rivers COPY Flashcards
precipitation
Moisture falling from clouds as rain, snow, or hail.
Interception
Vegetation prevents water from reaching the ground
Surface Runoff
Water flowing over the surface of the land into rivers
Infiltration
Water absorbed into the soil from the ground.
Transpiration
Water lost through the leaves of plants.
Upper Course of a River
Near the source, the river flows over a steep gradient from the hill/mountains. This gives the river a lot of energy, so it will erode the riverbed vertically to form narrow valleys
Lower Course of a River
Near the river’s mouth, the river widens further and
becomes flatter. Material transported is deposited
physical causes of flooding
Long periods of rain causes soil to become saturated leading to runoff.
Steep-sided valleys channel water to flow quickly into rivers causing greater discharge.
Impermeable rocks cause surface runoff to increase river discharge.
human causes of flooding
Tarmac and concrete are impermeable. This prevents
infiltration & causes surface runoff.
Formation of a Waterfall
1) River flows over alternative types of rocks.
2) River erodes soft rock faster creating a step.
3) Further hydraulic action and abrasion form a plunge
pool beneath.
4) Hard rock above is undercut leaving cap rock which
collapses providing more material for erosion.
5) Waterfall retreats leaving steep-sided gorge.
Formation of Floodplains and levees
The river channels get shallower during low flow conditions, causing deposition on the river bed.
This means that the river cannot hold as much water as before as the river bed has risen.
During a flood, sediment is deposited on the river banks; depositing coarser (heavier) sediment nearer to the river and finer sediment further away.
River Discharge
River discharge is the volume of water that flows in a river.
Hydrographs that discharge at a certain point in a river changes over time in relation to rainfall
Peak discharge
the discharge in a period of time
. Lag time
the delay between peak rainfall and peak discharge
. Rising limb
the increase in river discharge.
Falling limb
the decrease in river discharge to normal level
Factors affecting hydrographs
Basin size – small flashy *Drainage density - high = flashy
rock type - impermeable = flashy *Land Use urbanisation = flashy *Relief - steep = flashy
Soil moisture – saturated = flashy * Rainfall Intensity –
high = flashy .
opposite characteristics & precipitation = SUBDUED
The River Tees location and background
Located in the North of England and flows 137km from the Pennines to the North Sea at Red Car.
Geomorphic Processes Upper
– Features include V-Shaped valleys, rapids, and waterfalls.
High force Waterfall located close to Forest-in Teesdale drops 21m
and is made from harder Whinstone and softer limestone rocks.
Gradually a gorge has been formed.
geomorphic processes middle
– Features include meanders and ox-bow lakes. The
meander near Yarm encloses the town.
geomorphic processes lower
– Greater lateral erosion creates features such as floodplains & levees near Darlington. Mudflats at the river’s estuary.
Middle Course of a River
Here the gradient gets gentler, so the water has less energy and moves more slowly.
The river will begin to erode laterally making the river wider.
Soft Engineering
Soft engineering involves adapting to natural hazards and working with nature to limit the damage. For example, planting trees to limit flood risk.
Hard Engineering
Building structures to deal with natural hazards, such as dams to prevent flooding
Formation of Ox-bow Lakes Steps
Erosion of outer bank forms river cliff. Deposition inner bank forms slip-off slope.
Further hydraulic action and abrasion of outer banks, the neck gets smaller
Erosion breaks through the neck, so the river takes the fastest route, redirecting the flow
Evaporation and deposition cuts off main channel leaving an oxbow lake
Flood Relief Channel Social Issues:
Protection of wealthy properties in Maidenhead and Eton at the expense of less affluent areas further downstream at Wraysbury.
Flood Relief Channel Economic Issues:
It was the most expensive flood relief scheme
in the UK.
Floods in 2003 damaged weirs – the cost of maintenance is quite high.
Additional local relief measures are required
downstream; the scheme has not so much solved the
problem but shifted it elsewhere – serious flooding in
2014
Flood Relief Channe Environmental Issues:
Environmental Issues:
Extensive flooding in 2014 below the confluence of the
River Thames and the flood relief channel damaged
habitats. Concrete weirs are unattractive.
What are ‘interlocking spurs’?
‘Interlocking’ hillsides that look like a ‘zip’ formation.
How are interlocking spurs formed?
In the upper course, rivers aren’t powerful enough to erode laterally, so they wind around the hillsides creating a zig-zag shaped flow.
What are the characteristics of the upper course of a river?
Steep gradient Narrow v-shaped valley Narrow/shallow river Large angular sedimant load Mostly erosion taking place
What are the characteristics of the middle course of a river?
Shallower gradient Asymmetrical valley cross section Deeper river Smaller/rounded load Balance between erosion and transportation taking place
What are the characteristics of the lower course of a river?
Very low gradient U-shaped valley Wide/deep river Small suspended load Mostly deposition taking place
- when does deposition happen
when a rivers velocity decreases, and it no longer has the energy to transport its load, it deposits it.
- describe deposition
larger rocks transported mainly by traction are only carried short distances during periods of high flow. they are deposited in a rivers upper coarse.
smaller sediment is carried further downstream- mostly in suspension. it is depostied on a rivers bed and banks where velocity slows down due to friction lots of deposition occurs at a rivers mouth where its velocity reduces because of the gentle gradienct and also by interaction with tides
- formation of Gorges
a gorge is narrower, steep sided valley found downstream of a retreating waterfall.
gorges can form in other ways- at tje end off the last glacial period masses of water from melting glaciers poured off upland areas forming gourges on lime stone, when large underground caverns can accomodate an entire river.
— describe an estuarie
n estuary is where the river meets the sea. they are affected by tides, wave action and river processes. as the tides rise the rivers can flow into the sea, so velocity falls and sediment is deposited forming mudflats, which develop into salt marshes
- what causes flooding
river floods usually occur after long periods of rain- most frequently during winter
sudden floods, called flash floods, tend to occur in summer and associated with heavy rainstorms ]physical and human factrs can increase flood risk
- define and describe the human factors of flooding
Urbanisation- impermeable surfaces mean water flows quickly into drains, sewers and river channels
deforrestation- when trees are removed, much of the water which had been evaporated from leaves or stored on leaves and branches flows rapidly into river channels agriculture- exposed soil can lead to increased surface runoff
