Panna - Khajuraho New BG Rail Line

BRIDGES HYDROLOGY REPORT Bridge No: 115/1

Basic Data Sheet
1. Section- Panna-Khajuraho(KURJ)
2. Bridge No- 115/1
3. Type of Bridge- MINOR

4. Chainage 115221.846 m
5. Kilometerage- 115.222 km
6. River/Nala/Stream/Tributary - Nala
7. Proposed Span- 1X3X4m
8. Location-
a. Easting (m) 414722.64 m
b. Northing (m) 2754483.22 m
9. Catchment Area 0.36 sq. km
10. Shape of Catchment Fern
11. Length of longest stream from bridge site 1.1 km
12. Height of farthest point from point of
139.137 m
interest along the river-
13. Toposheet No G44U1(63D/1)
14. Topography- Plain
15. Land Cover Agricultural Land
16. Sub zone- Betwa 1 (c )
17. 50 Year 24 hr Rainfall (cm) 32 (from Plate 10 of RBF 16)

References for this report-

2
i. 2.RBF -16- Flood estimation methods for catchment less than 25 km in area by RDSO.
ii. 3.Flood estimation report of Betwa Subzone 1 (c) by CWC and RDSO.
iii. Code of practice for design of Substructures and foundations of bridges by RDSO.

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 Panna - Khajuraho New BG Rail Line
BRIDGES HYDROLOGY REPORT Bridge No: 115/1
Flood Estimation as per RBF-16
Proposed Bridge Span (m) : 1 X 3.00 m
Bridge Structure Type : RCC BOX
Catchment Area : 0.36 Sq Km
Length of Longest stream : 1.1 Km
RL of Farthest Point : 296.000 m
RL of Point of Interest : 156.863 m
Difference of RL : 139.137 m
Nature of Soil : Hilly Soils/Plateau
Average Bed Level : 156.863 m
Observed HFL : 158.000 m

A. Using Improved Rational Formula

Q50=0.278 CxIxA ; Where Q50= 50 yr Design Flood Discharge
C= Run-off Co-efficient, I=50 yr Rainfall Intensity lasting for tc hr
tc=Time of Concentration, A= Catchment Area
C=0.498(R.F)0.2 = 0.93266534
R= 50 Yr 24 hr Point Rainfall (Cm) = 32 Cm Plate 10 of RBF-16
F= Areal Reduction Factor = 0.72

Duration of Rainfall (Min)

Catchment Area in Sq Km
<30 30 to 60 60 to 100
< 2.5 0.72 0.81 0.88
2.5 -5 0.71 0.8 0.87
5- 13 0.7 0.79 0.86
13-25 0.68 0.78 0.85

Time of Concentration(tc)=[L3/H].345 = 0.201 hr = 13 min

Calculation Of Rainfall Intensity

tc hr ratio : 0.125 From Figure 4 RBF 16
1 hr ratio : 0.34 From Figure 4 RBF 16
Co-efficient K=tc hr ratio/1 hr ratio = 0.367647059
R-50 (24) : 320 mm
R-50(1)=R 50(24)x1h to 24h ratio : 108.8 mm
R-50 (tc)=K x R-50(1) = 40 mm
Intensity of Rainfall(I)=R-50(tc)/(tc) : 199.01 mm/hr
Design Flood Discharge : Q-50 = 0.278 C x I x A
Q50 = 18.576 cum/sec
B. Synthetic Unit Hydrograph Based Method
For Betwa Subzone (1c)
i) qp = 1.331x (L/S)-0.492 = 13.741 Cumec/sq km
ii) Qp = qp X A. = 4.947 Cumec
iii) Q50 = Qp x R50(tc) = 19.79 Cumec

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 Panna - Khajuraho New BG Rail Line
BRIDGES HYDROLOGY REPORT Bridge No: 115/1
C. Area Velocity method
A= Area of Cross Section of Flow = 6.673 sq m By Autocad Drawing
P= Wetted Perimeter = 8.17 r.m By Autocad Drawing
S= Longitudinal Bed Slope = 0.008095 From survey drawing
n=Manning's Roughness Co-efficient= 0.025 For Rocky strata/Barren Land
R=Hydraulic Mean Depth=A/P = 0.816568771 m
Manning's Velocity of flow,V=(1/n)R2/3S1/2 = 3.144 m/S
Discharge by Manning's formula,Q=AxV= 20.98 cumec
Design discharge = (Max of above three)= 20.98 cumec
Checking of Waterway
Required Wetted Perimeter, Pw (m) = 1.811C√Q Ref Para 4.5.3 of Substructure code
C= A coefficient normally taken as =2.67 Ref Para 4.5.3 of Substructure code
Required Wetted Perimeter, Pw (m) = 22.15 m, Reqd. Width = Pw-2x(OHFL-BL) = 19.87m
Bank to Bank Distance (in HFL condition)= 3.00 m (from survey)
Provided Span= 3.00 m hence, Afflux calculation required
Calculation of Afflux
Height of Afflux by Molesworth formula, h= [ V2 /17.88 + 0.01524 ] x [ (A/a)2-1]
Where, h= Height of afflux in meter ; V= Velocity of un-obstructed stream in m/s ; A= Un-obstructed sectional area
of the river in square meter ; a = Sectional area of the river at Obstruction in square meter.
Obstructed C/S
Unobstructed cross sectional area in sqm, A= 6.673 3.411
area in sqm=
Afflux for this bridge, h= 1.606 m Considered as = 1.61 m

