridge lines or valley lines at right angles valley contour are convex towards the stream.
5] Contour lines can not and anywhere, but close on themselves. Either within or outside the limits of map they can not merge or cross one another.
6] A series of closed contour on the map indicate a depression or a summit, depending whether the successes contour have lower or higher values inside
7] At ride line the contour lines form carves of U shape .At Valley lines they farm sharp curves of shape
USES OF CONTOUR:
1] Information regarding character of a tract of a country (such as flat undulating, Mountainous, etc) is abstained.
2] In agricultural work, contours maps are useful as guide lines in planning land improvement project .the tile drainage system can be conveniently planned whit contour maps
3] Cost estimates can be made with the help of the contour maps.
4. Maps which show both topography and land use capability classification are important in conversation of farm land.
5. The most economical and suitable site for engineering works such as reservoir, canal, road, waterways, .etc. can be selected.
6. Quantities of earthwork and runoff from watershed can be computed.
7. Contours may be used to determine area of the catchments and the capacity of the reservoir.
8. A suitable route of a given gradient can be marked on the map.
9. The possible route of communication between different places can be determined from contour map.
Survey for Contour Map [Grid Survey Method]
The area is divided into a series of square. The size of these squares depends upon the nature and extent of the ground. Generally, they have sides verifying from 5 to 20m or 5 to 30m. The corner of the squares are numbered serially, as 1, 2, 3 … A temporary bench mark is set up near the site. The elevations of the ground at the corners of the squares are taken and contour lines are drawn by interpolation, “the process of spacing the contour proportionately between the plotted points is turned interpolation”. For precise work, the proportional spacing of the corresponding contour between any two points is calculated and measured.
Introduction to Runoff
Over the land surface, for the generation of runoff, the primary source of water is Rainfall. A part of rainfall that intercepted by the vegetation, buildings and other objects and prevented to reach them on grand surface is called as interception. Part of rainfall stored in the surface depressions which in due course of time gets infiltrate or evaporated is referred as depression storage [ Initial detention).
When these entire loses are satisfied then excess rainfall moves over land surface is known as overland flow and draining the same into channel or stream is termed as “Runoff”.
Definition:
Runoff:
Runoff is that portion of the rainfall or irrigation water [or any other flow]. Applied which leaves a field either as surface or as subsurface flow.
When rainfall intensity reaching the soil surface is less than the infiltration capacity, all the water is absorbed in to the soil. As rain continues soil becomes saturated and infiltration capacity is reduced, shallow depression begins to fill with water, then the over flow starts.
Surface detention/ Detention storage:
The amount of water on the land surface in transit to words stream channels is called detention storage/surface detention.
Surface Runoff:
The runoff which travels over the ground surface to the channels of watershed
Subsurface Runoff:
The portion of unfiltered water which penetrated to shallow depth travels laterally and is intercepted by channels.
Runoff Cycle:
It is that part of hydrological cycles which galls between the phase of precipitation and its subsequent discharge in the stream channels or direct return to the atmosphere through evaporation and evapotranspiration.
Conditions Associated With Runoff Cycle:
This refers to the end of day period and beginning of the intense and isolated storm.
It is the stage after beginning of rainfall causes the overland flow, base flow, and development of channel storage.
It refers to the condition approaching the end of all isolated intense storm.
This is the stage indicating after end of rainfall where rainfall causes the overland low, base plot and development of channel storage.
Types of Runoff:
Surface runoff
Sub-surface runoff
Base flow
a. Surface Runoff:
That portion of rainfall which enters the stream immediately after the rainfall. It occurs when all loses is satisfied and rainfall is still continued and rate of rainfall [intensity] in greater than infiltration rate.
b. Sub-Surface Runoff:
That part of rainfall which first leaches into the soil and moves laterally without joining the water table, to the stream, rivers or ocean is known as sub-surface runoff. It is usually referred is inter-flow.
c. Base flow:
It is delayed flow defined as that part of rainfall, which after falling on the ground the surface, infiltrated into the soil and meets to the water table and flow the streams, ocean etc. The movement of water in this is very slow. Therefore it is also referred a delayed runoff.
Total runoff = Surface runoff + Base flow (including subsurface runoff)
Factors Affecting runoff
Runoff arte and volume from an area mainly influenced by following two factors
A. Climatic factors.
B. Physiographical Factors.
A. Climate factors:
It is associated with characteristics of which includes.
1.Types of Precipitation:
It has great effect on the runoff. E.g. A precipitation which occurs in the form of rainfall starts immediately as surface runoff depending upon rainfall intensity while precipitation in the form of snow does not result in surface runoff.
2. Rainfall Intensity:
If the rainfall intensity is greater than infiltration rate of soil then runoff starts immediately after rainfall. While in case of low rainfall intensity runoff starts later. Thus high intensities of rainfall yield higher runoff.
3. Duration of Rainfall:
It is directly related to the volume of runoff be cause infiltration rate of soil decreases with duration of rainfall. Therefore medium intensity rainfall even results in considerable amount of runoff if duration is longer.
4. 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. There fore, near outlet of watershed runoff will be more.
5. Direction of Prevailing Wind:
If the direction of prevailing wind is same as drainage system, it results in peak low. 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 factors such as temperature wind velocity, relative humidity, annual rainfall etc. affect the water losses from watershed area.
B Physiographic Factors:
It includes both watershed and channel characteristics, which area as follows,
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”.
Form Factor = Ratio of average width to axial length of watershed
= B/1 or A/1/1 = A/I2
Compactness Coefficient:
Ratio off perimeter of watershed to circumference of circle whose area is equal to area of watershed
Two types of shape:
Fun shape [tends to produce higher runoff very early]
Fern shape [tend to produced less runoff].
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.
4. Orientation of Watershed:
This affects the evaporation and transpiration losses from the area. 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.
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.
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 [velocity] 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
Drainage density = L/A
OR
Factors Affecting Runoff
The various factors which affect the runoff from a drainage basin depend upon the following characteristics.
1. Rainfall characteristics:
a. Type of storm and season
b. Intensity
c. Duration
d. Arial Distribution
e. Frequency
f. Antecedent precipitation
g. Direction of storm movement
2. Metrological factors:
a. Temperature,
b. Humidity
c. Wind velocity
d. Pressure difference
3. Watershed Factor:
a. Size
b. Shape
c. Altitude
d. Topography
e. Geology [Soil type]
f. Land use [vegetation], Orientation
g. Type of drainage network
h. Proximate to ocean and mountain range
4. Storage Characteristics:
a. Depressions
b. Ponds, lakes and pools.
c. Stream
d. Channels.
e. Check dams in gullies
f. Upstream reservoirs or tanks.
g. Ground water storage in deposits/aquifers
Direct Runoff and Time of Concentration
Direct Runoff
The part of runoff which enters the stream quickly after the rainfall or snow melting.
