Unit 2 - Estuarine Physics Flashcards
What are estuaries?
Estuaries are areas of transition between the land and the sea.
What is the classical definition of an estuary?
An estuary is a semi-enclosed coastal body ofwater which has a free connection with the open sea and withinwhich sea water is measurably diluted with fresh water derivedfrom land drainage
What is the modified definition of an estuary?
An estuary is a narrow, semi-enclosed coastalbody of water which has a free connection with the open sea atleast intermittently and within which the salinity of the water ismeasurably different from the salinity in the open ocean.
Why study estuaries?
Estuaries are highly productive ecosystems, provide food and drinking water, filter pollutants, and serve as transportation gateways.
What are fjords?
Glacially cut valleys
What are drowned river valleys?
Valleys flooded by the sea
How are tectonic topographies formed?
Through movements in the Earth’s crust
What are lagoons?
Bodies of water bounded by bars and spits, formed by coastal sediment processes
What are physical oceanography estuarine classifications based on?
circulation and mixing conditions, i.e., hydrodynamic behavior
What is the main driving agent for turbulence in estuaries?
Tides
What is tidal volume?
the volume of water brought into the estuary by the flood tide is driven by tidal strength
How are fjords, drowned river valleys, tectonic estuaries, and lagoons classified?
comparing tidal volume V w/ freshwater river discharge volume R transported by river over same period.
What assumption is made when applying continuity to an estuary according to Knudsen’s Relationship?
Assume steady state: water and salt volume in estuary not changing
What does the volume flux equation represent in Knudsen’s Relationship for an estuary?
Q1 - Q2 = QR
What does the salt flux equation represent in Knudsen’s Relationship for an estuary?
S1Q1 - S2Q2 = SRQR or S1Q1 = S2Q2
How can the volume flux Q1 be calculated in Knudsen’s Relationship for an estuary?
QRS2/(S2-S1)
How can the volume flux Q2 be calculated in Knudsen’s Relationship for an estuary?
QRS1/(S2-S1)
What are tidal volume (V) and river discharge volume (R)?
Quantities evaluated over one tidal cycle
How is net volume transport (M) calculated?
Vertical integral / velocity profile * cross-sectional area of estuary
What is net volume transport (M) equal to?
R÷one tidal period, independent of profile’s location
What are the units of M?
m3s-1
What are the units of V and R?
m3
What determines the actual velocity profile at any moment in time?
The phase of the tide
What are the characteristics of a well-mixed estuary?
Shallow, strong tidal or wind mixing. Flowtidal/Flowriver>10^3
What are the characteristics of a partially stratified estuary?
Deeper, less mixing, more freshwater input. Flowtidal/Flowriver 10-10^3
What are the characteristics of a salt wedge?
Very high runoff, narrow discharge channel. Flowtidal/Flowriver<1
What is the basis of the salinity classification scheme?
Observations of the salinity stratification along the estuary axis
How is R defined?
fresh water volume which enters estuary from river over one tidal cycle
What happens to the total salt content of the estuary in a steady state?
It does not change
What is the net volume transport at any location along the estuary in a steady state?
Constant and equal to the fresh water input R from the river
What are inverse estuaries?
Embayments with high evaporation rates
How does salinity change in inverse estuaries?
salinity in upper layer decreases towards sea; salinity in lower layer increases towards estuary head.
What do vertical salinity profiles show in inverse estuaries?
A gradual increase from the surface to the bottom, with a maximum in the vertical gradient near the interface between the two layers.
In what climate environment can evaporation exceed river input?
Arid climate
What is a salt plug estuary?
intermediate situation where evaporation marginally exceeds fresh water supply from rivers, making R/V only just negative.
Where are salt plug estuaries found?
common in regions w/ seasonally variable rainfall in tropics, where evaporation is permanently high and observed during dry season.
What is the circulation pattern of a salt plug estuary?
Combination of positive and negative estuary circulation
What happens to the salinity in a salt plug estuary as water moves towards the sea?
Salinity increases due to strong evaporation, becoming hypersaline
How does the circulation in the lower reaches of a hypersaline salt plug estuary differ from the upper reaches?
Inverse estuary circulation in lower reaches
