Lec #4 Esturaries and Deltas Flashcards
What are the effects astronomical tides have on the shore (3)
- the extent of the wave action and the flushing of estuaries
- the biological zonation of species
- chemical processes assciated with wetting and drying
What causes astronomical tides?
the phases of the moon, as well as the sun
What orientation of the moon and sun causes spring tides?
o O o (
What orientation of the moon and sun causes neap tides
o
O (
o
What are the key points on estuary characteristics (3)
Draining of river valleys
Tidally influenced
Mix of sea and fresh water
What are the three zones of the estuary
Inner, central and outter
What are the four types of estuaries?
fjord, canalaque, lagoons and rias
Explanation of fjords
deep elonganated basin, U shaped and a ledge that seperates them from the ocean, there is high river input and little mixing
Explanation of canalaques
high sided with limestone cliffs, found in the MED
Explanation of a lagoon
Large area of water which is in part isolated from the sea, which may have tidal isolation
What is the key process in estarine hydrodynamics
the mixing of salt and fresh water which mix through molecular diffusion
What occurs if molecular diffusion is not effected
the estuary can become stratified and a salt wedge exists in the bottom part of the water column
What is the area where mixing takes place, and explainataion of it
Turbidity maximum, it occurs on the extent of the salt marshes and entrain sediment which leads to chemical reactions
What are river deltas
These are landforms at the mouth of a river, that have been filled in with sediment from fluvial systems, often deltas can pro-grade towards the sea and consist of a network of braided channels
What is specific about theses delta channels and why
The channels are constantly chaing due to river flow, wave action and solid flows
What do deltas need for formation
Really high sedimentation
What are the three types of deltas
Wave dominated
Fluvial Dominated
Tide dominated
Explanation of a wave dominated delta
have exposure to ocean swell
Explanation of fluvial dominated delta
large catchment area, river discharges into protected sea, low energy from waves with a small tidal prism
Explanation of a tide dominated delta
Where the tide prism is larger than the river discharge
What does the number of channels in a delta relate to?
The slope gradient and the size of sediment being desposited
What is the delta front?
This is the most active part of the delta, most of the remaining sediment is deposited on the edge of the delta
What is the delta plain?
The delta plain may have single or multiple channels which distribute sediment and water
What is the prodelta?
Only the finest sediment will reach this zone does to large distance from the delta front
Effect of turbidity currents on deltas?
These are negativity buoyant, highly concentrated, near bed suspensions that flow downhill under their own weight carving new channels
What two things can occur at the delta mouth?
Jet plumes and density currents
What determines if it will be a density current or a jet plume (3)
Current speed
Slope of the seabed
Density distribution in the water
What are density currents
These are isopycnals out into the sea
What are the three types of isopycnals and a quick explanation
Homophycals (mixed)
Hypo - river water is less dense and floats
Hyper - river water is more dense and sinks
What are jet plumes?
These occur when water exists a basin at high speed into a deep water systems, also called axial jets
Name two properties about axial jets
- The have no interaction with the sea floor
2. Away from core water slows and sedimentation can occur
What is delta switching?
This occurs with the delta when an active region of the delta switches into another area, lobe switching can also occur within delta switching
