GCSE rivers Revision
RIVER – Summary Points
Drainage Basin
Drainage Basin – area of land drained by river/tributaries
Source – Place where a river begins/originates.
Tributary – A stream flowing into a river.
Mouth – River flows into sea
Watershed – Boundary of a Drainage Basin/Highest point all around a drainage
basin.
Confluence – Where two streams or rivers meet.
Hydrological/Water Cycle
Water Cycle – System of water sea/river- air – land – sea
Precipitation – rain snow sleet hail
Interception – Vegetation delays rain reaching ground.
Surface Runoff/Overland Flow – water running on surface (can’t infiltrate)
Infiltration – Water absorbed in to soil.
Throughflow – Water flowing through soil towards river.
Percolation – Water sinking through rocks.
Groundwater flow – water flowing from rocks into river.
Discharge – Water flowing in the river.
Evaporation - Water turning into water vapour in the air due to heating.
Condensation – Vapour changes back into water droplets due to cooling.
Long Profile
How the river changes shape from source to mouth.
Gradient – Steepness of slope
Depth – Top of water to bed.
Width – One side of river to other.
Discharge – Amount of water passing a certain point in a certain time.
- Cumecs – cubic metres of water per second.
Load – material river is carrying – pebbles,stones,mud
Long Profile
As you go from source to mouth we expect:
Gets less steep
Gets deeper
Gets wider
Discharge increases
Particles get smaller and more rounded.
For above explain why?
Methods of Erosion
Vertical erosion – Downward erosion – upper profile
Lateral erosion – Horizontal erosion – lower profile
Abrasion/Corrasion – Scraping load against rock. Sandpaper.
Attrition – Rocks hit each other breaking up.
Corrosion – Dissolves minerals chemical reaction
Hydraulic Action – Sheer force of water
Gradient is a measure of the slope of the land in degrees.
Depth is measured as an average of readings across a river with metre stick.
Width – measuring tape water’s edge on one bank to water’s edge at the other.
Discharge = Amount of water passing a certain pointgiven as cubic metres per
second(CUMECS). Calculation = Velocity x Cross Sectional Area
Load = Material river is carrying
Methods of Transportation – Carrying eroded material
Traction – Rolling – Large rocks
Saltation – Leap Frog/Bounce – Medium size particles
Suspension – Carried/Held within
Solution – Dissolved Load – Invisible
Deposition – Dropping the load the river was carrying
Happens
- When river slows down – less energy
- Heaviest material dropped 1st
- When a river reaches sea/lake
- Area of shallow water
- Load is increased
- On floodplain
Waterfall
Vertical erosion - Upstream
Hard rock overlying soft rock
Erodes soft rock easier.
Hydraulic Action/Abrasion = Plungepool
Undercutting
Overhang falls/breaks
Waterfall retreats
Steep sided Gorge
Meander
Lateral erosion – Side to side. Dominant Downstream
Erosion – Outside Bend – Faster Flow – More Energy – Deeper – Less friction
Deposition – Inside Bend – Slower flow – Less Energy – Shallow-Friction
Steep side – River Cliff
Gentle side – Slip off Slope
Oxbow lake = Cut off lake
Migrating Feature.
Floodplains
Floodplain –Flat area covered in water in a flood.
River Channel – Where the river flows.
Deposition – Process where flood waters drop the material they are carrying.
Bluff Line - Boundary of the flood plain where the higher land is.
Natural Levees
River overflows banks.
Coarsest/heaviest material is deposited first.
Builds up the ridges called levees.
Because energy is reduced.
Due to increased friction or slower velocity.
Physical Causes of Flooding
Heavy rainfall – thunderstorm
Prolonged Rainfall – Monsoon/ Series of Depressions
Melting Glacier
Underlying Rock Impermeable
Ground is Frozen
Human Causes of Flooding
Deforestation – Less Interception/Less storage/Less roots slowing water
Urbanisation – impermeable surfaces
Narrowing a River Channel – eg building a bridge
Building of Levees – when burst floods worse/may flood downstream
Somerset Levels 2014
Physical/Human Causes of Flooding in British Isles
Location – South West England
High water table/poor drainage/6880 hectares flooded farmland
Physical Causes
Clay – Impermeable bedrock
Grass – Low interception
Rain -207 mm in January/twice the norm
December – Severe winter storms – stores filled with water
High Tides – water backed up in rivers across Levels and Moors
Human Causes
Lacked Dredging –Rivers Tone and Parrett not dredged properly in 20 years
Reduced Capacity – silt/sediment built up making them narrower/shallower – couldn’t
hold as much water.
Pumped water away from homes/sent into the Levels from Taunton and Bridgewater
Impacts of Flooding
Negatives
Floodwater picks up pollutants spreading them
Spreads disease
People/animals drown
Roads/rail disrupted
Buildings/contents damaged
Crops on floodplain destroyed
Positives
Provides mineral rich sediment-fertile soil-grow crops
Provides water crops
Provides habitat for fish –people eat
Replenishes water supplies
Bangladesh/Egypt depend on floods
River Management Strategies
SOFT
Afforestation – Trees planted – store water/interception
Land Use Zoning – Highest risk land not used for housing/industry
Washlands –Areas allowed to flood
HARD
Building Dams – Store water/controlled release – recreation/hydroelectric
Levees – Build banks higher – Increases water storage
Floodwalls – Slimmer than levees in urban areas – take up less space.
Straightening/Deepening river (channelisation) – Water able to travel away from
area faster so less flood.
Diversionary Spillways/Storage Areas – Overflow channels which can store/divert
surplus water during times of flood.
Case Study – A River Management Scheme River Mississippi USA
18m people water supply
2001 Flood - $13m damage
4400 people migrate
Hard and Soft engineering and Evaluation
Hard -levees 15m high along 3000klm
Ev – +Protect that area from rising river levels but push problem downstream
-After flood silt deposited on river bed instead of flood plain reducing channel
capacity/ If burst make flood worse
Hard Dams 100 built eg Kentucky
Ev - +Reduce floods by storing water. Trap silt – preventing it reaching
delta/floodplain – Birds eg heron endanger – reduction of wetlands/more
fertiliser needed.
Hard – Cut off meanders, 1750 klms straightened
Ev +Faster moving water reduces floods in area of straightening. – Moves floods
downstream.
/Loses variety of habitats
-River tries to resume natural course – money to maintain
Hard – Diversionary Spillway Bonne Carre North of New Orleans (9klm spillway)
Ev +Reduced flood risk at New Orleans and Baton Rouge
-Costs money/ Only of full use during flood threat
Soft – Afforestation – Tennessee Valley –
Ev +Interception /Trees absorb water/Reduces soil erosion/Habitats
-Time taken for trees to mature
Soft – Safe Flooding Zones –
-Land cleared for pasture allowed to flood
Ev +Cheaper than compensating for destroyed property
+Wetland habitats preserved.R