The Long Profile and Channel Characteristics Flashcards
What is base level?
The lowest point that the river can erode to
Total erosion and deposition along the full course of a river are balanced, why may there still be an uneven profile?
Rates of erosion and deposition change along the course, results in formations like waterfalls
What are the 3 stages of a river?
Upper course
Middle course
Lower course
Characteristics of the upper course
Gradient is steep
River is high above sea level
Lots of potential energy
Characteristics of the middle course
Gradient decreases
Potential energy is converted into kinetic energy
River gains velocity
Characteristics of the lower course
River has little potential energy
Lots of kinetic energy
Flows faster - greater velocity
What do channel characteristics affect?
Velocity and discharge
Do velocity and discharge, increase or decrease downstream?
Increase
Why does discharge increase downstream?
Tributaries join the river and there is more surface runoff
Why does velocity increase downstream?
It’s influenced by gradient, discharge and channel characteristics
What is kinetic energy used for?
To overcome friction and causes erosion
How does the energy a river has effect efficiency?
More energy a river has for erosion and transportation, more efficient it is
What does an efficient river have?
High velocity
High discharge
Little friction
How is efficiency measured?
By hydraulic radius
Larger hydraulic radius, more efficient river
How do you calculate the hydraulic radius?
Wetted perimeter
What channels are more efficient?
Smooth, narrow and deep channels - have larger hydraulic radius’
Larger hydraulic radius means a smaller proportion of water in contact with wetted perimeter, friction is lower, less energy loss, increased velocity and discharge
What channels are less efficient?
Shallow and broader ones
How does channel roughness effect efficiency?
Protruding banks and large, angular boulders increase wetted perimeter which causes more friction.
Reduces efficiency, velocity and discharge
Where is channel roughness greatest?
Upper course
Why does channel roughness increasing mean that turbulent flow increases?
Turbulent flow is more effective at picking up particles from the river bed than smooth flow - causes greater erosion.
What does a long profile show?
The river’s gradient from its source to the sea
How the gradient of the river channel changes from the rivers source to its mouth by showing the height of the river bed
What is erosion like in the upper course?
Manly vertical, by abrasion and a bit of hydraulic action
Occurs in high energy conditions
Rough channel, cause turbulence, large bed load is dragged along river, intense downward erosion
What is transportation like in the upper course?
Mainly large particles (boulders) carried by traction or saltation during high energy conditions
What is deposition like in the upper course?
Little deposition, mainly largest particles deposited in the river bed as energy levels drop
What is erosion like in the middle course?
Mainly lateral and by abrasion
Sediment size decreases at this state through attrition of the larger particles
What is transportation like in the middle course?
More material carried by suspension as particle size decreases
Some larger particles moved by saltation
What is deposition like in the middle course?
Sand and gravel are deposited across the flood plain as the river floods and friction reduces
What is erosion like in the lower course?
Although discharge and velocity are high, erosion is less as turbulence is lower and sediment size is reduced
Some lateral erosion occurs during formation of meanders
What is transportation like in the lower course?
Mainly smaller particles (silt and clay) carried by suspension, or substances carried by solution
What is deposition like in the lower course?
Smaller particles (silt, clay and sand) are deposited on the flood plain when floods and in river mouth as sea absorbs rivers energy
What does a cross profile show?
Shows what a cross section of the river channel or valley looks like
What are the characteristics of the upper course in terms of its cross profile?
Valleys are steep v shapes
Vertical erosion creates narrow valley floors and steeply sloped sides
What are the characteristics of the middle course in terms of its cross profile?
Valleys are wider caused by lateral erosion
Deposition creates a floodplain on valley floor
What are the characteristics of the lower course in terms of its cross profile?
Valley is wide with gently sloping sides
Much wider floodplain caused by deposition
