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Mouth of a river
The place where a river meets the sea.
Source of a river
The place where a river starts in its upper course.
What is a long profile and how does it change along a river?
A section of the course of a river drawn from source to mouth. It changes along the river as the slope becomes less steep as it moves towards the mouth of a river.
Upper course
Where river starts and it is often an upland (higher above sea level) area. River's load = larger in upper course, hasn't been broken down by erosion yet.
Load
Particles of rock carried by a river
Lower course
Closer to where river ends, the land is a lot flatter. River's load = fine sediment, as erosion has broken down the rocks.
What is a cross profile?
The cross-section of the valley and channel of a river at a certain point in the river's course. It changes as it moves from upper course to lower course.
Lateral erosion
The wearing away of the landscape when a river erodes sideways.
What does the upper course look like in a cross profile?
It changes as it moves from upper course to lower course. As river flows downhill = increase in vertical erosion, but less lateral erosion. Channel = shallow & narrow.
Vertical erosion
When the land is eroded or worn away in a downwards direction, e.g. a river that is high up will erode vertically because gravity pulls the water downwards.
What does the middle course look like in a cross profile?
Some vertical erosion but increase in lateral erosion. Channel = wider and deeper as a result.
What does the lower course look like in a cross profile?
Lot less erosion - only some lateral erosion. Channel = widest and deepest.
What are the 3 fluvial (river) processes?
Erosion, transportation and deposition (in said order)
What is abrasion?
Wearing away of river bed & bank by load carried by river.
What is attrition?
Wearing away of load carried by river (smaller, rounder particles of rock).
What is hydraulic action?
Force of air and water on sides of river and in cracks
What is solution?
Removal of chemical ions (especially calcium), causes rocks to dissolve
What are the steps of erosion?
Abrasion
Attrition
Hydraulic Action
Solution
What is saltation? (transportation - the space hopper)
Large particles (gravel & coarse sand) lifted and dropped by river, so they bounce along riverbed
What is traction? (transportation - the forward roll)
Larger particles (pebbles & boulders) roll and slide along riverbed.
What is suspension? (transportation - the bridal lift)
Smaller particles (clay, silt, fine sand) carried along w/o touching river bed, suspended in water
What is solution? (transportation - one lump or two?)
Dissolved materials containing minerals, e.g. calcium & sodium carried in water
What are the steps of transportation?
Saltation
Traction
Suspension
Solution
What is sediment?
Naturally occurring rock material that is broken down by processes of weathering and is subsequently transported and deposited by the actions of fluids (water, ice, wind, etc.)
What is deposition - why do rivers deposit sediment?
River becomes less steep = has less energy. Less water in river, bc of drought/nearby factories using water. River bed is rough, slows down river. On inside of meander (bend), water becomes shallower - moves more slowly. At end of river's journey (mouth). When volume of water decreases. Human obstruction, e.g. dams.
What are some erosional river landforms? (upper course)
Interlocking spurs, waterfalls & gorges
What is an interlocking spur and their formation process?
In upper course of river, river's water volume & discharge = very low. River uses most of its energy 2 overcome friction with channel. Left over energy used for vertical erosion In upland areas, geology composed of hard rock/granite. Freeze-thaw weathering cracks rocks and gradually broadens it out. Gives valley steep, v-shaped cross profile. Repetition of this weakens rocks so fragments break lose and tumble down hillside as scree, which river removes. Winding path taken by river due to obstacles of harder rock in path. River takes easier route over land. Results in projections of high land entering valley. These projections r interlocking spurs.
What is scree?
a mass of small loose stones that form or cover a slope on a mountain.
How are waterfalls formed?
Often formed where layer of hard rock overlays layer of softer rock, leaving it to erode rock at faster rate, forming step in river bed. Hydraulic action force erodes softer rock and makes plunge pool and notch bigger over time. Helps notch grow so eventually there isn't enough support under harder rock and it collapses in2 plunge pool. This adds rocks & boulders 2 plunge pool, so process of corrosion work w/ hydraulic action to accelerate erosion of plunge pool and notch Erosion processes continue corroding notch & plunge pool. Ultimately harder rock above will collapse again, allowing waterfall 2 retreat upstream over time. As it retreats, leaves behind steep-sided gorge
What is corrosion?
solution
What are some erosional and dispositional river landforms? (middle course)
Meanders, oxbow lakes
How are meanders formed?
Fast-flowing water on the outside bank causes lateral erosion through hydraulic action and abrasion
This undercuts the bank, creating a river cliff, as material fall into river and get transported downstream
On inside bend, water travels slowly and changes direction sharply, losing energy and depositing sediment
Erosion wears away a cliff on outside bend and deposition creates slip-off slope on inside.
Define helicoidal flow
a corkscrew movement
How is an oxbow lake formed?
The meander bend has become very large so that the meander neck becomes very narrow because of continued lateral erosion
River floods so main flow of H2O cuts across the neck, breaking down the banks and carving a new channel
Floods recede reverting river to normal but with process repeating after every flood event, the new channel becomes main channel after continual vertical and lateral erosion
Meander loop becomes separated from ‘main’ channel as material gets deposited on top, creating separate oxbow lake.
What are some dispositional river landforms? (lower course)
Flood plains, levées, estuaries
How are levées formed?
River floods, friction with land causes deposition due to reduced velocity
Heaviest sediment is deposited closest to river
Continuous flooding builds up river banks higher
River bed builds up bed load over time, raising level of river, increasing probability of future flooding
How are flood plains formed?
How are estuaries formed?
What landforms does the River Tees have?
V-shaped valley, interlocking spurs, waterfalls, floodplains, leveés, meanders, oxbow lakes, estuary at mouth of river
What physical factors affect flood risk?
Prolonged rainfall (river will become saturated, excess rainfall will be surface run-off), heavy rainfall(less chance of rainfall soaked up by soil, so runs off in2 river), relief (steeper valleys = water runs in2 river quickly) , geology (w/ impermeable rocks, water won't pass through, it will become surface run-off)
What is relief?
Difference in height from surrounding terrain
What human factors affect flood risk?
vegetation (less plants = less water absorption, more surface run-off), urban land use (impermeable surfaces of building increases drains and sewers taking water 2 rivers)
