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### Fluids Discharge Measurement Structures and Systems

Civil Engineering and Design

Fluids Flow Design and Engineering

Hydraulics Design and Engineering

Fluids Discharge Measurement Structures and Systems

Basic Principles of Fluid Flow as Applied to Measuring Systems

400 Pages

Third Edition

M.G. Bos

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Open: Basic Principles of Fluid Flow as Applied to Measuring Systems

This book presents instructions, standards, and procedures for the selection, design, and use of structures, which measure or regulate the flow rate in open channels. It is intended to serve as a guide to good practice for engineers concerned with the design and operation of such structures. It is hoped that the book will serve this purpose in three ways: (i) by giving the hydraulic theory related to discharge measurement structures; (ii) by indicating the major demands made upon the structures; and (iii) by providing specialized and technical knowledge on the more common types of structures now being used throughout the world.

The text is addressed to the designer and operator of the structure and gives the hydraulic dimensions of the structure. Construction methods are only given if they influence the hydraulic performance of the structure. Otherwise, no methods of construction nor specifications of materials are given since they vary greatly from country to country and their selection will be influenced by such factors as the availability of materials, the quality of workmanship, and by the number of structures that need to be built.

The efficient management of water supplies, particularly in the arid regions of the world, is becoming more and more important as the demand for water grows even greater with the world’s increasing population and as new sources of water become harder to find. Water resources are one of our most vital commodities and they must be conserved by reducing the amounts of water lost through inefficient management. An essential part of water conservation is the accurate measurement and regulation of discharges.

TOC

BASIC PRINCIPLES OF FLUID FLOW AS APPLIED TO MEASURING STRUCTURES 17

General

Continuity

Equation of motion in the s-direction

Piezometric gradient in the n-direction

Hydrostatic pressure distribution in the m-direction

The total energy head of an open channel cross-section

Recapitulation

Specific energy

The broad-crested weir

Broad-crested weir with rectangular control section

Broad-crested weir with parabolic control section

Broad-crested weir with triangular control section

Broad-crested weir with truncated triangular control section

Broad-crested weir with trapezoidal control section

Broad-crested weir with circular control section

Short-crested weir

Critical depth flumes

Orifices

Sharpcrested weirs

Sharp-crested weir with rectangular control section

Sharp-crested weir with parabolic control section

Sharp-crested weir with triangular control section

Sharp-crested weir with truncated triangular control section

Sharp-crested weir with trapezoidal control section

Sharp-crested weir with circular control section

Sharp-crested proportional weir

The aeration demand of weirs

Estimating the modular limit for long-throated flumes

Theory

Energy losses upstream of the control section

Friction losses downstream of the control section

Losses due to turbulence in the zone of deceleration

Total energy loss requirement

Procedure to estimate the modular limit

Modular limit of short-crested weirs

Selected list of literature

AUXILIARY EQUIPMENT FOR MEASURING STRUCTURES

Introduction

Head measurement station

The approach channel

Tailwater level

Staff gauge

Stilling well

Maximum stage gauge

Recording gauge

The float-tape and the diameter of the float

Instrument shelter

Protection against freezing

Differential head meters

Selected list of references

THE SELECTION OF STRUCTURES

Introduction

Demands made upon a structure

Function of the structure

Required fall of energy head to obtain modular flow

Range of discharges to be measured

Sensitivity

Flexibility

Sediment discharge capability

Passing of floating and suspended debris

Undesirable change in discharge

Minimum water level in upstream channel

Required accuracy of measurement

Standardization of structures in an area

Properties and limits of application of structures

General

Tabulation of data

Selecting the structure

Selected list of references

BROAD-CRESTED WEIRS

Horizontal broad-crested weir

Descrip tion

Evaluation of discharge

Modular limit

Limits of application

The Romijn movable measuring/regulating weir

Description

Evaluation of discharge

Modular limit

Commonly used weir dimensions

Limits of application

Triangular broad-crested weir

Description

Evaluation of discharge

Modular limit

Limits of application

Broad-crested rectangular profile weir

Description

Evaluation of discharge

Limits of application

Faiyum weir

Description

Modular limit

Evaluation of discharge

Limits of application

Selected list of references

SHARP-CRESTED WEIRS

Rectangular sharp-crested weirs

Description

Evaluation of discharge

Limits of application

V-notch sharp-crested weirs

Description

Evaluation of discharge

Limits of application

Rating tables

Cipoletti weir

Description

Evaluation of discharge

Limits of application

Circular weir

Description

Determination of discharge

Limits of application

Proportional weir

Description

Evaluation of discharge

Limits of application

Selected list of references

SHORT-CRESTED WEIRS

Weir sill with rectangular control section

Description

Evaluation of discharge

Limits of application

V-notch weir sill

Description

Evaluation of discharge

Limits of application

Triangular profile two-dimensional weir

Description

Evaluation of discharge

Modular limit

Limits of application

Triangular profile flat-Vee weir

Description

Evaluation of discharge

Modular limit and non-modular discharge

Limits of application

Butcher’s movable standing wave weir

Description

Evaluation of discharge

Limits of application

WES-Standard spillway

Description

Evaluation of discharge

Limits of application

Cylindrical crested weir

Description

Evaluation of discharge

Limits of application

Selected list of references

FLUMES

Long-throated flumes

Description

Evaluation of discharge

Modular limit

Limits of application

Description

Evaluation of discharge

Modular limit

Limits of application

Throatless flumes with broken plane transition

Description

Parshall flumes

Description

Evaluation of discharge

Submerged flow

Accuracy of discharge measurement

Loss of head through the flume

Limits of application

H-flumes

Description

Evaluation of discharge

Modular limit

Limits of application

Selected list of references

Orifices

Circular sharp-edged orifice

Description

Determination of discharge

Limits of application

Rectangular sharp-edged orifice

Description

Determination of' discharge

Modular limit

Limits of application

Constant-head-ori fice

Description

Determination of discharge

Limits of application

Radial or tainter gate

Description

Evaluation of discharge

Modular limit

Limits of application

Crump-De Gruyter adjustable orifice

Description

Evaluation of discharge

Limits of application

Metergate

Description

Evaluation of discharge

Metergate installation

Limits of application

Neyrpic module

Description

Discharge characteristics

Limits of application

Danaïdean tub

Description

Evaluation of discharge

Limits of application

Selected list of references

MISCELLANEOUS STRUCTURESDivisors

Description

Evaluation of discharge

Limits of application

Pipes and small syphons

Description

Evaluation of discharge

Limits of application

Fountain flow from a vertical pipe

Description

Evaluation of discharge

Limits of application

Flow from horizontal pipes

Description

Evaluation of discharge

Limits of application

Brink depth method for rectangular canals

Description

Evaluation of discharge

Limits of application

Dethridge meters

Description

Evaluation of flow quantity

Regulation of discharge

Limits of application

Propeller meters

Description

Factors affecting propeller rotation

Head losses

Meter accuracy

Limits of application

Selected list of references

ANNEX 1

Basic equations of motion in fluid mechanics

Introduction

Equation of motion-Euler

Equation of motion in the s-direction

Piezometric gradient in the n-direction

Hydrostatic pressure distribution in the m-direction

ANNEX 2

The overall accuracy of the measurement of flow

General principles

Nature of errors

Sources of errprs

Propagation of errors

Coefficient errors

Example of error combination

Selected list of references

Errors in measurements of head

Error in discharge volume over long period

ANNEX 3

Side weirs and oblique weirs

Introduction

Side weirs

General

Theory

Practical C,-values

Practical evaluation of side weir capacity

Oblique weirs

Weirs in trapezoïdal channels

Selected list of references

ANNEX 4

Suitable stilling basins

Introduction

Straight drop structures

Common drop

U.S. ARS basin

Inclined drops or chutes

Common chute

SAF Basin

Riprap protection

Determining maximum stone size in riprap mixture

Filter material placed beneath riprap

Permeability to water

Stability of each layer

Filter construction

Selected list of references