1_Rivers

1_Rivers

1. Hydrological cycle

   • Stores
     • Ocean, Ice, Reservoir, Ground water
   • Flows
     • Rivers, Surface runoff, Through flow, Groundwater flow.
   • Processes
     • Evapouration, Condensation, Interception, Transpiration, Precipitation, Infiltration.
   • continuos transfer of water between the sea, the land and the atmosphere.

2. Drainage Basin

   • Source
     • where a river begins
   • Drainage basin
     • The area from which water drains into the river
   • Watershed
     • An imaginary line that separates two drainage basins
   • Confluence
     • The point where two rivers join together
   • Tributaries
     • smaller rivers which join the main river
   • Flood plain
     • Land that floods when a river overflows
   • Mouth
     • where the river flows into the sea or lake
   • River bed
     • The bottom of a river channel
   • River bank
     • The side of a river channel
   • Channel
     • rivers flow in it

3. 3 course river

   • Upper course
     • Steep sided with a small river channel. It has a small discharge. The area is hilly and in theuplands with a barran landscape, this makes human activity hard. It is usually in a "v" shaped valley.
     • Land Forms
       • V-shaped valley
         • The river erodes vertically (has little energy) as boulders, stones and rock particles are bounced and scraped along the channel bed. This causes a steep narrow gorge and the sides are attacked by weathering, this breaks up and loosens the soil and rock. The loosened material slowly creeps down the slope because of gravity or is washed into the river by rain. and material is washed away due to the rivers high velocity making the valley a "V" shape.
       • Interlocking spurs
         • Vertical erosion may be disrupted by protruding hillsides made of different types of rock. This can also cause rapids.
       • Waterfalls and Gorges
         • As the river moves through the upper course it cuts downwards. The gradient here is steep and the river channel is narrow. Vertical erosion in this highland part of the river helps create rapids and waterfalls.
         • When a river flows over alternating layers of hard and soft rock the lower soft rock is eroded much more quickly than the harder rock; therefore undercutting the harder rock. The hard over hand eventually collapses because nothing is holding it up. The collapsed rock falls into the plunge pool, causing more erosion of the softer rocks and a deeper plunge pool.
         • The process continues and the waterfall retreats upstream leaving a steep sided gorge
         • waterfalls can also be caused by Glacial erosion, a fall in erosion or earth movement.
         • High Force
   • Middle course
     • The river meanders and the area around the river is a flat flood plain with lots of vegetation and fertile farmland due to flooding and deposited sediments.The channel here is deeper meaning less friction and a faster flow with a bigger discharge, the river has more energy here and there is a gentle gradient later erosion has occured.
     • land forms
       • Meanders
         • Meanders are caused by deposition and erosion. The force of the water erodes and under cuts the river bank on the outside bend where the flow has the most energy. On the inside bend, where the flow is slower, material is deposited to form rocky beaches. These processes continue to form tight bends called meanders.
       • Ox-bow lakes
         • Over time the bends of a meander become very close together. eventually the river will break through the gap (usually during a flood when the river has a high discharge and high energy) the ends join and the water takes the easiest route. the meander is abandoned and eventually cut off. Over time it may dry up and just an outline would be left leaving an outline filled with soil and plants.
   • Lower course
     • This part of the river has a large discharge and can be miles wide e.g. Thames & Severn. The river is used for transport because it is close to the sea and many big cities are located on the lower course. This part ofthe river is very fast flowing. it is much wider and deeper and adjacent land is very flat. There is a very high risk of flooding on built up areas.
     • land forms
       • Floodpains
         • The river now has a wide floodplain. A floodplain is the area around a river that is covered in times of flood. A floodplain is a very fertile area due to the rich alluvium deposited by flood waters. This makes floodplains a good place for agriculture.
       • Levees
         • If the river overflows its banks, it deposits the material its transporting. The heaviest material is deposited is deposited near the river. Over many floods this material builds up into banks called leeves.
       • Deltas
         • Deltas are found at the mouth of large rivers - for example, the Mississippi. A delta is formed when the river deposits its material faster than the sea can remove it on the shallow sea causing a build up and 100's of channels. There are three main types of delta, named after the shape they create (birds foot (Mississippi) Cuspate (Ebro, Spain) Fan-shaped (Niger, Nigeria).
   • Depositional
     • Deltas Levees Floodplains
   • Erosional
     • Waterfalls Meanders "V"shaped valley Ox-bow lake Interlocking spurs

4. Transportation

   • Solution
     • Suspension
       • Saltation
         • Traction
           • Large boulders and rocks are rolled along the river bed
         • Small pebbles and stones are bounced along the river bed
       • fine, light material is carried along in the water
     • Minerals are dissolved in the water and carried along in solution

5. Hydrographs

   • discharge (cumecs) = velocity x volume
   • Rainfall is always a bar chart
   • Discharge is always a line Graph
   • Base flow
     • Peak discharge
       • Peak rainfall
         • Lag time
           • Rising limb
             • Receding limb
               • Fall in discharge back to base level
             • Increasing discharge as storm water enters the river channel
           • Time between peak rainfall and peak discharge
         • Highest rate of precipitation during rainfall event
       • Maximum discharge following rainfall event
     • starting and finishing flow of the river either side of increased discharge

6. Flooding

   • Causes
     • Human
       • farming
       • mandmade structures
       • Channelistation
       • Urbanisation
       • deforestation (roots don't absorb, no interception, no roots blocking the waters path)
     • Physical
       • Rainfall
       • Melting snow
       • Gradient of land
       • Rock type
   • Flood Management
     • Soft engineering
       • Works with nature
       • retention ponds: Allows run off to be temporarily stored and in turn lessens the risk of flooding.
       • flood plain zoning: avoid building building on a floodplain; use the land for farming.
       • Flood warning system: Allows evacuation of areas likely to flood and therefore a reduction in damage.
       • Afforestation: trees slow down the flow of water towards the river channel and also allow interception.
       • DO nothing: accept that flooding is a natural process and allow the river to flood.
     • Hard engineering
       • More expensive, greater impact, works against nature.
       • Channelisation: reduce water friction with the bed and banks, speeding up water flow. gets the water away from the area quickly.
       • Dams: built to control discharge. It holds back water allowing it to be released in a controlled way.
       • Levees: increases the potential maximum area of the river channel allowing it to hold more water before bursting its banks.
   • Sustainable urban drainage
     • wetland areas, permeable paving, naturlised swales (along side roads, ditches) , retention ponds, tree pits, green rooves, bio retention areas (plants).
       • looks nicer
       • improves water quality
       • reduces risks of flooding.

7. Suppllying water

   • water stress: where the amount of water in an area is limiting development and population
   • water deficit: the amount of water required to replace that which has been lost.
   • more rainfall on west coast due to the prevailing wind coming from the south-west and the topography of the land causing relief rainfall
   • boreholes are not long term solutions as they dry up

8. Erosion

   • Factors affecting river erosion:
     • Discharge (more power in the river)
     • Velocity (more load can be carried)
     • Rock resistance
     • Gradient

Imagens e arquivos do mapa