Marginal bunds and guide banks and their design procedure

1. TOPIC: MARGINAL BUNDS AND GUIDE BANKS AND THEIR
DESIGN PROCEDURE
PRESENTED TO : DR.MUJAHID KHAN
GROUP MEMBERS :
AMJAD ALI KHAN
HABIB AHMAD JAN
UZAIR KHAN
SHABIR JAN

2. CONTENTS
River training works
Objective of river training works
Types of river training works
Marginal bunds
Objective of marginal bunds
Guide banks
Shape of guide bank
Design procedure of guide bank
Numerical problems

3. RIVER TRAINING WORKS
The process of controlling the flow in river & river bed
configuration is called river training works.
 These are the structural measures adopted in rivers to avoid
outflanking & shifting its thalweg due to geomorphological
changes in the river.
 So, the river training works stabilize the river channel along a
certain alignment.

4. OBJECTIVES OF RIVER TRAINING
To prevent the river from changing its course .
To prevent flooding of surrounding countries by providing a safe passage of
floodwaters without overtopping the banks.
To protect the river banks by deflecting the river away from the attacked banks.
To ensure effective disposal of sediment loads.
To provide minimum river water depth required for navigation.
To prevent additional areas to be submerged due to afflux.

5. METHODS OF RIVER TRAINING
Different methods employed for the purpose of river training are as follows:
Marginal Bunds/Marginal Embankment
 Guide Bank
 Spurs/Groynes
Artificial Cutoffs
Pitching of Banks & Provision of Launching Aprons
Pitched Islands

6. MARGINAL BUNDS
There are the earthen embankments running parallel to the river & at some
distance from the river.
 These are the flood embankments in continuation of guide bunds designed to
contain the floodwater within the flood plains of the river

7. MARGINAL BUNDS

8. MARGINAL BUNDS

9. MARGINAL BUNDS

10. OBJECTIVE OF MARGINAL BUNDS
To confine the flood water from the river within an allowable cross-section.
 Spreading of flood water beyond these marginal bunds is prevented
 Protect the marginal land from inundation caused by floods.
Protect low-lying areas from being flooded.
 To contain the floods within the flood plain of the river

11. GUIDE BANK
Also called bell’s bund. It is defined as the site of a barrage, weir, bridge, etc. to
guide the river flow through the confined waterway without causing damage to the
structure and its approaches

12. SHAPE OF GUIDE BANK
The guide banks consist of two heavily built set of embankments with heavily
protected curved ends in the shape of bell mouth. The width of water way is kept
equal to the width of the structure from abutments. The river side slops of guide
banks are pitched with stones.

13. FIGURE

14. HOW ARE THEY PROVIDED
They are provided in the direction of flow, both upstream and downstream of the
barrage of one or both flanks depending or requirement. The guide banks are
usually provided in pairs, symmetrical in plan and may either be parallel or
converge slightly towards the structure, extending a little downstream but largely
on the upstream of the structure and curved inlands on both ends to provided a bell
mouth entry and smooth exit

15. WHY WE PROVIDE GUIDE BANKS
Rivers in flood plains submerge very large areas during flood periods. Naturally
when some structure is to be constructed across such a river (for example, bridge,
weir, etc.), it is very expensive to construct the work spanning whole width of the
river. To economies some training work may be constructed to confine the flow of
water within a reasonable waterway

16. CONTIN…
 The functions served by a guide bank are
Economical spanning of a wide river
Safe and expeditions passage of floods
 Protect adjacent lands, upstream of a weir or barrage from spills due to afflux
caused by the barrage construction
control and confine the flow axially through a restricted waterway so that the
river has no possibility to swing about and outflank the structure
 Prevent occurrence of crossflow immediately upstream of barrage
Protect the approach embankments (on either side of a bridge extending from the
river bank to the guide banks) from direct attack by the river

17. EFFECTS
 Increase in the rate at which flood wave passes down the river
 Increase in maximum discharge at all points downstream
Rise in the water surface elevation of the river during flood
 Increase in the velocity and scouring action through the embanked section
Reduction in water surface slope of the river above the embanked portion.

