Lecture 21- Estuarine geomorphology and processes I Flashcards
What is estuarine geomorphology?
-The study of estuaries as landforms: how they got there, how they operate, and how will they evolve -The interaction of processes and how they control the system
What are estuarine processes?
-Waves, tides, river flow and currents -change is associated with tide levels and sea levels -main process are detrmined by its location -have combination of river, sea and land -inflow and outflow (ebb) -also sediments brought there -barrier -tiddes= have strong control over salinity in the estuary -river flow= controls the flow of freshwater into the estuary -if weak flow= the mouth may close into the estuary
Why is geomorphology important for zoology?
-the landforms are what the ecology and biology exists on -sediments that compose the landforms are the primary habitat -species have preferences for different habitats, so species distribution changes as habitat changed both spatially and temporally -sediments are important sinks, stores and sources of nutrients and pollutants
What are the processes that drive hydrodynamics determined by?
-The processes that drive hydrodynamics are also determined by the morphology of the landscape. -the wave tide and flow are also influenced by the topography
What is a resident time of a sediment and what does it indicate?
-resident time of sediment= how long it stays -indicated the rate of change in the estuary
What are deltas and estuaries associated with?
-dynamic systems associated with the mouths of rivers
What are deltas composed of?
-river-derived sediment -Deltas form from deposition of sediment carried by a river as the flow leaves its mouth.
What are estuaries?
-tidal-influenced lower parts of river and their valleys -a semi-enclosed coastal body of water, which has a free connection with the open sea, and within sea water is measurably diluted with freshwater derived from land drainage
What is the distinction between a delta and an estuary?
-mouth can be closed off by sediment -delta only from the river -estuary is both marine and from river
Where will deltas occur?
-in an estuary
How are deltas and estuaries a continuum?
estuary into delta
What is the definition of an estuary?
-The tidally influenced lower parts of catchments where a river enters the ocean
What is the definition of a delta?
-An area of sediment deposition as a river flows to the ocean!
How are deltas and estuaries members of an evolutionary continuum?
- balance between the three things
- so estuary can change into a delta
- regression= down sea level
- progression= up sea level
What is the continuum of process dominance?
-
What are the two types of estuaries? (based on physical classifications of mixing)
- Wave dominated 2. Tide dominated (higher proportion of tide energy) (3. River dominated= she didn’t say it but it is)
What are the three types of deltas?
- RIver dominated 2. Wave dominated 3. Tide dominated
What is a wave dominated delta like?
- nile delta
- rich form around the edge
- this is due to the higher proportion of wave energy, they pick it up and deposit in a line
What is a tide dominated delta like?
- lot of channels due to inflow and outflow of the tides
- Ganges delta
What is a river dominated delta like?
- Gulf of Mexico
- plumes of sediment far off coast
- cloudy area off the river is sediment being transported off the coast
What is a tidal bore?
- a tidal phenomenon in which the leading edge of the incoming tide forms a wave (or waves) of water that travels up a river or narrow bay against the direction of the river or bay’s current. - have several waves on the edge of the estuary, they converge and push into the estuary -huge wave
What happens to waves in estuaries?
-become asymmetrical, extreme case: tidal bore
How are estuaries divided according to tidal wave changes?
hypersynchronous, synchronous, hyposynchronous.
What is hyposynchronous estuary?
- very sharp decrease in amplitude up estuary from high bottom friction. ex. - Delaware Bay
- tidal range decrease with the river -friction or depth is the dominant over the width
What is hypersynchronous estuary?
- bottom friction and shoreline convergence causes a loss of tidal energy.
- tide rises in amplitude, amplification, before falling at the mouth of the river, ex. Bay of Fundy
- the width is the dominant factor over the depth
- as you move upstream have increase in tidal amplitude (height and power)
Are ebb and flow often equal?
-no very unusual for them to be equal
What happens when you have shortened flood and lengthen ebb?
- have development of flood an ebb channels
- important in sediment plus nutrient transport and fish movement
What are waves like and how do they impact estuaries?
-usually high energy -can erode the beach profile -transport salt water into the freshwater bit of the estuary
What do fluvian process depend on?
-depends on amount of rainfall in the catchment, how large the catchment is (the contributing area into the river) -also the gradient= if steeper then more water
What is ebb?
-is the movement of a tide back toward the sea.
What is flow?
-tide coming in
How do residual currents form?
-from the mixing of fresh and salt water -salty water more dense -results from the densities and temp differences
How can we classify estuaries?
-on the basis of the degree of mixing -how well is the salt water mixed with the freshwater -important for biology, different organisms have different salinity ranges in which they can live
What are the 4 types of estuaries based on the degree of mixing?
1.Highly stratified (salt wedge) estuaries 2.Moderately stratified (partially mixed) 3.Non-stratified (well mixed, vertically homogeneous) 4.Negative stratification
What are the highly stratified (salt wedge) estuaries like?
- Greater river flow
- Occur commonly in deep estuaries
- Sediment dominated by river
- very clear layers of freshwater and salt water
- fresh on top as less dense
- form where greater amount of river flow, occur in estuaries that are deep, fjord type valleys
- sedimentation is dominated by river sediments so more mud etc.
- can be 100s of meter deep
- numbers= salinity value -0= fresh
What are the moderately stratified (partially mixed) estuaries like?
- most of estuaries are like this
- tide energy has greater proportion -less drastic change in salinity
- Majority of estuaries
- Shallow, tides overcome fluvial flow
- Stronger ebb at surface, flood at depth
What are the non-stratified (well mixed, vertically homogeneous) estuaries like?
- Tides fully over come fluvial flow
- Shallow, wide estuaries of have lateral differentiation of salinity
- non stratified, no distinction in freshwater and saltwaer
- salinity almost the same as you move vertically
- further inland the salinity value will increase or decrease
- wide mouth
What are the negative stratification estuaries like?
- inverse relationship here, salinity is higher at the mouth
- this is where it is dry, lot of evaporation, common in australia
- occurs in arid areas, high evaporation
What happened in this picture?
-the mouth closes off, that evaporates -salty -anoxic = no oxygen -build up of nuntrients
What is important in forming deltas and estuaries?
-Tide, wave and fluvial processes are important as well as the underlying topographic setting
