the river severn

• the river severn is 354km long
• an estuary is the tidal part of a river where freshwater from the river merges with salt water from the sea. it is therefore affected by fluvial and marine processes
• the river severn has a tidal range of 15 metres which is one of the highest in the world
• the severn estuary is 3.2 kilometres wide at the old severn bridge crossing (very wide)
• the river severn has mudflats that are visible at low tide and some are covered by salt marshes
• the severn estuary has a tidal bore (a huge wave that funnels up the river) which travels as far as gloucester on very high spring tides.
• large bores occur about 25 days a year and can travel at 8-21 kilometers per hour, getting faster upstream. they cause great damage to the banks and vegetation
• how is an estuary formed?

  1. a large river such as the severn entered the sea at a narrow mouth
  2. after the ice age, melting ice caused a rise in sea level, this caused low-lying valley sides either side of the river to become flooded
  3. the original channel of the river is now on the estuary floor where it provides a deep channel for shipping
• the salinity of the river increases towards the sea
• there are two sources of sediment - from the river and from the sea
• how are estuary mudflats formed?

  mudflats form in sheltered areas where tidal water flows slowly. as the river transports alluvium down to the sea, an incoming tide transports sand and marine silt up the estuary. where the waters meet, velocity is reduced which causes deposition and builds up layers of mud called mud flats
• within the mudflats there are many small streams and after a while the mudflats may become colonised by salt marsh vegetation
• the river severn starts as a boggy pool 600m above sea level in the cambrian mountains in south wales
• 2500mms of rainfall fall at the source each year
• the small stream of the 'infact river' cuts downwards to create the river severns V shaped valley
• the severn 'Break its neck waterfall' occurs in wales in the upper course and is 75ft high, it is situated off the A44 approximately 1.5 miles west of new radnor
• there are several active meanders on the river severn, there is one at abermule, Powys in mid-wales, the slip off slope consists of coarse material
• after the river severn passes through shrewsbury, it flows through the ironbridge gorge, at this point it has 60,000 litres of water passing per second and has descended to 13m above sea level
• there are several ox bow lakes on the river severn, one example occurs at UPPer Lode near tewksbury
• there are several examples of levees on the river severn, an artificial levee occurs at the base of Breiddon hills and there are natural levees at arlingham, gloucestershire
• there are many floodplains along the whole of the river severn, some are build on but many are left as farmland
• after gloucester, the river severn becomes an estuary. at this point it is 2kms wide and has one of the widest tidal ranges in the country. the difference between high and low tide can be as much as 15m
• by the time the river reaches weston super mare, the river is 14kms wide, 20m deep and carries 9 billion litres of water a day
• the river severns mouth is at weston super mare and joins the bristol channel
• in total the river severn is 354kms in length and has a drainage basin area of 11,420 square kms