Irrigation Engineering

👉 Garret's diagram is used to design channels. 

👉Garret's diagram is a graphical representation to obtain canal design parameters based on

• Kennedy's Theory
• Kutter's formula 

👉 Lacey's Silt Theory 

Lacey's design is based on stable channels in alluvium and he assumed some bed load and suspended load.

Lacey stated that a channel may not be in regime condition even if it is flowing with non-scouring and non-silting velocity. Therefore, he distinguished three regime conditions as follows :

1. True Regime

2. Initial Regime

3. Final Regime

👉 True Regime: A channel is said to be in regime condition if it is transporting water and sediment in equilibrium such that there is neither silting nor scouring of the channel.  But according to Lacey, the channel should satisfy the following conditions to be in regime condition.

Canal discharge should be constant.

The channel should flow through incoherent alluvium soil, which can be scoured as easily as it can be deposited and this sediment should be of the same grade as is transported.

Silt grade should be constant.

Silt charge, which is the minimum transported load should be constant

👉Initial Regime: 

• Channel is said to be in initial regime condition when only the bed slope of channel gets affected by silting and scouring and other parameters are independent even in non-silting and non-scouring velocity condition. 
• It may be due to the absence of incoherent alluvium. 
• According to Lacey’s, regime theory is not applicable to initial regime condition.   

👉 Final Regime: 

• If the channel parameters such as sides, bed slope, depth etc. are changing according to the flow rate and silt grade then it is said to be in final regime condition. 
• The channel shape may vary according to silt grade 

Design Steps:

Step1: Compute Lacey Silt Factor (f)

             
   d = average size of particle in mm

Step 2: Compute Velocity (V)

              
  Here V = Velocity of flow in m/sec

            Q = Discharge in m3/sec

             f = Lacey's silt factor

Step 3: Compute Area of the Channel by using

                                    Q = A.V

Step 4: Compute wetted perimeter (P) of the channel

           

Here, P is the wetted perimeter in m

          Q is the discharge in m3/sec       

Step 5: Compute Hydraulic radius (R)

               

          Here R is the hydraulic radius in m

                   V is the velocity in m/sec

                   f is the silt factor

Step 6: Compute Bed slope (S) by Lacey theory as

           

Note: Lacey Regime Scour depth (R) can be computed as

            

👉 Drawback of Lacey Silt Theory:

• Lacey did not explain the properties that govern the alluvial channel.
• In general, flow is different at bed and sides of the channel which requires two different silt factors but Lacey derived only one silt factor.
• The semi-elliptical shape proposed by Lacey as the ideal shape of the channel is not convincing.
• Lacey did not consider the silt concentration in his equations.
• Attrition of silt particles is ignored by Lacey.
• Lacey did not give proper definitions for the silt grade and silt charge.

    

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Building Material (Concrete)

 👉 Classification of Concrete

 (a) Based on Bulk density

     Extra light weight ⟶ < 500 kg/m3

     Light weight ⟶ 500 - 1800 kg/m3

     Dense weight ⟶ 1800-2500 kg/m3

    Super heavy weight ⟶ > 2500 kg/m3

(b) Based on Strength

   Low strength concrete ⟶ < 20 N/mm2

   Medium strength concrete ⟶ 20-40 N/mm2

   High strength concrete ⟶ > 40 N/mm2

👉 Curing Temperature of Concrete : 5 to 28 degree centigrade

👉Maturity of Concrete   

• The strength of concrete depends on both period of curing (i.e age) and temperature during curing.
• Maturity of Concrete = (Period x temperature)
• It is measured in °C hours or °C days.
• The maturity of concrete is defined as the summation of product time and temperature.
• Maturity = Σ (time x temperature)

