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1. AGE 505: Soil andAGE 505: Soil and
Water ConservationWater Conservation
References:References:
1.1.Soil and Water Conservation Engineering, by GlennSoil and Water Conservation Engineering, by Glenn
O. Schwab et. alO. Schwab et. al
2.2. Michael, A.M.: Irrigation: Theory and PracticeMichael, A.M.: Irrigation: Theory and Practice
3.3. Design of Small Dams: USDA: Bureau of LandDesign of Small Dams: USDA: Bureau of Land
ReclamationReclamation
4.4. Soil Conservation: N.W. HudsonSoil Conservation: N.W. Hudson
5.5. Field Engineering for Agricultural Development:Field Engineering for Agricultural Development:
N.W. Hudson.N.W. Hudson.

2. IntroductionIntroduction
 Measures that provide for the management of water and soilMeasures that provide for the management of water and soil
 Conservation practices involves the soil, the plant and the climate, eachConservation practices involves the soil, the plant and the climate, each
of which is of utmost importance.of which is of utmost importance.
 The engineering approach to soil and water conservation problemsThe engineering approach to soil and water conservation problems
involves the physical integration of soil, water and plants in the design of ainvolves the physical integration of soil, water and plants in the design of a
co-ordinated water managementco-ordinated water management
 The engineering problems involved in soil and water conservation may beThe engineering problems involved in soil and water conservation may be
divided into the six following phases:divided into the six following phases:
 Erosion controlErosion control
 DrainageDrainage
 IrrigationIrrigation
 Flood controlFlood control
 Moisture conservation andMoisture conservation and
 Water resource developmentWater resource development
The conservation of these vital resources implies utilization without waste so as to makeThe conservation of these vital resources implies utilization without waste so as to make
possible a high level of production which can be continued indefinately.possible a high level of production which can be continued indefinately.

3. Types of ErosionTypes of Erosion
Two major types of erosionTwo major types of erosion
 Geological erosionGeological erosion
 Accelerated erosionAccelerated erosion
Geological erosionGeological erosion: includes soil-forming as well as soil eroding: includes soil-forming as well as soil eroding
processes which maintain the soil in a favorable balance.processes which maintain the soil in a favorable balance.
Accelerated erosionAccelerated erosion: includes the deterioration and loss of soil: includes the deterioration and loss of soil
as a result of man’s activities. Although, soil removal areas a result of man’s activities. Although, soil removal are
recognized in both cases, only accelerated erosion isrecognized in both cases, only accelerated erosion is
considered in conservation activities.considered in conservation activities.
The forces involved in accelerated erosion are:The forces involved in accelerated erosion are:
1.1. Attacking forces which remove and transport the soil particlesAttacking forces which remove and transport the soil particles
andand
2.2. Resisting forces which retard erosion.Resisting forces which retard erosion.

4. Soil erosion by waterSoil erosion by water
Water erosion is the removal of soil from the lands surface by runningWater erosion is the removal of soil from the lands surface by running
water including runoff from melted snow and ice. Water erosion iswater including runoff from melted snow and ice. Water erosion is
sub-divided into raindrop, sheet, rill, gully and stream channelsub-divided into raindrop, sheet, rill, gully and stream channel
erosion.erosion.
Major Factors Affecting Erosion by WaterMajor Factors Affecting Erosion by Water
1.1. Climate, 2. Soil, 3. Vegetation and 4. TopographyClimate, 2. Soil, 3. Vegetation and 4. Topography
Climate: - Precipitation, temperature, wind, humidity and solarClimate: - Precipitation, temperature, wind, humidity and solar
radiationradiation
Temperature and wind: - evident through their effect on evaporationTemperature and wind: - evident through their effect on evaporation
and transpiration. However, wind also changes raindrop velocitiesand transpiration. However, wind also changes raindrop velocities
and angle of impact. Humidity and solar radiation are less directlyand angle of impact. Humidity and solar radiation are less directly
involved since they are associated with temperature.involved since they are associated with temperature.
Soil:Soil: Physical properties of soil affects the infiltration capacity ofPhysical properties of soil affects the infiltration capacity of
the soil. The extend to which it can be dispersed and transported.the soil. The extend to which it can be dispersed and transported.
These properties which influence soil include:These properties which influence soil include:

5. - Soil structureSoil structure
- TextureTexture
- Organic matterOrganic matter
- Moisture contentMoisture content
- Density or compactnessDensity or compactness
- Chemical and biological characteristicsChemical and biological characteristics

