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 A. Basic Mechanics 1. Laminar Flow 2. Turbulent Flow 3. Reynolds Number Re = driving forces = V D p = (velocity * depth * fluid density) resisting forces u (fluid viscosity) laminar < < turbulent \

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

I. The River Channel B. Flow Equations and Resisting Forces 1. Manning Equation 2. Chezy Equation V = C *(RS) 1/2

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 = aQ b d = cQ f v = kQ m

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

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

Distance Downstream

B. The Influence of Slope Slope (ft/mi)

B. The Influence of Slope

III. The Quasi-Equilibrium Condition C. Channel Shape ….in cross section: F = 255M 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

(pools and riffles)

Riffles are spaced ~ 5-7 times the channel width

(pools and riffles)

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IV. Channel Patterns Meanders…….

IV. Channel Patterns Meanders…….

IV. Channel Patterns Meanders…….

IV. Channel Patterns Meanders…….

A few final words on stream form…. braided

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

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….

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 V = C *(DS) 1/2 or

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

the graded river: Lane Diagram 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…

V. Rivers, Equilibrium, and Time Responses from adjusting load and discharge… ACTIVITYRESPONSESLOPE

V. Rivers, Equilibrium, and Time Responses from adjusting load and discharge… ACTIVITYRESPONSESLOPE Increase in load?????? Decrease in load?????? Increase in discharge?????? Decrease in discharge??????

V. Rivers, Equilibrium, and Time Responses from adjusting load and discharge… ACTIVITYRESPONSESLOPE Increase in loadAggradationincrease Decrease in load Increase in discharge Decrease in discharge

V. Rivers, Equilibrium, and Time Responses from adjusting load and discharge… ACTIVITYRESPONSESLOPE Increase in loadAggradationincrease Decrease in loadDegradationdecrease Increase in discharge Decrease in discharge

V. Rivers, Equilibrium, and Time Responses from adjusting load and discharge… ACTIVITYRESPONSESLOPE Increase in loadAggradationincrease Decrease in loadDegradationdecrease Increase in dischargeDegradationdecrease Decrease in discharge

V. Rivers, Equilibrium, and Time Responses from adjusting load and discharge… ACTIVITYRESPONSESLOPE Increase in loadAggradationincrease Decrease in loadDegradationdecrease Increase in dischargeDegradationdecrease Decrease in dischargeAggradationincrease

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…..