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Drainage Basin
The area within the watershed in a catchment system
Watershed
The highest point around the drainage basin containing the water system
Source
Where the river starts
Mouth
Where the river ends
Confluence
The meeting points between tributaries and the main channel
Tributary
Other streams of water that lead into the main channel
Channel
The main path that the river will take
Precipitation
Water Falling from the sky. Rain is the most important form of precipitation
Evaporation
The Surface level of water is absorbed by the sun and evaporated into the sky
Evapotranspiration
Water evaporates from puddles stream etc, and plant absorb water through transpiration. Together this total loss of water is called evapotranspiration
River Discharge
The volume of water flowing through the soil
Interception
When precipitation lands on vegetation and it’s a store in the drainage basin
Soil Water
Water being stored in the soil
Surface Water
Any store of water above ground in the drainage basin
Throughflow
Water flowing downhill through the soil
Baseflow
Water that reaches the channel through slow throughflow
Groundwater
Water stored underground
Permeability
How easily the precipitation can pass through things like rocks
Channel Storage
How much water the channel can store
Throughfall
The downward movement of water from the leaves onto the ground
Stemflow
Water running off a tree or a plant
Overland Flow
Water running across the soil into the Channel
Infiltration
The downward movement of water into the soil
Percolation
The movement of water through the bedrock
Soil Moisture
The amount of moisture stored in the soil
Soil Moisture Surplus
If precipitation exceeds evapotranspiration and the excess is not being used by plants
Soil Moisture Deficit
Evapotranspiration exceeds precipitation
Soil Moisture Recharge
Replacement of water lost during drier periods
Field Capacity
The maximum amount of water soil can hold
How Does Distance Downstream Affect River Discharge?
The further downstream the river you are, the greater the discharge is
How do climate characteristics affect discharge
In the summer, Alpine areas experience glacial melt which increases discharge
How does land use affect discharge
Deforestation decreases interception, increasing discharge
Afforestation increases interception, decreasing discharge
How does water abstraction affect discharge
Wells and boreholes remove groundwater stones decreasing discharge as base flow cannot occur
How do channel modifications affect discharge
Channel straightening increases discharge and river bank planting decreases discharge
What are river regimes
River regimes are annual hydrographs which show the levels of discharge of different rivers over a year
How does a river gradient change over its course
It is steeper at the top of the river and decreases as it goes down the river
How does the balance between erosion and deposition change?
Erosion is more dominant up river but as you go down the river deposition become more dominant
How does the size of material change along the profile?
As you go down the river material become smaller and more rounded
CASE STUDY: River Severn - Description
Upper Course - Soggy moorland, hills in mid Wales - plyulimon hills
Rain dumped on moorland as It come from Atlantic
Trickles become rivulets that form a stream
V-shaped valley
Erosion is dominant - ACASH
Difference in geology -> waterfalls/gorges
Middle Course - Sinuosity index increases
River begins to meander
Erosion is lateral and occurs on the outside bend. Deposition will occur on the inside
Oxbow lakes will eventually form
Lower Course - Floodplains prevalent
Human impact on the hydrological cycle… interception?
Drainage of urban areas can cause rivers to flow
Right at the mouth risk of flooding decreases due to width of channel
15m difference between HWM and LWM
Attraction of industry due to space around the estuary
What is ACASH
Attrition - Rocks have become smoother/more rounded as they knock into each other when being transported in the flow
Cavitation - Bubbles that formed in the water may implode under high pressure. This generates tiny jets of water which will, over time, erode the rock
Abrasion - Sediment cuts as ammunition for the river. As this material moves it will scrape away at the bed/banks
Solution - Rocks that contain soluble material (e.g. gypsum) can be dissolved as river water passes through the channel
Hydraulic Action - Joints/cracks from bedding planes expand as water passes through the channel, water is forced into cracks opening them up over time
What are the 3 C’s
Capacity - the volume of material that can be held in the channel
Competence - the ability that the river has to carry the largest sediment
Calibre - the size of each individual pebble or particle
When does deposition occur
Deposition occurs when:
there is a sudden reduction in gradient
the river enters a lake or sea
discharge has been reduced following a period of little rainfall
Where there is shallower water
There is a sudden increase in the volume of sediment available, such as at a confluence/ where a land slide has occurred
River overflows its bank so velocity outside the channel is reduced. (resulting in floodplain)
Explain why sediment size in a river may vary at different locations
Sediment size changes at different locations in a river channel for a number of reasons. In the upper reaches of a river sediment if often new so would be bigger, but as it travels down the river it would get more and more eroded, meaning that the sediment size would get smaller. In the upper reaches there is much more vertical erosion meaning that the sediment is much large and more sharp but as you move into the middle and lower reaches, the sediment size changes into more rounded as the erosion changes as the velocity and discharge of the river also increases.