18. DESIGN PROCEDURE OF GUIDE BANK
• Guide Bank are the Earthwork embankment for guiding the flood water of river
near a structure constructed across a river.
• Also Called Bell’s Bund.

19. DESIGN PROCEDURE OF GUIDE BANK
• Step:1 Clear Waterway
• The first step in the design of a bridge on an alluvial river is the estimation of
minimum & also safe waterway.
i. The Lacey’s Regime waterway or clear waterway
P=4.75(Q)^1/2
P=Width of channel in meter
Q= Discharge in cumecs
ii. An extra allowance of 20% may be made for thickness of bridge Piers.
L=1.2P

20. DESIGN PROCEDURE OF GUIDE BANK
• Step 2: Length of U/S & D/S Guide Bank.
i. Length of U/S Guide Bank=1.25L---1.5L
ii. Length of D/S Guide Bank= 0.25L
iii. Assume U/S Curve Head=120*-----145*
iv. Assume D/S Curve Head=45*----60*
v. Radius of U/S Curve Head=R=0.45L
vi. Radius of D/S Curve Head=R=0.25L

21. DESIGN PROCEDURE OF GUIDE BANK

22. DESIGN PROCEDURE OF GUIDE BANK
• Step:3 Cross-Section of Guide Bank
• Free board= 1.25m—1.5m
Top width(carriage way)= Not less than 4m
generally 5m
Side slope=2:1

23. DESIGN PROCEDURE OF GUIDE BANK
• Step 4 Design of Stone Pitching & Apron
• Slope Pitching Thickness=t=0.06(Q)^1/3
• Thickness of Apron=T=1.9t
• Length of Apron=1.5D
i. Straight Reach Guide Bank
D=1.25R-y
ii. For Curvilinear Reach Guide Bank:
D=1.5R-y
R=0.47(Q/f)^1/3
f=1.76(d)^1/2
d=dia of silt particle(mm)

24. NUMERICAL PROBLEM
• Design & Sketch a guide bank including launching Apron from Following Data:
• Max Discharge=Q= 10000 cumecs
• High Flood Level= 250m
• River Bed Level= 242m
• River Bed Material average size= 0.25mm

25. NUMERICAL PROBLEM
• Solution:
• Step 1: Clear Waterway
P=4.75(10000)^1/2
P= 475m
Allowing 20% Extra for Piers
L=1.2(475)
L= 570m
Step 2:
Length of u/s Guide bank=1.25L=1.25*570= 712.5m
Length of d/s Guide Bank=0.5*L=0.5*570= 142.5m
Radius of u/s curve Head=R=0.45L=0.45*570= 256.5m
Radius of d/s curve Head=R=0.25L=0.25*570= 142.5m

26. NUMERICAL PROBLEM
• Step 3: cross section of guide bank
H.F.L=250m
Assume free board= 1.5m
Top level of guide bank=250+1.5= 251.5m
Assume top width= 5m
Side slope=2:1
Depth of water above bed level=y=250-242=8m
Height of bank above river bed level=251.5-242= 9.5m

27. NUMERICAL PROBLEM
• Step 4: Design of stone pitching & apron:
Slope pitching thickness=t=0.06(10000)^1/3= 1.3m
Thickness of apron=T=1.9t=1.9*1.3= 2.47m
Length of Apron:
Straight Reach Guide Bank=(1.25R-y)
R=0.47(Q/f)^1/3
f=1.67(d)^1/2=1.67(0.25)^1/2= 0.88
R=0.47(10000/0.88)^1/3= 10.56m
D=1.25R-y=1.25*10.56-8= 5.2m
Length of Apron=1.5D=1.5*5.2= 7.8m
For curvilinear reach guide bank:(1.5R-y)
D=1.5*10.56-8
D= 7.84m
Length of Apron: 1.5D=1.5*7.84= 11.76m

28. Q/A ?