5: Estuaries Introduction Flashcards
What are the 3 variables that determine what sort of coastal boundary environment something is?
River, waves and tides
Why do some environments in Australia, even though sea level is stable, still resemble transgressive environments?
Because there is a temporal lag in between the sea level becoming stable and then the subsequent adjustment of the environment which is affected by this change
How long has sea level been stable in Australia?
6000 years
What are the 6 classifications that Colin has devised regarding the relative dominance of rivers, waves and tides?
Mature riverine estuary drowned river valley barrier estuary coastal lagoon tide-dominated delta tide-dominated estuary
Describe a drowned river valley environment
(from inland to seaward) alluvial flood plain minimal to some mangroves located on the corners of areas, then main central basin then buried sand and sand barriers on the outer sections
Describe the proposed progression of a drowned river valley
Eventually the alluvial sediment will infill the area behind the barrier so that there is a clear distinction between the fluvial and marine sections
Give an example of a drowned river valley
Sydney
Describe a barrier estuary environment
Similar to a drowned river valley in terms of the location of different types of deposit (alluvial sediment to mangrove to central section to buried sands to sand barriers) the main difference being however that the sand barrier stretches across the boundary to the sea with only a small opening at one end
Describe the progression of a barrier estuary environment
Infilling of the area with fluvial sediment behind the sand barrier due to weaker calmer environment
Describe a coastal lagoon environment
Almost identical to a barrier estuary environment except that the sand barrier boundary stretches right across the coastline so that an isolated lagoon is created
Describe the progression of a coastal lagoon environment
Behind the barrier the fluvial system will deposit material at the terminal of the channel and this will continue until the area is completely infilled with alluvial sediment. This will allow the fluvial channel to progress faster in a seawards direction. Eventually the channel will become strong enough that it will find a way through the sand barrier
Describe the characteristics of a Mature Riverine Estuarine environment
major tidal influence across the environment that is shared with a fluvial/river influence. The tides can stretch far across the landscape inland. Wave energy a major influence however at the fringe of the environment towards the sea
What is a major feature of tide-dominated systems that sets them apart from all the other identified environments?
There is a strong seasonal change that comes about due to the monsoonal changes.
What is consistent for both tide-dominated estuaries and tide-dominated deltas?
In the monsoonal wet season the rivers exert a stronger effect on the environment than the tides. However during the dry season the rivers become very weak obviously and so the tides have a much greater influence upon the whole landscape that sees them reach really far inland. Wave energy is much higher at the very edge
What distinguishes tide dominated estuaries from tide-dominated deltas?
Essentially, estuaries are usually younger environments that means the fluvial/river influence is weaker. This means there are usually less permanent features in these environments. Whereas in delta environments the river effect is a lot stronger through larger flooding events and so the tide is less able to fight back and so there is less competition regarding the creation of certain features.