Checking for Adequacy of Formation Level & Freeboard Provided & Discharge Capacity
Design Discharge for the bridge= 20.98 cumec
Velocity of Flow, V= 3.14 m/S
Required cross sectional area of flow,A=Q/V 6.67 sq.m
Provided span= 3.00 m
Height of water about BL= 2.224 m
Reduced level of Max Height of Water= 159.087 m (Calculated HFL)
Design HFL (Max of OHFL & CHFL)= 159.087 m
Required clearance of Bridge= 0.000 m
Thickness of Proposed Girder/Slab/Box= 0.35 m
Min. Formation Reqd. = Design HFL + Vertical Clearance+Br. Thickness+Afflux
Required minimum formation level= 161.043 m
Formation level adopted= 171.621 m OK
Freeboard provided= 12.534 m >1m OK
Discharge capacity= Velocity x Flow Area Provided. = 37.72670181 >20.979 cumec OK
Min. Vertical Clearance (Para 312(1) IRBM )
Ver. Clear.
Discharge in Cumecs Reqd. Clearance
(mm)
0-30 600 0.6
31-300 600-1200 0.6-1.2
301-3000 1500 1.5
Above 3000 1800 1.8

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 Panna - Khajuraho New BG Rail Line
BRIDGES HYDROLOGY REPORT Bridge No: 115/1
Calculation of Scour Depth :
Design Discharge for foundation = 1.3xQ = 27.27 cumec
Effective Width of waterway = 3m
Discharge per unit width,Db = 9.091 sq.m/s
Silt Factor Table as per Bridge substructure and Foundation code by
RDSO
Weighted
Type of Bed Material mean data of Value of 'f'
particle (mm)
Coarse Silt 0.04 0.35
0.08 0.5
Fine Sand
0.15 0.68
0.3 0.96
Medium Sand
0.5 1.24
0.7 1.47
Coarse Sand 1 1.76
2 2.49

Silt Factor considered= 2.600 From soil test report

1/3
Scour Depth by Lacey's Formula, D1= 0.473 (Qf/f) = 1.035 m

Scour Depth, D2=1.338(Db2/f)1/3 = 4.238 m

Scour depth to be considered as, D = 4.238 m
(Rock Layer to be considered for finding actual scour depth, which shall be provided along with laboratory testing
report, in the borelogs)
Scour depth multiplication factor Table as per Bridge substructure and Foundation code by
RDSO
Nature of River Depth of Scour
In straight reach 1.25D
At the moderate bend conditions e.g along apron or guide bund 1.5D
At a severe bend 1.75D
At a right angle bend or at nose of piers 2D
In severe Swirls e.g. against mole head of a guide bund 2.5 to 2.75D

River Type Scour Depth

Moderate Bend 1.5D
Design Scour depth = 6.36 m
Rock layer starts at depth = 10.00 m

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 Panna - Khajuraho New BG Rail Line
BRIDGES HYDROLOGY REPORT Bridge No: 115/1

Conclusion-
i) The Nala is a seasonal having a bank to bank width of 3 m.
ii) A catchment area of 0.36sq km drains through the bridge site.
iii) The design discharge of the bridge is calculated as 20.979 cumec.
iv) The required wetted perimeter for the bridge is worked out as 22.147 m and the linear waterway
provided is 3 m so, afflux calculation is done and considered for finding out minimum required formation
level
v) The design HFL of the bridge is maximum of CHFL & OHFL, and found to be 159.087 m
vi) The provided Freeboard for 20.979 cumec discharge is 12.534 m as against the minimum required
Freeboard of 1 m as per IRS substructure and foundation of bridges code cl no 4.9.1. Hence the criteria
of Freeboard is satisfied.
vii) The minimum required formation level for this bridge is 161.043 m and the formation level provided is
171.621m. Hence the proposed formation level i.e 171.621 m is safe.

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