To design soil conservation structure with proper capacity it is necessary to estimate peak runoff rate.
Peak runoff Rate:
It is the maximum rate of flowing runoff per unit time.
Rational Method:
This is the most common method to predict the peak runoff rate. The peak runoff may be defined as the capacity to be given a structure that must carry the runoff
1. in FPS:
Q = CIA
Where,
Q = Design runoff the ft3/sec.
I = Rainfall Intensity Inches/hr
A = Watershed area in acres.
2. in MKS:
Q = CIA/36 = [0.0276x CIA ]
Where,
Q = Peak runoff rate m3/sec
C = Runoff coefficient
I = rainfall intensity [cm/hr ] for duration equal to time of Concentration and for a given recurrence interval
A = Watershed area, [ Hectare ].
Time of Concentration:
It is the time required for the runoff water to flow from the most remote point of the area to the outlet.
Rainfall Intensity:
Rainfall intensity is defined as the rate of fall of precipitation, expressed in depth per time [mm/hr]
I = P/T
Where, I = Rainfall Intensity, mm/hr
P = Amount of rainfall, mm
T = duration of rainfall, hr
Runoff Coefficient
Runoff Coefficient is the ratio of between the peak runoff rate and intensity of rainfall.
The Rational Method is based upon following Two Assumptions:
1. Rainfall occurs at uniform intensity for duration at least equal to the time of concentration of watershed.
2. Rainfall occurs at a uniform intensity over the entire area of watershed.
The value of ‘C’ runoff coefficient in the rational formula should be taken from following table.
vegetative cover and land Slope
Soil Texture
Sand Loam
Clay and Silt Loam
Silty Clay
1. Wood Land
0 - 5 % slope
0.10
0.30
0.40
5 - 10% slope
0.25
0.35
0.60
10 - 30% slope
0.30
0.50
0.60
2. Pasture land
0 - 5 % slope
0.10
0.30
0.40
5 - 10% slope
0.16
0.36
0.55
10 - 30% slope
0.22
0.42
0.60
3. Cultivated Land
0 - 5 % slope
0.30
0.50
0.60
5 - 10% slope
0.40
0.60
0.70
10 - 30% slope
0.52
0.72
0.82
Runoff Measuring Devices
Unites of measurement of water:
Water is measured under two conditions –at rest and in motion water
Water at rest:
[Water in reservoirs ponds soil, tank] it is measured in units of volume such as liter, cubic meters, hectare centimeter and hectare –meter
Water in motion:
[water flowing in rivers canal ,pipelines ,field channels ]it is expressed in rate of flow such as liters pre second liters pre hour ,cubic meters pre second hectare centimeter pre hr and hectare –meter pre day
1
1) One liter = --------- cubic meter
1000
2) 1 ha –cm =100 meter cube =1, 00, 000 liter
3) 1 ha m =10000 meter cube =10 million liter
Measuring Device:
In field most commonly used devices for measuring water are
1. Weirs
2. Pre shall flumes
3. Orifices
4. Meter gates
In these devices ,the react of flow is measured directly by making reading on a scale which is part of instrument and computing the discharge rate from standard formulae .choice for the use of one or others devise depends on the expected flow rates site conditions.
Weir:
Weirs are used to measure the flow of runoff; an irrigation channel or discharged of a well or channel outlet at the source.
A weir is a notch of regular form through which the water stream is made to flow. A weir consists of a weir wall of concrete, timber or metal. Weir may be built as stationary structure or they may be made portable. The notch may be rectangular, trapezoidal or triangular.
It is desirable to install the weir at a point where there is dropped in elevation of channel bed.
Terminology:
Weir pond:
Portion of channel immediately upstream from the weir
Weir crest:
Bottom of weir notch
Head:
Depth of water flowing over the weir crest measured at some point in weir pond.
Sharp crested weir:
A weir having thin edged crest such that over flowing sheet of water has the minimum surface contact with crest.
End contraction:
Horizontal distance from end of weir crests to side of weir pond.
Bottom contraction:
Vertical distance from weir crests to bottom of weir pond.
Weir scale or gauge:
The scale fastened on the side of air or a stake in weir pond to measure the head on weir crest.
Nape:
The sheet of water which over flow a weir
Weirs:
1. Sharp Crested:
A. Rectangular weir:
B. Cipoletfe weir
C.V-notch weir
2. Broad crested.
a. Rectangular Weirs:
It takes its name from the shape of notch. They are used to measure comparatively large discharges.
b .Cipoletfe Weir:
It is contracted trapezoidal weir in which each side of notch has a slope of 1 horizontal to 4 vertical. It is named after its inventor “Cesare Cipolletti” an Italian engineer. It is used to measure medium discharges.
c. V- Notch Weir:
The 90o V- notch weirs are commonly used to measure small and medium size streams. The advantage of V- notch weir is its ability to measure small flows accurately.
General Requirement for the Setting and Operation of Weirs
Properly constructed and installs weirs proved most accurate devices for measuring flow. However improper setting and operation may result in large errors inn discharge measurements with weirs.
To ensure reliable results in measurement, he following precautions necessary in the use of weirs
1. The weirs should be set at lower end of a long pool sufficiently wide and deep to five smooth flow having velocity less than 15cm/sec.
2. Baffles may be put in weir pond to reduce velocity.
3. The weir wall must be vertical [not leaning to upstream or down stream].
4. The center line of the weir should be parallel to the direction of flow.
5. The crest of weir should be level so that water passing over it will be of same
Depth at all point along the crest.
6. Notch should be of regular shape and its edge must be rigid and straight.
7. The weir crest should be above the bottom of the approach channel.
8. The crest of weir is placed high enough so that water will fall freely below weir.
9. The depth of water flow over the rectangular weir should not less than about 5 cm and not more than about 2/3 crest width.
10. The scale or gauge used for measuring the head should be located at a distance of about four times the approximate head. Zero of scale should be exactly a same level s crest level of all weirs.