6. VegetationVegetation
Major effect of vegetation in reducing erosion are:Major effect of vegetation in reducing erosion are:
 Interception of rainfallInterception of rainfall
 Retardation of erosion by decrease of surface velocityRetardation of erosion by decrease of surface velocity
 Physical restraint of soil movementPhysical restraint of soil movement
 Improvement of aggregation and porosity of the soil byImprovement of aggregation and porosity of the soil by
roots and plants residueroots and plants residue
 Increase biological activitiesIncrease biological activities
 Transpiration – decrease soil moisture resulting inTranspiration – decrease soil moisture resulting in
increased storage capacity.increased storage capacity.
These vegetative influences vary with the season, crops,These vegetative influences vary with the season, crops,
degree of maturity, soil & climate as well as with kind ofdegree of maturity, soil & climate as well as with kind of
vegetative materials namely: roots, plant tops, plantvegetative materials namely: roots, plant tops, plant
residueresidue

7. TopographyTopography
Features that influence erosion are:Features that influence erosion are:
 degree of slopedegree of slope
Length of slopeLength of slope
Size and shape of the watershedSize and shape of the watershed
StraightStraight
ComplexComplex
ConcaveConcave
Convex.Convex.

8. RaindropRaindrop characteristicscharacteristics
 TheThe relationshiprelationship betweenbetween erosion and rain fallerosion and rain fall
momentum and energy id determined by raindropmomentum and energy id determined by raindrop
mass, size distribution, shap, velocity and direction.mass, size distribution, shap, velocity and direction.
The characterization and measurement of theseThe characterization and measurement of these
individual factors demand the utmost ingenuity andindividual factors demand the utmost ingenuity and
precision.precision. TheThe
energy equation that has been developed byenergy equation that has been developed by
wischmeier and smith (1958)wischmeier and smith (1958)
E=916 +331logiE=916 +331logi
w and s E=kinetic energy inw and s E=kinetic energy in

9.  The resistance of a soil to erosion depends on manyThe resistance of a soil to erosion depends on many
factors and so to measure erodibility numerically anfactors and so to measure erodibility numerically an
assessment has to be made of each factor.assessment has to be made of each factor.
 -nature of soil-nature of soil --
slope of landslope of land --
kind of crop.kind of crop.
Erosivity-is the aggressiveness or potential ability ofErosivity-is the aggressiveness or potential ability of
rain to cause erosion.rain to cause erosion.
Erodibility-is the vulnerability or susceptibilityErodibility-is the vulnerability or susceptibility
of the soil to erosion.of the soil to erosion.

10. Factors influencing erodibilityFactors influencing erodibility
 Two groups of factors.Two groups of factors.
 1.physical features of the soil. i.e what kind of soil1.physical features of the soil. i.e what kind of soil
 2.treatment of the soil . i.e what is done with it. the part2.treatment of the soil . i.e what is done with it. the part
concerned with treatment has much the greater effect.concerned with treatment has much the greater effect.
And is also most difficult to access. i.e average increaseAnd is also most difficult to access. i.e average increase
in soil loss per unit increase in E I.in soil loss per unit increase in E I.
These is a great deal of experimentalThese is a great deal of experimental
evidence to suggest a link between erosive power andevidence to suggest a link between erosive power and
the mass and velocity of falling drops.the mass and velocity of falling drops.
Ellison(1944).Ellison(1944).

11.  Bisal(1960) suggests in a similar lab.Bisal(1960) suggests in a similar lab.
G =k D V1.4G =k D V1.4
S=weight of soil splashed in gramsS=weight of soil splashed in grams
k=constant for the soil typek=constant for the soil type
D=drop diameter in mmD=drop diameter in mm
v=impact velocity m/s.v=impact velocity m/s.
In both these studies the combination of power of dropIn both these studies the combination of power of drop
velocity and drop mass are not very different fromvelocity and drop mass are not very different from
combining mass and velocity into the parametercombining mass and velocity into the parameter
kinetic energy.kinetic energy.

