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Geography > 11. River Landscapes > Flashcards

11. River Landscapes Flashcards

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1
Q

How does a profile of a river change as it goes downstream?

A
  • steep gradient with narrow and shallow channel in the upper course (fast), friction
  • gentler gradient with wider deeper river on floodplain in the middle course
  • lower course has an almost flat gradient and goes extremely fast (less water touches river bed) and deep, and is extremely wide and flat
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2
Q

What types of landforms and erosion takes place in the upper course?

A
  • erosional landfroms, e.g waterfalls
  • most vertical erosion
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3
Q

What types of landforms and erosion takes place in the middle course?

A
  • erosional and depositional landforms like meanders
  • transportation
  • mix of vertical and lateral erosion
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4
Q

What types of landforms and erosion takes place in the lower course?

A
  • lateral and vertical erosion (more lateral)
  • mostly depositional landforms (levees)
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5
Q

What is hydraulic action for rivers?

A
  • force of water hitting riverbeds and banks
  • effective when water is fast and there is lots of it
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6
Q

What is attrition for rivers?

A
  • stones carried by rivers knock against each other, making them more round
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7
Q

What is abrasion for rivers?

A
  • load carried by rivers repeatedly hits riverbed/banks
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8
Q

What is solution for rivers?

A
  • river flows over limestone and chalk, rock slowly dissolves in rivers
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9
Q

What types of rocks are transported when in rivers?

A
  • larger rocks, upper course by traction during periods of high flow
  • finer sediment downstream by suspension, deposited on banks or bed of river when friction increases
  • lots also happens at river mouth where gentle gradient reduces velocity
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10
Q

What is an interlocking spur?

A
  • the river does not have enough power to cut through the ‘spurs’ of land and so goes around them creating interlocking spurs
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11
Q

What are waterfalls and what are they caused by?

A
  • places in a river where the water drops down (mostly in the upper course)
  • caused when water flows over a more reisistant rock and then over less resistant which will erode faster (creating a step), which eventually leads to a plinge pool and waterfall
  • Hydraulic Action and Abrasion also erode the softer rock under the harder rock, until the harder rock falls and the whole process starts again
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12
Q

What is a gorge and how is it formed?

A
  • a gorge is a steep-sided valley created due to waterfall retreat
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13
Q

What is a meander and how is it caused?

A
  • meanders are found in low laden areas and are curves in the river due to the thalweg (fastest route)
  • the thalweg of the meander is shifting from side to so it causes deposition on the inside bend(slif off slope) and erosion on the outside bend (where river is fastest), which leads to the meander migrating sideways
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14
Q

What are oxbow lakes and how are they formed?

A
  • as you go donwstream the size of meanders increase, and erosion of the outside bend can cause a meander neck (where the 2 ends of the curve are close)
  • in the time of a flood, the river can cut the neck of the meander causing a straighter path
  • less water in the curve of the meander means more deposition and it is cut off from the main stream making an oxbow lake
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15
Q

What are floodplains are how are they formed?

A

-wide areas of marshy land on each side of a river due to meanders (middle and lower course)
- made of silt and alluvium (deposited) and is extremely fertile
- made due to lateral erosion of meanders as they erode valley sides so the floodplains are very flat

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16
Q

what are levees and how are they formed?

A
  • they are raised river beds on the sides of rivers caused by flooding
  • found in lower course
  • during floods water flows over the channel and loses velocity rapidly due to friction
  • this means it starts depositing sediment, with the largest peces first as these require the most energy (alluvium is finer sediment and is spread more)
  • after many floods this increases
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17
Q

What is an estuary?

A
  • an estuary is where the river meets the sea
  • large deposits of sediment cause mudflats and salt marshes
  • as salt water mixes with river water and causes it to slow, reducing velocity leading to deposition which can lead to mudflats and then salt marshes (if vegetation comes)
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18
Q

What is some general info about the River Tees?

A
  • located in North East England
  • 85Miles long
  • flows east into North sea
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19
Q

What are the landforms of erosion present in the River Tees?

A
  • High force waterfall (largest in England)
  • formed where dolerite (hard igneous rock) is over softer limestone
  • this has lead to steep sided gorge
20
Q

What are the landforms of EROSION AND DEPOSITION in the River Tees

A
  • meanders and floodplains from in area south east of Darlington
21
Q

What are the landforms of depositions in the River Tees

A
  • floodplains and levees form in the middle and lower sections due to flood
22
Q

What is flooding and when does it occur?

A
  • flooding occurs when the capacity of the river channel is exceeded
  • generally caused by prolonged periods of intense rainfall
23
Q

What is the lag time(rivers)

A
  • time taken between peak rainfall and peak discharge
  • essentially time between the rainfall and the flooding occuring
24
Q

What are 4 human factors that increase flood risk

A
  1. deforestation - lack of trees reduces interception and infiltration increasing overland flow
  2. urbanisation - impermeable concrete and tarmac causes more overland flow (water flows into drains also)
  3. agriculuture - bare soil and ploughing increases flow
  4. climate change - rising global temps increase storm frequency and intensity
25
Q

What are 7 physical factors that increase flood risk?

