Rivers

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.
         • e.g. High Force - river Tees. near middleston on tees, within the north Pennines area, county durham, England.
   • 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. Erosion

   • Corrasion/Abrasion
     • the process by which the bed and banks are worn down by the rivers load. The river throws particles agaisn't the bed and banks, sometimes at high velocity
   • Attrition
     • Material carried by the river bump into each other and so are smoothed and broken into smaller particles.
   • Solution/corrosion
     • This is a chemical actions of the river water.The acids in the water slowly dissolve the bed and banks.
   • Hydraulic action
     • This process involves the force of water against the bed and banks
   • Factors affecting river erosion:
     • Gradient
     • Rock resistance
     • Velocity (more load can be carried)
     • Discharge (more power in the river)

5. 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

6. 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

7. 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.
   • Teweksbury (2007)
     • Teweksbury is a town in England, Europe. It is around 10 miles from Glouscester and 15miles from Worcester (north) which are in the west-middlelands of the UK. it is located in Gloucestershire just west of the M5 motorway (junction 9). it lies on the confluence of the river Severn and Avon.
     • causes
       • Human
         • water fell on hard impermeable surfaces due to new developements
           • No flood defenses
             • rivers are too big to manage
               • fast runoff causes pluvial flooding, drains can't cope.
       • Physical
         • Surronded by floodplains
           • At the confluence of 2 rivers
             • lots of Tributary rivers
               • 140mm of rain in a few hours
                 • the river has a big catchment area
     • effects
       • 800 homes effected. - S
       • 500 businesses effected -E, S
       • half the the town was under 3ft of water- En, E, S
       • makes houses smells, ruins furniture- S, E
       • sediments dropped improved the fertility of the land- En
       • treatments works lefts 7000 people without clean water all over Gloucestershire - E, S
       • Transport routes were cut off when A38 & A438 were flooded- S, E
       • Tourism was effected- campsites flooded during July
     • responses
       • short term
         • 25 000 sand bags distrubuted
         • Army and RLNI helped rescue people
         • super markets gave food and Severn Trent gave water
         • fireservice rescued 529 people
         • 133 portloos we given
       • Long term
         • embankment in upton-on-severn (£4mil)
         • flood warning sytem
         • an impermeable wall was built around the water treatment works
   • Pakistan (2010)
     • Pakistan, located in central Asia, is north-west of india and south-east of afghanistan.Pakistan partially boarders the indian ocean and is 796 065 kilometres squared- 1/5th of its land was flooded. The indus river (3 200km long) flows all the throug it. its discharge is 6 600cubis metres per second.
     • causes
       • Physical
         • monsoon rainfall
           • snow melt
             • Gradient of the land
               • permeable rock causes water to travel quicker
       • Human
         • Deforestation
           • urbanistaion
             • Dumping waste causes waste build up in river
     • effects
       • 5 000 miles of roads and railways were washed away- E
       • 6.5 million acres (500 00 tonnes of wheat, 2 million bales of cotton) were washed away in the punjab and sindh provinces- E, En
       • 6 million people needed food aid- S
       • 20 000 000 people were made homeless (over 10%)- S
       • 700 000 houses were damaged- S, E
       • worst flooding for 80 years- killed 1 600 people- S
       • increased diseases such as cholera, malaria, malnutrition- S
       • political threat of more people joining the taliban due to the government being at blame- P, S
     • responses
       • short term
         • 21 helicopter 150 boats given
         • international aid: food water shelter, hygiene and health items.
         • 400 metric tonnes of tents blankets water and food
       • long term
         • UK- £134 million donation + £10 million bridge project.
         • US provided $3 million to establish 15 centres for illness
         • enlarged tax for wealthier residents in pakistan
         • in 2011 800 000 farms were provided crop packages.
         • families were given training programs to build their own homes

8. 3 gorges dam

   • located in the east of china along the yangtze river which has a mouth at the yellow sea near shanghai. its downstream of chongqing and yangtze is one of china's largest rivers.
   • effects
     • positive
       • prevents the flooding of 100 million people downstream- S, E
         • protect 25 000Ha of farmland- S, E
           • hydroelectric power makes of 10% of china's electricity- E, En
             • regulated water level means ships can travel upstream- E
               • provided jobs- S
                 • generates the equivilent of 50 million tonnes of raw coal, replaces 100million tonnes of CO2 being released- En
     • negative
       • 13 cities and 13000 archaelogical sites have been submerged- S
         • 1.4 million people were forced from their homes- S
           • causes geological diasters such as landslides- En
             • rubbish is deposited upstream due to the slow moving river (less energy)- En
               • 500 million tonnes of silt each year will be trapped lowering the reservoirs capacity- E, En
                 • wildlife such as river dolphins may become extinct- En
                   • worried that in the event of an earthquake the dam may break and drown million of people- S
                     • $25.5 billion cost

9. 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.
   • Kielder water
     • it is located in Northumbaland, England, just south of the scottish boarder.
     • Effects
       • Positive
         • can act as a flood prevention measure- S
           • the hydroelectric power station can generate 6MW of power- E, S, En
             • made 8 sites of special scientific interest covering 7 800ha containing unique plants and animals such as red squirrels- En
               • tourism raises £6 million a year- E
                 • lake is 11km long and helps in times of water shortages- S
                   • 150 million trees provides huge volumes of timber and up to 260 jobs- E, S
       • Negative
         • 2 700 acres of farmland were lost as a result of the scheme - En
           • the reservoir flooded an area of scenic natural beauty- En
             • the forest at kielder is made of only one type of tree (monoculture)- En
               • 58 families were displaced from their homes- S
                 • due to the dam holding back sediment there is a depletion of river bed downstream which reduces spawning grounds for fish and invertebrates- En
   • 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

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