12.  Rose (1960) challenges the above assumption thatRose (1960) challenges the above assumption that
results such as these proves that splash erosion isresults such as these proves that splash erosion is
dependent only on the k.E. of natural or artificial rain,dependent only on the k.E. of natural or artificial rain,
and shows that if such a relationship exist it is equallyand shows that if such a relationship exist it is equally
valid , though different relationship will exist betweenvalid , though different relationship will exist between
erosion and momentum or any other function of masserosion and momentum or any other function of mass
and velocity .since mass occurs in the same form in theand velocity .since mass occurs in the same form in the
formula for both momentum and energy, it isformula for both momentum and energy, it is
necessary to vary velocity in order to resolve thenecessary to vary velocity in order to resolve the
problem of whether energy or momentum is the betterproblem of whether energy or momentum is the better
index of erosivity. Conclusively-it has been shown thatindex of erosivity. Conclusively-it has been shown that
for natural rain the relationships between intensity andfor natural rain the relationships between intensity and
either momentum or kinetic energy are equally closeeither momentum or kinetic energy are equally close
and of the same pattern.and of the same pattern.

13. Estimating erosivity from rainfallEstimating erosivity from rainfall
datadata
 The EIzo index. R=EIzoThe EIzo index. R=EIzo
This is the product of kinetic energy of theThis is the product of kinetic energy of the
stem and the 30-mints intensity. This latter termstem and the 30-mints intensity. This latter term
requires some explanation .requires some explanation .
-It is the greatest-It is the greatest
average intensity experienced in any 30-min periodaverage intensity experienced in any 30-min period
during the stem.during the stem.
-This amount could be doubled to set the same-This amount could be doubled to set the same
dimension as intensity, i.e. inches/hour, mm/hr. Thedimension as intensity, i.e. inches/hour, mm/hr. The
measure of erosivity is described as the EIzo index. itmeasure of erosivity is described as the EIzo index. it
can be computed for individuals storms, and the stormcan be computed for individuals storms, and the storm
values can be summed over periods of time to givevalues can be summed over periods of time to give
weekly, monthly, or annual values of erosivity .weekly, monthly, or annual values of erosivity .

14. Application of an index of erosivityApplication of an index of erosivity
 The ability to access numerically the erosive power ofThe ability to access numerically the erosive power of
rainfall has two main applications. In practical soilrainfall has two main applications. In practical soil
conservation it helps :conservation it helps :
1.to improve the design of1.to improve the design of
conservation works.conservation works. 2.in research, it helps to2.in research, it helps to
increase our knowledge and understanding of erosion.increase our knowledge and understanding of erosion.

15. Soil detachment and transportationSoil detachment and transportation
 The process of soil erosion involves soil detachmentThe process of soil erosion involves soil detachment
and soil transportation .and soil transportation .
Generally, soil detachability increases asGenerally, soil detachability increases as
the size of the soil particles increase and soilthe size of the soil particles increase and soil
transportability increases with a decrease in particletransportability increases with a decrease in particle
size.size.
 detachment causes damage because:detachment causes damage because:
1.1. The soil particles are removed from the soil mass andThe soil particles are removed from the soil mass and
thus easily transported.thus easily transported.
2.2. The five materials and plant nutrients are removed.The five materials and plant nutrients are removed.
3.3. Seeds may be separated and washed out of the soil.Seeds may be separated and washed out of the soil.

16. Sheet erosionSheet erosion
Uniform removal of soil in thin layers from sloping land-Uniform removal of soil in thin layers from sloping land-
resulting from sheet or overland flow occurring in thinresulting from sheet or overland flow occurring in thin
layers. minute rilling takes place almost simultaneouslylayers. minute rilling takes place almost simultaneously
with the first detachment and movement of soilwith the first detachment and movement of soil
particles. the constant meander and change of positionparticles. the constant meander and change of position
of these microscopic rills.of these microscopic rills.

17. Rill erosionRill erosion
Removal of soil by water from small but well definedRemoval of soil by water from small but well defined
channels or streamlets where there is a concentrationchannels or streamlets where there is a concentration
of overland flow. Obviously,rill erosion occurs whenof overland flow. Obviously,rill erosion occurs when
these channels have become sufficiently large andthese channels have become sufficiently large and
stable to be readily seen.stable to be readily seen.

18. Gully erosionGully erosion
Gully erosion produces channels larger then rills. TheseGully erosion produces channels larger then rills. These
Channels carry water during and immediately afterChannels carry water during and immediately after
rain.rain.

19. Principles of gully erosionPrinciples of gully erosion
The rate of gully erosion depends primarilyThe rate of gully erosion depends primarily
 on the runoff producing characteristics of theon the runoff producing characteristics of the
watershedwatershed
 the drainage areathe drainage area
 soil characteristicssoil characteristics
 the alignmentthe alignment
 size and shape of gullysize and shape of gully
 the slope in the channel.the slope in the channel.

