Rivers Flashcards
Infiltration definition
When water breaks through the soil
Surface flow definition
Water that flows over the surface such as tarmac
Through flow definition
Water that flows through the soil
Percolation definition
Water that sinks deeper into bedrock
Groundwater
water that flows through the bedrock
Transpiration definition
Evaporation from plant leaves
Interception
When precipitation is stopped from reaching the ground by something (e.g. a tree)
Drainage basin definition
A catchment area for precipitation. The rain is drained by one river and it’s tributaries.
Meaning of long river profile
The gradient of the river from source to mouth
What does the Bradshaw model show
Increase as we travel upstream :
-Discharge
-Channel width
-Channel depth
-Average velocity
-Load Quantity
Decrease as we go upstream :
-Load particle size
-Channel bed roughness
-Slope angle
Upper course
-Vertical erosion with hydraulic action, abrasion and attrition
-Traction and saltation at high flow
-Large angular load size
-Steep gradient and narrow river channel
-Boggy saturated land
Middle course
-Channel is deeper and wider
-Vertical erosion decreasing in importance more lateral erosion and deposition
-Suspension main transportation
-Load becomes smaller less angular
-Wider and shallower valleys
-More energy and high volume of water
Lower course
-Channel as it’s widest and deepest and may be tidal
-Deposition>erosion
-Fine material deposited
-Large load but small and round size
-Low energy level, high volume and large discharge
-Lots if industry
Waterfall formation
- Band of hard rock lies over softer and less resistant rock
- As water flows over the cliff it splashed back causing erosion (abrasion and hydraulic action)
- Soft rock eroded more quickly causing under cutting of the hard rock
- The harder rock forms an overhang
- When softer rock can no longer support its weight, it collapses
- Large boulders are deposited at the base of the waterfall
7.The greater power of the water falling to the base moves the material around eroding the base into a deep plunge pool - The cycle begins again and the waterfall begins to retract backwards forming a gorge
Floodplain
-Wide flat area of marshy land on either side of a river, Made of alluvium a sediment deposited by a river when it floods,
-Used for farming as the soils are very fertile
-Wide due to meanders migrating across the floodplain due to lateral erosion. when they reach the edge they erode the valley side.
-When a river floods it deposits silt, creating very flat floodplain. Layer upon layer builds up over many years to form a thick deposit of fertile alluvium
Levee
-Raised river bed found alongside a river in its lower course. It is formed by flooding over many years.
How are Levees formed
-Ridge of sediment deposited naturally to build up the levee.
-During low flow conditions deposition takes place raising the river bed and reducing the capacity of the channel. When flooding occurs water flows the channel sides. Here velocity decreases rapidly leading to deposition of sediment on river banks. First coarser sands are deposited and then the finer silt and mud gradually it can be raised up to 2m.
Estuaries
-Most river mouth form wide tidal estuaries in areas where sea levels have risen
-Transitions zones between river and coastal environments affected by wave action as well as river processes
How are estuaries
-Mudflats develop into natural habitats called salt marshes whcih happen when river water is unable to be discharged into the sea during a rising tide, meaning the velocity falls and sediment deposited. These deposits form extensive mudflats.
Abrasion
Where sand and rocks scrape at the banks and the bed and wear them away
attrition
Rocks and stones knock against each other and wear away
Hydraulic action
In a fast flowing river water is forced into the cracks in the bank and breaks it up
Where is the River Tees
The Source is high up in the Pennines (893m ASL) close to Cross Fell at Tees Head. In the North of England flows for 85 miles to reach the North Sea
Outline the River Tees upper course
Has the High Force Waterfall close to Forest-In-Teesdale has a 20m drop into a turbulent plunge pool. An impressive gorge runs approximately 700m. Consists of resistant whin sill rock overlying weaker carboniferous limestone Reservoir.
Outline the River Tees middle course
Becomes less steep and meanders develop with increased lateral erosion. River Tees meanders through a lower gradient past Bernard Castle
What is vertical erosion in the upper course
- Large boulders carried by river near the source
- River cuts downwards by vertical erosion
- Soil and loose rock washed downhill following heavy rainfall
4.Deepens river valley creating steep sided v shaped valley
What are interlocking spurs
Alternate hills in the river valley formed when rivers wind and bend to avoid areas of hard rock
How is the cross section of a meander formed
-As a river goes around a bend, most of the water is pushed towards the outside. This causes increased speed and therefore increased erosion. The lateral erosion on the outside bend causes undercutting the bank forming river cliff.
