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The reasons why river levels discharge fluctuate (GEOLOGY Rock Type…
The reasons why river levels discharge fluctuate
Land use
Urbanistation
Building on a floodplain creates impermeable surfaces such as tarmac roads, concrete driveways and slate roof.
Water is transferred quickly to drain and sewers and then into urban river channels.
Deforestation
Much of the water that falls on trees is evaportated or stored temporarily on leaves and branches.
Trees also use up water as they grow.
When trees are removed much more water is suddenly availble and transmitted rapidly
Agriculture
In arable farming, soil is left unused and exposed to the elements for periods of time.
This can lead to more surface runoff.
This is increased if the land is ploughed up and down steep slopes, as water can flow quickly along the furrows.
GEOLOGY Rock Type
porous
pervious
permeable
Permeable rocks encourage a slow transfer by groundwater flow
impermeable
Impermeable rocks such as shales and clays encourage water to flow overland and into river channels. This speeds up water flow and makes flooding more likely.
relief
The relief of the land can also have an impact.
Steep slopes tend to reduce the amount of infiltration of water into the ground, this water can then flow quickly down to rivers as overload flow.
In addition, steep slopesalso can cuases more through flow within the soil.
Gentle slopes or flat land allow water to penetrate into the soil and increase lag times.
Amounts and type of rainfall
The most obvious rasons for river flooding. Long steady prolonged rainfalll will produce rivers which rise slowly but can flood.
Snowfall in another factor to take into account, rivers fall in the UK as precipitation is often sotred as snow during cold snaps.
However, when temperture warms and that snow melts many days' worth precipitation can end up in rivers and cause flooding.