What is a thalweg
Line of maximum velocity in the river, occurs the maximum distance it can from the bed and banks as that is the path of least resistance, travels the outside bank to the outside bank of meanders - river cliffs may form on the outer bank
Laminar Flow
Water flowing downwards over a smooth surface in a simple sheet, with no eddies or meanders
Conditions needed - Smooth,Straight Channel
Turbulent Flow
Water flows in a series of erratic eddies, both vertical and horizontal, in a downstream direction with no regular pattern
Conditions needed - Channel bed roughness and friction influenced, Swirling vortices and eddied throughout the water, both horizontal and vertical
Helicoidal Flow
Spiralling cross channel motion
Conditions needed - Channels carrying lots of material may create pools/rifts
What are the 3 main channel types
Straight Channel - SI <1.0, Rare because helicoidal flow dominates most rivers, resulting in meandering
Braided Channel - SI 1.0-1.5, These are rivers that contain a large number of islands and bars made of sediment. Need to be in an area where discharge varies a lot during the year
Meandering Channel - SI >1.5
Human Activity Modifications - PACTS CUT
P - Precipitation - directly alter levels of precipitation through cloud seeding. Chemicals such as silver iodide + salt released into atmosphere by plane. The aim is for these chemicals to act as a condensation nuclei
A - Abstraction of water - removal of water for human use (Domestic, Agricultural, Industrial)
C - Changing channel characteristics, Canalisation - improving the water network for accessibility/efficiency of transport, Straighter and deeper channels, Moves water efficiently, decreases lag times, Influence of concrete channels
T - Transferring water between drainage basins - 3 major industrial sites in the north of England - Headwaters further up profile (upper course) - reservoir on the Tyne
S - Storing water behind dams or groundwater recharge
Irrigation within agriculture
HEP (sustainable alternative energy source)
Control of flooding
Dams/reservoirs control the release of water downstream
C - Changing agricultural land use
U - Urbanisation
T - Tree cover (deforestation vs afforestation)
What are the 3 main parts to flood management
Forecast and Warning (FIRE)
Hard Engineering Solutions (SPREAD)
Soft Engineering Solutions (SAFER)
What is FIRE
F - Flood forecasting and warning service
I - Insurance
R - Reliant Housing
E - Emergency Services
What is SPREAD
S - Straightening of channel
P - Platforms for raising buildings
R - Reservoirs and dams
E - Embankments and levees
A - Artificial diversion spillways
D - Dredge the river
What is SAFER
S - Sacrificing 'washlands' downstream
A - Afforestation
F - Floodplain zoning and land use management
E - Establishing wetlands and riverbank conservation
R - River restoration schemes
CASE STUDY: River Quaggy
Where is it Located?
It passes through the south-east of London boroughs of Bromley, Greenwich and Lewisham. It rises from two sources near Farnborough hospital near Locksbottom
How was the River Quaggy managed previously and what did they change
Since the 1960s it was heavily managed with artificial channels and culverts but they restored the river and let it run through the park
CASE STUDY: 3 Gorges Dam
Where is it located?
It is a dam downstream of the city of Chongqing, the Chang Jiang flows through a deep, narrow sections of its valley known as the 'Three Gorges'
CASE STUDY: Bangladesh 1998 Statistics
30 million people affected
780 - 1500 deaths
550 000-900 000 houses damaged
