Types of weirs
What is the purpose of weirs?
A weir is a small dam built across a body of water, such as a river. We use them to help control the flow of water. Weirs can help raise the water level so that boats can pass through, and they can also reduce the flow of water to prevent flooding.
How are weirs classified?
They can be classified as rectangular, triangular and trapezoidal weirs based on the geometry of flow section. They can be classified into sharp crested and broad-crested weirs based on the sharpness of the crest.
What is a standard weir?
Standard Contracted Rectangular Weirs. The fully contracted rectangular weir (figure 7-1) is the most frequent standard weir used in irrigation. To be fully contracted, all overflow plate sides and ends must be located at least a distance of 2h1max (two maximum measurement heads) from the approach flow boundaries.
What is a weir structure?
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. Weirs are also used to control the flow of water for outlets of lakes, ponds, and reservoirs.
What are advantages of weirs?
Weirs can be built to measure water flow rate, to alter the flow of rivers, or to prevent flooding. Additionally, small-size weirs can be used in large hydropower developments as a way to mitigate potential harm that may come about as a result of dam development.
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 is weir height?
The weir height should never be less than 1 foot (0.3 m). The approach section should be straight upstream from the weir for a distance of at least 20 times the maximum expected head of liquid, and should have little or no slope. The crest must be set higher than the maximum downstream elevation of the water surface.
What is weir length?
The Length is the bottom width of the weir. The height is measured from the bottom of the weir opening to the top of the water level ponded behind the weir (not the water level right as it leaves the weir).
How do weirs measure flow?
Weirs to Measure Flow
It works by raising the water level upstream of the weir, and then forcing the water to spill over. The more water is flowing over the weir, the deeper the water will be upstream of the weir. So measuring flow rate (CFS) can be done by simply measuring the depth of the water upstream.
How many types of notches are there?
Lesson 22. TYPES OF NOTCHES, RECTANGULAR AND TRIANGULAR NOTCHES, RECTANGULAR WEIRS
| Types of notches | Discharge/flow rate | |
|---|---|---|
| a. | Rectangular | |
| b. | Triangular | |
| c. | Trapezoidal | Q = Q1 + Q2 |
| d. | Stepped | Q = Q1 + Q2 + Q3 |
What is the difference between a notch and a weir?
A notch may be defined as an opening provided in the side of the tank or vessel such that the liquid surface in the tank is below the top edge of the opening. A weir may be defined as any regular obstruction in an open stream over which the flow takes place.
What is not the way of classifying weir based on the emerging Nappe?
Explanation: Trapezoidal crested weir is not the way of classifying weir based on their shape of crest.
How are weirs built?
How was the weir built? The site was prepared by excavating the gound to form the weir pool and the level bed of the weir. A step was cut in the edge of the river bed to form the toe of the weir. Between the first two rows of stakes, large flat stones were laid on edge across the face of the weir to prevent seepage.
Why V notch is used?
V notch weirs really are just that – a thin plate weir with a ‘V’ notch cut into it. The weir is placed to obstruct open channel flow and allow water to flow over the notch. This enables us to accurately measure the flow, by measuring the head upstream of the V notch.
What is ogee weir?
Concept: Generally, ogee weirs are provided for the spillway of a storage dam. The crest of the ogee weir slightly rises and falls into parabolic form. Flow over ogee weir is similar to flow over rectangular weir, cippoletti weir.
Where is a notch used?
Notches are commonly used in material impact tests where a morphological crack of a controlled origin is necessary to achieve standardized characterization of fracture resistance of the material. The most common is the Charpy impact test, which uses a pendulum hammer (striker) to strike a horizontal notched specimen.
What is the angle of V notch?
V notch: In this notch, both the sides are cut at a 45° angle to the edge of the sheet.
What is use of Venturi meter?
Venturimeter is a device used to measure the rate of flow of fluid flowing through a pipe. Venturimeter is a device which is used for measuring the rate of flow of fluid flowing through a pipe.
What is trapezoidal weir?
This calculates the flow rate over a Cipolletti weir, a commonly used weir in many irrigation districts. The weir opening has a flat, level bottom and the sides that have a particular slope. The water before the weir should be held in a relatively calm and smooth pool.
How do you calculate notch?
The formula for calculating the notch frequency is, notch frequency= 1/4πRC, where π equals 3.14, R is the resistance, and C is the capacitance.
How do you calculate V notch?
V Notch Weir Equation for Notch Angle Other than 90 Degrees
That equation is: Q = 4.28 Ce Tan(θ/2)(H + k)5/2, where Q and H are as previously defined, θ is the angle of the v notch, Ce is the effective discharge coefficient, and k is a head correction factor.
How is weir coefficient 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.
Where is rectangular notch used?
The rectangular weir (notch) is a common device used to regulate and measure discharge in irrigation projects. The current research was based mainly on laboratory experiments studying the hydraulic characteristics of rectangular notches.