Limitation in the use of weirs:
1. Weirs are not always suitable for measuring flow.
2. They are not accretes unless proper conditions are maintained
3. They require a considerable loss of head which is mostly not available in channels on flat grads.
4. Weirs are not suitable for water carrying silt
5. Weirs are not easily combined whit turnout structures.
Parshall Flumes
It is open channel type measuring devices that operates whit a small drop in head. The loss of head for free flow limit is only about 25%of that weir sand or silt in the flowing water does not affect its operation or accuracy .it allows accurate measurement even when partially submerged.
The walls of throat section are paroled and the floor is inclined downwards small flumes are made of sheet metal while large ones are made of concert .the size of flume is determined by width of its throat size ranges from 7.5m to several meters.
To determine discharge two scales Ha and Hb are provided at the upstream and down stream section of the flumes.
Width of throat
Free flow limit Hb/Ha
2.5 to 7.5 cm
0.5
15 to 22.5 cm
0.6
30 to 240 com
0.7
Cutthroat Flume:
It is attempt to improve par shall flume by simplifying construction details .the flumes has flat bottom ,vertical walls and a zero length throat section .since it has flat non throat ,it was given the name “cutthroat “most advantage of this flume is economy. It can operate either as a free or submerged flow structure.
Orifices
Orifices in open channels are usually circular or rectangular opening in vertically bulkhead through water flows. The edge of opening is sharp and often constructed of metal.
Free flow orifices:
It can be used to measure comparatively small stream like the flow into border strips, or check basin. They consist of sheet of iron, steel, or aluminum plate that contains accurately machined circular opening ranging from 2.5 cm to 7.5 cm. A plastic scale may be fixed directly on upstream flow of orifices with zero coinciding with the center of orifice.
Submerged Orifices:
Submerged orifices may be divided in to two types:
1) Those having orifices of fixed dimension.
2) Those in which the height of opening may be varied.
The discharge through standard submerged orifices may be obtained using above equation.
Principles of Soil and Water Conservation
In general, depth of soil varies from place to place to great extent. But the top 30 cm soil depth is very useful for both human being and wild life. This layer is continuously exposed to the action of atmospheric activities. Two main active forces, water and wind always tend to detach the top soil layer and to transport them from one placed to another.
Soil Erosion:
It is three phase phenomenon consisting the detachment of individual soil particles from the soil mass and their transport by erosive agents such as running water and wind when energy to transport the particles is not available then third phase called deposition take place.
Definition:
“It is defined as detachment, transportation and deposition soil particles from one place to another place under influence of wind, water or gravity forces”.
Important Points:
1. When eroding agents have sufficient capacity to transport more quantity of materials than the materials supplied through detachment then erosion is turned as “detachment limited “.
2. When materials supplied are greater than materials transported then erosion is turned as transport limited.
Two energy forms are involved in erosion process.
a. Potential
b. Kinetic
PE = m.g.h
PE =potential energy in joules
M = Mass of body in kg
G = acceleration due to gravity
H = elevation Difference.
KE = ½ mv2
KE = Kinetic energy
m = mass of body in kg
V = Velocity of running water or falling raindrops
3. A large amount of energy is lost against frictional resistance of soils surface.
4. Only 3 to 4 % energy is remained with running water to detached soil particles.
5. Critical water velocity responsible for soil erosion is a function of particle size.
6. Critical velocity value increases with increase in grain diameter. (Greater than 0.5mm)
7. Fine particles are harder to get e rode by water flow due to cohesiveness of play clay minerals.
8. Soil particles of 0.01mm in diameter requires of flow velocity of 60m/s and to detached the soil particles but not deposited until the flow velocity reduces below 0.1m/s. d
Types of Erosion
It broadly classified in to two:
A. Geologic erosion:
B. Accelerated Erosion:
1. Wind Erosion
2. Water Erosion.
Raindrop/ splash erosion.
Sheet erosion.
Rill erosion.
Gully erosion.
Stream erosion.
C. Other types of Soil erosion:
1. Glacial erosion
2. Snow erosion
3. Organic erosion
4. Anthropogenic erosion
A. Geologic erosion:
It refers to the formation of and loss of soil simultaneously which maintain the balance between formation and various losses.
It is normal process which represents the erosion of soil in its normal conduction without influence of human being. It is also known as natural or normal erosion. The various topographical features such as existing of stream channels, valleys, etc. are the results of geologic erosion.
B. Accelerated erosion:
It is an excess of geologic erosion. It is activated by naturals and man’s activities due is changes in natural cover and soil conditions.
Accelerated erosion takes place by the action of water, wind, gravity and glaciers. Various forces involved in this are:
1. Attacking force of water or wind which remove and transport the soil particle from one place to another.
2. Retarding forces which resists the erosion. In general accelerated erosion is known as soil erosion or erosion.
It is sub classified as:
1. Water erosion:
Rain drop erosion
Sheet erosion
Rill erosion
Gully erosion
Stream erosion
2. Wind erosion:
It is the process of detachment transportation and deposition of soil particles by the action of wind. Basic cause of wind erosion is:
1. Soil is loose, finely divided and dry
2. Soil surface is smooth and bare.
3. Wind is strong to detach the soil particles from soil surface.
Raindrop Erosion:
It is also known as splash erosion. It results from soil splash caused by the impact of falling raindrops. Factor influencing the rate of erosion are:
1. Climate, Rainfall, temperature.
2. Soil its resistance to dispersion and its infiltration rate.
3. Topography – steepness and length of slope.
4. Plant cover—living or dead vegetation.
Falling raindrops breaks soil aggregate and detach soil particles from soil mass. Fine soil particles are taken into suspension and the splash thus become muddy. The major effect of surface flow of water is to carry off the soil loosened by splash erosion.
Sheet erosion:
Sheet erosion may be defined as:
Removal of the fairly uniform layer of soil from the land surface by the action of rainfall and runoff
More or less uniform removal of soil in the form of thin layer or in sheet form by flowing water from a given width of sloping land
1. Sheet erosion, Two basic erosion processes are involved.
2. Soil particles are detached from the soil surface by falling rain drop.
3. The detached soil particles are transported away by runoff from their original place.
The eroding and transporting power of sheet flow are dependant upon the depth and velocity of sheet flow for a given size, shape and density of soil particle.
Rill Erosion:
It is sometime known as micro channel erosion. It is the removal of soil by running water with the formation of a areas of small branching channels. There is no sharp time of demarcation where sheets erosion ends and more readily visible than sheet erosion. It is regarded as a transition stage between sheet erosion and gully. Rill of small depth can be ordinary form tillage.
