The River Mersey (water cycle)

Question 1

How long is the River Mersey?

Answer 1

70 miles

Question 2

Where is the mouth of River Mersey?

Answer 2

Liverpool bay

Question 3

What are the characteristics of the Mersey upper catchment?

Answer 3

• Upper catchment is made up of the River Mersey, Tame, Goyt, Collin and Sinderland Brook.
• Mix of predominantly rural uplands (permeable) with the lower catchment highly urbanised (impermeable).
• Home to 1.2 million people.
• History of flooding in Didsbury, Sale and Altrincham at greatest risk.
• 2,600 residential + commercial properties are at a 1% annual probability of flooding. Set to rise to 2,900 in the future due to the effects of climate change.

Question 4

What is the geology of the area?

Answer 4

• The most permeable rock is to the west where the most urbanised areas are.
• Upper part of the catchment has moderately permeable land.
• In the rural areas to the east, permeable rocks allow for a steady drainage of rainwater back into the river.

Question 5

Describe the rainfall of the area.

Answer 5

• Highest rainfall in the east where the rural, higher areas are, indicating relief rainfall.
• Rainfall across the area is higher than the UK average of 926mm per year.
• Rainfall has increased from 1941-1970 to 1961-1990. This is increasing due to climate change.

Question 6

Describe the land use of the area.

Answer 6

• West of the area is heavily urbanised, resulting in impermeable surfaces, despite permeable rocks beneath causing a quick flow of water to the river.
• East are mountains, health and bog areas. The area correlates to moderate permeable rocks meaning lots of infiltration + percolation into underground rocks causing a slow flow of water to the river.

Question 7

How have people impacted the local water cycle?

Answer 7

• Major management + modification of the river system.
• In urban areas, many watercourses have been culverted (straightened) or channelised through development which quickens the flow of water.
• Reservoirs in the Tame, Goyt and Etherow subcatchments have an influence on flows within the catchment as they can hold more water so the flow of water is slower.
• Manchester ship canal receives water from upper Mersey and river Irwell providing drainage + flood alleviation function.
• There are operational wastelands which provide a valuable flood risk management. Area of land allowed to flood - soft management.
• Flood warning, making space for water are sustainable re-developments.

Question 8

Describe the flooding here in the catchment.

Answer 8

• Extensive urban areas in the South of Manchester causes infiltration rates to decrease massively.
• Most significant flooding in the upper catchment occurred in 1965. River breached its banks.
• The need to manage the area is high due to the high proportion of the catchments population living in these areas (70%).
• Levels in the river are increasing + becoming more frequent. Evidence = recent high in 2011 is 3.59m.
• Highest level ever recorded is 3.64, in 2000.

Question 9

What are the causes of flooding here?

Answer 9

• Surface water flooding is known to occur here in urban areas of this catchment. It is as a result of short intense storms, where the capacity of the urban drainage system is exceeded and water is forced to flow across the ground.

Question 10

How is the catchment managed?

Answer 10

• Twenty million pounds has been invested in the last 10 years on the development of flood alleviation in Didsbury.
• Over 67km of raised flood defences in this catchment.
• Three flood storage areas Didsbury.
• Working with local authorities to ensure only appropriate defences are allowed on the floodplain.
• Promoting awareness and flood risk mapping.

Question 11

How will flooding be affected in the future?

Answer 11

• Wetter winters increasing the likelihood of large-scale flooding.
• Estimated that by 2100 the number of properties at risk from flooding will increase by around 11%.
• Increase in urbanisation + change in rural land use increases flooding.