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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A jet of water from a hose exerts a force on whatever it hits. Measured head h should be greater than 0.

V Notch Weir Discharge Calculator and Equations

To make further use of oger equation we need an expression relating the width of flow across the weir to the depth below the free surface. Discharge and Head Calculations, Equations, and Guidelines for water flow measurement in streams and channels. To make this website work, we log user data and share it with processors.

As in the case of orifice, annd 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 notcyes and sides. Feedback Privacy Policy Feedback. The lift force on an aircraft is exerted by the air moving over the wing. Published by Alessandro Illes Modified over 3 years ago.

We will also assume that the velocity through any elemental strip depends only on the depth below the free surface. 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.

Department of the Interior, Bureau of Reclamation. When the crest length of a rectangular weir is less than the width of the channel, there will be lateral contraction. If you compare it to the graphs shown in the references, it looks nearly identical which implies that our fits are very good.


Standard method for open-channel flow measurement of water with thin-plate weirs. Our equations are shown below. 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.

The graph shown is from our fits. The notch angle must be between 20 o and o 0. Thus in this case, the effects of sides of the weir is eliminated or suppressed. Discharge Head Discharge, Q: Available from Global Engineering Documents at http: 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.

V-Notch Triangular Weir Calculator. A weir is a notch on a large scale, used, for example, to measure the flow of a river, and may be sharp edged or have a substantial breadth in the direction of flow. About project SlidePlayer Terms of Service. Water flow measurement in open channels using weirs and venturi flumes – Part 1: In the forgoing theory, it has been assumed that the velocity of the liquid approaching the notch is weire small so that its kinetic energy can be neglected; it can ajd be assumed that the velocity through any horizontal element across the notch will depend only on its depth below the free surface.

A notch is an opening in the side of a measuring tank or reservoir extending above the free surface. Water surface downstream of the weir should be at least 0. 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.

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 approach to the weir will be substantial and the head h producing flow will be fllw by the kinetic energy of the approaching liquid to a value. The bottom of the “V” should be at least 1. When the water on the downstream side of a weir rises above the level of the crest, the weir is said to be a weiirs weir.


For a notch of any shape shown in figure, consider a horizontal strip of width b at a depth h below the free floa and height d h. Registration Forgot your password?

Flow Over Notches and Weirs

To produce automated calculations, LMNO Engineering used a curve fitting program to obtain the equations weir best fit the C and k curves. When the length of crest of the weir is same as the width of the channel, the weir is said to be suppressed weir.

It is usually a device for measuring discharge. Please contact us for consulting or other questions.

As a result, the discharge through the strip will be. If you wish to download it, please recommend it to your friends in any social system. Our calculation does not account for partially contracted weirs, but for most practical purposes the difference in C is inconsequential. American Society for Testing and Materials. Parshall submerged Parshall, Trapezoidal, Rectangular, and U shape.

The momentum equation is a statement of Newton. Auth with social network: To use this website, you must agree to our Privacy Policyincluding cookie policy. International Organization of Standards. Weir Assumptions We will assume that the velocity of the fluid approaching the weir is small so that kinetic energy can be neglected.

It doesn’t matter how thick the weir is except where water flows over the weir through the “V. Occurs if head is being computed and a very low Q is entered e. Input results in oover negative head due to the compiler’s machine precision. This is an initial check of user input.

Units in V-notch weir calculation: Head Correction Factor, k: