Rivers- Geography

Rivers- Geography

1. Rivers on maps

2. Erosion, transportation and deposition

   • There are four processes of erosion
     • Hydraulic action- the force of the water breaks rock particles away from the river channel.
     • Corrasion- eroded rocks picked up by the river scrape and rub against the channel, wearing it away.
     • Attrition- eroded rocks picked up by the river smash into each other and break into smaller fragments. Their edges get rounded off as they rub together.
     • Corrosion- river water dissolves some types of rock, e.g chalk and limestone.
   • Transportation
     • Transportation is the movement of eroded material.
     • There are four processes of transportation
       • Traction- large boulder- like particles are rolled along the river bed by the force of the water.
       • Saltation- pebble- sized particles are bounced along the river bed by the force of the water.
       • Suspension- small particles like silt and clay are carried along by the water.
       • Solution- soluble materials are dissolved in the water and are carried along.
     • The material eroded is transported downstream.
   • Deposition
     • Deposition is when a river drops eroded material it's transporting.
     • Deposition happens when a river slows down (loses velocity)
     • There are a few reasons why rivers slow down and deposit material
       • The volume of the water in the river falls.
       • The amount of eroded material in the water increases.
       • The water is shallower, e.g on inside of bend.
       • The river reaches it's mouth.

3. Weathering and the river valley

   • Weathering
     • Rocks in a drainage basin are broken down by weathering.
     • 3 main types of weathering
       • Mechanical weathering
         • Mechanical weathering is the breakdown of rock without changing its chemical compostion.
         • An example of mechanical weathering is freeze- thaw weathering
           • 1. It happens when the temperature alternates above and below 0 degrees celcius (the freezing point of water)
           • 2. Water gets into the rock that has cracks, e.g granite.
           • 3. When the water freezes it expands, which puts pressure on the rock.
           • 4. When the water thaws it contracts, which releases the pressure on the rock.
           • 5. Repeated freezing and thawing of the water widens the cracks and causes the rock to break up.
       • Chemical weathering
         • Chemical weathering is the breakdown of rock by changing its chemical composition.
         • Carbonation weathering is a type of chemical weathering which happens in warm and wet conditions.
           • 1. Rain water has carbon dioxide dissolved in it, which makes it a weak carbonic acid.
           • 2. Carbonic acid reacts with rock thatcontains calcium carbonate, e.g limestone, so the rocks are dissolved by the rainwater.
       • Biological weathering
         • Biological weathering is the breakdown of rocks by living things.
         • An example of biological weathering is plant roots break down rocks by growing into cracks on their surfaces and pushing them apart.
   • The river valley
     • A rivers long profile and cross profile may vary over its course.
     • The path of a river as it flows downhill is called its course.
     • Rivers have an upper course (closest to the source of the river) a middle course and a lower course (closest to the mouth of the river)
     • Rivers flow in channels in valleys.
     • They erode the landscape- wear it down, then transport the material to somewhere else where it is deposited.
     • The shape of the valley and channel changes along the river depending on where erosion and deposition is having the most impact (the dominant process).
     • The long profile of a river shows you how the gradient (steepness) changes over the different cources.
     • The cross profile shows you what a cross- section of a river looks like.

4. Drainage basins

   • A drainage basin is an area of land drained by a river.
   • The part of the hydrological cycle that happens on land goes on in drainage basins.
   • Drainage basins are open systems; there are inputs of water to drainage basins, water flows through them and is stored in them and there are outputs of water from drainage basins.
     • Inputs; precipitation
     • Flows; surface runoff, channel flow, infiltration, throughflow, groundwater flow and percolation.
     • Stores; channel storage, groundwater storage, interception storage and surface storage.
     • Outputs; evaporation, transpiration and river flow into the sea.
   • Water shed- the boundary to separate drainage basins. They're ridges of high land so the water will fall off either side into a drainage basin.
   • Tributary- a smaller river that joins a main river. (e.g a stream)
   • Source- where a river starts, usually in an upland area (e.g mountains)
   • Confluence- a point where two rivers join.
   • Mouth- where a river flows into the sea or a lake.

5. River landforms

   • Erosional
   • Depostitional

6. The hydrological cycle

   • The hydrological cycle shows how water moves around.
   • Has different parts- sea, land and atmosphere.
   • 1. Water evaporates from the land and the sea. Evaporation is when water is heated by the sun and turns into water vapour. Transpiration is the evaporation of water from plants. Evapotranspiration is of them happening together.
   • 2. Water vapour is moved inland by the wind.
   • 3. The water condenses to form clouds and then falls over the land as precipitation.
   • 4. Water moves from one place to another in many ways (called flows or transfers)
     • Infiltration- when water soaks into the soil.
     • Percolation- when water moves vertically down through soil and rock.
     • Throughflow- when water in the soil flows downhill.
     • Groundwater flow- when water in the rock flows downhill.
     • Surface runoff- when water flows overground.
     • Channel flow- the flow of water in a river.
   • 5. Water can also be held on the land in stores.
     • Channel storage- when water is held in a river.
     • Groundwater storage- when water is stored in rock and solid. A rock that stores water is called an aquifer.
     • Interception storage- When water lands on things like plant leaves and doesn't hit the ground.
     • Surface storage- when water is held in things like lakes, reservoirs or puddles.
   • 6. The water eventually end up in the sea, where it evaporates and goes around the cycle again.

7. The storm hydrograph

8. Flooding- causes

   • Physical factors
     • Prolonged rainfall
       • After a long period of rain, the soil becomes saturated. Any further rain can't infiltrate, which increases runoff into rivers. This increases discharge quickly, which can cause a flood.
     • Heavy rainfall
       • Heavy rainfall means there's a lot of runoff. This increases discharge quickly, which can cause a flood.
     • Snowmelt
     • Geology
     • Relief (how the height of the land changes)
       • If a river is in a steep- sided valley, water will reach the river channel much faster because water flows quicker on steeper slopes. This increases discharge quickly, which can cause a flood.
   • Human causes

9. Flood management

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