Yh Flashcards
Source
The start if the river
Meander
A winding curve or bend of a river
Floodplain
An area that us flat and vulnerable to flooding, often occurs in lower section
Confluence
Is the meeting point (or junction) of where two ricers meet
Tributary
Is a smaller part that eventually joins to a main river
Drainage basin
An area of land where precipitation collects and drains off into a river through surface runoff
Watershed
Is the boundary line between two drainage basins
Mouth
When the river joins the end and flows out to a sea
Upper course
Gradient is very steep, bed load sise is big, very shallow and has a high velocity (speed)
Middle course
Gradient us less steep, bedload size is less big, getting deeper, less velocity.
Lower course
Flat, small bedload size (fine particles), very deep, little velocity.
Upstream
Gradient- steep Bedload size- big Channel depth- shallow Channel width- narrow Human activity- less
Downstream
Gradient- flat Bedload size- small Channel depth- deep Channel width- wide Human activity- more
Describe how the shape and characteristics of river channels change from source to mouth
Near the source of the river (upper course), the river channel will be narrow and shallow, having a big bed load size. Here the gardient is very steep which can result in the river having a high velocity. The middle course of the river the sides are often still quiet steep, the bed load size is not as big and the depth of the river increases. the gradient becomes less steep, resulting in the velocity of the river being less fast. Near the mouth of the river (lower course), the river is wider, floodplain is flat with very gentle sides, the depth of the river increases dramatically. The gradient is gentle, flat causing the velocity of the river to be slow.
Erosion
means the wearing away of the landscape.
- Abrasion: where the sand and pebbles erode the river bank and beds.
- Attrition: where rocks ans stones wear away as they collide into each other. - Solution: where rocks are dissolved.
- Hydraulic action: where fast flowing water erodes the river banks.
Transportation
Transportaion: is the movement of sediment by a river.
- Suspension: very small bits of soil and rock are carriedn in the river.
- Traction: large rocks dragged and rolled along the river bed.
- Saltation: smaller stones and pebbles bounce along the river bed.
Deposition
Deposition: is where sediment from a river is dropped as the energy from the river is not suffiecient to carry the sediment any further.
Causes of flooding
Heavy rainfall: increase in precipitation in a short period of time causes a river to over flow.
- Impermeable rock: when it does rain all the water has no where to be absored therfore it will build up resulting into flooding.
- Hard baked soil: this acts like an impermeable rock, causing a major decrease in infiltration but increase in chances of flooding.
- Steep slopes: as the slopes are very steep the water running down it has no time to infiltrate, as there is an increase in surfae run off, the watr will built up at the bottom that could result into flooding.
- Deforestation: there are not trees/plants to intercept (decrease) causing an increase in overland flow.
- Building on floodplains (urbanisation): due to the impermeable rock, water is unable to infiltrate, this increases surface fun off; the water will flow done to the river causing the levels of the river to increase which will result into flooding.
Flood hydrographs
Flood hydrographs: they show the relationship between rainfall (precipitation) and how much water is in a river (discharge)
Peak discharge: the highest level of the river
Lag time: the difference between peak discharge ad peak rainfall
Peak rainfall: highest level of rainfall
explain how human actions have increased flood risk.
Clearing vegetation has increased the rate of surface run off as less rainfall is being absorbed by the plants and trees as they have been cut down, this results to a shorter lag time. There would further be a decrease in interception as thos plants and trees that have been cut down are not able to interceot and absorb the rainfall. Building on a floodplain has also decreased the amount of rainfall beign infiltrated into the ground. This is beacause the water from the rainfall is unable to be infiltrated within the impermeable rock. This causes river levels to increase resulting in flooding, as it has resulted into a shorter lag time.
Impacts of flooding
Impacts:
- Lose of jobs
- Damage of possessions
- Lose of stock, pets, business’
- Re-building of houses
- Decrease in tourism
- Damage of cars
- Insurance premiums went up
- Escape was hard
- People lifted to safety
- Flooded houses, ruined furniture
Floodplain formation
In the lower course of the river the main process is lateral erosion and deposition. The river is carrying a very large amount of sediment. At a meander Bend the river of Rosie out the bend and the river widens. Usually it moves downstream and outwards. After time, the meander roads into the hills and creates a very fertile and flat area next to the river. This is called the river floodplain. When the river floods the water suddenly spreads out over the floodplain.Suddenly the river flows slower because friction increases.
Levee formation
Floodplains and levies are formed by deposition in times of river flood. Rivers load is composed of different sized material. When a river floods it suddenly spreads out and the water slows down because affection, it deposit is the heaviest of these particles first. The larger particles, often shingle, will form the levy which is a natural material. The Sands, silts and clays are similarly sorted With the sons been deposited next, then the silhouettes and finally the smallest please. Every time the river floods deposition builds up the floodplain which is the flat land either side of the river.
Delta formation
When a river reaches another body of water such as the sea or an ocean, it loses velocity and deposits sediment.If the river deposits sediment faster than coastal processes erodes it, Sediment builds up in layers in a fan-shaped Delta. The river splits into many distributaries channels called deltas and creates large areas of wet land.
Meander formation
Erosion through hydraulic action and abrasion causes the outside bends to get closer together, Until there is only a small bit of land left between the bends (Called the neck)
The river breakthrough this land, usually during a flood, and the river flows along the shortest course.
Deposition eventually cut off the meander forming an ox bow lake.
V-Shaped valley formation
The riverbed gets eroded much faster than the rest of the river. It is more prone to erosion.
The river has been eroded downwards due to abrasion and solution and hydraulic action. As it erodes downwards the sides of it become more unstable due to weathering and undercutting by the river. The sides want to slide into the river channel and create even more erosion.
The sides have collapsed, and the river valley has taken shape of the V shape
