CANAL FALLS
Whenever the available natural ground slope is steeper than the designed bed slope of the channel,
the difference is adjusted by constructing vertical ‘falls’ or ‘drops’.
Types of falls
1. Ogee falls:
Water is gradually led down by providing convex and concave curves.
2. Rapid falls:
Long slopes of 1 : 15 to 1 : 20 with boulder facings are known as rapids. They are quite
satisfactory but very expensive and hence became obsolete.
3. Trapezoidal Notch Falls:
It consists of a number of trapezoidal notches across the channel wit h
a smooth entrance and a flat circular lip projecting downstream from each notch. There will be
neither drawdown nor heading up of water, as the channel approaches the fall. Now these are
obsolete since simpler, economical and better modern falls are developed.
Well type/cylinder/syphon well falls:
This type consists of two wells, one for inlet and another for
outlet connected by a pipe. The down stream well is necessary in the case of falls greater than 1.8
m and for discharge greater than 0.29 cumecs. This type of falls are very effective for larger drops
with smaller discharges.
Simple vertical drop (Sarda type fall):
1. It is a raised crest fall with a vertical impact
2. It is simple and economical
3. In it canal drops into a water cushion.
Straight Glacis Falls:
1. In this type, a straight glacis, sloping generally at 2 : 1, is provided after a raised crest.
2. It is suitable up to 60 cumecs discharge and 1.5 m drop.
Montague Type Fall:
In this type the straight glacis is replaced by a parabolic glacis to improve
energy dissipation.
Inglis fall or Baffle fall:
For as straight glacis type fall a baffle platform and a baffle wall are
added.
- Vertical drops – suitable up to 15 cumecs and upto 1.5 m fall.
- Straight glacis – suitable for discharge up to 60 cumecs and 1.5 m fall.
- Baffle fall – suitable for all discharge and more 1.5 m fall.
- Well type – suitable for high drops and low discharge
