Canal fall structures are required when the slope of the ground is steeper than the permissible slope of the canal. This results in excessive filling which increases construction costs. Canal falls provide a sudden drop in the canal bed to allow it to run in excavation or filling depending on the command area. There are different types of canal falls such as ogee, rapid, stepped, trapezoidal notch, well type, simple vertical drop, straight glacis, and Montague falls. Each type is suited to different site conditions and canal discharges. Canal fall structures are an integral part of irrigation systems and help reduce waterlogging and scouring.
Canal fall structures are required when the slope of the ground is steeper than the permissible slope of the canal. This results in excessive filling which increases construction costs. Canal falls provide a sudden drop in the canal bed to allow it to run in excavation or filling depending on the command area. There are different types of canal falls such as ogee, rapid, stepped, trapezoidal notch, well type, simple vertical drop, straight glacis, and Montague falls. Each type is suited to different site conditions and canal discharges. Canal fall structures are an integral part of irrigation systems and help reduce waterlogging and scouring.
Canal fall structures are required when the slope of the ground is steeper than the permissible slope of the canal. This results in excessive filling which increases construction costs. Canal falls provide a sudden drop in the canal bed to allow it to run in excavation or filling depending on the command area. There are different types of canal falls such as ogee, rapid, stepped, trapezoidal notch, well type, simple vertical drop, straight glacis, and Montague falls. Each type is suited to different site conditions and canal discharges. Canal fall structures are an integral part of irrigation systems and help reduce waterlogging and scouring.
Canal fall structures are required when the slope of the ground is steeper than the permissible slope of the canal. This results in excessive filling which increases construction costs. Canal falls provide a sudden drop in the canal bed to allow it to run in excavation or filling depending on the command area. There are different types of canal falls such as ogee, rapid, stepped, trapezoidal notch, well type, simple vertical drop, straight glacis, and Montague falls. Each type is suited to different site conditions and canal discharges. Canal fall structures are an integral part of irrigation systems and help reduce waterlogging and scouring.
A vertical drop which is provided to step down the canal bed and then it is continued with permissible slope is called canal fall structure or simply canal fall. OR The structure built to safe guard the drop is called canal fall structure. This structure is an integral part of an irrigation system.
Why canal fall structures are required?
The longitudinal slopes of canals are fixed as per sediment transport capacity, i.e, for non- silting and non-scouring velocity. It may happen that the ground on which the canal is to be laid is steeper than the designed bed slope. This results in excessive filling. This excessive filling will increase the cost of construction. If there is a difference between ground water table and the water level in the canal, then it may causes excessive seepage which results in water logging. To avoid this, the bed of canal is given a sudden drop or fall at a suitable place, so that it may run partly in excavation and partly in filling, depending upon the command areas. When the slope of the ground is more or less uniform and the slope is greater than the permissible slope of the canal. Then canal falls are necessary.
Types of Canal Falls:
The following are the different types of canal falls that may be adopted according to the site condition: Ogee Canal Falls: Ogee curve is the combination of convex and concave curves. So, Ogee fall consists of both convex and concave curves gradually. This gradual combination helps to provide smooth transition of flow and also reduce the impact. If the canal natural ground surface is suddenly changed to steeper slope, ogee fall is recommended for that canal. Stone pitching is provided in the upstream and downstream of the fall.
M Akbar Rafique (2013-BT-CIVIL-14)
Water Resources Engineering Assignment.
Rapid Canal Falls:
Rapid fall consists a long sloping glacis. It is constructed if the available natural ground surface is plane and long. For this, a bed of rubble masonry is provided and it is finished with cement mortar of 1:3 ratio. To maintain the slope of bed curtain walls are provided at both upstream and downstream. Rapid falls are high priced constructions.
M Akbar Rafique (2013-BT-CIVIL-14)
Water Resources Engineering Assignment.
Stepped Canal Falls:
As in the name itself, stepped fall consist vertical steps at gradual intervals. Stepped fall is the modification of rapid fall. It is suitable for the canal which has it upstream at very high level as compared to downstream. These two levels are connected by providing vertical steps or drops as shown in figure.
Trapezoidal Notch Canal Falls:
In case of trapezoidal notch falls, a high crested wall is built across the channel and trapezoidal notches are provided in that wall. Trapezoidal falls are very economical and suitable for low discharges. Now a days this type of falls are using widely because of their simplicity and popularity.
M Akbar Rafique (2013-BT-CIVIL-14)
Water Resources Engineering Assignment.
Well Type Canal Falls:
Well type falls are also called as syphon drop falls. In this case, an inlet well with pipe at its bottom is constructed in upstream. The pipe carries the water to downstream well or reservoir. If the discharge capacity is more than 0.29 cumecs then downstream well is preferred otherwise reservoir is suitable.
Simple Vertical Drop Falls (Sarda Type Fall):
Simple vertical drop fall or sarda fall consists, single vertical drop which allows the upstream water to fall with sudden impact on downstream. The downstream acts like cushion for the upstream water and dissipate extra energy. This type of fall is tried in Sarda Canal UP (India) and therefore, it is also called Sarda Fall.
M Akbar Rafique (2013-BT-CIVIL-14)
Water Resources Engineering Assignment.
Straight Glacis Canal Falls:
This is the modern type of construction, in which a raised crest is constructed across the canal and a gentle straight inclined surface is provided from raised crest to the downstream. The water coming from upstream crosses the raised crest and falls on inclined surface with sufficient energy dissipation.
Montague Type Canal Falls:
Montage fall is similar to straight glacis fall but in this case the glacis is not straight. It is provided in parabolic shape to introduce the vertical component of velocity which improves the energy dissipation to more extent.