Tractive approach of canal design

1. DESIGN OF HYDRAULIC STRUCTURES
Course Code: 101612
Branch: Civil Engg.
Credit: 03
Prepared By:
Rajkishor,
Assistant Professor,
Department of Civil Engineering,
Bhagalpur College of Engineering, Bhagalpur

2. DESIGN OF HYDRAULIC CHANNEL BY TRACTIVE APPROACH
Sediment Transport:
 Whenever water flows in a channel (natural or river), it tries to scour
its surface.
 Silt or gravel or boulders get detached from the bed or sides of the
channel.
 These are swept in downstream by the moving water.
 This phenomenon is known as sediment transport.
 Sediment transport further results in silting and scouring which may
damage channels or reservoirs.
Sediment Load:
 The sediment in a canal is a burden to be borne by the
flowing water which is known as sediment load.

3. SEDIMENT LOAD
BED LOAD
SUSPENDED LOAD
 Bed load is that in
which the sediment
moves along the bed
with occasional
jumps into the
channel.
 While the suspended
load is the one in
which the material is
maintained in
suspension due to the
turbulence of the
flowing water.

4. Bed Formation:
• At very low velocities, the bed doesn’t move at all.
• For example, In case of fine sand (lesser than 2mm dia) when
velocity is increased gradually, then-

6. Till now, The flow is in
SUB-CRITICAL stage.

8. Mechanics of Sediment Transport:
• Considering the soil to be incoherent (c =0), each soil particle can
be studied separately, there are no cohesive force between the
particles such as in sand or gravel.
• Tractive force or Drag force or Shear force is the basic
mechanism involved in sediment transport, exerted by water in the
direction of flow.
• This force is nothing but pull of water on the wetted area.

11. Distribution of tractive stresses or shear stresses
generated in a trapezoidal channel section

12. Incipient Motion of Sediment:
is defined

15. After balancing and simplifying these forces and using ‘c’ as denotation for
subscript of critical condition, we have

18. For no scouring condition-
it

19. (For no scouring condition)