4. UK Evolving Physical Landscape: River Discharge, Flooding, Management Flashcards
What shows Change in River Discharge?
Hydrograph
What is a Hydrograph and what does it show?
Change in river discharge
Volume of water per second - measured in CUMECS (m3/s)
Storm Hydrographs show impact in a storm
Key elements:
1. Peak discharge - highest
2. Lag time - delay between peak rainfall and peak discharge
3. Rising Limb - increase in river discharge as rainfall flows into river
4. Falling Limb - decrease in discharge as returns to normal level
What are the factors affecting Storm Hydrographs?
What are the Physical and Human factors that affect lag time, discharge and the shape of the Hydrograph?
Geology - more run-off over impenetrable rock
Soil Type - not as absorbent as sand
Slope - steeper then higher run off
Drainage Basin Type - circular than shorter lag and higher discharge than narrow basins
Antecedent Conditions - previous wet or cold weather can increase run off
Urbanisation - roads / gutters / drains - high run off into river
Deforestation - trees store water from ground - reduces run off - cutting down trees increases
What is Flooding?
Why is River Eden prone to Flooding? Physical and Human factors?
Physical - Cumbria -prevailing SW winds - wet and mild - wettest part of UK - intense rain - hard impenetrable rock - can’t soak water - run off to river. Snowfall common on high ground in winter - melt to form a lot of water quickly
Human - built up area - lots of development on flood plain - affects ability to absorb and store floodwater - little soil / vegetation - little infiltration of rain - high run off. Natural woods been cleared from upland areas increasing run off. Parts of valley drained for farming - drainage ditches - water flows rapidly into river channel
What factors in 2015 contributed to Flooding in Eden Basin?
Antecedent - 2nd wettest winter on record - soil saturated
Heavy Rainfall - Storm Desmond 300mm of rain / 24 hrs
Short Lag time - rainfall quickly reached main channel at Carlisle
Blockages - debris blocked bridges
Insufficient drainage - system couldn’t cope and overflowed
Why is risk of Flooding increasing in the UK?
Increased frequency of storms - climate change - more extreme
Land Use change - population grows - urban expansion - increase in impenetrable surfaces - increased run off. Removing vegetation. Development on flood plains so increased risk to people if flood defences fail
How does Flooding threaten People?
Death
Damage - Roads, bridges
Contamination - sewage - disease
Possessions damaged
People made homeless
Businesses shut down
How does Flooding threaten the Environment?
Contamination and Pollution
Farmland ruined by silt and sediment
River banks eroded - increased deposition downstream
Uproot trees etc and may kill vegetation
What are the types of Hard Engineering that can reduce the risk and effects of Flooding?
Flood Walls - artificially increase height of river bank
Embankments - hight banks to stop water flowing into populated areas - earth or natural materials - less unsighly
Flood Barriers / Gates - e.g. Thames barrier - river estuaries to stop flooding from storm surges - protect large areas of land / urban areas e.g. London
Flood Barriers / Demountable - temporary protection
What are the types of Soft Engineering that can reduce the risk and effects of Flooding?
Flood Plain retention - maintain river flood plain by not building on it - slows water down - stores water - no money spent but restricts development
River restoration - make river more natural - remove man made levees - flood naturally - less risk of downstream flooding as discharge is reduced - river left in natural state