20. Gully development processesGully development processes
1.1. Water fall erosion at the gully head.Water fall erosion at the gully head.
2.2. Channel erosion caused by water flowing through theChannel erosion caused by water flowing through the
gully or by raindrop splash on unprotected soil.gully or by raindrop splash on unprotected soil.
3.3. Alternate freezing and thawing of exposed soil banks.Alternate freezing and thawing of exposed soil banks.
4.4. Slides or mass movement of soil in the gully.Slides or mass movement of soil in the gully.

21. Four stages of gully developmentFour stages of gully development
Stage1Stage1 Channel erosion by down ward scour of theChannel erosion by down ward scour of the
topsoil. Thistopsoil. This stage normally proceeds slowlystage normally proceeds slowly
where the topsoil is fairlywhere the topsoil is fairly resistant to erosionresistant to erosion
Stage2:Stage2: upstream movement of the gully head andupstream movement of the gully head and
enlargement of the gully in width and depth. The gullyenlargement of the gully in width and depth. The gully
cuts to the horizon and the weak parent material iscuts to the horizon and the weak parent material is
rapidly removed.rapidly removed.
stage3:stage3: Healing stage with vegetation to grow in theHealing stage with vegetation to grow in the
channel.channel.
Stage 4:Stage 4: Stabilization of the gully. The channel reachesStabilization of the gully. The channel reaches
a stable gradient, gully walls reach and stable slopea stable gradient, gully walls reach and stable slope
and vegetation begins to grow in sufficient abundanceand vegetation begins to grow in sufficient abundance
to anchor the soil and permit development of newto anchor the soil and permit development of new

22. Sediment movement in channelsSediment movement in channels
Sediments in streams is transported by :Sediments in streams is transported by :
1.1. SuspensionSuspension
2.2. SiltationSiltation
3.3. Bad load movement.Bad load movement.
Suspension:Suspension: suspended sediment is that whichsuspended sediment is that which
remains in suspension in flowing water for aremains in suspension in flowing water for a
considerable period of time without contact with theconsiderable period of time without contact with the
stream bed.stream bed.
saltation:saltation: sediment movement by saltation occurssediment movement by saltation occurs
where the particle skip or bounce along the streamwhere the particle skip or bounce along the stream
bed. In comparison to total sediment transportedbed. In comparison to total sediment transported
,saltation is considered relatively unimportant.,saltation is considered relatively unimportant.

23. Sediment movement in channelsSediment movement in channels
Bed load:Bed load: Bed load is sediment that moves in almostBed load is sediment that moves in almost
continous contact with the stream bed being rolled orcontinous contact with the stream bed being rolled or
pushed along the bottom by the force of the water.pushed along the bottom by the force of the water.
Mavis (1935),developed anMavis (1935),developed an
equation for unigranular materials ranging in diameterequation for unigranular materials ranging in diameter
from 0.35 to 0.57 millimeters and specifically from 1.83from 0.35 to 0.57 millimeters and specifically from 1.83
to 2.64.to 2.64.

24. Universal soil loss equationUniversal soil loss equation
Smith and wisehmeier (1957,1962) developed an equationSmith and wisehmeier (1957,1962) developed an equation
for estimating the average annual soil loss.for estimating the average annual soil loss.
A=RKLSCPA=RKLSCP
Am=2.24RKLSCP metric unit.Am=2.24RKLSCP metric unit.
A=average soil loss +/a tons/acre.A=average soil loss +/a tons/acre.
R=rainfall erosivity index.R=rainfall erosivity index.
k=soil erodibity index.k=soil erodibity index.
L=slope length factorL=slope length factor
S=slope gradient factor.S=slope gradient factor.
C=cropping management factor.C=cropping management factor.
P=conservation particle factor.P=conservation particle factor.
Ls= topographic factor evaluated.Ls= topographic factor evaluated.

25. Personal managementPersonal management
soil loss under standard management .This variessoil loss under standard management .This varies
normally from 0-1.normally from 0-1.
P:values depends on law and slope it also depends onP:values depends on law and slope it also depends on
the type of farming system we have.the type of farming system we have.
Example A:Determine soil loss from the followingExample A:Determine soil loss from the following
condition.condition.
K=0.1 ton/acreK=0.1 ton/acre
S=10%S=10%
L=400L=400
C=0.15C=0.15
Field is to be confouredField is to be confoured
p=0.6p=0.6

26. A= RKLSCP.A= RKLSCP.
=0.1=0.1 ×× 400 x 0.1 x 0.18 x 0.6 x R400 x 0.1 x 0.18 x 0.6 x R
B=Also determine soil loss from the following condition.B=Also determine soil loss from the following condition.
K=0.1 ton/acreK=0.1 ton/acre
L=400L=400
S=80%S=80%
C=0.18C=0.18
P=0.6P=0.6
if the soil loss is 6.7 ton/acre what is the max slope lengthif the soil loss is 6.7 ton/acre what is the max slope length
and corresponding tar ale spacing to reduce soil loss toand corresponding tar ale spacing to reduce soil loss to
3 tons/acre .3 tons/acre .

