Class Notes
(808,126)

Canada
(493,084)

Wilfrid Laurier University
(17,900)

Geography
(296)

GG282
(10)

James Hamilton
(10)

Lecture 11

# Lecture 11.pdf

Unlock Document

Wilfrid Laurier University

Geography

GG282

James Hamilton

Winter

Description

Fluvial Processes
April 10, 2014 1:29 PM
• Introduction to Stream Flow
• Channel processes
○ Stream boundary conditions
○ Sediment
Entrainment, transport
Load
○ Trenhaile Chapter 10
Introduction to Stream Flow
• Stream Velocity
○ In general, velocitiesare higher where:
Channel bed and banks are 'smooth'
Channel gradients are steep
Channel width to depth ratio is low
○ May be measured directly
○ Estimated using a flow formula such as the:
Chezy Equation,
Darcy-WeisbachEquation, or the
Manning Equation
○
○ Values of n, more friction= higher n
• How do channel width and depth influence velocity?
○ Consider the hydraulic radius ®
• Hydraulic Radius (R)
○ What is the impact of R if we hold width constant but increase depth?
If depth = 1m and width= 10m
□ R is 10m2/12m
□ R= 0.83
If depth= 3m and width= 10m
R is 30m2/ 16m
R= 1.9
○ If we increase R, what happens to velocity?
○ How does R vary between channels, is there a difference between wide and shallow
channels and narrow deep channels?
○ Width= 10m, depth =0.5m
R= (10m2)/11m=0.45m
○ Width= 5m, depth= 2m
R= (10m2)/9m=1.1m
○ Wide and shallow channel:
R is relatively small
○ Deep and narrow channel:
R is relatively large
• Examine the impact of R on stream velocity using the manning equation • Examine the impact of R on stream velocity using the manning equation
• Manning Equation
○
• In a channel:
○ Width, depth, gradient and bed materials will change, thus velocity and flow conditions
will vary
Channel Processes
• Stream Boundary Conditions
○ Laminar and Turbulent Flow
○
○ Laminar Flow
Water molecules movein parallel paths that slide over one another with little
mixing
○ Turbulent Flow
Water molecules movealong highly variable paths with considerable mixing
○ Reynolds Number (Re):
Used to define the transition from laminar to turbulent flow:
□ Re= (vR)/v
Where
□ v= velocity
□ R= is length (distance)
□ v(second v)= Kinematic Viscosity (measure of the resistance of a fluid to
deform)
When Re<500the flow is laminar
For turbulent flow, the Re is higher
○ Froude Number (Fr): Nature of the Turbulence
Fr= ((v)/(gd)^0.5)
□ Where v is velocity,d is depth, g is accelerationdue to gravity (m/s2)
When Fr<1: flow is more tranquil
When Fr>1: flow is more chaotic and erosive
Chanel Processes: Boundary Layer
• Velocity profiles for smooth turbulent (a) and roug

More
Less
Related notes for GG282