Catchment Area Calculation
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NILRATAN SARKARCatchment Area Calculation
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NILRATAN SARKARCATCHMENT AREA CALCULATION
Catchment area as per Topo sheet in sqcm = 129.300 Sqcm
Scale(Topo Sheet) 1 cm = 500.000 m
Area = 32325000 Sqm
Catchment area as per Topo sheet in sqkm = 32.325 Sqkm
DISCHARGE CALCUALTIONS USING DICKEN'S FORMULA
Catchment Area (A) = 32.325 SqKm
Coef. of discharge (C) = 14.000 (11.0 TO 14.0 in Rayalaseema &
Telangana regions where rain fall is 60 - 120 cm)
3/4
M. F. discharge (Q) = C A
3/4
= 14.000 x 32.325
= 189.794 Cumecs
Add 30% extra for CA < 500 SqKm
= 0% x 189.794
= 0.000 Cumecs
Max. Flood Discharge (Q) = 189.794 Cumecs
DISCHARGE CALCUALTIONS USING RYVE'S FORMULA
Catchment Area (A) = 32.325 SqKm
Coef. of discharge (C) = 8.500 ( 6.8 FOR Area with in 25km from coast)
( 8.5 FOR Area with in 25km to 160 from coast)
( 10-12 FOR Limited Areas near hills)
2/3
M. F. discharge (Q) = C A
2/3
= 8.500 x 32.325
Max. Flood Discharge (Q) = 86.354 Cumecs
Max. Flood Discharge (Q) = 192.440 Cumecs (Refer Area Vel. Cal. @Crossing)
Design Flood Discharge (Q) = 192.440 Cumecs
Say 192.440 Cumecs
Lacey's Bed width Calculations
Discharge, Q = = 324.000
P= = 4.75 Q^0.5 = 85.500 m
Bed width/L.W.W. = 60.000% x 85.500
= 51.300 m
LWW as per Lacey's BW = 51.300 m
L.W.W. calculations
1) LWW as per Lacey's BW = 51.300 m
2) LWW as per Site condition = 45.000 m (i.e Length of water way at O'MFL)
3) LWW as per MFL Cal.:
Sill Level at Crossing = +97.200 m
MFL at Crossing = +100.050 m
Depth of flow at Crossing = 2.850 m
Velocity of flow at X'ing(Vv) = 1.22 m/s (as obtained from Area Velocity Calculations)
Assuming Afflux (x) = 0.300 m
2 2
Head due to Afflux (ha) = V d
2
= 0.062 m
2g (d+x)
Combined head (ha + x) = 0.362 m
Velocity of Flow through vents = 0.9 2g(ha+x)
Vv = 2.399 m/s
LWW as per MFL Cal. = Q / (Vv d)
= 28.148 m
Max. of the above, LWW = 51.300 m
.'.Design Linear Water Way = 51.300 m
Clear Span of Each Vent = 8.000 m
No. of Vents required = 51.300 8.000
= 6.413
However proposing 6 Vents of 8.000 m clear span
Total Span of Each Vent = 8.760 m
Total length of the bridge = 52.560 m
RCL Fixation
MFL = 100.050 m
Vertical clearance = 1.200 m
Deck slab depth = 0.650 m
Afflux = 0.300 m
Wearing coat = 0.075 m
Road top level (RCL) = 102.275 m
Bottom deck level = 101.550 m
Drain Bed Slope Calculations:
I.
Level at 400 U/S = + 98.200
Level at 400 D/S = + 96.000
Diff. in levels = 2.200
Distance = 800
.'. Slope = 1 in 363.636
II.
Level at 400 U/S = + 98.200
Level at point of Crossing = + 97.200
Diff. in levels = 1.000
Distance = 400
.'. Slope = 1 in 400.000
III.
Level at point of Crossing = + 97.200
Level at 400 D/S = + 96.000
Diff. in levels = 1.200
Distance = 400
.'. Slope = 1 in 333.333
Average Slope = 1 in 363.636
Say 1 in 364.000
DRAIN M.W.L CALCULATIONS
@ CROSSING
Drain Discharge Q '===> 192.44 M3/ Sec
Bed slope : ===> 1 in 364.000
Value of 'n' : ===> = 0.0300
Max. water level assumed: ===> = 100.050
Side Slope of Channel: ===> 2.0 :1
Hori.
Depth of Peri-
Level Dis- Area
flow meter
tance
in m in m in m in Sq.m in m
100.200 A= 160.614 m2
99.900 10.000 0.150 0.375 5.002
99.650 10.000 0.400 2.750 10.003 P= 127.986 m
99.435 10.000 0.615 5.075 10.002
99.400 10.000 0.650 6.325 10.000 R= A/P
99.200 10.000 0.850 7.500 10.002 = 1.255 m
98.590 10.000 1.460 11.550 10.019
97.350 10.000 2.700 20.800 10.077 V = 1/n * R2/3 * S1/2
97.200 10.000 2.850 27.750 10.001
97.500 10.000 2.550 27.000 10.004 = 1.221 m/sec
97.840 10.000 2.210 23.800 10.006
99.000 10.000 1.050 16.300 10.067 Q= A xV
99.500 10.000 0.550 8.000 10.012
99.950 10.000 0.100 3.250 10.010 = 197.760 Cumecs
100.310 10.000 0.139 2.780
100.550 10.000 > Drain Discharge.
100.900 10.000
100.920 10.000 Hence the assumed MWL
100.930 10.000 is Correct.
100.940 10.000
100.950 10.000
SCOUR DEPTH CALCULATIONS FOR PIER
Discharge(in Cumecs), Q = 189.794 m3/sec
Bed Width(in metres), b = 51.300 m
Silt Factor, f = 1.000
MFL = +100.050
Scour Depth multiplication factor, x = 2.000
Discharge / metre width(in Cumecs/m), q = Q / b = 3.700 m3/sec/m
2 1/3
Normal scour depth R = 1.35(q / f ) = 3.229 m
Max scour depth = x. R = 6.459 m
Grip Length (Max. of R/3,1.2) = 1.200 m
Max scour level = MFL - scour depth - GL = +92.391
How ever the foundation is taken upto +92.000
Hence safe.
SCOUR DEPTH CALCULATIONS FOR ABUTMENT
Discharge(in Cumecs), Q = 189.794 m3/sec
Bed Width(in metres), b = 51.300 m
Silt Factor, f = 1.000
MFL = +100.050
Scour Depth multiplication factor, x = 1.270
Discharge / metre width(in Cumecs/m), q = Q / b = 3.700 m3/sec/m
2 1/3
Normal scour depth R = 1.35(q / f ) = 3.229 m
Max scour depth = x. R = 4.101 m
Grip Length (Max. of R/3,1.2) = 1.200 m
Max scour level = MFL - scour depth - GL = +94.749
How ever the foundation is taken upto +94.500
Hence safe.