👉Strength of Concrete 

(a) Compressive Strength Test

• Test Specimen : 150 x 150 x 150 mm cubes 

                                  : Cylinder of 150 mm diameter and 300 mm height

• Test specimens are stored at a temperature of 27 ± 3 °C at 90 % humidity for 24 ± 1/2 hour from the time of addition of water to the dry ingredients.
• 7 days strength of concrete should be at least 2/3 of 28 day strength of concrete.
• Average of the three values is taken as the compressive strength of concrete, provided the individual variation is not more than ± 15 % of the average.
• Cube Strength = 1.25 x cylinder strength

(b) Flexural Tensile Strength Test ( Modulus of Rupture Test)

• Direct measurement of tensile strength is difficult.
• Indirect test for assessing the tensile strength of concrete.
• Concrete is filled in the mould size 150 x 150 x 700 mm

Modulus of Rupture = p.l / bd2  when a > 200 mm

                                = 3pa / bd2   when 200 mm > a > 170 mm

Here,

    a = distance between the line of fracture and the nearest support, measured on the centre line of the tensile side of the specimen (cm)

b and d is measured width and depth of specimen respectively

l = length of the span on which the specimen is supported (cm)

p = maximum load applied to the specimen

(c) Split Tensile Strength Test

• Standard test cylinder of concrete specimen of 300 mm x 150 mm diameter is placed horizontally between the loading surfaces of compression testing machine

 

                   Split Tensile Strength (σ ) = 2P / πDL

Where, P = Applied load

            D = Diameter of the cylinder

            L = Length of the cylinder

👉 Cube Strength > Cylinder Strength > Modulus of Rupture > Split Tensile Strength

👉 Generally tensile strength of concrete is 10 % of its compressive strength

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Fluid Mechanics

 Do You Know?

👉          Device                               Measurement

            Venturimeter                           rate of flow

             Flow nozzle                           rate of flow

             Orifice meter                          rate of flow

             Bend meter                             rate of flow

             Rotameter                               rate of flow

               Pitot tube                               Velocity of flow

         Hot wire anemometer                 Air & Gas velocity

         Current meter                             Velocity in open channel

👉Classification of Jump

Hydraulic Jump (HJ):  Hydraulic jump is an example of steady rapidly varied flow(RVF)

Hydraulic jump occurs when a supercritical stream meets a Subcritical stream of sufficient depth.

👉Classification of jump 

     Type                     Initial Froude Number (F1)                 EL/E1 (%)

Undular Jump                           1-1.7                                               0

Weak Jump                             1.7-2.5                                            5 -18

Oscillating jump                     2.5-4.5                                            18-45

Steady jump                              4.5-9                                             45-70

Strong Choppy                          > 9.0                                               > 70

Engineering Hydrology

 Do you Know?

👉Evaporation Measurement

(a) Using Evaporimeter Data

(b) Empirical Evaporation Equation

(c) Analytical Methods

👉Types of Evaporimeter

(a) Class A Evaporation Pan (US Weather Bureau)

(b) ISI Standard Pan (Used in India)

(c) Colorado Sunken Pan 

(d) US Geological Survey Floating Pan

👉     Lake Evaporation = Pan coefficient x pan evaporation

👉          Types of Pan                   Average value               Range

            Class A Land Pan                    0.70                           0.60-0.80

        ISI Pan (Modified Class A)         0.80                           0.64-1.10

        Colorado Sunken Pan                  0.78                           0.75-0.86

        US GS Floating Pan                     0.80                          0.70-0.82

👉Empirical Formulae

Empirical formulae are based on Dalton's Law.

(a) Meyer's Formula

👉Analytical Methods

(a) Water-Budget method

(b) Energy-balance method

(c) Mass-transfer method

👉Measurements of Actual Evapotranspiration

(a) Phytometer (Measures only transpiration)

(b) Lysimeter 

(c) Field experimental plots

👉Estimation of Potential Evapotranspiration 

(a) Penman's Equation

Based on combination of the energy-balance and mass-transfer approaches.

