17-10-2016, 03:36 PM
1459478399-DesignPrinciplesforSardaTypeandStraightGlacisFall.pdf (Size: 430.62 KB / Downloads: 9)
Design Principles for Sarda Type Fall:
This type of falls are constructed on Sarda canal in Uttar
Pradesh. It is a fall with raised crest and with vertical
impact. The soils in Sarda command comprised sandy
stratum overlain by sandy-clay on which depth of
cutting was to be kept minimum. This made it obligatory
to provide number of falls with small drops. In Sarda
type falls (q) discharge intensity varied from 1.6 to 3.5
cumec/m and drop varied from 0.6 to 2.5 m.
This type of fall is not flumed.
For canal discharge 15 cumec and more
Crest length of fall = Bed width of the canal.
For distributaries and minors
Crest length of fall = Bed width + Depth of flow.
Body wall: When the discharge of a canal is less than 14
m^/sec the section of body wall is kept rectangular
When the discharge of a canal is more than 14 m3/sec
the section of the body wall is kept trapezoidal with
upstream batter 1: 3 and downstream batter 1: 8.
For rectangular body wall:
Top width ‘b’ = 0.552 √d
Base width ‘B’ = H + d/√p
For trapezoidal body wall Top width b = 0.522 √(H + d)
The edges are rounded with a radius of 0.3 m.
Base width B is determined by the batter given to u/s
and d/s sides.
Here H is depth of water above the crest of the fall in metres. (It includes velocity of approach also).
d is the height of the crest above the downstream bed
level in metres.
Discharge Over Crest:
The discharge formula used in this type of fall under
free fall condition is:
Q = CLH {H/b}1/6
where L is length .of crest in m and Q is discharge in
cumec.
Value of C for trapezoidal crest is 2 and for rectangular
crest 1.85.
For submerged flow conditions (above 33%
submergence) neglecting velocity of approach the
discharge is given by the following formula