Introduction to Water Engineering, Hydrology, and Irrigation

Mohammad Albaji

• Editore: CRC Press
• Anno: 2022
• ISBN:
  9781000595413
• Edizione: 1
• Argomento: Ciencias biológicas
• Categoria: Ciencia medioambiental

This book is designed as an undergraduate text for water and environmental engineering courses and as preliminary reading for postgraduate courses in water and environmental engineering- including introductory coverage of irrigation and drainage, water resources, hydrology, hydraulic structures, and more. The text and exercises have been classroom tested by undergraduate water and environmental engineering students and are augmented by material prepared for extramural short courses. It covers basic concepts of agricultural irrigation and drainage, including planning and design, surface intakes, economics, environmental impacts wetlands, and legal issues.

Features:

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• Numerous illustrations throughout to clarify the concepts presented

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• Examines and compares the advantages and disadvantages of several methods of irrigation practice

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• Explains the integral components including pumps, filters, piping, valves, and more

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• Considers fertilizer application and nutrient management

This comprehensive and well-illustrated book will be of great interest to students, professionals, and researchers involved with all aspects of water engineering, hydrology, and irrigation.

1 Hydraulic engineering

DOI: 10.1201/9781003293507-1

Reading for comprehension

Hydraulic engineering as a sub-discipline of civil engineering is concerned with the flow and conveyance of fluids, principally water and sewage. One feature of these systems is the extensive use of gravity as the motive force to cause the movement of the fluids. This area of civil engineering is intimately related to the design of bridges, dams, channels, canals, and levees, and to both sanitary and environmental engineering.

Hydraulic engineering is the application of fluid mechanics principles to problems dealing with the collection, storage, control, transport, regulation, measurement, and use of water. Before beginning a hydraulic engineering project, one must figure out how much water is involved. A hydraulic engineer is concerned with the transport of sediment by the river, the interaction of the water with its alluvial boundary, and the occurrence of scour and deposition. “The hydraulic engineer actually develops conceptual designs for the various features which interact with water such as spillways and outlet works for dams, culverts for highways, canals and related structures for irrigation projects, and cooling-water facilities for thermal power plants” (Figures 1.1, 1.2, 1.3).

Figure 1.1 Hydraulic flood retention basin (HFRB); (https://en.wikipedia.org/wiki/File:Hydraulic_Flood_Retention_Basin.webp).

Figure 1.2 View from Ahvaz cable bridge, Ahvaz, Iran (By Mohammad Albaji).

Figure 1.3 Riprap lining a lakeshore; (https://en.wikipedia.org/wiki/Riprap).

Fundamental Principles

A few examples of the fundamental principles of hydraulic engineering include fluid mechanics, fluid flow, behavior of real fluids, hydrology, pipelines, open channel hydraulics, mechanics of sediment transport, physical modeling, hydraulic machines, and drainage hydraulics.

Fluid Mechanics

Fundamentals of hydraulic engineering define hydrostatics as the study of fluids at rest. In a fluid at rest, there exists a force, known as pressure, that acts upon the fluid's surroundings. This pressure, measured in N/m², is not constant throughout the body of fluid. Pressure, p, in a given body of fluid, increases with an increase in depth. Where the upward force on a body acts on the base and can be found by equation:

$p=\rho gy$

where

ρ = density of water

g = specific gravity

y = depth of the body of liquid

Rearranging this equation gives you the pressure head p/ρg = y. Five basic devices for pressure measurement are a piezometer, manometer, differential manometer, Bourdon gauge, as well as an inclined manometer.

As Prasuhn states:

On undisturbed submerged bodies, pressure acts along all surfaces of a body in a liquid, causing equal perpendicular forces in the body to act against the pressure of the liquid. This reaction is known as equilibrium. More advanced applications of pressure are those on plane surfaces, curved surfaces, dams, and quadrant gates, just to name a few.

Behavior of Real Fluids

Real and Ideal Fluids

The main difference between an ideal fluid and a real fluid is that for ideal flow p₁ = p₂ and for real flow p₁ > p₂. Ideal fluid is incompressible and has no viscosity. Real fluid has viscosity. Ideal fluid is only an imaginary fluid as all fluids that exist have some viscosity.

Viscous Flow

A viscous fluid will deform continuously under a shear force, whereas an ideal fluid doesn't deform.

Laminar Flow and Turbulence

The various effects of disturbance on a viscous flow are stable, transition, and unstable.

Bernoulli's Equation

For an ideal fluid, Bernoulli's equation holds along streamlines.

$p/\rho g+u^2/2g=p_1/\rho g+u_1^2/2g=p_2/\rho g+u_2^2/2g$

Boundary Layer

Assuming a flow is bounded on one side only, and that a rectilinear flow passing over a stationary flat plate that lies parallel to the flow, the flow just upstream of the plate has a uniform velocity. As the flow comes into contact with the plate, the layer of fluid actually “adheres” to a solid surface. There is then a considerable shearing action between the layer of fluid on the plate surface and the second layer of fluid. The second layer is therefore forced to decelerate (though it is not quite brought to rest), creating a shearing action with the third layer of fluid, and so on. As the fluid passes further along the plate, the zone in which shearing action occurs tends to spread further outwards. This zone is known as the “boundary layer.” The flow outside the boundary layer is free of shear and viscous-related forces so it is assumed to act like an ideal fluid. The intermolecular cohesive forces in a fluid are not great enough to hold fluid together. Hence a fluid will flow under the action of the slightest stress and flow will continue as long as the stress is present. The flow inside the layer can be either viscous or turbulent, depending on the Reynolds number.

Applications

Common topics of design for hydraulic engineers include hydraulic structures such as dams, levees, water distribution networks, water collection networks, sewage collection networks, s...