(b) Blanney-Criddle Formula

👉Measurement of Infiltration

(a) Flooding type infiltrometer

(b) Rainfall simulator

👉Empirical Infiltration Equations

(a) Green-Ampt method

(b) Horton Infiltration Equation

(c) Huggins-Monka Equation

(d) Soil Conservation Service Practice

(e) Antecedent Precipitation Method

👉Horton's Equation

  

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Building Material

 👉Classification of Tree

(a) Exogenous                               (b) Endogenous

⟶ Conifers (Soft Food) and Deciduous (Hard wood) are the types of Exogenous tree

👉Endogenous Tree 

• Trees grow inwards
• Example: Bamboo, Cane, Palm

👉Exogenous Tree 

• Trees grow outwards
• annual rings are used for predicting age of the tree

👉 Conifers (Evergreen trees)    

• Trees yield softwood
• Distinct annual rings

👉Deciduous or Broad leaf trees    

• Do not show distinct annual rings
• Trees yield hard wood
• Example: Teak, Mahogany, Sheesham, Oak, Sal, Babool

👉 Difference between Softwood and Hardwood 

                                         Softwood                             Hardwood

Colour :                              Lighter                                  Darker

Growth:                              Faster                                    Slower

Weight:                              Lighter                                  Heavier

Density:                             Low                                       High

Annual rings:                     Distinct                                 Indistinct

Strength:                      Strong along the grains               Strong along and across the grains

Conversion:                         Easy                                     Difficult

Fire resistance:                    Poor                                     Moderate             

👉Detailed Cross sectional view of the trunk of an exogenous tree

(a) Pith

• Innermost central portion or core of the tree called Pith or Medulla
• As the plant becomes old, the pith dies up and decays.

(b) Heartwood (Truewood)

• Inner annual rings surrounding the pith consistute the heartwood
• Dark in colour
• It indicates dead portion of tree

(c) Sap Wood (Alburnum or Xylem)

• Outer annual rings between heart wood and cambium layer in the sap wood
• It is usually light in colour and weight. It contains sap

(d) Cambium Layer

• Cambium is very thin layer of tissue between sapwood and inner bark

(e) Inner Bark (Phloem)

• It gives protection to the cambium layer from any injury
• Phloem transports food from leaves to the roots

(f) Outer Bark (Cortex)

• Outermost protective layer
• Consist of cells of wood fibre

(g) Medullary Ray

• Thin radial fibres extending from pith to cambium layer are known as medullary rays
• Function of these rays is to hold the annual rings tightly together

Engineering Hydrology

👉 Do You Know

• Tensiometer is used to measure capillary potential
• Phytometer measures Transpiration
• Lysimeter measures Evaporation
• Infiltrometer measures Infiltration
• Speed of wind is measured using Anemometer.
• Average annual rainfall over whole of India is 119 cm.

👉Measurement of Precipitation

• Rain Gauges
• Pluviometer
• Ombrometer
• Hyetometer

👉 Types of Gauges

• Non-Recording Gauges

(a) The Non-Recording gauge used in India as SYMONS Raingauge

• Recording Gauges

(a) Tipping Bucket Type

(b) Weighing Bucket Type

(c) Natural Syphon Type

⟶ The record from Tipping bucket gives data on the intensity of rainfall

⟶Weighing bucket gives the idea of mass curve of rainfall (Plot of the accumulated rainfall against the elapsed time)

⟶In India Natural Syphon Type is adopted as Recording Rain Gauge.(This type of gauge gives a plot of the mass curve of rainfall) 

👉Inconsistency of Records

Some of the common cause of inconsistency of the records are:

• Shifting of raingauge station to a new location
• Neighborhood of the station undergoing a marked change
• Replacement of old instrument by new one
• Method of observation 

👉Inconsistency of record is corrected by using DOUBLE MASS CURVE technique. 

