“the great sculptor of the landscape” Fluvial Processes “the great sculptor of the landscape”

I. The River Channel A. Basic Mechanics 1. Laminar Flow 2. Turbulent Flow

I. The River Channel B. Flow Equations and Resisting Forces Discharge = velocity * depth * width Q = V*A 1. Manning Equation

1.Manning Equation v = R 2/3 S ½ n Where v = average flow velocity r = hydraulic radius s = channel slope (unitless) n = Manning roughness coefficient R = A/P A = Area P = Wetted Perimeter

Q = A R 2/3 S ½ N Where Q = average flow discharge A = area of channel R = hydraulic radius S = channel slope (unitless) n = Manning roughness coefficient R = A/P A = Area P = Wetted Perimeter

II. The Erosion Process

II. The Erosion Process D. Water Sheet Wash

A. Erosion

Rill Erosion

Gully Erosion

II. Sediment in Channels A. Transportation 1. Suspended load 2. Bedload B. Entrainment and Erosion

II. Sediment in Channels A. Transportation 1. Suspended load 2. Bedload 3. Washload B. Entrainment and Erosion C. Deposition

II. Sediment in Channels A. Transportation 1. Suspended load 2. Bedload 3. Washload B. Entrainment and Erosion C. Deposition “ a battle between velocity and gravity”

III. The Quasi-Equilibrium Condition  

III. The Quasi-Equilibrium Condition   A. Hydraulic Geometry

III. The Quasi-Equilibrium Condition   A. Hydraulic Geometry Q = V*A

III. The Quasi-Equilibrium Condition   A. Hydraulic Geometry Q = V*A Q = V * w * d

III. The Quasi-Equilibrium Condition   A. Hydraulic Geometry Q = V*A Q = V * w * d w = aQb d = cQ f v = kQ m

M = 0.26 A. Hydraulic Geometry M = 0.4 “at a station trends” M = 0.34

M = 0.5 A. Hydraulic Geometry M = 0.4 “distance downstream trends” M = 0.1

Distance Downstream

B. The Influence of Slope (ft/mi)

B. The Influence of Slope

III. The Quasi-Equilibrium Condition C. Channel Shape

III. The Quasi-Equilibrium Condition C. Channel Shape ….in cross section: F = 255M-1.08 Where F = width to depth ratio (W/D) M = % silt and clay in channel

IV. Channel Patterns ….in plan view (bird’s eye) Straight Meandering Braided Transition between Straight And Meandering is when Sinuosity is 1.5

IV. Channel Patterns From: Montgomery and Buffington, 1997

High Gradient, Confined Channels Cascades

High Gradient, Confined Channels Step-Pool

Moderate to Low Gradient, Unconfined Channels Plane Bed

Plane-Bed Channels

Moderate to Low Gradient, Unconfined Channels Pool Riffle

Sebaskachu R (Labrador) - tortuous meandering river developed on marine silt and fine sand. Copyright © Norm Catto 2002

Extremely Low Gradient, Unconfined Channels Dune Ripple

(pools and riffles)

(pools and riffles) Riffles are spaced ~ 5-7 times the channel width

(pools and riffles)

(pools and riffles) `

IV. Channel Patterns Meanders…….

IV. Channel Patterns Meanders…….

IV. Channel Patterns Meanders…….

IV. Channel Patterns Meanders…….

Meanders…….

A few final words on stream form…. Anastomosing channels braided

A few final words on stream form…. The factors responsible are……

A few final words on stream form…. Why do channels take on a certain pattern?????

A few final words on stream form….

A few final words on stream form…. Why do channels take on a certain pattern????? It’s primarily due to the relationship between slope and discharge (or velocity)

A few final words on stream form…. Why do channels take on a certain pattern????? It’s primarily due to the relationship between slope and discharge (or velocity) The ole’ Chezy Equ: V = C *(RS)1/2 or V = C *(DS)1/2

V = C *(DS)1/2 A few final words on stream form…. It’s primarily due to the relationship between slope and discharge (or velocity) The ole Chezy Equ: V = C *(DS)1/2 V = velocity C = roughness D = depth of flow S = slope of channel

V = C *(DS)1/2 V = velocity C = roughness D = depth of flow S = slope of channel The change in slope is a RESPONSE to changes in channel shape, NOT a cause of braiding Increasing the slope of a stream DOES NOT cause it to braid.

V. Rivers, Equilibrium, and Time “the profile of streams”

knickpoints

V. Rivers, Equilibrium, and Time the graded river: (page 227)

V. Rivers, Equilibrium, and Time the graded river: (page 227) “one in which, over a period of years, slope is delicately adjusted to provide, with available discharge and with prevailing channel characteristics, just the velocity required for the transportation of the load supplied from the drainage basin. The graded stream is a system in equilibrium; its diagnostic characteristic is that any change in any of the controlling factors will cause a displacement of the equilibrium in a direction that will tend to absorb the effect of the change.” Mackin, 1948

Factors affecting stream morphology • Width • Depth • Slope • Velocity Lane Diagram the graded river: Factors affecting stream morphology • Width • Depth • Slope • Velocity • Discharge • Flow resistance • Sediment size • Sediment load Leopold et al (1964)

V. Rivers, Equilibrium, and Time Responses from adjusting load and discharge… Mass in = Mass out + change in storage and… Energy in = Energy out

V. Rivers, Equilibrium, and Time Responses from adjusting load and discharge… ACTIVITY Local Stream Gradient Response Increase in load Aggradation Decrease in load Degradation Increase in discharge Degradation Decrease in discharge Aggradation

V. Rivers, Equilibrium, and Time The reservoir problem…..

V. Rivers, Equilibrium, and Time The reservoir problem….. Chris Greene Lake Charlottesville

V. Rivers, Equilibrium, and Time The reservoir problem…..