27. we want max Ls value to reduce soil lose to 3 tons/acre.we want max Ls value to reduce soil lose to 3 tons/acre.
Ls=2x 3/67 =0.9Ls=2x 3/67 =0.9
Therefore =70’Therefore =70’ max slope lengthmax slope length
V.IV.I /70 = 8/100/70 = 8/100 ⇒⇒ V.I = 5.6’V.I = 5.6’
practical application of using universal soil losspractical application of using universal soil loss
equation.equation.
1.1. To predict erosion.To predict erosion.
2.2. To select crop management practices.To select crop management practices.
3.3. To predict erosion from catch crops.To predict erosion from catch crops.

28. Land useLand use
 Very suitableVery suitable →→ land classification.land classification.
 Fairly suitableFairly suitable →→ according to suitability factor.according to suitability factor.
 Not suitableNot suitable →→ a particular crop.a particular crop.
Land capability classification.Land capability classification.
 The type of soil.The type of soil.
 Depth of soil.Depth of soil.
 Texture.Texture.
 Land slope.Land slope.
 Past erosion on the land.Past erosion on the land.

29. Soil erosion by windSoil erosion by wind
Wind erosion is more frequent when the mean annualWind erosion is more frequent when the mean annual
rainfall is low.rainfall is low.
Major factor that affects soil erosion by wind are:Major factor that affects soil erosion by wind are:
1.1. climateclimate
2.2. Soil characteristicsSoil characteristics
3.3. VegetationVegetation
climateclimate::
 Rainfall affects soil moisture.Rainfall affects soil moisture.
 Temperature humidity.Temperature humidity.
 Wind.Wind.

30. Wind characteristics that affects soilWind characteristics that affects soil
erosion.erosion.
 Duration.Duration.
 Turbulent of the wind (velocity).Turbulent of the wind (velocity).
For any given soil condition the amount the amount ofFor any given soil condition the amount the amount of
soil which will be blown depends on two factors:soil which will be blown depends on two factors:
 The wind velocity.The wind velocity.
 The roughness of the soil surface.The roughness of the soil surface.
Soil:Soil:
factorsfactors  soil texture.soil texture.
 density of soil particle and density of soildensity of soil particle and density of soil
mass.mass.
 organic matter content.organic matter content.
 soil moisture.soil moisture.

31. Vegetation:Vegetation:
 height of vegetation.height of vegetation.
 density of cover.density of cover.
 types of vegetation.types of vegetation.
 seasonal distribution of vegetation.seasonal distribution of vegetation.
Types of soil movement by windTypes of soil movement by wind
1.1. Suspension.Suspension.
2.2. Saltation.Saltation.
3.3. Surface. creepSurface. creep

32. These three distinct types of movement usuallyThese three distinct types of movement usually
simultaneously.simultaneously.
suspensionsuspension →→ particle were carried about 1m aboveparticle were carried about 1m above
on the surface.( i.e. above 3ft)on the surface.( i.e. above 3ft)
saltationsaltation →→ This is caused by the pressure of theThis is caused by the pressure of the
wind on the soil particle and its collision with otherwind on the soil particle and its collision with other
particles.particles.
surface creepsurface creep →→ This movement is mostlyThis movement is mostly
pronounced on the surface of the soil.pronounced on the surface of the soil.

33. Mechanics of wind erosionMechanics of wind erosion
wind erosion process may also be broken into the threewind erosion process may also be broken into the three
simple but distinct phases:simple but distinct phases:
1.1. Initiation of movement.Initiation of movement.
2.2. Transportation.Transportation.
3.3. Deposition.Deposition.
1.1. Initiation of movement.Initiation of movement.
Initiation of movement as a result of turbulence andInitiation of movement as a result of turbulence and
wind velocity.wind velocity.
Fluid threshold velocityFluid threshold velocity→→ The main velocityThe main velocity
required to produce soil movement by direct action ofrequired to produce soil movement by direct action of
wind.wind.