A
  • relief - steep slopes mean less infiltration and increase overland flow
  • rock type - impermeable rocks mean less percolation and more overland flow
  • soil - frozen or saturated soil means less infiltration and more overland flow
  • weather - heavy prolonged rainfall can mean flooding happens faster and periods of high temp after snow can mean overland flow
  • seasonal variations - increased temp in spring means snow in mountanoius aread (or monsoon season means high rain)
  • if there are many tribituaries taking water to the main channel causing large increase in discharge
  • vegetation - less vegetation means more risk as reduced interception
26
Q

What is interception?

A
  • water that does not reach the soil but is stopped by leaves and branches
27
Q

What is infriltration?

A
  • process where water soaks into or is absorbed by the soil
28
Q

What is percolation?

A
  • downard movement of water from soil into rock beneath
29
Q

What is discharge

A
  • volume of water flowing along a river
  • measured in cumecs (cubic metres per second)
30
Q

What do factors that mean increased flood risk lead to on a hydrograph?

A
  • short lag time
  • steep rising limb
  • high discharge
31
Q

What is hard engineering (rivers)

A
  • involves building structures or changing the river channel
32
Q

What are dams+resovoirs and what are their advantages/disadvantages?

A
  • controls river flow by blocking water flow letting it into river in a controlled way (resovoir behind dam)
  • can also be used for HEP energy production
  • provides recreation opportunities
  • BUT expensive
  • BUT loss of farmlands and homes due to resovoir
  • BUT displacement of people
  • BUT resovoir will silt over time
  • BUT affects fish breeding
33
Q

What are embankments and what are their advantages/disadvantages?

A
  • artificially raising the banks of the river to increase channel capacity
  • increased capacity means less frook risk
  • new river bank habitats created
  • BUT expensive
  • BUT visually unattractive especially if made of concrete
  • BUT may fail and lead to more serious flooding
34
Q

What are straightening channels and what are their advantages/disadvantages?

A
  • straightens channels by removing meanders
  • speeds up movement of water
  • easy navigation for boats
  • BUT expensive
  • BUT affects river ecosystems because of velocity change
  • BUT increases flood risk downstream as discharge reaches those areas faster
35
Q

What are flood relief channels and what are their advantages/disadvantages?

A
  • channels built to allow excess water to flow around high value areas
  • effective in reducing flood risk
  • new habitats
  • insurance costs lowered for those who live nearby
  • BUT expensive
  • BUT regular maintenance needed
  • BUT can be unattractive
36
Q

What is river restoration and what are the advantages/disadvantages?

A
  • SOFT ENGINEERING - restores river to natural state with meanders and wetlands
  • increase habitats
  • restores wetland areas
  • slows down water flow reducing flood risk downstream
  • BUT expensive
  • BUT some areas will flood
37
Q

What is floodplain zoning and what are the advantages/disadvantages?

A
  • SOFT ENGINEERING - restricts land use in areas that have high flood risk and ensures high value building are not in these areas
  • low costs
  • conserves habitats
  • BUT restrictions on where housing can be built may affect economic development
  • BUT can only be in places where development has not occurred
38
Q

What afforestation and what are the advantages/disadvantages?

A
  • SOFT ENGINEERING - planting of trees to increase interception and infiltration (trees also use large amounts of water)
  • cheap
  • absorbs and stores co2
  • slows water transfer increasing lag time
  • BUT can increase acidicity of soil
  • BUT farmland lost
39
Q

What are flood warnings and what are the advantages/disadvantages?

A
  • SOFT ENGINEERING - monitoring of rivers to provide warnings to people when floods may occur
  • helps people evacuate and prepare
  • less expensive than hard engineering
  • BUT expensive monitoring eqipment
  • BUT people may ignore warnings
40
Q

What is some general info about Banbury

A
  • north of oxford, population of 45,00
  • most of town is built on floodplain of RIver Cherwell (Thames)
41
Q

What is Banbury’s history of flooding?

A
  • 1998 - 12.5 million and railway station damaged
  • 2007 - flood and affected businesses
42
Q
A
43
Q

What is the main measure that has been put in place to protect Banbury

A
  • 2.9km earth embankment parallel to M40 that created flood storage area (hold 3 million cubic metres of water)
  • on natural floodplain
  • rate of flow downstream to Banbury can be controlled
44
Q

What are smaller additional measures put in place in Banbury?

A
  • A361 road in flood storage area raised
  • new floodwalls to protect business and properties
  • pumping station to tranfer excess rainwater to river
45
Q

What are the social costs/benefits to do with the Banbury defence project?

A
  • quality of life to locals increased with new footapaths and green areas
  • reduced anziety and depression due to fears of flooding
46
Q

What are the economic costs/benefits to do with the Banbury defence project?

A
  • 18.5 million pounds
  • donated by council and environmental agency
  • protects 440 houses and 73 commercial properties (benefits of over 100 million)
47
Q

What are the environmental costs/benefits to do with the Banbury defence project?

A
  • 100,000 tonnes of earth required for embankment which created another resovoir nearby
  • Biodviersiy ACtion Plan created
  • parts of floodplain will be allowed to flood if river levels are high

Geography (19 decks)

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