Gully erosion:
It is removal of soil by excessive concentration of running water, resulting in the formation of channels ranging in the formation of channels ranging in size from 30cm to 10m or gully is to a large ton be filled by normal tillage practice.
Stream Bank erosion:
Stream channel [bank] erosion is the sourcing of material from the side and bottom of a stream or water channel and the cutting of bank by running water. It is mainly due to removal of vegetation, over grazing or cultivation on the area near to the streams banks.
Other forms of erosion:
1. Glacial erosion [due to mass of ice moving very slowly].
2. Snow erosion [due to slow and creeping movement of snow towards slope.]
3. Anthropogenic erosion [ due to activities of human being]
Factors Affecting Soil & Water Erosion
Factors Affecting Soil Erosion
Factors such as rainfall, runoff, wind soil, slope, plant cover and presence or absence of conservation measures are responsible for soil erosion. But mainly three following factors affect the erosion.
1. Energy:
It include The potential ability of rainfall, runoff and wind to course erosion and other factor which affects the power of erosive agents such as reduction in length of runoff or wind blow through construction of terrace, bunds etc. in case of water erosion and wind breaks or shelter belts incase of wind erosion.
2. Resistance:
It is referred to that factors which affect soil erodibility and soil erosion. Mechanical and chemical properties of soil are responsible for infiltration rate of soil which reduces runoff and decreases soil erodibility. Cultivation decreases the erodibility of clay but increases erodibility of sandy soils.
[Erodibility—susceptibility of soil to get erosion]
[Erosivity—Ability of rain to cause erosion]
3. Protection:
It refers to plant covers which intercept the raindrop falling on ground surface reducing their impact on soil. Plant cover also reduces the runoff and wind velocity, there by soil erosion. Different plant cover offers different protection so suitable cover can be developed to control erosion.
Factors affecting Water Erosion:
Water erosion is due to dispersive and transporting power of water. Factors affecting are:
1. Climatic factors:
This includes rainfall characteristics, atmospheric temperature and wind velocity
2. Soil characteristic:
This affect infiltration rate of soil, Infiltration rate depends upon permeability of soil, surface condition and presence of moisture in it.
3. Vegetation:
It creates the obstacle for raindrops as well as glowing runoff. A good vegetative cover completely reduces the effect of rainfall on soil erosion.
4. Topographic effect:
The land slope, length of slope and shape of slope are main factors which influences soil erosion. As slope of land increases from mild to steep, erosion increases
Measures for Soil and Water Conservations
It is the technique in which deterioration of soil and it looses is reserve by using it within its capabilities and applying conservation technique for production as well as improvement of soil.
Soil and Water Conservation Measures
Agronomical Measure ( Biological)
Engineering Practices
1. Contour cultivation
1. Terracing
2. Strip Cropping
a. Diversion terrace:
a. Contour strip cropping
i. Magnum type.
b. Field strip cropping
ii. Nichols type.
c. Buffer strip cropping
iii. Broad based type
d. Wind strip cropping
iv. Narrow based type
3. Tillage practices
b. Retention Terrace
c. Bench terrace
a. Mulch Tillage
b. Vertical mulching
2. Banding
c. Minimum tillage
a. Contour banding
d. Conventional tillage
e. Listening
i. Narrow based
ii. Broad based
4. Soil management practices
5. Supporting Practices (Interplanting, fertilizer application)
c. Side bunds
6. Vetiver grass planting
d. Lateral bund
e. Supplemental bunds
f. Marginal bund
g. Shoulder bund
A. Agronomical measures:
Agronomical measures or practice if growing vegetation non mild sloppy land to cover them and to control the erosion from there. Agronomical measures include contouring, strip cropping and tillage practices to control the soil erosion. The use of these measures is entirely dependant upon the soil types, land slope and rainfall characteristic. It plays second line of defense after mechanical or engineering measures. It is more economical, long lasting and effective.
1. Contour cultivation:
It refers to all the tillage practices, mechanical treatments like planting, tillage and intercultural, performed nearly on the contour of the area applied across the land slope.
Inflow rainfall regions the primary purpose of contour cultivation is to conserve the rain water in to soil as much as possible.
In humid regions its basic purpose is to reduce the soil erosion or soil loss by retarding the overland flow. In this system, the furrows between the ridges made on the contours hold the runoff water and stored them into the soil. Thus they reduce the runoff and soil erosion.
2. Strip Cropping:
It is also a kind of agronomical practice, in which ordinary crops are planted or grown in form of relatively narrow strips across the land slope. These strips are so arranged, that the strips crops should always be separated by strips of close-growing and erosion resistance crops. Strip cropping check the surface runoff and forces them to infiltrate in to the soil, which facilitates to the concentration of rain water. It is more effective than contouring [about twice effective as contouring] but it does not effect on soil erosion.
Stages:
Controls erosion by
Reducing the runoff flowing through the close growing sod strips.
Increasing the infiltration rate of soil under cover condition.
Types of strip cropping:
Contour strip cropping.
Field strip cropping.
Buffer strip cropping.
Wind strip cropping.
3. Tillage practices:
It is defined as mechanical manipulation of soil to provide a favorable environment for good germination of seed and crop growth, to control the weeds, to maintain infiltration capacity and soil aeration. Tillage practice protects and maintains a strong soil structure to fight against erosion.
Types of tillage operation [practices]
a. Mulch tillage:[ application of many plant residues or other material to cover top soil surface ].
Mulching material:
Cut grasses, straw material, wood chips. Saw dusts, paper and sand stones, glass wools, metal foils and stone plastic.
Types of Mulch:
Natural, synthetic, petroleum, conventional, Inorganic, organic.
b. Vertical Mulching:
Insertion of stuffed plant residue vertically into subsoiler marks to keep the slot open.
c. Minimum Tillage:
Preparation of seedbed with minimum disturbance of soil
d. Conventional tillage:
Ploughing, secondary cultivation with harrowing and planting
e. Listing:
Used for controlling soil erosion.
i. Hard ground listing.
ii. Loose ground listing.
4. Soil management practices:
Various soil and land management practices are –
Those practice which helps to maintain the soil filtration rate at high level to reduce runoff to a negligible amount.
Practices which helps in safe disposal of runoff from field.
The cultural practices which are helpful for creation of high infiltration rate are essential based on farming techniques, tillage or minimum tillage and use of cover crops. Where as the safe disposal of runoff from the field is carried out by physical manipulation of soil surface. Including land shaping, leveling construction of ridges, bunds and water ways
5. Supporting Practices:
It involves application of fertilizers to soil either to make more fertile or to recover the fertility loss during different physical action. Application of fertilizer plays sometimes a significant role to developed abundance vegetative growth e.g. grass waterways and terrace outlet are generally established on low – fertile sub soil.
