What Is Canal Fall?
Canal Fall is a sturdy masonry foundation built upon its canal when the natural land level is steeper than that of the planned canal bed slope. When the variation in slope is greater, a single fall could be built. If it is larger, therefore falls were built at reasonable intervals on a daily basis.
Irrigation canals are built with certain allowable bed slopes such that there really is no silting and scouring in the canal bed. However, owing to the volatile nature of a country slope, it’s often not able to move the canal at the required bed slope mostly in alignment.
Typically, the slope of the natural earth’s surface is never regular in alignment. Often the slope of the ground can be flat and often very uneven with an abrupt shift of elevation. In these situations, a vertical drop is given to go along the canal bed, and afterwards the allowable slope is maintained till a further step down is required.
This would be intended to prevent needless massive earthwork in pouring. These vertical drops were recognized as canal falls.
Necessity or Importance of Canal Falls:
If the slope of the field abruptly shifts to a steeper slope, the permitted slope of the bed cant be retained. In order to stabilize the slope, it needs extreme earthwork in filling.
In this kind of situation, falls are created to prevent undue earthwork during filling Where the slope of the land is somewhat consistent as well as the slope is higher than that of the permitted slope of the canal bed.
Location of Canal Falls :
The level of a channel by and large runs similarly to the degree of ground on which the waterway is being developed. In the event that the landform has many high points and low points, the degree of trench doesn’t have to run in like manner.
Since bringing down the degree of a trench and afterward raising its level again won’t travel water. The water will gather at the low-lying part of the trench and begin streaming as a flood. Therefore, when going across an abnormal ground depth, the level of the canal would not be disturbed.
The level of the canal would flow straight down, dropping then increasing its level. The soil level imperfection is eliminated by filling. That’s unusual level ground. And if there was a long-range slope in the field, then we’ve got doing to run the canal forward. This dilemma has been overcome by building the collapse of the canal.
Types of Canal Falls:
The different types of canal falls are as follows.
- Ogee Fall.
- Stepped Fall.
- Well Type Fall.
- Straight Glacis fall
- Montague Type Fall.
- Trapezoidal Notch Fall.
- Simple Vertical Drop Fall.
- English Falls or Baffle Fall.
#1. Rapid Canal Fall-
Rapid fall involves a long sloping glacis. These are built when the usable surface of the natural soil is flat as well as long. For such a reason, a bed of rubble masonry is supported as well as completed with such a 1:3 proportion cement mortar. The slope of the bed curtain walls is preserved either upstream as well as downstream. Rapid falls are super expensive structures.
#2. Ogee Canal Fall-
The ogee curve is a mixture of convex curves as well as concave curves. Thus, Ogee Fall comprises both convex as well as concave curves. Such an incremental approach aims to guarantee smooth flow transfer and then also decreases effects.
Unless the natural layer of the canal is abruptly shifted to a steeper slope, ogee fall is advised with this canal. Stone pitching is given upstream as well as downstream of a break.
#3. Stepped Canal Fall-
stepped fall consists of vertical steps at incremental intervals. Stepped fall is a variation in rapid fall. It is ideal for a river that is upstream at a rather significant level relative to downstream. Such 2 levels are linked by vertical steps or drops.
#4. Well Type Canal Fall-
Well type falls are also termed syphon drop falls. Throughout this situation, an inlet well with a pipe there at the bottom is built upstream. The conduit takes the water to the well or even a reservoir downstream.
Unless the discharge volume is even more of about 0.29 cumecs, therefore the downstream well is recommended else the tank is appropriate.
#5. Straight Glacis Canal Fall-
That would be the key development of engineering where a raised crest is built over the canal and now a gentle rectangular surface is given from the raised crest to either the downstream. The water that comes upstream reaches the elevated crest and sinks to the inclined surface with ample energy dissipation.
#6. Montague Type Canal Fall-
Montage Fall is identical to that of straight glacis fall, although in this situation the glacis wasn’t straight. The vertical velocity element, which enhances energy dissipation to a greater extent, is given in the parabolic form.
#7. Trapezoidal Notch Canal Fall-
Throughout the event of a fall of a trapezoidal notch, a high crested wall is erected around the channel as well as trapezoidal notches were also supplied within this wall. Trapezoidal precipitation is very inexpensive and ideal for low discharges.
Today’s world, this form of decline is commonly used along with its ease and popularity.
#8. Simple Vertical Drop Fall (Sarda Type fall)-
Simple vertical drop fall is also called as sarda drop uses a single vertical drop that causes the upstream water to plunge with quite a rapid downstream effect. The downstream serves as a cushion for upstream water but dissipates excess steam. Such a form of fall is being attempted in the Sarda Canal Uttar Pradesh and is hence also known as the Sarda Fall.
#9. English or Baffle Canal Fall-
Throughout this scenario, the straight drop of glacis is established as a baffle platform with such a baffle wall. It was sufficient for every discharge. The baffle wall is built near the toes of a straight glacis only at an appropriate distance at the maximum of the build. The key aim of the baffle wall is to establish a hydraulic hop from a straight glacier to a baffle platform.
Advantages of Canal Fall:
The advantages of canal fall are as follows.
- A canal drop is built over the canal to lower the bed level in order to preserve the planned slope if there is a rise in the ground level to preserve the designed slope since there is a rise in the ground level.
- Canal collapse is planned to reduce the slope of the canal bed. If the angle of the canal bed is not lowered, the amplitude of the running water rises to an extra-ordinary level.
- If, on a sloppy site, the depth of the canal bed is not reduced, the building of the canal at a level higher than that of the ground becomes difficult.
- Construction of the fall of the canal would be used to produce steam.
- Some of the canal falls are rendered in the slope to lower the pace of the water falling in the canal. When the canal sinks sideways, the free-falling water destroys the bottom of the canal.
Disadvantages of Canal Fall:
The disadvantages of canal fall are as follows.
- The irrigation channel with an embankment, namely the filling, does have the drawback of:
- Higher building as well as repair costs.
- Higher seal as well as percolation loss.
- The adjacent area is flooded owing to some potential break in the embankment.
- Difficulties of irrigation activities.
- As a result, the irrigation canal could not be placed in high banks. Falls are then applied at suitable areas to reduce the level of demand of the irrigation canal.
- The canal water instantly downstream of the collapsed structure contains enormous kinetic energy where, although not demolished can scour the canal bed but also banks downstream of the fall. It will also jeopardize the stability of the fall system. As a result, a fall in the canal is often followed by steps to disperse excess energy that, in effect, is a result of the construction of the fall.
- The location of the fall is largely determined by the topography of the region but the need to combine the fall with many other structural elements, including the bridge, the regulator, respectively. Throughout the context of main canals, the construction costs must be regarded.
- In addition, the relative economy of increasing the number of smaller falls (attaining balanced earthwork but ease of installation) compared to the smaller number of major falls (resulting in lower construction costs and improved power generation) has also been figured on.
- Throughout the situation of channels that irrigate the command area immediately, a reduction should be made until the channel bed is drained. The full supply level of the river should be held just below ground surface for a length of up to around 500 meters downstream of the fall, as the command area in this range can be irrigated by channels upstream of the fall.