34. Impact threshold velocityImpact threshold velocity →→ the minimum velocitythe minimum velocity
required to initiate movement from the impact of soilrequired to initiate movement from the impact of soil
particle carried in saltation.particle carried in saltation.
2.2.TransportationTransportation →→ the quantity of soil moved isthe quantity of soil moved is
influenced by the particle size gradation of particle, windinfluenced by the particle size gradation of particle, wind
velocity and distance across the erodindg area.velocity and distance across the erodindg area.
The quantity of soil moved varies as the cube ofThe quantity of soil moved varies as the cube of
the excess wind velocity over and above the constantthe excess wind velocity over and above the constant
threshold velocity directly as the square of the particlesthreshold velocity directly as the square of the particles
diameter and increases with the gradation of the soil.diameter and increases with the gradation of the soil.

35. Six shape bulk densitySix shape bulk density
consider them as groups. we use equivalent diameter toconsider them as groups. we use equivalent diameter to
test the level of compa:test the level of compa:
Standard particleStandard particle →→ is any spheres with bulk density ofis any spheres with bulk density of
2.65.this has certain erodibility.2.65.this has certain erodibility.
Soil particleSoil particle →→ this also has a diameter shape andthis also has a diameter shape and
bulk density.bulk density.
Equivalent diameterEquivalent diameter →→ is the diameter of standardis the diameter of standard
particle that has an erodibility which is equal to theparticle that has an erodibility which is equal to the
erodibility of soil particle.erodibility of soil particle.
Ed = bxd/2.65Ed = bxd/2.65 →→ diameter of soil particle.diameter of soil particle.

36. Q x ( V-Vc )Q x ( V-Vc )
Vc=threshold velocity.Vc=threshold velocity.
V=wind velocityV=wind velocity
when V = Vc =no movement.when V = Vc =no movement.
Deposition:Deposition: deposition of sediment occurs when thedeposition of sediment occurs when the
gravitational force is greater then the force holding thegravitational force is greater then the force holding the
particles in the air.particles in the air.
→→ this generally occurs when there is a decrease in windthis generally occurs when there is a decrease in wind
velocity.velocity.

37. SoilSoil physical factorsphysical factors played also a major roll.played also a major roll.
→→ Mechanics of wind.Mechanics of wind.
→→ soil moisture condition.soil moisture condition.
→→ effect of organic matter.effect of organic matter.
i.e. various climate factors.i.e. various climate factors.

38. Control of wind erosion.Control of wind erosion.
Two major types of wind erosion control consist ofTwo major types of wind erosion control consist of
1.1. Those measures that reduce surface windThose measures that reduce surface wind
velocity(vegetation tilling soil after rain)velocity(vegetation tilling soil after rain)
2.2. Those that affect soil characteristics such as:Those that affect soil characteristics such as:
 conservation of moisture and tillage.conservation of moisture and tillage.
 contouring (teracing)contouring (teracing)
generallygenerally →→ vegetative measurevegetative measure
→→ tillage practicestillage practices
→→ mechanical methods.mechanical methods.

39. Damages done by windDamages done by wind
1.1. crop damagecrop damage
 particularly at seeding stageparticularly at seeding stage ..
 expose of land use.expose of land use.
2.2. The change in soil textureThe change in soil texture
3.3. Health.Health.
4.4. Damage to properties (road and building).Damage to properties (road and building).

41. Contouring,stip cropping and tillage.Contouring,stip cropping and tillage.
 One of the base engineering practices in conservationOne of the base engineering practices in conservation
farming is the adjustment of tillage and cropfarming is the adjustment of tillage and crop
management from uphill to downhill to contourmanagement from uphill to downhill to contour
opertions contouring,strip cropping and terracing areopertions contouring,strip cropping and terracing are
important conservation practices for controlling waterimportant conservation practices for controlling water
erosion.erosion. SurfaceSurface
roughness, ridges, depression and related physicalroughness, ridges, depression and related physical
characteristics influenceing depression storage ofcharacteristics influenceing depression storage of
precipitation.precipitation.

42. contouringcontouring
When plow furrows, planter furrows,and cultivationWhen plow furrows, planter furrows,and cultivation
furrows run uphill and downhill then forms naturalfurrows run uphill and downhill then forms natural
channels in which runoff accumulates. As the slope ofchannels in which runoff accumulates. As the slope of
these furrows increases the velocity of the waterthese furrows increases the velocity of the water
movement increases with resulting destructive erosion.movement increases with resulting destructive erosion.
In contouringIn contouring
tillage operations are carried out as nearly as practicalstillage operations are carried out as nearly as practicals
on the contour. a guide line is laid out for eash plowon the contour. a guide line is laid out for eash plow
land and the back furrows or dead furrows are plowedland and the back furrows or dead furrows are plowed
on these lines.on these lines.

