Rivers processes Flashcards
Describe the long profile of a river
Starts steep in the upper course and then becomes increasingly flat towards the lower course
How does the cross profile of a river change from source to mouth?
Starts narrow and V shape, gets wider with a flatter bottom towards the mouth
What is the Bradshaw model and what does it show?
How a river changes from source to mouth- quicker, wider, deeper, smaller particles, more discharge
Why does a river deposit material?
on inside of meanders when there’s more friction, when the river slows down and has high capacity. Overloaded with sediment, might be an obstruction in the river
What is lateral erosion and where does it take place?
Middle course to produce wide valleys
Which part of the river’s course do you find waterfalls and gorges?
Upper course
What role does rock type play in the formation of waterfalls and gorges?
Band of hard rock overlays soft rock. Soft rock erodes quicker causing an overhang.
What are interlocking spurs and where are they found?
Hillsides that interlock as the river winds around them. Found in upper course
What is a meander?
bend in a river
Why is the current faster on the outside of the bend?
The river is deeper, there is less friction to slow the water down
Describe how oxbow lakes are formed
Erosion causes the outside bends of a meander to get closer together until there’s only a small bit of land left. During times of flood the river breaks through so the river takes the shortest course. Material is deposited along the river banks cutting off the meander.
What is a flood plain and a levee?
A floodplain- wide valley floor on either side of a river in the lower course, Levee- deposited mounds of material either side of the river in the lower course
Why does the water level in an estuary change over the course of a day?
Water is tidal so water rises and falls with the tide. When it’s high the water flood the valley and silt is carried there.
What is the name of the waterfall along the River Tees?
High Force
Name 2 ways water gets into a river
Rainwater can flow overland- surface runoff, soak into the ground (infiltration) and flow through the soil to get into the river or directly into the river. Percolation - where water soaks through rocks. Through flow - lateral movement of water through rock.
What is the falling limb and rising limb of a hydrograph?
Falling limb shows the decrease in river discharge as the river returns to normal level. Rising limb is the river level increasing to peak discharge after the rainfall event
Name 2 physical factors that would increase the risk of flooding
Prolonged rainfall, steep slopes, impermeable rocks. Saturated ground. Rapid snowmelt
What is the lag time in a hyrdograph? Why is there a lag time?
The time between peak rainfall and peak discharge. There’s a delay between peak rain and peak discharge as the water travels slowly through soil and comes in different routes to reach the river
How would changing land use increase flood risk?
The building materials made from impermeable rock increasing the speed of surface run off. man made drains also channel water quickly into the river. Deforestation.
What are river embankments?
Raised walls along river banks that allow the river to hold more water
How might channel straightening affect villages further down?
it will reach the villages downstream quicker leading to increased erosion and flood risk
Why was the flood management scheme required in Boscastle?
Severe flash flooding 2004. Damaged homes and access to work was restricted - tourism was severely effected.
Describe the hard engineering that was used in Boscastle
Widening the river, flood culverts, raised height of the bridge. Braided the river upstream. Raised the height of the car park.
Describe the soft engineering that was used in Boscastle
Coppicing of trees
What are the environmental issues associated with flood management scheme in Boscastle?
Many trees and large area of rare grassland will be removed and replanted. Fish and aquatic life were disturbed when the river was widened.