👉To convert the point rainfall values at various stations into an average value over catchment, several methods are available

(a) Arithmetical mean method

(b) Theissen- polygon method

(c) Isohyetal method

👉Accuracy: Isohyetal method > Theissen-polygon method > Arithmetical mean method

👉Frequency of Point Rainfall

The purpose of the frequency analysis of an annual series is to obtain a relation between the magnitude of the event and its probability of exceedence (P)

If the annual extreme series is arranged in descending order of magnitude and each position given a number 1 to N, 1 being given to Ist i.e largest value and N given to last value or least value. Then probability P of a rainfall at position m being equaled or exceeded is given by :

                             Method                                            Probability (P) 

                       

                             Weibull                                                 m/(N+1)

                             

                             California                                                m/N

                              Hazen                                                     (m - 0.5)/N

                              Blom                                                    (m-0.44)/(N+0.12)

👉 Probable Maximum Precipitation(PMP)

The probable maximum precipitation (PMP) is defined as the greatest or extreme rainfall of a given duration that is physically possible over a basin.

                    PMP =  Mean annual rainfall + k. σ

                        σ = standard deviation of series

                        k = Frequency factor

👉Isopleth

A line drawn on the map along which the value of a particular property is uniform .

             Name                              Isopleth of (i.e line joining places of equal) 

             ISOBAR                                              Pressure

            ISOBATH                                         Depth in sea

         

            ISOCHRONE                     Travel time from a common centre

            ISOHALINE                                      Salinity

            ISOHELS                                           Sunshine

 

           ISOHYETS                                         Rainfall

            ISONIF                                          Snow fall amount

            ISOTHERM                                     Temperature

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Concrete Technology

👉 Typical phase composition levels in ordinary Portland cement (OPC)

               C3S/Alite/Tricalcium Silicate  ⟶  45-60%

               C2S/Belite/Dicalcium Silicate  ⟶ 15-30%

                C3A/ Tricalcium Aluminate     ⟶ 6-12%

                C4AF/Tetra Calcium Aluminoferrite  ⟶ 6-8%

👉 The crystal structure of different phases are:

            C3S/Alite/Tricalcium Silicate   ⟶ Irregular Structure, Several polymorphs

            C2S/Belite/Dicalcium Silicate  ⟶ Rounded Structures, Several polymorphs

             C3A/ Tricalcium Aluminate     ⟶ Cubic in pure form

             C4AF/Tetra Calcium Aluminoferrite  ⟶ Series of solid solution

👉The temperature at which the reaction occur to form to different phases of cement:

           Formation of C3S  ⟶ > 1250 °C

           Formation of C2S  ⟶  900 - 1200 °C

            Formation of C3A  ⟶ Cooling Stage

           Formation of C4AF  ⟶ Cooling Stage

👉 Lime saturation factor (LSF) is particularly important because it indicates the amount of free lime. (Too much free lime can cause Unsoundness of the cement).

                                             LSF = C/ (2.8S + 1.2 A + 0.65 F)

                         C, S, A and F are the % amounts of CaO, SiO2, Al2O3 and Fe2O3

       The range of LSF in between 92 - 98 %

👉C3S/Alite/Tricalcium Silicate

• Responsible for early strength development
• High reactive due to irregular structure, high heat of hydration

👉C2S/Belite/Dicalcium Silicate

• Less irregular structure than C3S ⟶Less reactivity
• Later strength

Environmental Engineering

 👉Conventional Water Treatment

1. Screening (for the removal of large floating and suspended materials).

•  Mostly used at intake site

2.Aeration (for the oxidation of iron and manganese, removal of dissolved gasses and VOCs).

• Optional unit, and may not be provided if target impurities are not present in water

3. Sedimentation (for the removal of suspended sediments of specific gravity >1).

• Plain (or primary) sedimentation may not be provided, as in most cases, settling units are provided after coagulation and flocculation for chemical assisted settling.
• In many conventional water treatment systems settling unit is combined with flocculation unit, named as clariflocculator.

4. Coagulation and Flocculation

Successive steps intended to overcome the forces stabilizing the fine suspended or colloidal particles, allowing particle collision and growth of floc.