43.  Disadvantage: is used alone on steeper slopes orDisadvantage: is used alone on steeper slopes or
under conditions of high rainfall intensity and soilunder conditions of high rainfall intensity and soil
erodibility, these is an increased hazard of gullyingerodibility, these is an increased hazard of gullying
because row breaks may release the stored water.because row breaks may release the stored water.
 Strip cropping: strip cropping consist of a series ofStrip cropping: strip cropping consist of a series of
alternate strips of various types of crops laid out so thatalternate strips of various types of crops laid out so that
all tillage and crop management practices areall tillage and crop management practices are
performed across the slope or on the contour.performed across the slope or on the contour.

44. The three general types of stripThe three general types of strip
cropping are:cropping are:
1.1. Contour strip cropping with layout and tillage heldContour strip cropping with layout and tillage held
closely with the exact contour and with the cropsclosely with the exact contour and with the crops
following a definite rotational sequence.following a definite rotational sequence.
2.2. Field strip cropping with strips of a uniform widthField strip cropping with strips of a uniform width
placed across the general slope.placed across the general slope.
3.3. Buffer strip cropping with strips of some grass orBuffer strip cropping with strips of some grass or
legume crop laid out between contour strips of cropslegume crop laid out between contour strips of crops
in the regular rotations, then may be even or irregularin the regular rotations, then may be even or irregular
in width.in width.

45. when contour strip cropping is combined with contourwhen contour strip cropping is combined with contour
tillage or teuracing, it effectively divides the length oftillage or teuracing, it effectively divides the length of
the slope,checks checks the velocity of runoff,filters outthe slope,checks checks the velocity of runoff,filters out
soil from the runoff water and facilitates absorbtion ofsoil from the runoff water and facilitates absorbtion of
rain.rain.
strip cropping layoutstrip cropping layout
The three general methods of laying out strip croppingThe three general methods of laying out strip cropping
are:are:
1.1. Both edges of the strips on the contourBoth edges of the strips on the contour
2.2. One or more strips of uniform width laid out from a keyOne or more strips of uniform width laid out from a key
or base contour line.or base contour line.
3.3. Alternate uniform width and variable width correction orAlternate uniform width and variable width correction or

46. methods of layout vary with topography and with eachmethods of layout vary with topography and with each
individual’s preference.individual’s preference.
Tillage practicesTillage practices: tillage is the mechanical: tillage is the mechanical
manipulation of the soil to provide soil conditions suitedmanipulation of the soil to provide soil conditions suited
to the growth of crops, the control of weeds and for theto the growth of crops, the control of weeds and for the
maintenance of infiltration capacity and aeration.maintenance of infiltration capacity and aeration.
Indiscriminate tillage, tillage without thought ofIndiscriminate tillage, tillage without thought of
topography , soil climate and crop conditions will leadtopography , soil climate and crop conditions will lead
to soil deterioration through erosion and loss ofto soil deterioration through erosion and loss of
structure.structure.

47. TERRACINGTERRACING
This is a method of erosion control accomplished byThis is a method of erosion control accomplished by
constructing broad chennels across the slope of rollingconstructing broad chennels across the slope of rolling
land.land.
Reasons for constructing teraceReasons for constructing terace
If surface runoff is allowed to flow unimpeded down theIf surface runoff is allowed to flow unimpeded down the
slope of arable land these is a danger that its volumeslope of arable land these is a danger that its volume
or velocity or both may build up to the points where I isor velocity or both may build up to the points where I is
not only carries the soil dislodged by the splash erosionnot only carries the soil dislodged by the splash erosion
but also has a scouring action of its own.but also has a scouring action of its own.
various names given to this techniques are:various names given to this techniques are:
 terraces (U.S.A).terraces (U.S.A).
 ridge or bund (common wealth countries).ridge or bund (common wealth countries).

48. functionsfunctions
 To decrease the length of the hillside slope , therebyTo decrease the length of the hillside slope , thereby
reducing sheet and rill erosion.reducing sheet and rill erosion.
 Preventing formation of gullies and retaining runoff inPreventing formation of gullies and retaining runoff in
areas of inadequate precipitation.areas of inadequate precipitation.
 In dry regions such conservation of moisture isIn dry regions such conservation of moisture is
important in the control of wind erosionimportant in the control of wind erosion
Types of terraces ( terrace classification)Types of terraces ( terrace classification)
a . two major types of terraces are:a . two major types of terraces are:
1.bench terrace .1.bench terrace .
2.broad base terrace.2.broad base terrace.

