Coastal Geography, Estuaries Flashcards
Estuary
A semi-enclosed coastal water body that receives inputs of water and sediment from both the open ocean and rivers
What are the three main characteristics of estuaries?
Typical funnel shape, two way flows, easily catch sediment
What are the four classification types of estuaries?
Water balance, geomorphology, vertical salinity structure, hydrodynamics
Is fresh or salt water more dense
Fresh water is less dense than salt water so it flows above it
What two factors does mixing depend on?
Volume and speed of flow
What are the two types of sediment in estuaries?
Bedload and suspended sediment
Bedload
Larger/heavier sediment that is fluvially transported via traction and saltation
Suspended sediment
Already dissolved sediment that is fluvially transported via suspension and solution
What two factors does water circualtion depend on?
Tidal flow and river flow
What are the three types of estuarine circulation?
Salt wedge, partially mixed, fully mixed
What are the two requirements for a salt wedge estuary?
Requires a small tidal range (<2m) and a large river flow
What are the two requirement for a salt wedge estuary?
Requires a small tidal range (<2m) and a large river flow
What is the one main characteristics of a salt wedge estuary?
The differences between saline and fresh water produces a wedge of salt water below the fresh river water
What are the two main requirements for a partially mixed estaury?
Requires a large tidal range (>3m) and a small river flow
What are the two main characteristics of a partially mixed estuary?
The mixing of tidal currents and river flow produces a vertical salinity gradient.
Saline resides at the bottom while fresh resides above
What are the three main requirements for a fully mixed estuary?
Requires a very large tidal range (with strong currents), a very low river flow, and a very wide estuary mouth (>500m)
What are the two main characteristics of a fully mixed estuary?
No vertical salinity variation.
Lateral salinity gradient is produced by coriolis forces (earth rotation)
Floculation
The bonding of clay and silt particles due to electrostatic attraction
What type of sediment is found in a salt wedge estuary, and what is its origin?
Course sediment is deposited at the tip of the salt wedge whilst finer sediment is carried to the estuary mouth. At the salt wedge, floccualtion occurs.
Orign: River sources
What type of sediment is found in a partially mixed estuary, and what is its origin?
Course sediment is deposited near the mouthwhilst finer sediment is carried landward. Turbidity maximum occurs at the peak of suspended fine sediment at the limit of salt water
Origin: Most is from marine sources
Turbidity maximum
A concentration of suspended sediment that reduces water clarity
What two factors does the morphology of an estuary depend on?
Whether it is wave dominated (microtidal) or tide dominated (macrotidal)
What are the tidal ranges of wave and tide dominated estuaries?
Wave dominated (microtidal): <2m
Tide dominated (macrotidal): >4m
What are the three distinct zones of a wave dominated (microtidal estuary)?
- A sandy barrier and tidal delta
- A muddy lagoon
- A sandy and gravelly river delta
What are the thee distnict zones of a tide dominated estuary?
- A sandy tidla bar complex
- A sandy tidal flat
- A sand and gravelly river channel
Tidal delta
A fan-shaped deposit of sediment formed on the landward side of an estuary
