River Catchment - Mersey Flashcards
Inputs into catchment
Rain
Channel flow from upstream
Surface runoff
Throughflow
Outputs out of catchment
Evaporation
Channel flow down stream
How many miles ?
70 miles from source
Cities it flows through
Manchester
Sale
Liverpool
What it 1.45 miles south east of Mersey
Flixton girls school
Stores of water in catchment
Reservoirs
Ridgegate
What rivers is the upper Mersey catchment made of?
Mersey
Tane
Goyt
Where is rural land located
Uplands to the east
Where is urbanised land located ?
Lower catchment to west
Bedrock in the catchment
The most permeable rock was in the west but now it has been urbanised.
Rural areas in east there is permeable rock eg peat that water can infiltrate onto this allows for steady drainage of water back into river
Rainfall in the area
Rainfall above average of 926mm
Highest rainfall in east where rural higher than is - indicates relief rainfall
water flows quickly as surface run off down steep slopes - less through flow
Rainfall increased from 1941-1990
To the west
Initially was the most permeable rock meaning infiltration / percolation / interception could occur but not heavily urbanised meaning rain flows as overland flow/ surface runoff quickly into channel - flashy HG
To the east
Permeable land
Mountains / heath / pest
Lots of infiltration/ interception / percolation
Less overland flow meaning water steadily flows into channel - subdued HG
What has increased flow in the river ?
Channelising the river, quick velocity as water course is straight
Why is the area flooding?
Heavy rain.
Urbanised areas - more surface runoff less infiltration.
Example of flooding
Upper merysey 1965
Breached its banks causing widespread damage to livestock
Why do we need to manage the area?
Heavily populated about 70% of the upper catchment is populated
Flooding is known to occur in urban areas as a result of short intense storms when capacity of drainage system is exceeded and water forced to flow across ground
Normal level of the Mersey at Ashton weir in average weather
0.31m and 0.37m
Highest ever level at Ashton weir recorded
3.64m on 6th nov2000
Name a location with over 500 properties at risk
Didsbury
Engineering schemes in upper Mersey
£22 million pound invested in last 10 years on flood alleviation schemes.
Over 67km raised flood defence
Storage in places like sale - reduce peak flow of 35%
Activities reducing probability of flooding
Maintaining / improving flood defences / structures
Working with local authorities - land use management as golf courses can be built on flood plain not houses
Activities reducing consequence of flooding
Flood risk mapping
Warning services
Promoting awareness
Name 3 factors which will impact flooding in future
Climate change
Change in land use
Rural land management
How is climate change going to impact flooding in future
Frequent/ intense storms
Wetter winters
Future scenarios in upper catchment
20% increase in peak flow
By 2100 the number of properties at risk of fluvial flooding will be increased by around 11% to 300 properties
In some areas the number of properties at risk in 1% AEP could increase up to 77% higher
Physical impacts affecting drainage basin
Permeable surfaces.
Vegetation.
Steep slopes.
Rock type.
Human factors affecting river discharge
Urbanisation
Engineering
