River Landscapes in the UK Flashcards
All 42 cards in this deck
Describe the long profile of a river from source to mouth.
A concave curve: a steep gradient in the upper course that becomes gentler downstream towards the mouth.
How does the cross profile of a river valley change from the upper course to the lower course?
Upper course: narrow, steep-sided, V-shaped valley. Lower course: wide, flat valley floor with a flood plain and gentle sides.
True or false? A river channel is at its deepest and fastest flowing near its source.
False. The channel becomes wider and deeper downstream, and average velocity increases because there is less friction.
Which river erosion process wears away the banks as the force of the water forces air into cracks in the rock?
Hydraulic action.
Which river erosion process wears away the bed and banks as the river's load is scraped along them?
Abrasion.
True or false? Attrition is the wearing away of the river bed and banks by the load.
False. Attrition is stones in the load colliding with each other and becoming smaller and rounder; wearing of the bed and banks is abrasion.
Which river erosion process dissolves soluble rocks such as limestone and chalk?
Solution.
What is the difference between vertical and lateral erosion in a river?
Vertical erosion deepens the channel (dominant in the upper course); lateral erosion widens it sideways (dominant in the middle and lower course).
Which two transportation processes move material along the river bed?
Traction – large, heavy pebbles rolled along the bed; saltation – smaller pebbles bounced along the bed.
Which two transportation processes carry material within the water itself?
Suspension – fine, light sediment carried within the flow; solution – minerals dissolved in the water.
Why does a river deposit its sediment?
Because its velocity and energy fall, so it can no longer transport its load; the heaviest material is dropped first.
e.g. at the mouth, on the inside of a meander, or when discharge falls after a flood.How do interlocking spurs form?
In the upper course the river has little energy for lateral erosion, so it winds around areas of more resistant rock, leaving ridges of higher land that interlock like teeth.
What are the steps in the formation of a waterfall?
e.g. a river flowing over a band of hard rock onto softer rock- The softer rock downstream is eroded faster by hydraulic action and abrasion, leaving a step of hard rock.
- Water falls over the step, eroding a plunge pool below and undercutting the hard rock to leave an overhang.
- The unsupported overhang collapses and the waterfall retreats upstream.
How is a gorge formed?
By a waterfall retreating upstream over many years, leaving a narrow, steep-sided valley behind it.
Where do erosion and deposition happen on a meander?
Erosion on the outside bend, where flow is fastest and deepest, forming a river cliff; deposition on the inside bend, where flow is slow, forming a slip-off slope.
What are the steps in the formation of an ox-bow lake?
e.g. a large meander on a flood plain- Erosion on the outside bends narrows the neck of the meander.
- During a flood the river breaks through the neck and takes the shorter, straighter route.
- Deposition seals off the old bend, leaving an ox-bow lake.
True or false? Levées are only ever built by people.
False. Natural levées are raised banks formed when a river floods and deposits its coarsest load first, nearest the channel.
How is a flood plain formed?
Repeated flooding deposits layers of fine silt (alluvium) across the valley floor, and migrating meanders widen it by lateral erosion.
Why does deposition take place in a river's estuary?
The incoming tide slows the river's flow, so fine silt and mud are deposited, building mudflats and salt marsh exposed at low tide.
What evidence on an OS map shows that a river is in its lower course?
Widely spaced contours (flat flood plain), a wide meandering channel, ox-bow lakes, embankments, and land close to sea level.
Name two landforms of erosion found in the upper course of the River Tees.
High Force waterfall and the gorge downstream of it (also interlocking spurs and a V-shaped valley).
How does prolonged or heavy precipitation increase flood risk?
Rain falls faster than it can infiltrate, so the soil becomes saturated and water reaches the river quickly as surface runoff, raising discharge.
How does impermeable rock in a drainage basin affect flood risk?
It increases flood risk – water cannot infiltrate, so it runs over the surface and reaches the river quickly.
How does urban land use increase flood risk?
Concrete and tarmac are impermeable, and drains and gutters carry rainwater straight to the river, so peak discharge is higher and lag time shorter.
True or false? A drainage basin with steep slopes has a longer lag time than one with gentle slopes.
False. Steep relief speeds up surface runoff, so water reaches the river sooner and lag time is shorter.
What is lag time on a flood hydrograph?
The time between peak rainfall and peak discharge.
What do the rising limb and the falling (receding) limb of a flood hydrograph show?
Rising limb – discharge increasing as water reaches the river; falling limb – discharge decreasing back towards base flow.
What is the difference in shape between a flashy hydrograph and a subdued hydrograph?
Flashy: short lag time, steep rising limb and high peak discharge. Subdued: long lag time, gentle limbs and a low peak discharge.
Give one benefit and one cost of using dams and reservoirs to manage flooding.
Benefit: river flow is controlled and water is stored, and the reservoir can supply water and generate HEP. Cost: very expensive, and land, settlements and habitats are drowned behind the dam.
Give one benefit and one cost of channel straightening.
Benefit: water flows faster and more directly out of the area, reducing local flood risk. Cost: flood risk increases downstream where the water arrives quickly, and habitats are lost.
Give one benefit and one cost of embankments.
Benefit: raised banks increase the channel's capacity so it can hold more water, and they are relatively cheap. Cost: they look unnatural and flooding is severe if they are breached.
Give one benefit and one cost of a flood relief channel.
Benefit: excess water is diverted around a settlement, lowering discharge in the main channel. Cost: expensive to build and maintain, and flood risk may be moved downstream.
Give one benefit and one cost of flood warnings and preparation.
Benefit: people can move possessions upstairs or evacuate, so fewer deaths and less damage. Cost: they do not stop the flood, and some people do not receive or act on the warning.
Give one benefit and one cost of flood plain zoning.
Benefit: building is restricted on the highest-risk land, so damage and surface runoff are reduced. Cost: it limits land available for development and does nothing for buildings already there.
Give one benefit and one cost of planting trees in a drainage basin.
Benefit: interception and uptake by roots reduce runoff, lengthening lag time and lowering peak discharge; cheap and good for habitats. Cost: less land available for farming or building.
Give one benefit and one cost of river restoration.
Benefit: returning the river to its natural course and flood plain slows the flow, stores flood water and improves habitats, with little maintenance. Cost: land must be given over to flooding, and local flooding still happens.
Why was the Jubilee River flood management scheme (Maidenhead, Windsor and Eton) required?
Around 5,500 homes and businesses on the Thames flood plain were at serious risk of flooding, as in the 1947 floods.
What strategy was used in the Jubilee River flood management scheme?
An 11.6 km man-made flood relief channel that diverts high flows of the Thames around Maidenhead, Windsor and Eton and returns them downstream.
Give one social issue caused by the Jubilee River scheme.
It increased flood risk downstream – Wraysbury and Datchet flooded in 2003 – causing conflict between protected and unprotected communities.
Give one environmental issue of the Jubilee River scheme.
Algae and weed growth in the slow-flowing channel harmed water quality, and the weirs and banks were damaged by erosion (though new wetland habitats were created).
True or false? On a flood hydrograph, peak discharge happens at the same time as peak rainfall.
False. Peak discharge comes after peak rainfall, because water takes time to reach the river — the gap is the lag time.
True or false? Solution is both a process of erosion and a process of transportation in a river.
True. Solution erodes soluble rock such as limestone, and the dissolved minerals are then carried along in the water.