4.7 River Landscapes And Human Activity

Question 1

Explain how human factors can affect flood hydrographs?

Answer 1

Deforestation:
Vegetation and trees decrease how much water touches the surface and increases the resistance to surface run-off. The roots also absorb water from the surrounding soil. When the trees are cut down, the surface run-off is increased.
Urbanisation:
Concrete and roads are impermeable so the water cannot infiltrate and disperse underground. This means that water builds up and causes a large amount of surface run-off.
Land use change (crop farming):
When the soil is changed into farmland then the soil has channels in between the actual crops so the water runs down these quicker. This increases the surface run-off. When the soil is saturated then the precipitation can flow down these channels even quicker so there is a smaller lag time.
Land use change (cattle grazing):
Cattle eat grass/vegetation. There is less resistance (similar to deforestation) so surface run-off now and there is also less surface storage (interception). Increasing the amount of surface run-off.

Question 2

Explain how physical and human factors cause river flooding in the River Eden?

Answer 2

Physical

Storm Desmond caused very heavy rainfall (341mm of rain fell in 24 hours)
Wet antecedent conditions (second wettest November ever recorded)
The River Eden has two drainage basins (the Lake District and the Pennines)
The Lake District and Pennines are mountainous, reaching almost 1000m high.
Impermeable rock is common in this area, mainly igneous in the Lake District and limestone in the Pennines.
The River Eden’s river levels were already high in November.
Cumbria is on the west coast of the UK facing the prevailing SW winds- it receives a lot of frontal and relief rain.
The reservoirs in the Lake District quickly became full and couldn’t store any more water.
Snowfall is common on higher ground in the autumn/winter which melts when it rains/warms.

Human

Natural woodland had been cleared for farming and sheep farming has increased in intensity.
Parts of the Eden’s drainage basin has been drained to make way for farmland.
Drainage ditches have been dug in the drainage basin to increase the surface flow to the main river.
There was an issue with drainage. The drains weren’t big enough to hold all the rain and quickly blocked with storm debris.
The rivers in the area had not been dredged effectively after previous storms- the river capacity was reduced.
Carlisle (population of 75,000) is an urban city- it has many impermeable roads and concrete.

Question 3

What are the effects of flooding on people and the environment?

Answer 3

Homes are flooded
People have to live in temporary housing
Local services have to temporarily shut down.
Residents suffer from anxiety, stress.
Businesses close
Transport and infrastructure are damaged
Costs a lot
Large insurance claims
Farmers lose expensive borderings (stone walls) and sheep drown
House prices fall in flood risk areas
River banks erode. Future flooding risk increased.
River are contaminated with sewage and waste
Soils erode, habitats destroyed, ecosystems affected.
Saturated grounds lead to decomposition of plants and animals, gives of noxious gases.
Saturated grounds lead to landslides.