The cipoletti weir functions as if it were a following notch without end contractions
trapezoidal notch
Understanding the Cipoletti Weir and Notch Types
The question asks about the type of notch the Cipoletti weir functions as, particularly in relation to end contractions. Let's break down what a Cipoletti weir is and how it works.
What is a Cipoletti Weir?
A Cipoletti weir is a specific type of weir used for measuring the flow rate of water in open channels. Its distinguishing feature is its shape.
- It is a trapezoidal weir.
- The bottom edge (crest) is horizontal, like a rectangular weir.
- The sides are sloped outwards.
- The standard side slope for a Cipoletti weir is 1 horizontal to 4 vertical (1H:4V). This means for every 1 unit horizontally outwards, the side goes 4 units vertically upwards.
End Contractions and Cipoletti Weir Design
When water flows over a weir, if the sides of the weir opening are narrower than the channel, the flow contracts laterally as it approaches the weir. This is known as end contraction. End contractions reduce the effective width of the flow over the weir, affecting the discharge rate.
Standard rectangular weirs without suppressed contractions require adjustments or a reduction in the effective crest length in the discharge formula to account for these contractions.
The innovative design of the Cipoletti weir, with its precise 1H:4V side slope, is specifically intended to compensate for the effect of end contractions. The increased flow area provided by the outward-sloping sides exactly balances the reduction in flow caused by the end contractions.
How it Functions
Because the sloping sides compensate for the end contractions, the discharge formula for a Cipoletti weir is simplified. It can be calculated using a formula similar to that for a rectangular weir where end contractions are completely suppressed or ignored. This makes flow measurement simpler as it avoids complex calculations for contraction effects.
So, while the Cipoletti weir is physically a trapezoidal notch, its design allows it to function in a way that simplifies calculations, effectively acting like a rectangular weir where the impact of end contractions is nullified.
Considering the options provided, the Cipoletti weir is fundamentally a trapezoidal notch designed with a specific slope (1:4) to compensate for end contractions.
| Weir Type | Shape of Notch | Handling of End Contractions |
|---|---|---|
| Rectangular Weir | Rectangular | Requires calculation adjustment if contracted |
| Triangular Weir (V-notch) | Triangular | No end contractions (usually fills the channel width or used in narrow channels) |
| Cipoletti Weir | Trapezoidal (with 1H:4V slope) | Side slope compensates for end contractions |
Therefore, the Cipoletti weir is a trapezoidal notch that functions by compensating for end contractions, simplifying the discharge calculation.
Important Questions from Open Channel Flow
- A trapezoidal channel carries $5\text{ m}^3\text{.s}^{-1}$ of water under uniform flow condition. The channel has a bottom width of $2\text{ m}$, side slope of $2:1$ (horizontal: vertical), and a bed slope of $1\%$. If the Manning roughness coefficient is $0.03$, the conveyance of the channel, in $\text{m}^3\text{.s}^{-1}$, is
- Two rectangular channels, A and B, join to form a large rectangular channel, C. Each rectangular channel is lined with the same material and has the same bottom slope. The bottom widths of Channels A and B are $2\text{ m}$ and $1\text{ m}$, respectively. If the flow depth in each channel is $2\text{ m}$, the bottom width of Channel C (in m) is ________. (Rounded off to two decimal places)
- Water is flowing at the rate of 15 m$^3$/s through a rectangular channel of 5 m width.
If the acceleration due to gravity ($g$) is 9.81 m/s$^2$, the critical velocity for the flow is ______ m/s (rounded off to three decimal places). A Hydraulic Jump is said to be Oscillating Jump if its Froude number is ________.
The Francis formula for the discharge over cippoletti weir is
