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Types of Flow

               Types of flow

Fluid flows are classified as:

  1. Steady and unsteady flow
  2. Uniform and non-uniform flow
  3. Laminar and turbulent flow
  4. Compressible and incompressible flow
  5. Rotational and irrotational flow
  6. Ideal and real flow
  7. One, two and three-dimensional flow

               Steady and unsteady flow

Steady flow is that type of flow in which fluid parameters (velocity, pressure, density etc.) at any point in the flow field do not change with time. This means that the fluid particles passing through a fixed point have the same flow parameters like velocity, pressure, surface tension etc. The parameters may be different at the different cross-section of the flow passage.

Mathematically, a steady flow is defined as


Unsteady flow is that type of flow in which fluid parameters (velocity, pressure, density etc.) at a point changes with time.

Mathematically, an unsteady flow is defined as


             Uniform and Non-uniform flow

Uniform flow is defined as that type of flow in which the velocity of flow of a fluid at any instant does not change with respect to space. In other words, it is the flow in which the velocity of flow remains constant throughout the flow field at any given time.


Mathematically, for uniform flow


where     ∂ Ʋ = change in velocity

                ∂ s = length of flow in a direction, s.

Non-uniform flow is defined as that type of flow in which the velocity of flow changes with respect to space at any given time.

In other words, it is the flow in which the velocity of flow is different for a different section in the path of flow.                                 


Mathematically, for non-uniform flow


              Laminar and Turbulent flow

Laminar flow is defined as that type of flow in which each fluid particle has a definite path and paths of individual particles do not cross each other.


Laminar flow is also called streamline or viscous flow. This type of flow occurs in smooth pipes having the low velocity of flow. It also occurs in liquids having high viscosity.

 Turbulent flow is defined as that type of flow in which each fluid particle does not have a definite path and the paths of individual particles cross each other.

In other words, it is the flow in which fluid particles move in a zigzag path.                      


When a fluid is flowing in a pipe, the type of flow is determined by a non-dimensional number, called Reynold’s number.

For laminar flow, Reynold number  ˂  2000

For turbulent flow, Reynold number  ˃ 4000

             Compressible and Incompressible flow

The flow in which the density of fluid changes, due to pressure and temperature variations, from point to point during the flow is called compressible flow.

In other words, it is the flow in which the density of a fluid is not constant during the flow.

Mathematically, for compressible flow

              P ≠  constant

The flow in which the density of fluid does not change during the flow is called incompressible flow.

In other words, it is the flow in which the density of a fluid is constant during the flow.

Mathematically, for incompressible flow

              P =  constant

Liquids are generally incompressible which means that pressure and temperature changes have a very little effect on their volume. Gases are compressible fluids.

           Rotational and Irrotational flow

 Rotational flow is that type of flow in which fluid particles also rotate about their own axes while flowing along a streamline.


 Irrotational flow is that type of flow in which fluid particles do not rotate about their own axes while flowing.             


              Ideal and Real flow

An ideal flow is the flow of a non-viscous fluid. In the ideal flow, no shear stress exists between two adjacent layers or between the fluid layer and boundary, only normal stresses can exist in ideal flows.

The flow of real (viscous) fluids is called real flow. In real flow, shear stress exists between to adjacent fluid layers. These stresses oppose the sliding of one layer over another.

         One, Two and Three-dimensional flow

 One dimensional flow is the flow in which parameters (velocity, pressure, density, viscosity and temperature) vary only in one direction and the flow is a function of only one co-ordinate Axis and time. The flow field is represented by streamlines which are straight and parallel.

Mathematically, for one-dimensional flow


Two-dimensional flow is the flow in which fluid parameters vary along two directions and the flow is the function of two rectangular space coordinates (x and y-axis) and time. The flow field is represented by streamlines which are curves.

Mathematically, for two-dimensional flow


 Three-dimensional flow is the flow in which flow parameters change in all the three directions and the flow is the functions of three mutually perpendicular co-ordinate Axis (x, y, z-axis) and time. The streamlines are space curves.


Mathematically, for three-dimensional flow



Book- Fluid Mechanics(Hydraulics), Writer- A.K. Upadhyay

Classification Of Channels

             Classification of channels

Channels can be classified as:

1.Prismatic channels and non-prismatic channels

2.Natural and Artificial channels

3.Rigid boundary and mobile boundary channel

                    Prismatic channel

A channel is said to be prismatic channel if the cross-section and bed slope does not change along the length of the channel.

Example: A laboratory flume laid at a constant bed slope and uniform cross-section.

               Non-Prismatic channel


A channel is said to be non-prismatic channel if there is a change in cross-section and bed slope along the length of the channel.

Example: A river with varying cross-section and bed slope.

                      Natural channel

Rivers and streams are natural channels. Natural channels have the irregular cross-section. So it is difficult to define the flow depth for natural channels.

                    Artificial channel

Human-made channels are called artificial channels. Irrigation Canals, sewage pipes, aqueducts etc. are examples of artificial channels. Artificial channels have regular cross-sections like triangular, trapezoidal, rectangular, circular etc.