Inter planting refers to seeding of grass or legume crops in combination of maize or other crops to achieve better result on erosion control.
6. Vetiver Grass Planting:
It is most effective vegetative material foe soil and water conservation, land rehabilitation and embankment stabilization. Vegetative hedge formed with thick growth of vetiver grass forms a protective barrier across slope which slows down sheet erosion and deposit the slit behind hedges.
B. Engineering Practices:
It is used to control the soil erosion in highly sloped areas
1. Terracing
a. Diversion terrace
Magnum type.
Nichols type
Broad based type.
Narrow based type.
b. Retention terrace
c. Bench terrace.
2. Banding:
a. Contour banding
Narrow based
Broad based
b. Graded banding
Narrow based
Broad based
c. Side bunds [formed at extreme ends of contour bunds running along the slopes of land]
d. Lateral Bund [Constructed between two side bunds along slope].
e. Supplemental bunds (between two contour bund so as to limit horizontal spacing)
f. Marginal bund [Formed at margin points of watershed]
g. Shoulder bund [Formed at outer edge of terrace]
Terracing
Terracing:
“A terrace is an embankment or ridge of earth constructed across a slope to control runoff and minimize soil erosion”.
A terrace reduces the length of the hill side slope, there by reducing sheet and rill erosion and prevents formation of gullies.
Types of Terraces:
There are two measure types of terrace.
Bench Terrace: which reduce the land slope
Ridge Type Terrace: Which remove or retain water on sloping land.
Depending on the width of the base, ridge type terrace may be classified as:
Narrow Based Terraces
Broad Based Terraces.
Broad based terraces are sometimes referred to as magnum terraces after the inventor, priestly magnum, who introduced B.B. terrace by widening narrow ridge.
Bench Terrace:
A bench terrace is shelf like embankment of earth with a level or nearly level top and a step or vertical downhill face constructed along the contour of sloping land.
Broad Base Terrace:
A broad base terrace has a ridge 25 to 50cm high and s to 9am wide with gently slopping sides and a dish stopped channel along the upper side constructed to control erosion by diverting runoff at anon –erosive velocity.
It may be level or have a grade towards one or both ends .based on greed; it is divided or classified as:
a] Graded Terrace
b] Level Terrace
A grads terrace has a constant or variable grade along its lengthened used to convey excess runoff at safe velocity into a vegetated waterway or channel.
A level terrace follows the contour line, in control to a graded terrace and recommended in areas having permeable soil.
Bench Terraces:
Bench terracing is one of the oldest mechanical methods of erosion control having been used for manly centuries in many countries .bench terrace, though not very scientifically designed have been extensively used in India in the mountainous regions of Kerla of H.P and Assam.
Bench terracing consists of transforming relatively steep land into a series of levee or nearly level strips or steps running across the slope .the strips are separated by almost vertical risers. The risers if sloping may be of earth construction .steep risers are supported by masonry [stones ].bench terracing is adopted only on slopes steeper then 15%[for more then 8%]and where soil condition are favorable .the use of bench traces retards erosion losses and makes cropping operations on these slopes possible and safe.
Types of bench Terraces:
There are three types of bench terraces
A] Based on slope
B]based on use /application
1] Level and table top
1] Hill type
2] Sloping inwards
2] Irrigated type
3] Sloping outwards
3] Orchard type
4] Puertorican or California type
A] Classification based on slope
1] Table top bench terrace:
Table top bench terrace are suitable for areas receiving medium rainfall which is evenly distributed and which have highly permeable and deep soils .in paddy fields it may be used for slopes as mild as 1% and used where irrigation facilities are available
2] Sloping outwards bench terrace:
In heavy rainfall areas, bench terraces of sloping inwards type are more effective. It prevents inponding of water and useful for crops susceptible to water logging.
3] Sloping outwards bench terrace:
Bench terraces sloping outwards are effective only in low rainfall areas whit a permeable soil of medium depth at lower ends graded channels are provided for safe disposal of runoff
4] Puertorican Type:
In this type of terrace, the soil is excavated little during every ploughing and gradually developing bench by pushing the soil downhill against a mechanical of vegetative barrier. Mechanical or vegetative barrier is established across the land at suitable interval and the terrace is developed gradually over the years ,by pushing soil downhill and subsequent natural leveling.
B] Classification based on use:
Depending upon the purpose for which they are used ,bench terraces are classified as follows:
1. Hill type Bench Terraces:
It is used for hilly areas whit a reverse grad towards the hill.
2. Irrigated Bench Terraces:
Level benches are adopted under irrigated conditions. The level table top terraces are referred to as irrigated bench Terries.
3. Orchard Bench Terraces:
Narrow width terraces [about 1 mm] for individual trees are prepared in this type. These are also referred as intermittent terraces and step terraces. The conversion of land into bench terraces over a period of time is referred as gradual bench terracing.
Steps in design of bench Terraces:
For the design of the bench terraces for particular area, the average rainfall, the soil type, soil depth, slope and farming practices of the area should be known. The design consists in determining the
Type of the bench terrace.
Terrace spacing or the depth of the cut.
terraces width and
Terrace cross section.
Step I Selection of the type of bench terrace depends upon the rainfall and soil, condition.
Step II Terrace Spacing: It is normally expressed in terms of the vertical interval between two terraces. It depends upon soil, slope, surface condition, grade and agriculture use. The vertical interval is dependant upon the depth of cut. Since the depth of cut and fill are to be balanced, V.I. is equal to double the depth of cut. The depth of cut should not be too high as to exposed bed rock
Consideration:
Find Out the maximum depth of productive soil,
maximum admissible cutting depth—D/2 or d
Given land slope, [S]
From this, The width of the terraces [W] can be computed for a given slope [S]
By formula
200d
W = ----------------
S
Depth of Cut:
Case a:
When terrace cuts are vertical by similar triangles
WS
D = -----------------
100
Case b:
When batter slope is 1:1
D/2 S WS
--------------- = --------------- D = ------------------ = V. I.
W/2+D/2 100 [100-S]
Case C:
D/2 S 2 WS
------------------- =---------------- D = ---------------- = V. I.
W/2+D/4 100 200-S
Step III: Terrace cross section:
Design of terrace cross consists of deciding
1] The battler slope
2] Dimensions of shoulder bund
3] Inward slope of then terrace and the dimensions of the drainage channel in case of terrace sloping inward, and
4] Outward slope in case of terraces sloping outward.