49.  Bench terraceBench terrace→→ reduces land slopereduces land slope
 Broad base terraceBroad base terrace →→ removes or retain water onremoves or retain water on
sloping land.sloping land.
broad base terracebroad base terrace →→ has its primary functionshas its primary functions
classified as:classified as:
 gradedgraded
 level.level.
graded terracegraded terrace →→ primary purpose of thus type is toprimary purpose of thus type is to
remove excess water in such a way as to minimizeremove excess water in such a way as to minimize
erosion.erosion.
level terracelevel terrace →→ primary purpose of thus type of terraceprimary purpose of thus type of terrace
is moisture conservation erosion control is a secondaryis moisture conservation erosion control is a secondary
objective.objective.

50. soil profile .soil profile .the embankment for thus type of terrace isthe embankment for thus type of terrace is
usually constructed of soil of soil taken from both sidesusually constructed of soil of soil taken from both sides
of the ridge. This is necessary to obtain a sufficientlyof the ridge. This is necessary to obtain a sufficiently
high embankment to prevent over topping and breakinghigh embankment to prevent over topping and breaking
through by the entrapped runoff water.through by the entrapped runoff water.
TERRACE DESIGNTERRACE DESIGN
The design of terrace system involves the properThe design of terrace system involves the proper
spacing and location of terraces, the design of channelspacing and location of terraces, the design of channel
with adequate capacity and development of a farmablewith adequate capacity and development of a farmable
x-section.x-section.

51. Terrace spacingTerrace spacing
spacing is expressed as the vertical distance betweenspacing is expressed as the vertical distance between
the channels of successive terraces. The verticalthe channels of successive terraces. The vertical
distace is commonly known as the V.I .distace is commonly known as the V.I .
V.I = as + b = V.I =0.3( as + b)V.I = as + b = V.I =0.3( as + b)
a = constant for geographical location.a = constant for geographical location.
b = constant for soil erodibility.b = constant for soil erodibility.
s = average land slope above the terrace in %s = average land slope above the terrace in %

52. Terrace gradesTerrace grades
 Terrace grades :Terrace grades : refers back apart from the fact that itrefers back apart from the fact that it
must provide good drainage ,it must also removemust provide good drainage ,it must also remove
runoff at non erosive velocity.runoff at non erosive velocity.
 Terrance length:Terrance length: size and slope of the field outletsize and slope of the field outlet
possibilities, rate of runoff as affected by rainfall andpossibilities, rate of runoff as affected by rainfall and
soil in filtration and chemical capacity are factors thatsoil in filtration and chemical capacity are factors that
influence terrace length.influence terrace length.

53. Planning the terrace systemPlanning the terrace system
 a.a. selection of outletsselection of outlets: or disposal area:: or disposal area:
 vegetated outlets ( preferable)vegetated outlets ( preferable)
The design runoff for the outlet is determined byThe design runoff for the outlet is determined by
summation of the runoff from individual terrace. outletssummation of the runoff from individual terrace. outlets
are of many types such as :are of many types such as :
 natural draws.natural draws.
 constructed channels.constructed channels.
 sod flumes.sod flumes.
 permanent pasture or meadow.permanent pasture or meadow.
 road ditches.road ditches.

54.  b.b. Terrace locationTerrace location : factors that influence terrace: factors that influence terrace
location includes; land slope, soil conditionslocation includes; land slope, soil conditions..
 Lay out procedure :Lay out procedure :
 determine the predominant slope above thedetermine the predominant slope above the
terrace.terrace.
 obtain a suitable vertical interval.obtain a suitable vertical interval.
 stakes the Wight channel isstakes the Wight channel is
terrace construction :terrace construction : a variety of equipment isa variety of equipment is
available for terrace construction which necessitated aavailable for terrace construction which necessitated a
classification of four machine according to thuds ofclassification of four machine according to thuds of
moving soil.moving soil.

55.  EquipmentEquipment
 soil moisturesoil moisture
 crop and crop residuescrop and crop residues
 degree and regularity of landdegree and regularity of land
 soil tilthsoil tilth
 gullies and other obstructiongullies and other obstruction
 terrace lengthterrace length
 terrace cross-sectionterrace cross-section
 experience and skill of operatorexperience and skill of operator
Factors affecting rate ofFactors affecting rate of
constructionconstruction