Discharge Ampl

Br.no 60

AMPL I.

Estimation of design discharge in respect of Bridge No: 60 @ Ch :33127.676 m Proposed bridge 3 x 30.5. PSC Slab Physiographic Parameters:

1 2 3 4 5 6 7 8 9

Catchment area Length of longest stream from source to bridge site (L) Bed Level Level at the farthest point: Height of farthest point along the point of interest along river Length of the Stream from bridge site to nearer to the C.G Soil Sub zone Proposed formation level

A L BL FL H Lc

= = = = = = = = =

45.75 Sq Km 11.000 Km 510.280 m 535.28 m 25.000 m 3.250 Km SANDY CLAY 3(d) m

S

=

2.298

(i) Time from center of unit excess rainfall duration t peak of unit hydrograph Round this value to nearest 0.5 value L Lc 0.261 [ ] Tp=1.757

tp

= =

4.01 4.50

(ii) Peak Discharge of Unit Hydrograph per catchment area

qp

=

II. Calculation of Equivalent Stream Slope (S) Equivalent slope

S

=

Segment Length

S.No

R.L

Distance

1 2 3 4 5 6 7 8 9 10 11

(m) 510.280 512.6 514.9 517.2 519.5 521.8 524.1 526.4 528.7 531.0 533.3 535.3

(Km) 0.000 1.000 2.000 3.000 4.000 5.000 6.000 7.000 8.000 9.000 10.000 11.000

Total \

Li 0.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000 11.000

SLix(Di-1+ Di)/L2 Height Above Datum Di 0.000 2.3 4.6 6.9 9.2 11.5 13.8 16.1 18.4 20.7 23.0 25.0

Di-1+Di Li(Di-1+Di)

0.000 2.300 6.900 11.500 16.100 20.700 25.300 29.900 34.500 39.100 43.700 48.000

0.00 2.30 6.90 11.50 16.10 20.70 25.30 29.90 34.50 39.10 43.70 48.00 278.0

Equivalent Slope

m/Km

III. Calculation of Sythetic Unit Hydrograph Parameters

S

= (iii) Width of the 50% Discharge Ordinate of Unit Hydrograph

(iv) Width of the 75% Discharge Ordinate of Unit Hydrograph

(v) Width of rising side Discharge Ordinate of 50% Unit Hydrograph

(vi) Width of rising side Discharge Ordinate of 75% Unit Hydrograph

(vii) Base width of the Unit Hydrograph

(viii) Unit Duration of Unit Hydrograph

1.260 tp-0.725 0.423

m3/s/Km2

W50 W50

= =

1.974(qp)-1.104

W75 W75

= =

0.961(qp)-1.125

WR50 WR50

= =

1.150(qp)-0.829

WR75 WR75

= =

0.527(qp)-0.932

TB

= =

5.411 (tp)0.826

tr

Page 1

hrs hrs

=

5.1

2.527

2.34

1.174

hrs

hrs

hrs

hrs

19.00

hrs

1.0

hrs

Br.no 60 (ix) Time to start of rise to the peak of Unit Hydrograph

Tm

=

(x) Peak Discharge of Unit Hydrograph

Qp

=

Page 2

5.0

hrs

3 19.372 m /s

Br.no 60 Estimated Unit Hydrograph Parameters were plotted on graph paper . The Plotted papers were joined to draw synthetic unit hydrograph 1Hour SUG Ordinates

Synthetic Unit Hydrograph

16

20.0

14

18.0

12

16.0 Discharge in Cumecs

10

14.0 12.0

8

10.0 6

8.0 6.0

4

4.0 2

2.0 0.0

0

02

0

4

5

6

10

8

10

12

15

14

16

20

18

25

20

22

Time in Hours

The summation of Discharge Ordinates of the unit Hydrograph of 1hr interval Thoeritically equal to Q= (A x d)/0.36*tr)

Where

A

=

Catchment Area

d

=

1.0 cm Depth

Theoritical Discharge Revise the Ordinates of Hydrograph equal to therotical Discharge

IV. Estimation of Design Storm a) Design Storm Duration The Design Storm Duration

Q

=

Hr.