The height of the embankment [bound] should be increased sufficiently to provide for shrinkage of soils, so that the ultimate slope, as per design can be obtained after compaction.
Step IV: The cross- section of shoulder bund along outer edge of terrace should also be designed suitably to make the bund stable against slipping and overt to piping.
Contour and Graded Bunding
Contour Bunding
Counter Bunding are carried out in many parts in India- notably in Maharashtra, Gujarat, Tamilnadu, Karnataka and Andhra Pradesh.
Contour Bunding:
It consists of building earthen embankments across the slope of the land, following the contour as closely as possible. A series of such bunds divide the area into strips and act as barriers to t5he flow of water, thus reducing the amount and velocity of the runoff.
Peripheral bunds:
Bunds area also constructed along field boundaries without reference to contour. These bunds are called peripheral bunds. They serve as fences, and give protection from water and wind erosion in low rainfall areas. They are not suitable in heavy rainfall areas.
No cultivation is allowed on the earthen embankments of contour bunds. Therefore under contour bunds an area of about 5 percent is lost under the bunds and is not available for cultivation.
Contour bunds can save soils from erosion to the extent of 25 to 162 tones/ hectare annually. It maintains soil fertility and increases water infiltration into the soil considerably,
Contour bunds in deep black soils have been a failure because of the nature of soil, which cracks during hot weather and cakes during the monsoon. So they are not stable in black soils. Further the poor drainage properties of deep black soils gives raise to long stagnation of water against contour bunds and make it unstable. Contour bunds are also not successful in very shallow soils having a depth loss than 7.5cm.
General principles of design
1. Spacing of Contour bund:
Bund spacing is expressed as the vertical or the horizontal distance between corresponding points on two adjacent bunds. Although the horizontal spacing is useful in determining the row arrangement. Vertical distance is commonly known as the vertical interval or V. I.
Bund spacing should not be so wide as to cause excessive soil erosion between adjacent bunds. Spacing may be increased or decreased 10 to 20% to suit local conditions.
Table-1 Spacing of Contour bunds: Recommended by Gadkary
Slope of land [ c ]
vertical interval [ m ]
Approx horizontal distance [ m ]
0 to 1
1.05
105
1 to 1/2
1.2
98
1/2 to 2
1.35
75
2 to 3
1.5
60
3 to 4
1.65
52
2. Bund Grade:
Since the contour bunds are laid along the contours, they are level bunds.
3. Bund length:
In general, 400 to 500m is the maximum length of bund. The bund retains the runoff and carries it over the distance equal to bund length in one direction. The length of bund should be such that the velocity of water flowing between bunds should be non- erosive.
4. Bund cross section:
The height of bund should provide sufficient storage above the bund to handle the expected runoff. In normal practice sufficient practice is provided to take care of runoff from rains expected in 10 year recurrence interval. The cross section area of of the storage space required can be calculated by the following formula
[Runoff, cm] X [Bund horizontal interval in m]
Cross section area of storage space = ------------------------------------------
100
The height of bund should permit frees board of about 20% as design depth [after allowing settlement of the ridge.] Specific at bund cross section are given in table:--
Table: specification for bund cross-sections
Depth of soil
Base width 'm'
Top width 'm'
Height 'm'
Side slope
1. Shallow soils [7.5 to 22.55cm]
2.67
0.38
0.75
1 1/2 : 1
2. Medium soils [ 22.5 to 45cm ]
3.12
0.6
0.85
1 1/2 :1
3. medium deep soil [ 45 to 90 cm]
4.25
0.6
0.9
2:01
Design Criteria for Bunds:
The following factors are to be considered while developing design criteria for contour bunds.
1. Allowable submergence of land:
The amount of land submerged due to pending and duration of pending will affect crops.
Therefore the level of waste weir and the amount of land to be submerged should be decided by the cropping practice to be followed and the infiltration rate for the soil.
2. Moisture Conservation:
For paddy lands it is desirable to store all the rain water for the use of the plants. Therefore the bunds should be of such dimensions as to permit no runoff. For other crops, the capacity of the bund should be decided by the average consumptive use of the crop proposed and the maximum length of dry period in growing season. The heights of waste weirs should be such that the bunds store just sufficient water to meet requirement of crop.
3. Economy in Construction:
The cost of Bunding includes two main atoms which vary according to the spacing of the bunds.
i. Expenses of the earthwork
ii. Value of land lost permanently due to construction of bunds.
The sum of these two should be minimum
4. Critical Length:
Another approach in fixing the spacing of bunds by determining the critical length of land between adjacent bunds. Increase in drainage area increases both velocity and amount of runoff gathering in narred channel. But the critical length approach, the attempt is to space bunds in such a way that the velocity remains within non-erosive limit.
5. Seepage consideration:
While designing the bund cross- section, the seepage through bunds due to accumulation of water behind it should be taken into account. The seepage rate is affected mainly by the head of water impounded, the side slopes of the bound and the permeability of the soil.
Graded Bunding:
Definition:
“Graded bunds or graded terraces or channel terraces are the bunds or terraces laid along a pre-determined longitudinal grade very near the contour but not exactly along contour”.
Suitability:
The graded bunds, commonly used in India are comparable to the narrow base terraces. They are used for the safe, disposal of excess runoff high rainfall areas and rigious where the [Clay] soil is relatively impervious. Farming operations are not done on bunds or bund channels.
Function:
These terraces act primarily as drainage channel to regulate and conduct runoff at non erosive velocity.
To make the runoff water to trickle rather than to rush out.
Types of Pumps
Basically four principles involved in pumping water:
Atmospheric pressure.
Positive displacement
Centrifugal force
Movements of columns of water caused by the difference in specific gravity.
Pump Characteristic:
Terminology:
Capacity:
It is volume of water pumped per unite time. It is measured in liters seconds.
Static suction head:
It is vertical distance from center of pump to free level of water to be pumped.
Static discharged Head:
It is vertical distance from the center line of the pump to discharge water level.
Total Suction Head:
It is vertical distance from the center line of the pump to free level of the liquid to be pumped minus, all friction looses in suction pipe and fitting plus any pressure head existing on the suction supply.
Total Discharge head:
It is sum of static discharge head, friction and exit looses in discharge piping plus the velocity head and pressure head at the point of discharge.
Friction head:
It is the equivalent head expressed in meters of water required to over come the friction caused by flow through the pipe and pipe fittings.
