11.8 The River Severn and its estuary

Question 1

What is an estuary

Answer 1

The tidal part of a river where freshwater from the river merges with saltwater from the sea

Question 2

What is tidal range

Answer 2

The difference in height between high tide and low tide

Question 3

What are the characteristics of an estuary

Answer 3

• high tidal range: River Severn had a tidal range of 15 metres
• very wide: Severn Estuary is 3.2 km wide at the old Severn Bridge Crossing
• it will have mudflats that are visible at low tide and some of the mud will be covered by salt marshes
• it may have tidal bores

Question 4

Explain tidal bores

Answer 4

They are huge waves that funnel up the river (as far as Gloucester) at a speed of 20km/hr. They occur about 25 days a year and cause great damage to river banks and vegetation

Question 5

Features of estuaries

Answer 5

• the salinity increases towards the sea
• there are two sources of sediment (from the river and from the sea)
• the estuary is tidal so fluvial and marine processes operate

Question 6

How are estuaries formed

Answer 6

Melting of ice after the last ice age caused flooding of the low lying valley

Question 7

How are estuary mudflats formed

Answer 7

• When the sea water meets with the river current there is a loss of energy and the deposition of sediment takes place
• The mudflats are revealed at low tide
• They are fertile and small streams (creeks) are colonised by cordgrass (a type of salt marsh vegetation)