               Rigid Boundary channel

A channel is said to be a rigid boundary channel if the material on the bed and sides of a channel is not easily movable.

Example: concrete lined canal, a metal flume.

             Mobile Boundary  channel

A channel is said to be a mobile boundary channel if the material on the bed and sides of a channel is loose and easily movable due to the flow of water. Analysis of mobile boundary channel is more complicated due to sediment erosion, deposition and resulting in additional resistance to flow.


Book- Fluid Mechanics(Hydraulics), Writer- A.K. Upadhyay

Road pavements- Flexible, Rigid, & Semi-rigid pavement

                    Road pavement

The part of the road which is finished with a hard smooth surface is known as a pavement. It helps in making them durable and able to withstand traffic.

                Types of road pavement

                (a) Flexible pavements


The pavements which have a very low flexural strength and are flexible in their structural behaviour under the wheel loads are called flexible pavements. Because of the low flexural strength, the pavement deforms if the sub-grade deforms, in flexible pavments the vertical load of traffic is transmitted to the lower layers by grain to grain transfer. A well compacted granular structure forms a good flexible pavement layer.

The load transferring ability of the flexible pavement depends on the type of material and thickness of payment. The pavement thickness is so designed that the stress on the sub-grade soil is kept within its bearing capacity and the sub-grade is prevented from excessive deformations. In flexible pavement the sub-grade plays an important role as it carries the vehicle load transmitted through the pavement. The strength and smoothness of the pavement depend to a great extent on the deformation suffered by the sub-grade.

All bituminous pavements, Water Bound Macadam (W.B.M), gravel pavements etc., are the example of flexible pavements.

                (b) Rigid pavements


Rigid pavements are those which possess a considerable flexural strength of flexural rigidity.

A Rijid payment derives its capacity to withstand loads from flexural strength. The rigid pavement has the slab action and is capable of transmitting the loads to a wider area. The Rigid pavment does not get deformed to the shape of the lower surface as it can bridge the minor variations of the lower layer.

Cement concrete pavement is the best example of the Rigid pavement.

                (c)  Semi-rigid pavement

Semi-rigid pavements represent an intermediate state between the Flexible and the Rigid pavement. The flexural strength of such type of pavment is much lower than the concrete slab, but it derives support by the lateral distribution of loads through the pavement depth as in flexible pavement.

Lean cement concrete, soil cement and lime-puzzolanic concrete construction are examples of semi-rigid pavements.


Book- Highway Engineering, Writer- A.K. Upadhyay

Weir, Barrage, Dam

                WEIR, BARRAGE AND DAM
An impervious barrier which is constructed across a river to raise the water level on the upstream side is known as Weir. Here the water level is raised up to the required height and the surplus water is allowed to flow over the Weir. Generally, it is constructed across an inundation river.
When adjustable gates are installed over a weir to maintain the water surface at different levels at different times, then it is known as Barrage. The water level is adjusted by operating the adjustable gates or shutters. The gates are placed at different tiers and these are operated by cables from the cabin. The gates are supported on the piers at both ends. The distance between pier to pier is known as Bay.
The high impervious barrier constructed across a river valley to form a deep storage Reservoir is known as Dam. The surplus water is not allowed to flow over the dam, but it flows through the spillways provided at some designed level.


Book- Irrigation Engineering, Writer- N N Basak

Types of water demand

              Types of water demand

The following are the various types of water demand of a town or city:

              1.Domestic demand


The domestic demand includes the water required in the houses for drinking, cooking, bathing, washing of clothes and utensils, sanitary blocks, private vehicles, gardening, etc. The requirement of water for domestic animals is also included in this demand. In Indian towns or cities,  the domestic consumption of water under normal condition is taken as 135 lits/day/capita  ( as per I.S: 1172- 1971). In developed countries, the water demand is very high due to their advanced lifestyle.

               2.Commercial demand


It includes the water demand in commercial centres like the office building, hotels, restaurants, shopping centres, cinema houses, motor garages, laundries, diaries etc. For this purpose, the demand is assumed as 25 lits to 40 lits. capita/day.

               3.Industrial demand

The industrial demand for water depends on the type of industry in the area. The number and type of industries such as cloth mill, paper mill, cotton mill, sugar mill, chemical industry, hume pipe, rolling mill, etc. should be recorded. The water demand for this purpose is generally assumed as 20% to 25% of the total water demand of the city or town.

                  4.Public demand


It includes the water requirement for public places such as public sanitary blocks, parks, swimming pools, etc. The water demand for this purpose is considered as 5% of the total consumption of water in the town or city.

                  5.Fire demand

In case of any outbreak of fire in busy areas of a town or city, sufficient quantity of water may not be available for fire-fighting from the surface sources such as Pounds, ditches, open wells etc. Again these sources may not exist within busy areas of the town or city. Hence, the requisite amount of water for fire-fighting should always be kept is stored in underground reservoirs in specific places and fire hydrants should be established in main pipelines at an interval of about 100 m to 150 m. In the event of a fire, the fire brigade pump is connected to the Fire hydrant and the jet of water is thrown under high pressure over the fire.