Pressure head:
It is pressure expressed in meters of water in a closed vessel from which pumps takes its suction or against which the pump discharges.
Hp = P/w
Hp – Pressure head, m
P – Pressure inside vessel kg/m2
W – Specific weight of water kg/m3
Velocity Head:
It is the pressure expressed in meters of water required to create the velocity of flow.
Hv = V^2 / 2g
Hv = velocity head, m
V = velocity of water through the pipe m/sec.
g = Acceleration due to gravity, m/sec2. [g = 9.81m/sec.]
Net positive suction Head [NPSH]:
It is the total suction head minus the vapor pressure of water at the pumping temperature both expressed in meter
Maximum practical Suction lift of pump:
Maximum practical Suction lift of pump can be computed by –
Hs = Ha – Hf – es – NPSH – Fs
Where,
Hs = maximum practical suction lift or elevation of water surface, m
Ha = Atmospheric press at water surface [10.33 m at sea level]
Hf = Friction looses in strainer pipe fitting and values on suction line, m.
es = Saturated vapor pressure of water, m .
NPSH = net positive suction head.
es = Factor of safety [0.66m]
Water horse power [WHP]:
It is the theoretical horse power required for pumping.
Discharge in liters per sec. x total head in m.
WHP = ----------------------------------------------------------
75
OR,
Discharge in cubic meters per sec. x Total head in m.
= ---------------------------------------------------------
273
Shaft horse power [WHP]:
It is power required at pump shaft.
WH
SHP = -----------------------------
Pump efficiency
[SHP is always greater than WHP]
Efficiency:
It is the ratio of power output to power input.
Water WHP
Pump efficiency = ---------------------------
SHP
Brake Horse power:
It is actual horse power required to be supplied by the engine or electric motor for driving the pump.
With direct driven pump [ drive efficiency 100%]
BHP = SHP
With belt or other indirect drives.
WHP
BHP = -----------------------------------------------------
Pump efficiency x drive efficiency
WHP
3. H.P. Input to, electric motor = ---------------------------------------------
Pump efficiency x drive efficiency x motor efficiency
BHP x 0.746
4. Kilowatt input to electric power = ----------------------------------
Motor efficiency
Centrifugal Pumps, Vertical Turbine Pumps and Submersible Pumps
A. Centrifugal Pumps
Definition:
It may be defined as one in which an impeller rotating inside a close fitting case draws in the liquid at center and by virtue of centrifugal force throws out the liquid through an opening at the side of casing.
Centrifugal pumps are most widely used in irrigation practice. They are simple in construction, easy to operate, low initial cost and produce a constant steady discharge. This type of pump is well adapted to usual pumping services such as irrigation, water supply and sewage services.
Principles of Operation:
A centrifugal pump is rotary machines consisting of two basic parts:
1. Rotary element or impeller, and
2. Stationary element or casing
Principles:
The underlying hydraulic principle is the production of high velocity and the partial transformation of this velocity in pressure head.
Impeller is a wheel or disc mounted on shaft and provided with a number of vanes or blades surrounds the impeller.
In some pumps, a diffuser consisting of series of guide vanes or blades surrounds the impeller
Operation:
The pump is filled with water and the impeller is rotated. The blades cause the liquid to rotate with the impeller and in turn impart high velocity to the water. Centrifugal force causes it to be thrown outward from the impeller in to casing.
Outward flow through impeller reduces pressure at the inlet allowing more water to be drawn in through suction pipe. Due to conversion of high velocity into pressure, water is pumped through discharge pipe It is done either in volute casing or in diffuser casing.
Techniques Used for Priming:
A foot value to hold the water in pump.
An Auxiliary pistons pump to fill the pump causing and suction line with water.
Connection to an outside source of water under pressure for filling the pump.
Use of self- Priming construction.
B. Vertical Turbine Pumps:
Vertical turbine pump [deep well turbine pump] is vertical axis centrifugal or mixed flow type pump comprising of stages which accommodate rotating impellers and stationary bowls possessing guide vanes.
These pumps are used where the pumping water level is below the limits of Volute centrifugal pump. They have higher initial cost and are more difficult to install and repair. The pressure head developed depends on the diameter of impeller and the speed at which it is rotated. The pressure head developed by single impeller is not great. Additional head is obtained by adding more bowl assemblies or stage.
Construction:
It has three parts:
1. Pump Element:
The pump element is made up of one or more bowls or stages. Each bowl consists of an impeller and diffuser.
2. Discharge Column:
It connects the bowl assembly and pump head and conducts water from former to later.
Discharge head:
It consists of base from which the discharge column, bowl assembly and shaft assembly are suspended.
C. Submersible Pumps:
An vertical turbine pump close coupled to a small diameter submersible electric motor is termed as “submersible pump”. The motor is fixed directly below the intake of the pump. The pump element and the motor operate under submerged condition. It can be used in very deep tube well where a long shaft would not be practical.
Construction:
It consist of pump and motor assembly, a discharge column, a head assembly and a water proof cable to conduct the electric current to a submerged motor.
Pump element:
It consists of propelling shaft, usually made of stainless steel and bronze impellers. Water enters the pump through a screen located between motor and the pump.
Electric Motor:
The motor is enclosed in steel case filled with light oil of high electric strength. A mercury seal placed directly above the amateur prevents oil leakage or water entrance at point where the drive shaft passes through the case to the impellers.
Concepts of Watershed Management
Soil, vegetation and water are most important vital natural resources for the existence of the man and his animals. These three interdependent resources can bee managed collectively, conveniently, simultaneously and efficiently on watershed basis (unit of management.)
Watershed:
Definition:
“Watershed can be defined as a unit of area covers all the land which contributes runoff to a common point or outlet and surrounded by a ridge line”. It is also known as ridge line.
Delineation procedure of watershed:
Watershed delineation is to describe or sketching out the area bounded by ridge line, contributing runoff at common point and dividing or separating it from the adjoining area.
The delineation of priority area can be performed to some extent by reconnaissance survey and study of topo -sheets. However, this technique is slow and also not provides very accurate information. Normally, the photographs of 1:15,000 can also be used for the purpose.
The demarcation of priority areas should be accomplished on watershed basis, because a comprehensive watershed management approach is essential for caring out for proper soil conservation measures. It is also necessary that, that the size of watershed to be delineated should be ranges from 10,000 to 20,000 ha, because for small watershed the formulation of soil conservation working plans and their execution over reasonable period is practically possible and easy, too.
