What is sharp crested weir?
Sharp crested weirs (also called thin-plate weirs or notches) are used to obtain discharge in open channels by solely measuring the water head upstream of the weir. Weirs are extensively used in irrigation practices, laboratories and industry.
How is weir discharge measured?
Weirs allow water to be routed through a structure of known dimensions, permitting flow rates to be measured as a function of depth of flow through the structure. A triangular weir with a small notch angle is found to be accurate in discharge measurements; however, it can only be used to measure small discharges.
What happens when the water flows approaching a weir?
Flow measurement As the liquid approaches the weir, the liquid level gradually drops and the flow velocity increases. Downstream from the weir, a jet is formed.
Why V notch is preferable over rectangular weir as a flow measuring device?
It is used to meter flow of water in the channel, by measuring the head of water over the v notch crest. The v notch weir is especially good for measuring a low flow rate, because the flow area decreases rapidly as the head over the v notch gets small.
What are the advantage of broad crested weir?
Broad crested weir: They are used to measure the discharge of rivers hence they have comparatively sharp sharps. Additionally, the advantage of a wider crested weir having a critical depth meter, is that it operates more effectively with a higher drifted water level than sharp-crested weirs.
What is the purpose of a broad crested weir?
Broad crested weirs are robust structures that are generally constructed from reinforced concrete and which usually span the full width of the channel. They are used to measure the discharge of rivers, and are much more suited for this purpose than the relatively flimsy sharp crested weirs.
What is ventilation of weir why it is required?
Ventilation of notch or weirs: The air below the nappe and the walls are trapped. This air gradually carried along with flowing water and the pressure between the nappe and wall is reduced below atmospheric pressure. Eventually negative pressure is developed and as a result, the nappe starts to depress.
What is standard weir?
Weirs are structures consisting of an obstruction such as a dam or bulkhead placed across the open channel with a specially shaped opening or notch. Common weir constructions are the rectangular weir, the triangular or v-notch weir, and the broad-crested weir.
What’s the point of a weir?
Commonly, weirs are used to prevent flooding, measure water discharge, and help render rivers more navigable by boat. In some locations, the terms dam and weir are synonymous, but normally there is a clear distinction made between the structures.