Book-Environmental Engineering, Writer-N N Basak

Historical development of roads in India



The history of the development of road construction is linked with the history of human civilization. The first and oldest mode of travel was footpath with people found the most convenient and the shortest way to approach to their hunting and fishing ground. People use tamed animals for transport which required bridle paths of greater width and heights. After the invention of the wheel, animal-drawn carts continued to be the popular mode of transport for quite a long time. This had necessitated providing hard surfaces for wheeled carts. The first hard surface was discovered in Mesopotamia at about 3500 B.C. A brief review of road development in India is given below.

                 Roads in Ancient India


The excavations of Mohenjodaro and Harappa have established the existence of roads in India at about 3500 B.C. As per the early records,  in early periods the roads were mainly for administrative and military purposes. During Aryan period in 400 B.C., there were “Mahapathas” as a means of communications as referred in Rig Veda ( part 1, para 5). Kautilya the first Prime Minister of Emperor Chandragupta Maurya laid down rules in his book titled  Arthasastra. Rules have been mentioned regarding the depth of roads for various purposes and for different types of traffic. The punishment for obstructing roads have also been mentioned. At the beginning of 5th century, the roads had been improved by Emperor Ashoka.

                 Roads in Mughal Period


The roads were greatly improved in India during the Mughal period. Many of the highway built or maintained by Mughals received great appreciation from the foreign visitors. The road from Delhi to Daulatabad was constructed by Muhammad Tughlaq. The roads from Agra to Allahabad and from Ujjain to Bijapur were constructed by Muslim emperor.

                   Roads in British Period


The period covering the decision the decline of the Mughals and the beginning of the British rule was a period of neglect of the road system. During this period,  the condition of roads deteriorated. The early British interest was only in maintaining roads of military importance. William Bentinck took steps to build the modern Grand Trunk Road from Calcutta to Delhi with permanent bridges and good stones. Lord Dalhousie gave further Momentum to road construction by forming the P.W.D in place the military board in 1885. With the development of Railways, the attention of the government was shifted from road development. The work of road construction and maintenance was given secondary importance. Major Roads,  except those of military importance, were neglected and attention was mainly on the feeder Roads.

                   Appointment of   Jayakar Committee

In 1927, the central government appointed Indian road development committee under the chairmanship of M.R. Jayakar to report on the condition of the existing road and to suggest ways and means for their future development. The Jayakar committee submitted its report on 1928 with the recommendations that since the provincial governments and the local bodies unable to look after all the roads, the road development in the country should be taken up by the central government.


Historical development of roads, Book-Highway Engineering, Writer-A.K. Upadhyay

Transportation, Highway, Waterway, Airway

The term transport is derived from latin word Transportare that is trans over and portare means to carry thus transport means to carry from one place to another. the term transportation idicates a Means or system of convenience and it is thus an act of transporting. 

      It is difficult to imagine those all days when people lived in a distance and could not reach to their relatives easily. The introduction of transport facilities in the modern age has narrowed down the distance between various parts of the country or world.
                         Modes of transport
  1. Land transport 2. Water transport 3. Air transport



What is Hydrology & Hydrologic cycle


 The science of studying the different forms of water available above the earth surface or below the earth surface is known as hydrology. Even Hydrology includes those portion of the  science which deals with the estimation of runoff and its transportation from one place to another.

                            Importance of Hydrology

 The study of Hydrology is useful for the design and operation of engineering projects for the  control and use of water. The knowledge of hydrology is very essential for the applications:

(a). Determination of the capacity of a reservoir from the rainfall records and the yearly discharge  observation of a river.

(b). Determination of peak flow of a river.

(c). Determination of suitable site for hydro-electric power generation.

(d). Sources of water supply in a town or city.

(e). Methods to be adopted for the flood control.

                                  Hydrologic cycle


  The water from the surface sources like lakes, rivers, ocean, etc. converts to vapour by evaporation  due to solar heat. The vapour goes on accumulating continuously in the atmosphere. This vapour is  again condensed due to the sudden fall of temperature  and pressure. Thus clouds are formed.  These clouds again causes the precipitation (i.e Rainfall).Some of the vapour is converted to ice at  the peak of the mountains. The ice again melts in summer and flows as rivers to meat the sea or  ocean. These processes of evaporation, precipitation and melting of ice go on continuously like an  endless chain and thus a balance is maintained in the atmosphere. This phenomenon is known as                  Hydrologic cycle.

                   Component of Hydrologic cycle

     1 . Evaporation

     2 . Transpiration by plant

     3 . Condensation

     4 . Precipitation

     5 . Interception

  1. Infiltration

     7 . Ground water flow

     8 . Surface flow


 Hydrology & Hydrologic cycle – Book Irrigation Engineering,   Writer – N N Basak