• Destabilization (or Coagulation)

Reduce the forces acting to keep the particles apart after they contact each other (i.e., lower repulsion forces).

Chemical Addition, Rapid Mixing, “Pin‐point” Floc Formation

• Flocculation

Process of bringing destabilized colloidal particles together to allow them to aggregate to a size where they will settle by gravity.

Slow Mixing, Floc Growth, Increased Diameter

Particles in Water

• Dissolved Solids: < 1 nm (10‐6 mm) in size

Electrically charged and can interact with the water, so they are completely stable and will never settle out of the water. Not visible even with microscope.

• Colloidal solids or Non‐settleable solids: 1‐1000 nm in size

Do not dissolve in water although they are electrically charged. Still, the particles are so small that they will not settle in water and cannot be removed by filtration alone. Can be seen only with a high‐powered microscope.

•  Suspended or settleable solids: > 1000 nm (10‐3 mm) in size

Larger particle that can be seen through eyes. These are usually supported by buoyant and viscous forces in water and may settle (or float) in non‐flowing water. Also, these can be removed by simple filtration.

Coagulation and Flocculation Steps

Selection of Suitable Coagulant

                         ↓

Finding Optimum Dose of Coagulant

                         ↓

Addition of Coagulant and rapid mixing

                         ↓

Allowing floc formation through slow mixing

                         ↓

Separation of flocs from water through settling/flotation/filtration

Selection of Coagulant

Required Basic Characteristics:

Nontoxic at the working dosage; High charge density; Insoluble in the neutral pH range

Aluminum and iron salts are the most commonly used coagulants in water treatment:

Aluminium coagulants include:                           Iron coagulants include:

Aluminium sulfate (Alum)                                            Ferric sulfate

Aluminium chloride                                                     Ferrous sulfate

Sodium aluminate                                                         Ferric chloride

Polyaluminum Chloride (PAC)                                Ferric chloride sulfate

Other coagulants:

Organic coagulants, polyelectrolytes, hydrated lime, magnesium carbonate and various polymers etc.

Organic Coagulants vs Inorganic Coagulants

Organic coagulants

Generally used for solids & liquids separation and sludge generation. Polyamines function by charge neutralization alone, and are effective at treating higher turbidity raw water and wastewater. Melamine Formaldehydes and Tannins coagulate the colloidal material in the water, as well as absorb organic materials such as oil and grease. These are particularly well suited to operations that generate hazardous sludge.

Inorganic coagulants

These are mostly Al or Fe based, and are both cost‐effective and applicable for a broad variety of water and wastewater. Inorganic coagulants are particularly effective on raw water with low turbidity and will often treat this type of water when organic coagulants cannot.

Advantages of alum are that it readily dissolves with water, and does not cause the unsightly reddish brown staining of floors, walls and equipment like ferric sulphate. However, it is effective only at certain pH range, and good flocculation may not be possible with alum in some waters. With ferric sulphate, coagulation is possible at pH values as low as 4.0, and the floc formed is heavier than alum floc, as well as does not redissolve at high pH values.

Coagulant Aids

•  In some waters, even large doses of primary coagulant fails to produce a satisfactory floc. In such cases, the coagulation process is often enhanced through the use of coagulant aids. Coagulant aids also help to create satisfactory coagulation over a broader pH range.
•  Insoluble particulate materials such as clay, sodium silicate, pure precipitated calcium carbonate, diatomite, and activated carbon are common coagulant aids. They are used in waters that have low concentrations of particles (few nucleating sites). Because their density is higher than most floc particles, floc settling velocity is increased by the addition of such coagulant aids.
• Polymeric coagulant aid those help in bridging small floc to agglomerate rapidly into larger and denser floc are also used to reduce the amount of primary coagulant required. These are usually slightly anionic polyacrylamides with very high‐molecular weights. In some studies, non‐ionic or cationic types have also been proven effective. Synthetic organics such as anionic polyelectrolyte, and natural organics such as starch, starch derivatives, proteins, and tannins have been used as coagulant aids.
• The coagulant add dosage must be carefully controlled to avoid lowering the water quality.

