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What is weir with end contraction?

Author

Jessica Burns

Published Mar 20, 2026

What is weir with end contraction?

End Contraction: The horizontal distance from the ends of the weir crest to the sides of the weir pond. Weir Scale or Gauge: The scale fastened on the sides of the weir or on a stake in the weir pond to measure the head on the weir crest. Nappe: The sheet of water which overflows a weir is called a nappe.

Subsequently, one may also ask, what is meant by end contraction affect in notches and weirs?

When the length of the weir is less than the width of the stream, we find there will be a lateral contraction at each end such a weir is called a contracted weir. According to Francis each lateral contraction (also called end contraction) is equal to 0.1 H.

One may also ask, what happens when the water flows approaching a weir? Let the upstream level of the liquid be z0 above the level of the weir crest. As the liquid approaches the weir, the liquid level gradually drops and the flow velocity increases. Downstream from the weir, a jet is formed.

Herein, what is a weir contraction?

A contracted weir means that the ditch or canal leading up to the weir is wider than the weir opening itself. The water before the weir should be held in a relatively calm and smooth pool.

What is ogee weir?

An ogee crest weir is a common weir type whose cross-sectional profile corresponds to the shape of the underside of a sharp-crested weir nappe. Just as the shape or trajectory of the sharp-crested weir nappe changes with flow rate, so does the ogee crest profile.

What is Cipolletti weir?

Cipoletti Weir. A standard Cipoletti weir is trapezoidal in shape. The crest and sides of the weir plate are placed far enough from the bottom and sides of the approach channel to produce full contraction. The sides incline outwardly at a slope of 1 horizontal to 4 vertical.

What is Hydraulic weir?

A weir is a small dam built across a river to control the upstream water level. Over time, the term weir has taken on a more general definition in engineering to apply to any hydraulic control structure that allows water to flow over its top, often called its crest.

What is suppressed weir?

The term 'Suppressed weir' as it applies to the area of reclamation can be defined as ' A rectangular weir that has only the crest far removed from the channel bottom, the sides are coincident with the sides of the approach channel, so no lateral contraction of water passing through the weir is possible'.

What is the difference between broad crested weir and sharp crested weir?

The sharp crested weir will help in measuring the discharge of the water from the small rivers and canals and the weir is placed in the direction of the flow of water. The broad crested weir is one which the water flow discharge in measured from large water bodies like big canals.

What is a trapezoidal weir?

Trapezoidal weir is also called as Cippoletti weir. This is trapezoidal in shape and is the modification of rectangular weir with slightly higher capacity for same crest strength. The sides are inclined outwards with a slope 1:4 (horizontal : vertical)

How does the velocity of approach affect the discharge over a weir?

Velocity Head in Approach. As flow approaches a weir, the water surface becomes lower due to acceleration of the flow by the force of gravity (figure 5-6). Figure 5-6 -- Weir approach flow. Any increase in velocity above standard conditions, therefore, will result in measuring less than the true head on the weir.

Which notch gives maximum discharge?

We have found from the experiment that the rectangular notch gives better discharge than the V-notch. The values which we got creates a standard trend of all the data. Here the theoretical discharge value for V-notch is 0.0068 and for rectangular notch is 0.0145.

What are the advantages of using triangular notch or weir over rectangular one?

Triangular notch will provide more precise results during measuring low discharge as compare to result obtained from rectangular notch. Only one reading of H will be required for determination of discharge in case of triangular notch.

What is the reduction in crest length due to each end contraction?

What is the reduction in crest length due to each end contraction? Explanation: Francis through his experiment had derived this empirical relation. Explanation: In Francis formula, the effective length is L-0.2H.

How do you calculate discharge using rectangular notch?

The formula for Discharge in Rectangular Notch is -(Where B = width of notch, and H = height of liquid above the sill of the notch)
  1. 3 2 C d L 2 g H 3 / 2.
  2. 3 2 C v L 2 g H 3 / 2.
  3. 3 2 C c L 2 g H 3 / 2.
  4. 2 3 C d L 2 g H 3 / 2.

What is called the sheet of water flowing through a notch or over a weir?

The sheet of water flowing over a notch or a weir is known as. A. Sill or crest.

What is velocity of approach in weir?

19. Velocity of Approach  Velocity of approach is defined as the velocity with which the water approaches or reaches the weir or notch before it flows over it.

What is triangular notch?

