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Flow Over Notches and Weirs A notch is an opening in the side of a tank or reservoir which extends above the surface of the liquid. It is usually a device for. –As it has sharp edges, the flow over the notch is FRICTIONLESS (Ff=0). –these are generally used to measure small discharge across CANAL. WEIR: -These. The bottom edge, over which the liquid flows, is known as sill or crest of the notch and the sheet of liquid flowing over a notch (or a weir) is known as nappe or.

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Available from Global Engineering Documents at http: Occurs if head is being computed and a very low Q is entered e.

Measured head h should be greater than 0. For a notch of any shape shown in figure, consider a horizontal strip of width b at a depth h below the free surface and height d h. My presentations Profile Feedback Log out.

Our equations are shown below. International Organization of Standards. Please contact us for consulting or other questions. This is an initial check of user input.

NPTEL :: Civil Engineering – Fluid Mechanics

The V-notch design causes small changes in discharge to have a large change in depth allowing more accurate head measurement than with a rectangular weir. Published by Alessandro Illes Modified over 3 years ago. Input results in a negative head due to the compiler’s machine precision. The equation for flow through trapezoidal notch is obtained from the equations for rectangular and V-notches. It may be sharp crested but also may have a substantial width in the direction of flow – it is used as both a flow measuring device and a device to raise water levels.


When the crest length of a rectangular weir is less than the width of the channel, there will be lateral contraction. Introduction Weirs are typically installed in open channels such as streams to determine discharge flowrate.

It is usually a device for measuring discharge. Department of the Interior, Bureau of Reclamation.

A weir is a notch on a larger scale. We will also assume that the velocity through any elemental strip depends only on the depth below the free surface. V-Notch Triangular Weir Calculator. As a result, the discharge through the strip will be. Units in V-notch weir calculation: The method of determining the theoretical flow through a notch is the same as that adopted for a large orifice.

All of the references show similar curves for C and k vs. As in the notchhes of orifice, the actual discharge through a notch or weir can be found by multiplying the theoretical discharge by a coefficient of discharge to allow for energy losses and the contraction of the cross-section of the stream at the bottom and sides. This is a satisfactory assumption for flow over a notch or weir in the side of a large reservoir, but, is the notch or weir is placed at the end of a narrow channel, the velocity of wiers to the weir will be substantial and the head h producing flow will be increased by the kinetic energy of the approaching liquid to a value.

The graph shown is from our fits. American Society for Testing and Materials. Auth with social network: The basic principle is that discharge is directly related to the water depth above the crotch bottom of the V; this distance is called head h.

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Notches and Weirs

If the bulk of the weir is thicker than 0. The notch angle must be between 20 o and o 0.


Feedback Privacy Policy Feedback. Discharge Head Discharge, Q: A weir is a notch on a large scale, used, for example, wers measure the flow of a river, and may be sharp edged or have a substantial breadth in the direction of flow. A jet of water from a hose exerts a force on whatever it hits. To produce automated calculations, LMNO Engineering used a curve fitting program to obtain the equations which best fit the C and k curves. The bottom of the “V” should be at least 1. Standard method for open-channel flow measurement of water with thin-plate weirs.

Flow Over Notches and Weirs

These are acceptable assumptions for tanks with notches or reservoirs with weirs, but for flows where the velocity approaching the weir is substantial the kinetic energy must be taken into account e. It doesn’t matter how thick the weir is except where water flows over the weir through the “V. Parshall submerged Parshall, Trapezoidal, Rectangular, and U shape.

Discharge and Head Calculations, Equations, and Guidelines for water flow measurement in streams and channels.

Note that the value of v 1 is obtained by dividing the discharge by the full cross sectional area of the channel itself, not that of the notch. Share buttons are a little bit lower. A notch is an opening in the side of a measuring tank or reservoir extending above the free surface.