Kautilya institute of
technology and engineering
2017-18
B.tech 4th Year 8th Semester
Civil engineering
SRMINAR report
SARDA FALL
Submitted to:
Submitted by:
ravi chouhan(d1)
14ektce787
ACKNOWLEDGEMENT
CONTENTS
CANAL FALLS
Canal falls are solid masonry structure which is constructed on the
canal if the natural ground slope is steeper than the designed channel
bed slope. If the difference in slope is smaller, single fall cane be
constructed. If it is of higher then falls are constructed at regular
suitable intervals.
Location of Canal Falls
Location of canal fall depends upon the following factors
1. Topography of canal
2. Economy of excavation or filling
The above two will decide the location of canal fall across canal. By
understanding topographic condition we can provide the required
type of fall which will give good results. At the same time, the provided
falls is economical and more useful. So, economical calculation is also
important. Unbalanced earth work on upstream and downstream
result the project more uneconomical.
Types of Canal Falls and their Importance
The important types of falls which were used in olden days and those
which are being used in modern days are described below:
o Ogee falls
o Rapids
o Stepped falls
o Trapezoidal notch falls
o Well type falls
o Simple vertical drop falls
o Straight glacis falls
o Montague type falls
o English falls or baffle falls
o SARDA FALL
Sarda Type Fall:
It is a fall with a raised crest. The body wall is constructed like a weir
(Fig. 19.13). Below the fall suitable device is provided for dissipating
excess energy of falling water. This type of falls were constructed on
the Sarda canal in Uttar Pradesh and hence the name. As the crest of
the fall is raised silting of the upstream canal is possible.
DESIGN PRINCIPLES OF SARDA TYPE FALL
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.
Crest Dimensions:
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 (Fig. 19.22 (a)).
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
ADVERTISEMENTS:
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.
ADVERTISEMENTS:
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
where Cd = 0.65
HL = drop in water surface
and h2 = depth of d/s water level over top of crest.
Crest Level:
The height of crest above the upstream bed level is fixed in such a way
that the depth of flow u/s of the fall is not affected. From the discharge
formula mentioned above since Q is known value of H can be
calculated.
R . L of crest = F . S . L on the u/s – H.
The stability of body wall should be tested by usual procedure when
the drops exceeding 1.5 m are to be designed. In the body wall drain
holes may be provided at the u/s bed level to dry out the canal during
closures for maintenance, etc.
Cistern dimensions: Dimensions of the cistern may be fixed from the
Bahadurabad Research Institute formula given in article 19.17, i.e.,
LC = 5√E.HL and
X = ¼ (E.HL)2/3
Total Length of Impervious Floor:
As for any hydraulic structure total length of the impervious floor
should be designed on the basis of Bligh’s theory for small structures
and Khosla’s theory for other works. Maximum seepage head is
experienced when on the u/s water is upto the crest level of the fall
and there is no flow on the d/s side. Referring Fig. 19.22 maximum
seepage head is given by ‘d’.
Length of d/s impervious floor:
The maximum length of the d/s impervious floor is given by the
following relation.
Ld = 2D + 2.4 + HL in metres.
The balance of impervious floor may be provided under the body wall
and on the u/s.
Thickness of the Floor:
The d/s floor should be made thick enough to resist uplift pressures.
However, minimum thickness of 0.3 to 0.6 m (depending upon the size
of the drop) of concrete under 35 cm of brick masonry may be
provided on the d/s. On the u/s brick masonry is not necessary. The
brick on the edge laid on the d/s impervious concrete floor provide
additional strength and affords easy repairs to the floor.
Cut-off:
A sufficient depth of cut-off below the floor should be provided at the
d/s end of the floor for providing safety against steep exit gradient.
The depth of cut-off may range from 1 to 1.5 m. Sometimes deeper
cut-offs may be necessary to reduce horizontal floor length to satisfy
Khosla’s principle of exit gradient. For falls having 1 m and above head
on the crest should be provided more cut-offs. Cut-off at u/s end of
floor is also provided which may be smaller in depth.
Other Protective Works:
Provision of other accessories like upstream wings, staggered blocks
on the cistern floor, downstream wings, bed and side pitching is
generally done on the basis of thumb rules. For big structures,
however, actual design calculations may be done. For general
arrangement see Fig. 19.13.
Upstream wing walls:
For small falls upto 14 cumec the upstream wings may be splayed at
1: 1. For higher discharges u/s wing walls are kept segmental with a
radius equal to 6 H and continued thereafter tangentially merging into
the banks. The wings may be embedded into the bank for about 1 m.
Downstream wing walls:
For the length of the cistern the d/s wing walls are kept vertical from
the crest. Thereafter they are wasped or flared to a slope of 1: 1. An
average splay of 1 in 3 for attaining the required slope is given to the
top of the wings. The wings may be taken deep into the banks.
Staggered blocks:
Staggered block of height dc should be provided at a distance of 1.0
dc to 1.5 dc from the d/s toe of the crest for clear falls. In case of
submerged falls the blocks may be provided at the end of the cistern.
A row of staggered cubical blocks of height equal to 0.1 to 0.13 of
depth of water should invariably be provided at the end of the d/s
impervious floor.
Bed and side pitching:
The d/s bed pitching with bricks 20 cm thick over 10 cm ballast is
provided horizontally for a length of 6 m. Thereafter for lengths up to
5 to 15 m for falls varying from 0.75 to 1.5 m may be provided with
down slope of 1 in 10. The side pitching with bricks on edge with 1: 1
slope is provided after the return-wing on the downstream. A toe wall
should be provided between the bed pitching and the side pitching to
provide a firm support to the latter.
