River Severn = travels 354 km to estuary in Bristol Channel
Estuaries:
● Estuary = tidal part of a river where the
channel broadens out as it reaches the sea
○ Freshwater from river merges with
salt water from the sea
○ Affected by both fluvial and marine
processes
→ Characteristics:
● High tidal range
● Very wide
● Mudflats are visible at low tide
○ Salt marsh = an area of coastal
grassland that is regularly flooded by
seawater
● Tidal bores = huge waves that funnel up the
river and cause damage to river
banks /vegetation
→ Formation:
1. Water is tidal → river level r ises/falls
everyday
2. Water floods banks, carrying silt and sand
onto valley floor
3. When tide reaches highest point → water is
moving really slowly and sediment is
deposited
4. More mud builds up , creates large mudflats
○ At low tide, wide/muddy banks are
exposed
■ Salinity increases towards
the sea
■ 2 sources of sediment (river
and sea)
Estuary mudflats:
● River spreads out and slows down as it approaches the sea
● Deposition is encouraged as the hydraulic radius is dropped and river becomes less efficient
○ Hydraulic radius = ratio of the channel’s cross-sectional area of the flow/its wetted perimeter
■ A measure of efficiency → high HR means that river is more efficient
● River transports alluvium to sea , tide transports sand/marine silt up estuary
● Where waters meet , velocity is reduced and deposition occurs
● Causes bars or islands of sediment to build in the middle of the main channel
● Layers of sediment build a marsh into the sea → can be eroded away by strong currents /waves