-Water on the inner bend is slower, causing the water to slow down and deposit the material, creating a gentle slope of sediment, known as a slip-off slope
What is the thalweg
Fastest flow
How are oxbow lakes formed
Over time, continual erosion and deposition narrows the neck of the meander. Often during a flood the river will cut through the neck of the meander. The river continues on its straighter path and the meander is abandoned. The fastest current will now be flowing in the centre of the river channel and deposition is more likely to occur beside the banks. New deposition seals off the ends and the cut-off becomes an ox bow lake that will eventually dry up, except during periods of very heavy rainfall.
Outline the lower course of the River Tees
There is a sweeping meander at Sockburn which may eventually develop into an ox-bow lake as the neck of the meander becomes. The River flows roughly East from its source for around 85miles to reach north Sea
Outline the Tees Estuary
-Wide with mudflats formed by sea-level rise at the end of the last ice age. Parts of estuary are important for wildlife and have become sites of special scientific interest. Iron and steel engineering/chemical works have developed along the estuary
Why is the River Tees lower course not typical
It has been artificially altered as in the 19th rock two meanders were cut off and a straight wide channel was implemented from Stockton to Yarm so boats could navigate through easier. All the rocks are just mud.
List the causes of flooding
-Areas that have been deforested (less interception)
-Geology (Prevents infiltration, increases surface run-off and river discharge)
-Heavy rainfall (increased surface run-off)
-Snow melt (increased surface run-off)
-Relief (less time to infiltrate so more surface run-off)
-Urbanisation (Impermeable ground means less infiltration)
Outline planting trees as a soft engineering flood defence
More interception as flow of river slow transfer to river channel. Water is soaked up by trees and evaporated through plants/leaves
Relatively cheap and positive environmental effects
Outline floodplain zoning as a soft engineering flood defence
-Restricts land use to certain locations on a floodplain.
-However this can cause land cost to fall and be difficult to implement due to developments already on the land
-High value land kept out of flooding risk
Outline dams/reservoirs as hard engineering flood defences
-During high rainfall water can be stored. Such as Clywedog Reservoir constructed in the 1960s to prevent River Severn flooding
-Very expensive, some residents have to move and often floods large areas of land
-Flood prevents, irrigation, hydro-electric power generation, water supply
Outline embankments as hard engineering flood defences
-Raising a river’s banks so the channel can hold more water before floods occur
-May look unattractive
-Cheaper and more sustainable
Outline channel straightening as hard engineering flood defences
-Cutting through meanders to create a straight channel
-May increase flood risk further downstream, unnatural environment and can damage wildlife habitats and some may be unattractive
-Protect vulnerable locations from flooding and prevents banks from collapsing
Why was a river scheme needed in Leeds
-On Boxing Day 2015 storm Eva caused widespread flooding in parts of Yorkshire and caused a red weather warning
-Rose from approximately of 0.9, to 2.95m on the 27th December
-Affected city centre and Kirkstall Road area
£36 million damage to Leeds
What was done in Leeds to reduce flood risk
-Moveable weirs; at Crown Point in the city centre and further downstream Knostrop can be lowered to create more room for flood water, reducing flood up to 1m
-Merging river and canal by removing a 600m stretch of land
-Flood walls, glazed panels and embankments along river to raise its capacity in times of flood
-New woodland to reduce surface run-off
-Using sites to store flood waters when river levels are high
Social impacts of the river defences in Leeds
-Reduced levels anxiety
-Main routes will remain open in flood reducing disruption for people
Economic impacts of the river defences in Leeds
-Cost of scheme about £50 million so far.Expected to be nearer £100million when fully completed.
-By protecting houses and businesses there are financial benefits
-During Storm Dennis 2020 similar river levels led to less flooding
Environmental impacts of the river defences in Leeds
-Thousands if trees help the environment through the natural flood management.
-Use of new technology means moveable weir helps nature. Quality of life improved
-Some habitats destroyed
