Hydro: Channel Morphology

Question 1

What factors affect amount of energy of the river?

Answer 1

Discharge: Volume and velocity

Velocity more significant as a doubling of velocity results in 4times increase in energy

Question 2

What is channel morphology?

Answer 2

A river’s ability to perform geomorphological work which is determined by the amount of energy

Question 3

Compare turbulent flow and laminar flow.

Answer 3

Turbulent flow: vertical & horizontal eddies where water is constantly interchanged between adjacent zones of flow; chaotic movements

Laminar flow: characterised by uniform velocity and no transverse movement. usually only occurs near the laminar sublayer.

Question 4

What is the formula for river discharge?

Answer 4

Q=AV

A: cross section area of river
V: mean river velocity

Question 5

What is the formula for river velocity? (Manning’s Eqn)

Answer 5

V= 1.49R^2/3 S^1/2 / n

R: hydraulic radius
S: channel slope

Question 6

How to measure channel slope? (S)

Answer 6

Height above sea level/ length of channel

Question 7

How does channel roughness affect velocity?

Answer 7

The higher the value, the rougher the bed, the lower the velocity

Question 8

what’s the formula for hydraulic radius?

Answer 8

R= cross sectional area/ wetted perimeter

More balanced width depth ratio -> larger hydraulic radius -> higher velocity

Semi circle is the ideal shape.

Question 9

How does velocity of a stream vary downstream?

Answer 9

S decreases (gentler) 
R increases (due to increase in channel size) 
n falls (compensates decrease in S) 

Hence velocity increases slightly downstream despite decrease in gradient