The steps for demarcation of small size watershed are described as under:
1. Divide the entire watershed into different sub-watersheds following important tributaries.
2. Again, divide each sub watershed into small size, following distinct tributaries and streams passing through respective sub watershed.
3. further, sub-divided each small part of watershed [as obtained in step (2) in size ranges from 10,000 to 20,000 ha.]
Causes of watershed Deterioration:
Deterioration of watershed takes place due to faulty and bad management through the activity of man and his animals. These activities are:
1. Faulty agriculture, forestry and pasture management leading to degradation of land.
2. Unscientific mining and quarrying.
3. Faulty road alignment and construction.
4. Industrialization
5. Fire.
6. Apathy of the people.
Results of watershed Deterioration:
1. Less production from agriculture, forests, grass lands etc.
2. Erosion increases and decreases biomass production
3. Rapid siltation of reservoirs, lakes and river beds.
4. Less storage of water and lowering of water table.
5. Poverty as a result of less food production.
Classification of Watershed
A. A large numbers of terms are very frequently and loosely used to classify watershed in different sizes [based on size]
a. Micro watersheds
b. small watersheds
c. Large watersheds, etc
Small watersheds:
“Small watersheds are those where the overland flow is the main contributor to peak runoff / flow and channel characteristic do not affect the overland flow”.
Large Watersheds:
“Large watersheds are those give peak flows are greatly influenced by channel characteristics and basin storage”.
B .Watersheds is also classified into different categories based on area that the watersheds contain:
Sr. No
Type of Watershed
Area Covered
1
Micro Watershed
0 to 10 ha
2
Small Watershed
10 to 40 ha
3
Mini Watershed
40 to 200 ha
4
Sub Watershed
200 to 400 ha
5
Macro Watershed
400 to 1000 ha
6
River basin
above 1000 ha
C. Classification based on shape:
a. Square b. Triangular c. Rectangular
d. Oval e. Fern leaf shaped f. Palm shaped
g. Polygon shaped h. Circular i. Secator shaped
Function of watershed:
The main function of watershed is to receive the incoming precipitation and then dispose it off. This is the essence of soil and water conservation.
Morphological characteristics of watershed:
Each individual watershed has several remarkable characteristics, which affect its functioning. Seven such characteristic have been identified.
Size [area]
Shape.
Topography
Geology, rock and soil
Climate
Vegetation
Land use
1. Size:
Size of watershed determines the quantity of rainfall received retained and disposed off [runoff]. Larger the watershed, larger be the channel and storage of water in basin. Large watershed characteristics are topography, geology, soil, climate and use and vegetation.
2. Shape:
Watershed may have several shapes like square triangular rectangular, oval, palm, fern leaf shape etc.
Shape of watershed determines the shape index [form factor Ff = WB/Lb]
That is the length: width ratio which in turn has a great effect on runoff disposal. Larger the watershed, higher is the time of concentration and more water will infiltrate, evaporate or get utilized by the vegetation. Reverse is the situation when watershed is shorter in length as compared to width.
Compactness coefficient Cc:
“Compactness coefficient of a watershed is the ratio of perimeter of watershed to circumference of circular area which equals the area of the watershed”. The C.C. is independent of size of watershed and dependent only on the slope.
3. Topography:
Slope, length, degree and uniformity of slope affect both disposal of water and soil loss. Degree and length of slope also affect time of concentration [Tc] and infiltration of water.
Drainage: Topography regulates drainage. Drainage density [length of all drainage channels – unit area], length, width depth of main and subsidiary channel, main outlet and its size depend on photography. Drainage pattern affect time of concentration.
4. Geology rock and soil:
Geological formation and rock types affect extent of water erosion, erodibility of channels and hill faces, sediment production. Rocks like shale’s, phyllites erode easily where as igneous rocks do not erode.
Physical and chemical properties of soil, specially texture, and structure and soil depth influence disposition of water by way of infiltration, storage and runoff.
5. Climate:
Climate parameters affect watershed functioning and its manipulation in two ways.
Rain provides incoming precipitation along with its various characteristic like intensity, frequency and amount of rainfall.
Parameters like rainfall, temperatcive, humidity, wind velocity, etc. regulates factors like soil and vegetation.
6. Vegetation:
Depending upon the type of vegetation and its extent, this factor regulates the functioning of watershed ex. Infiltration, water retention, runoff production, erosion, sedimentation etc.
7. Land use:
Type of land use, its extent and management are the key factors which affect watershed behavior. Judicious land use by users [human beings] is of vital importance to watershed management and functioning.
Watershed Management
Definition:
“Watershed management is a concept which recognizes the judicious management of three basic resources of soil water and vegetation, on watershed basis, for achieving particular objective for the well being of the people”. It includes treatment of land most suitable biological as well as engineering measures.
Objective of watershed management:
Production of food, fodder, fuel.
Pollution control
Over exploitation of resources should be minimized
Water storage, flood control, checking sedimentation.
Wild life preservation
Erosion control and prevention of soil, degradation and conservation of soil and water.
Employment generation through industrial development dairy fishery production.
Recharging of ground water to provide regular water supply for consumption and industry as well as irrigation.
Recreational facility.
Steps in watershed management:
Watershed management involves determination of alternative land treatment measures for, which information about problems of land, soil, water and vegetation in the watershed is essential.
In order to have a practical solution to above problem it is necessary to go through four phases for a full scale watershed management.
Programme:
Recognition phase.
Restoration phase.
Protection phase.
Improvement phase.
1. Recognition Phase:
It involves following steps
Recognition of the problem
Analysis of the cause of the problem and its effect.
Development of alternative solutions of problem.
Necessary information is obtained from different surveys like soil survey, land capability survey, agronomic survey, forest, engineering and socio economic survey, etc. This information serves as a basis for fixing and determining the watershed problems, priorities in land treatment measures, and causes and effects of problems on land and people.
2. Restoration Phase:
It includes two main steps.
Selection of best solution to problems identified
Application of the solution to the problems of the land
As per the priorities, treatment applied initially to critical areas. After this proper measures like biological and engineering measures are applied to all types of lands.
3. Protection Phase:
This phase takes care of the general health of the watershed and ensures normal functioning. The protection is against all factors which may cause determined in watershed condition.
4. Improvement phase:
This phase deals with overall improvement in the watershed and all land is covered. Attention is paid to agriculture and forest management and production, forage production and pasture management, socio economic conditions to achieve the objectives of watershed management. Health, family planning, improving cattle, poultry, etc. are taken depending upon intensity.
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