Coagulant Doses: Zones of Effectiveness

Zone 1: Low dosage, insufficient coagulant added to produce destabilization.

Zone 2: Dosage sufficient to cause efficient and rapid destabilization

Zone 3: Dosage high enough to cause restabilization (charge reversal or polymer –foldback)

Zone 4: Dosage high enough to get sweep floc which results in good destabilization.

Colloid concentration expressed in terms of surface area S1 < S2 < S3 <S4.

Coagulation Practices based on Colloids and Alkalinity Levels

1. High Colloid, low alkalinity: The strategy here is to add coagulant without worrying about pH. The lower pH is better because destabilizing is by charge neutralization. Generally, there is no concern with overdosing because the colloidal surface area is too large.

2. High colloid concentration, high alkalinity: The choices are to destabilize by adsorption/charge neutralization at neutral pH (a larger dose at higher pH), or add acid to lower pH. Economics dictate choices.

3. Low colloid concentration , high alkalinity: For this case we can either destabilize by high dosage to give sweep floc or we can add coagulant aid such as bentonite (aluminium phyllosilicate clay) to get destabilization at lower dosage.

4. Low colloid concentration, low alkalinity: This is the most difficult case and generally requires added alkalinity or collides. Sweep floc is difficult to form as pH drops and it’s easy to overdose at low pH and low colloid concentration.

Coagulant Dose Optimization in Laboratory: Jar Test

In practice, irrespective of what coagulant or coagulant aid is used, the optimum dose are usually

determined by a Jar Test. A typical Jar Test apparatus consists of four to six beakers of 1‐2 L volume, provided with a variable‐speed stirrer.

Procedure: 

Beakers filled with the raw water and varying amounts of coagulant dose are administered. The contents are rapidly mixed for about a minute and then allowed to flocculate at a slower pre‐worked speed (usually 20‐30 rpm) for desired time (usually 15‐30 mins). Thereafter, the contents are allowed to settle for desired time (usually 20‐ 40 mins), and the optimum dose is determined based on the measured turbidity of supernatant water (alternatively, judgement may be made based on visual inspection).

Jar test may be used to optimize:

• pH
• Mixing Speed for Flocculation
• Flocculation time

Importance of Optimum Coagulant Dosing Coagulant over‐dosing may leads to

o Increased treatment costs

o Restabilization of colloids

o Increases sludge mass

o Public health concerns

Coagulant under‐dosing may leads

o Lesser degree of removal

o Failure to meet the water quality targets

Traffic Engineering

 Do You Know?

👉Various methods of carrying out Speed and Delay study

   (a) FLOATING CAR or RIDING CHECK METHOD

   (b) LICENSE PLATE or VEHICLE NUMBER METHOD

   (c) INTERVIEW TECHNIQUE

   (d) ELEVATED OBSERVATIONS

   (e) PHOTOGRAPHIC TECHNIQUE

👉Origin and Destination Studies (O & D Data)

Origin and destination studies of vehicles determines their numbers, origin and destination in the concerned zone of study.

👉 Methods of collection of O & D Data)

(a) ROAD SISE INTERVIEW METHOD

(b) LICENSE PLATE METHOD

(c) RETURN POST CARD METHOD

(d) TAG ON CAR METHOD

(e) HOME INTERVIEW METHOD

(f) WORK SPOT INTERVIEW METHOD

👉Representation of O & D Data

(a) O & D Table

(b) Desire Lines

(c) Pie Chart

(d) Contour Lines

Note: Desire lines are straight lines connecting the origin points with destinations.

👉 Accident Studies

Accident studies are used to find out the reason and cause behind accident and to take preventive measures in term of design control.

The various records that are maintained in accident studies are:

(a) Location Files

(b) Spot Maps

(c) Condition Diagram

(d) Collision Diagram