The V-notch or triangular notch is sharp crested notch, which is maily used to determine the low rate of flow. Let, H = Height of the liquid above the apex of the notch. θ = Angle of the notch. Cd = Coefficient of discharge.

What is the shape of Ogee weir?

Ogee weirs are usually designed in the shape of ogee curve. The crest of the ogee weir is slightly rising and falls into parabolic form. This ogee shaped structure is used as weir, ogee spillway in dam and ogee fall in irrigation canal.

What is weir flow?

A flow measuring weir is simply a structure over which water flows in such a way that volumetric flow rate can be calculated…. it lets you know how much water is flowing. Many times a flow measuring weir is simply a thin plate across a flow stream, but weirs can also be broad, thick structures.

What are some disadvantages of a weir?

Disadvantages of Weirs
  • Spacious Upstream Weir Pool Required.
  • Cold Weather Can Compromise Readings.
  • Discharge Must Be Free-Spilling.
  • Weir Maintenance Is Extensive.
  • Weirs and Flumes From Tracom.

Why should the weir have a sharp crest?

Sharp crested weirs (or notches) are generally used to measure the discharge in small open channels where accuracy is required. Because such weirs can be accurate to ±2% or even ±l %, they are often used as measuring devices in hydraulics laboratories, but they also have practical applications.

What is the weir equation?

The Weir formula is a formula used in indirect calorimetry, relating metabolic rate to oxygen consumption and carbon dioxide production. According to original source, it says: Metabolic rate (kcal per day) = 1440 (3.94 VO2 + 1.11 VCO2)

What is weir elevation?

For V-notch weirs, the point of the triangle is the crest. The lowest elevation of the notch over which water flows is the zero reference elevation against which head is measured. For weirs where the notch does not span the full channel, the flow on sides of the channel must turn to pass through the notch opening.

What is difference between weir and barrage?

A weir is an impermeable barrier that is built across a river to raise the water level on the upstream side. On the other hand, a barrage involves adjustable gates installed over a dam to maintain the water surface at different levels and at different times. The water level is adjusted by opening the valves or gates.

What is end contraction?

An end contraction is when the length of the weir (L) is less than the width of the Channel and a nappe contracts either one or both sides of the weir.

What is weir in fluid mechanics?

A weir /wɪər/ or low head dam is a barrier across the width of a river that alters the flow characteristics of water and usually results in a change in the height of the river level. They are also used to control the flow of water for outlets of lakes, ponds, and reservoirs.

What is the main effect of a weir as a channel control?

The main purpose of broad crested weir used in open channels is to raise and control upstream (U/S) water level.

How do weirs affect rivers?

Weirs stop natural processes and impact river channels in two main ways; Upstream – Sediment transport is interrupted by the weir, sediment (e.g. gravel) accumulates upstream. The river begins at one elevation and incises downward through its bed while leaving its floodplain behind [higher]) throughout its course).

What happens when a weir becomes drowned?

As well, as water passes over the top of the weir, the motion can alter the dissolved oxygen levels. If the water is over or under-oxygenated (called hypoxia or anoxia), this can harm the local ecosystem. Weirs are particularly dangerous to humans - and are thus commonly called "drowning machines".

How is weir discharge calculated?

The equation recommended by the Bureau of Reclamation in their Water Measurement Manual, for use with a suppressed rectangular weir is: Q = 3.33 B H3/2, where Q is the water flow rate in ft3/sec, B is the length of the weir (and the channel width) in ft, and H is the head over the weir in ft.

What are the causes of failure of weir on a permeable foundation?

CAUSES OF FAILURE OF WEIRS ON PERMEABLE SOILS AND THEIR REMEDIES
  • Piping or undermining.
  • By uplift pressure.
  • By suction due to standing wave.
  • By scour on the U/S and D/S of the weir.

What is weir length in distillation column?

The outlet weir height typically is 51 mm, this is the height that has been used in obtaining most of the FRI data with the trays with downcomer. In vacuum distillation, operating in the spray regime, typical weir height is 0 to 25 mm, while absorbers and strippers may use 102 mm weir height(1).

What is the relationship between the discharge Q and head over the crest of weir h in case of rectangular weir *?

Bos (1989) derived discharge formula for rectangular weir using energy consideration principle. Where Q is discharge , b is weir width, h is head over the weir, g is acceleration due to gravity and Cd is discharge coefficient. But viscous effect and stream line curvature due to weir contraction are neglected.

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