Ordinate

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

0.0 2.0 4.0 10.0 15.0 19.00 16.00 12.0 9.00 8.0 6.0 5.0 4.0 3.0 3.0 2.4 2.0 2.0 1.7 1.5 1 0.75 0

127.31 3 127.08 m /s

(Refer Flood Estimation Report for 3d sub zone) TD

TD = 1.1xtp

=

5.00

hrs

b) Estimation of Point Rainfall and Areal Rainfall for Storm Duration R50 24 hour point rainfall (Refer Plate 9) = 24 cm Conversion factor (Refer Fig.10) = 0.69 R50 5 hour point rainfall = 16.56 cm Areal Reduction Factor for 45.75 Sq.Km catchment area (Refer Ann-4.2) = 0.975 R50 hour areal rainfall = 16.143 cm This 50 year design storm hour areal rainfall has been split in to 1-hour rainfall increments using time distribution coefficients given in Annexure-4.1 or fig-11 of F.E.R-3(d)

Duration

hr 1 2 3 4 5

coefficient

0.64 0.83 0.91 0.97 1

Storm Rainfall

Rainfall Increment

Loss Rate/Hr

Effective Hourly Rainfall

cm 10.332 13.399 14.690 15.659 16.143

cm 10.332 3.067 1.291 0.969 0.484

cm/hr 0.225 0.225 0.225 0.225 0.225

cm 10.107 2.842 1.066 0.744 0.259

V. Estimation of Peak Discharge For estimation of peak discharge, effecitve rainfall increments were arranged against ordinates in descending order. Sum of product of U.G ordinates and gives total direct surface runoff and base flow gives Total Peak Discharge

Time

S.U.G 1-Hour Ordinates Ef. Raifall

Direct Runoff

5

(m3/s) 19.37236

10.10672

(m3/s) 195.791

6.35

14.52927

2.842229

41.29551

7.7

9.686181

1.066465

10.32997

(Hours)

cm

Page 3

Br.no 60 10

7

0.743599

5.20519

11

5

0.259299

1.296496

12

4

0

Total Base Flow for the catchment area Peak Discharge

0 253.92

m3/s (Refer para 3.6)

=

=Direct surface runoff + base flow

=

Page 4

4.58

m3/s

3 258.49 m /s

Br.no 60 VI. Water way calculation (i) Design discharge as per Synthetic Unit Hydrograph method (ii) Assumed velocity

Q V

= =

(iii) Required area of water way

A0

=

3 258.49 m /s 2.44 m/sec

83.38

sqm

(iv) Poposed Linear water way

=

(v) Required Depth of water way = area of water way / Proposed Linear water way

=

(vi) Designed HFL

=

(vii) Required Vertical Clearance Provided Vertical Clearance

= =

1.108 1.108

m m

(viii) Thickness of the slab

=

2.25

m

= =

1.00 3.36

m m

=

4.269

m

(ix) Free board Required (Minimum) Free board Provided (FL-Designed HFL) (x) Bed level to formation level Hence proposed bridge is 3 x 30.5 x PSC Slab VII. Scour depth calculation (i) Design discharge Q is

=

Add 30% for foundation discharge

=

1. 811 xCx

0.91

m

511.19 m

3 258.49 m /s 3 336.04 m /s

Q

According to Lacey's formula Linear Water way= Where C= Coefficient taken as 2.67 (ii) Normal scour depth

91.500 m

D=0.473(Q/f)0.345

where for value of ' f ' refer 4.6.5 as per Bridge Substructure Code (iii) Maximum scour depth for abutment = 1.5*D (iv) Height from bottom of foundation to HFL is (v) Depth of Curtain wall / Drop wall below bed level References: 1 Bridge substructures & Foundation code 2 Flood Estimation Methods (RBF: 16) (If Catchment area <25 Sq.Km) 3 Flood Estimation Report for Mahanadi Sub zone -3(d) of February-1997

Page 5

=

77.74

m

=

2.72

m

=

1.76

= = =

4.09 4.54 3.62

m m m