Lecture 8-River Dynamics 2

Question 1

Q = Av = wdv

Answer 1

Formula for discharge
Q= discharge
A= area of the cross section (width x depth)
v= velocity (mean)
Units will be cubic meters per second

Question 2

Flume

Answer 2

A rectangular channel /tube used in hydrology labs

Question 3

Average velocity

Answer 3

Different processes and forces act on the flow pushing it forward and holding it back, at the bed velocity is equal to zero (no-slip condition or viscosity ) water in the middle of the cross section is more turbulent, at the surface it is moving faster than the mean

Question 4

Open channel flows

Answer 4

Will have 3 sides - air flow over the top

In terms of flow type it will be boundary layer flow (final stage wl turbulent flow over laminar flow @ the base

Question 5

Flow classification of boundary layer in an open channel is dependent on:

Answer 5

1. Relative magnitude of gravity, viscous and turbulent forces
2. Rate of change of mean velocity or mean depth with respect to time (temporal)
3. Rate of change of mean velocity or mean depth in downstream direction (spatial)

Question 6

Reach

Answer 6

A manageable section of river which we can observe

Should be fairly straight and consistent depth /width

Question 7

Reynolds equation

Re = VR / υ

Answer 7

Re= Reynolds number
V= velocity
R= hydraulic radius
υ = coefficient for kinematic viscosity (stickiness at the base)

Question 8

Hydraulic radius formula

R =A/P

Answer 8

A= area = width x depth
P= wet perimeter = 2x depth + width

Question 9

Reynolds number meaning

Answer 9

Re < 500 mean viscous forces are dominant, flow is laminar
Re > 500 means turbulent forces are dominant
Re > 2000 means fully turbulent

Question 10

Which equation is used to determine if flow is laminar or turbulent?

Answer 10

The Reynolds equation

Need to know velocity and the channel width and depth

Question 11

υ

Answer 11

Kinematic viscosity
= 1.307 x 10 to the power of -6
Units= m 2 s -1

Question 12

Froude number

Fr =V / sqrt(gY)

Answer 12

Will the power of turbulence over come an obstacle in the water or will it pond, backfill behind the object
Ratio of turbulent force to gravity force
V = velocity
g = gravity = 9.8m s-2
Y = depth

Question 13

Froude number meaning,

Answer 13

Fr <1 means gravity exceeds flow velocity (can pond and head back upstream) → subcritical (tranquil)
Fr >1 turbulent forces are greater → supercritical (rapids)
Fr =1 critical i-can pond and head