Formation and types of estuaries Flashcards
What are the main characteristics of coastal plain estuaries?
Drowned pre-existing river valleys
Shallow, deeper and wider at mouths with stronger tides
Extensive mud flats and saltmarshes
Common temperature latitudes as river flow less than tidal prism
Commonest type in UK e.g. Severn, Thames, Humber, Chesapeake Bay USA
What are the main characteristics of a bar built estuary?
Drowned river valleys but high levels sedimentation restricting flooding
Wave activity and transport of sediment forms bar at mouth
Tidal activity low
Very shallow < a few metres deep
Governed by river flow
Often tropical, but do get on the east coast of UK e.g. the Alde and Ythan
What are the main characteristics of a fjord?
Drowned glacial troughs
Steep sided, rectangular, long
Deep inner basins but shallow at mouth due to a Sill. Sill restricts tidal flow
River discharge small but greater than tidal prism
Found high latitudes (Scotland, Norway, New Zealand)
What are the main characteristics of a tectonic estuary
Tectonic activity causes rise in sea level
Faults, eruptions
San Francisco Bay created when tectonic activity along San Andreas fault caused land movement and relative sea level rise (flooding of Sacramento River valley)
What are the key features of a micro-tidal estuary?
<2m range
River may form inner delta
limited intertidal areas
wind and waves dominate outer regions
e.g. Poole Harbour, Cancun Bay (Mexico)
What are the key features of a meso-tidal estuary?
2-4m range
Extensive intertidal regions along banks and near mouth
often covered by vegetation -seagrass, salt
marshes
e.g. Clyde, Ythan, Orwell
What are the key features of a macro-tidal estuary?
4-6m range
Extensive mud flats along banks of the estuary,
Intertidal flats often bare mud
Sand bodies linear, central channel or at mouth
e.g. Thames, Tyne, Exe
What are the key features of a hyper-tidal estuary?
> 6m range
Extensive mud flats along banks in inner estuary
Central channel often bare rock
e.g. Bay of Fundy, Severn, Somme
What are the key features of hyper-synchronous tide shape?
Convergence>friction
Tidal range and currents increase towards head until reach riverine section
Estuary funnel shaped
Tide dominated or macro-tidal estuaries
Tidal cycle becomes distorted, asymmetrical flood and ebb
Creating a ………BORE………… (continuous waves)
Severn
Range = ~7m at mouth; ~ 14m at Avonmouth
Current = 10 knots mouth; 13 knots upper
What are the key features of a synchronous tide shape?
Convergence=friction
Tidal range and current constant along estuary
Often mesotidal
What are the key features of a hypo-synchronous tide shape?
Tidal range decreases along estuary
Tend to have restricted mouths
High velocities at mouth
Wave dominated or microtidal estuaries
Barriers – spits at mouth
Large central basin
