River Processes And Pressures Flashcards
What are the river characteristics upstream in the upper course?
Lower discharge Narrower channel width Shallower channel depth Slower velocity Smaller load quantity Bigger load particle size Steeper slope angle gradient
What are the characteristics downstream in the lower course?
Higher discharge Wider channel width Deeper channel depth Faster average velocity Bigger load quantity Smaller particle size
What is the process of rock movement across a river bed?
Traction- big boulders roll along the river bed
Saltation- small pebbles bounce along the river bed
Suspension- fine light material is carried along by the river
Solution- Minerals are dissolved in the water
What is a meander and how is it formed?
A large bend in a river. It is formed by fast flow on the outside bend eroding this side and slow flow on the inside bend building up deposition on this side. High energy on the outside bend creates a river cliff and low energy on the inside bend creates a slip off slope.
What is an oxbow lake and how is it formed?
A meander neck is eroded by abrasion and hydraulic action.
The meander neck is flooded through as the meander neck becomes too narrow
The energy becomes slower in the meander as the direction the current travels through the shortest distance. This causes deposition to build up and cut off the idea bow lake from the current.
What are interlocking spurs?
Steep valley sides eroded vertically by upper course rivers
How are waterfalls formed?
A plunge pool forms as attrition forms smaller rocks that, though abrasion, erodes the soft rock
The hard rock the falls down due to gravity as it is left unsupported
This will continue to happen and make the waterfall recede as the soft rock continues to erode at a quicker rate than soft rock which eventually falls down. This will eventually form a gorge.
How are floodplains and levees created?
A flood occurs letting water spill out of its once contained area. Thicker, bigger sediment builds up on the channel edge forming levees and smaller sediment forms floodplains.
After many floods, the water becomes contained as the leaves and floodplains become more built up
How are deltas formed?
A river splits into different channels when meeting a calm sea (sea levels are consistent) because of the build up of sediment creating landforms and channels.
What are antecedent conditions and how do they cause river flooding?
When there is a period of prolonged rain making the ground saturated so when there is another period of heavy rain, the ground can’t absorb anymore water, so there will be more surface runoff increasing the discharge of a river making it more likely to flood
What are hard engineering ways to mange rivers?
Flood walls- barriers built along the river so the river can hold more water so there is less of a flood risk
Embankments- levees put along the side of the river which increases water capacity
Flood barriers- when storm surges occur, the floodgates close stopping sea water from emerging
What are soft engineering river management methods?
River restoration- Trees and sediment are out around the river to increase interception
Floodplain retention- restores and maintains floodplains
