P1: Rivers Flashcards
long profile
How the Steepness of the River changes from source to mouth.
Upper course - steep
Middle course - shallow
Lower course - almost flat near the mouth
Cross profile
How the river and its valley change shape.
Upper course - V - shaped valley
Middle - sloped hills and shallow river
Lower course - Flat sides and deep river.
Vertical erosion
Happens in the upper course
Lateral erosion
In the lower course because the gradient is lower.
Attrition
The load collides into each other and becomes smaller fragments
Solution
Water dissolves certain rocks
Hydraulic action
Water forces air into crack which then explode under pressure.
Abrasion
The process of scraping or wearing something away
Traction
large boulders are rolled
saltation
The bouncing of sediment
suspension
fine clay and sediment is lifted and carried
Deposition
When sediment can not be carried anymore by the river because the energy drops leading to the sediment being dropped on the riverbed.
Interlocking spurs
Occurs where there are bands of resistant and less resistant rock. Vertical erosion is high as there is a steep gradient so it cuts out a v- shaped valley. Weathering wears the valley sides. River winds around the more resistant rock
Rapids
vertical bedding- differential erosion.
There is turbulent flow on the steps.
Waterfall / gorge
Vertical bedding - vertical erosion is dominant.
differential erosion happens by abrasion and hydraulic action forms rapids.
Undercutting occurs - because splash back happens where the most turbulent flow is. Creates an overhang. A plunge pool forms. Gravity causes the cap rock to collapse. This makes the plunge pool deeper.
V- shaped valley
formed where vertical erosion is dominant usually in the upper course.
Meander cross section
The point of fastest flow is the thalweg.
Around the inside of the meander deposition occurs. Water is flung to the outside because of the centrifugal force, this erodes the river cliff.
Meander formation
The straight river encounters areas of difference which causes uneven velocity across the river.
Slow velocity on the inside + deposition.
Fast velocity on the outside + erosion.
Meander gets more pronounced and the neck gets more narrower.
Eventually two meanders connect and flow straight.
Oxbow lake.
Ox-bow lake
The oxbow lake gets cut off when two meanders meet. leaves a meander scar as it dries up.
Sometimes this is caused by a flood.
levees
build up parallel to a river on a raised bank. formed after multiple floods take place. The sediment is picked up by the river in the centre where the flow is fastest and the heaviest sediment is deposited first when the river discharge slows down. The smaller pieces of sediment are slowly deposited as the energy of the river decreases. sediment dropped off at a stratified rate
Flood plain
is a wide valley floor on either side of the river which is there to be flooded. When a river floods the water slows down, loses energy and deposits the material. Meanders widen as the migrate of floodplains.
Estuary
found at river mouths.
The land is close to sea level and the river valley is at its widest.
When the water floods its banks it carries silt and sand over onto the valley floor and deposits the sediment.
Over time more mud builds up creating mudflats. at low tides these are exposed.
River tees
Cow green reservoir - releases water when precipitation is low
Ox-bow lakes at Portrackmersh- straightened for transport in 1810.
Tees barrage - built for flood control
Tees estuary - 22 miles inland. Seals sand is a mudflat.
How does Prolonged rain affect flood risk?
Ground would be saturated if there is a lot of rain already.
Rain continues until soil-water can not store the water. Water enters rivers leading to floods.
How does Heavy rain affect flood risk?
During winter there are many bands of depression. This means that the soil will be saturated from previous rainfalls. when it can no longer store water, surface runoff is increased. Rainwater enters rivers quicker leading to higher discharge and floods.
How does sudden snow melt affect flood risk?
Sudden increases in temp in below freezing areas will melt the snow very quickly. The water will run across the ground as the soil can no longer store and surface runoff is increased.
This causes floods
How does the geology affect flood risk?
The rock found in mountains is impermeable rock such as slate. the rock increases the surface runoff.
How does the relief affect flood risk?
relief - height and slope of land.
Steep slopes - surface runoff on mountain sides before rain can inflitrate the soils.
Hydrograph
Peak discharge - the point where the volume of water is at its highest.
lag time - the delay between peak rainfall and peak discharge.
Rising limb - the increase in river discharge
falling limb - the decrease in river discharge.
Dams and reservoirs
Dams are barriers and reservoirs are formed behind it.
Adv - reservoirs control water flow, produce hydroelectric power,
Disadv - very expensive, materials are deposited in the reservoir, so farmland downstream will be less fertile
channel straightening
meanders are removed to create straight lines.
Adv - Water leaves the area more quickly,
Disadv - flooding downstream, causes erosion.
embankments
raised wall along riverbanks.
Adv - river can hold more so less floods.
Disadv - expensive and risk of severe flooding if water rises above this level.
Flood relief channel
Channels are built to divert water.
Adv - Gates can mean the water can be controlled.
Disadv - increased discharge where the relief channel rejoins the river.
Warning and preparation
People are aware and can be ready for the flood such as using sand bags.
Adv - Gives people time to evacuate
Disadv - they don’t prevent floods and could give a false sense of security.
Flood plain zoning
Restrictions to prevent building on the flood plain in areas that will flood.
Adv - flood risk is reduces and the impact is reduced
Disadv - There is a housing shortage already so we need more buldings
Planting Trees
Increases interception
Adv - Discharge and flood risk decrease, provides habitats for wildlife. Prevents soil erosion.
Disadv - Less land available for farming
River restoration
Making the river more natural by removing man- made levees so the floodplain can naturally flood.
Adv - Discharge reduced so less chance of flooding downstream
Disadv - Local flood risk can increase.
