OFFICE OF THE EXECUTIVE ENGINEER P

Hydraulic Calculation1.Flood calculation by Area Velocity Method (As per Article- 5 of IRC SP-13)

Q=A x V

A=3311 m2 Area

A =Cross sectional area

in m2

P=600.66 m

P = Perimeter calculated in m

S=1/382

S =Slope as per drain LS taken at

proposal site

n=0.033

n = Rugosity coefficient

(as per IRC SP-13)

V=I/nx(A/P) 2/3 x(S) 1/2

V =Velocity in m/sec.

=1/0.033 3311.00 2/3 1 1/2600.66 382

=4.84 m/sec.

Q=16018.98 cumecs

Say 16019 cumecs

2.Scour depth Calculation

A. For discharge of 16019 cumecs

Case 1 ( As per Panel Discussion & Important Papers: IRC 1990) q2 1/3

dsm= mean scour depthdsm = 1.34 -----

q= Unit discharge

ft

f= Silt Factor

q=Q/(L+2L)

Where Q=Total Discharge

=16019/ (96+2x75)

L=Length of main cause way

=65.12

=96m

L=Length of protected flanks

=2 x 75

(65.12)2 1/3dsm = 1.34 -----------

1.5

=18.95 m

As per caluse no. 703-2-3-1of IRC 78-1983 considering Scour at the pier two times of calucated scour depth below the highest flood level but rock is available on the site, so foundation level is considered as 1.5 in rock.Afflux CalculationAs per IS: 7784 (Part -I) 1975

Molesworth Formula at 1700 cumecs V2 A2h =(--------- + 0.0152) (--------- - 1)

17.85 a2

Where,

h=afflux in m,

v=Velocity in the unobstructed stream in m/s,

A=the unobstructed sectional area of the river in m2

a=the obstructed sectional area of the river at the cross drainage work in m2.

As per Annexure- 1

A=1028.60 n2

V=1.657 n/sec, HFL : 229.560m =

So, soffit of Deck slab : 229.60+0.60= > 230.20m

Average river bed level = 224.80m

Nos. of pier =29

Area : A1 = 06x 4.80 = > 2.88 m2

229.60-224.80 (Average Ground level

= 4.80 m.

0.6 x0.6

A2 (----------------) x 2 = > 0.36

2

A = A1 + A2

=2.88 + 0.36

3.24 m2

For 29 piers 3.24x 29 = 93.96 m2

Soffit of deck (-) Average ground level

0.75 + 0.4 230.20 (-) 224.80

For Abutment =5.40 x (---------------)

2

= 3.105 x 2

= 5.40 m

= 6.210 m2

=>Total obstructed area=93.96 + 6.21

(Piers & Abutment)=100.17 m2

a = 1028.60 - 100.170 = 928.43 m2 (v\V2 A2

h = (---------- + 0.0152) x (---------- - 1) 17.85 a2

(1.657)2 (1028.60)2

= (---------- + 0.0152) x (-------------- - 1)

17.85 (928.43)2

= 0.383 m

Say 0.400m.

Afflux flood level =229.56+ 0.04

= 229.60m.

=> Obstruced Velocity

V=Q/a

=1704.87

=1.84 m/sec

However we consider design velocity 4.0 m/sec.

Afflux flood level =229.60 m + 0.60 m.

Soffit of deck slab=230.20

Top of deck slab=230.95 m + thickness of wearing coat

C:\DATA ONE\BRIDGE DESIGN\CHAP RIVER SUBMER BRIDGE\Hydraulic Calculations CHAP BRIDGE.doc