Unit 2 - Estuarine Physics

Question 1

What are estuaries?

Answer 1

Estuaries are areas of transition between the land and the sea.

Question 2

What is the classical definition of an estuary?

Answer 2

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

Question 3

What is the modified definition of an estuary?

Answer 3

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.

Question 4

Why study estuaries?

Answer 4

Estuaries are highly productive ecosystems, provide food and drinking water, filter pollutants, and serve as transportation gateways.

Question 5

What are fjords?

Answer 5

Glacially cut valleys

Question 6

What are drowned river valleys?

Answer 6

Valleys flooded by the sea

Question 7

How are tectonic topographies formed?

Answer 7

Through movements in the Earth’s crust

Question 8

What are lagoons?

Answer 8

Bodies of water bounded by bars and spits, formed by coastal sediment processes

Question 9

What are physical oceanography estuarine classifications based on?

Answer 9

circulation and mixing conditions, i.e., hydrodynamic behavior

Question 10

What is the main driving agent for turbulence in estuaries?

Answer 10

Tides

Question 11

What is tidal volume?

Answer 11

the volume of water brought into the estuary by the flood tide is driven by tidal strength

Question 12

How are fjords, drowned river valleys, tectonic estuaries, and lagoons classified?

Answer 12

comparing tidal volume V w/ freshwater river discharge volume R transported by river over same period.

Question 13

What assumption is made when applying continuity to an estuary according to Knudsen’s Relationship?

Answer 13

Assume steady state: water and salt volume in estuary not changing

Question 14

What does the volume flux equation represent in Knudsen’s Relationship for an estuary?

Answer 14

Q1 - Q2 = QR

Question 15

What does the salt flux equation represent in Knudsen’s Relationship for an estuary?

Answer 15

S1Q1 - S2Q2 = SRQR or S1Q1 = S2Q2

Question 16

How can the volume flux Q1 be calculated in Knudsen’s Relationship for an estuary?

Answer 16

QRS2/(S2-S1)

Question 17

How can the volume flux Q2 be calculated in Knudsen’s Relationship for an estuary?

Answer 17

QRS1/(S2-S1)

Question 18

What are tidal volume (V) and river discharge volume (R)?

Answer 18

Quantities evaluated over one tidal cycle

Question 19

How is net volume transport (M) calculated?

Answer 19

Vertical integral / velocity profile * cross-sectional area of estuary

Question 20

What is net volume transport (M) equal to?

Answer 20

R÷one tidal period, independent of profile’s location

Question 21

What are the units of M?

Answer 21

m3s-1

Question 22

What are the units of V and R?

Answer 22

m3

Question 23

What determines the actual velocity profile at any moment in time?

Answer 23

The phase of the tide

Question 24

What are the characteristics of a well-mixed estuary?

Answer 24

Shallow, strong tidal or wind mixing. Flowtidal/Flowriver>10^3

Question 25

What are the characteristics of a partially stratified estuary?

Answer 25

Deeper, less mixing, more freshwater input. Flowtidal/Flowriver 10-10^3

Question 26

What are the characteristics of a salt wedge?

Answer 26

Very high runoff, narrow discharge channel. Flowtidal/Flowriver<1

Question 27

What is the basis of the salinity classification scheme?

Answer 27

Observations of the salinity stratification along the estuary axis

Question 28

How is R defined?

Answer 28

fresh water volume which enters estuary from river over one tidal cycle

Question 29

What happens to the total salt content of the estuary in a steady state?

Answer 29

It does not change

Question 30

What is the net volume transport at any location along the estuary in a steady state?

Answer 30

Constant and equal to the fresh water input R from the river

Question 31

What are inverse estuaries?

Answer 31

Embayments with high evaporation rates

Question 32

How does salinity change in inverse estuaries?

Answer 32

salinity in upper layer decreases towards sea; salinity in lower layer increases towards estuary head.

Question 33

What do vertical salinity profiles show in inverse estuaries?

Answer 33

A gradual increase from the surface to the bottom, with a maximum in the vertical gradient near the interface between the two layers.

Question 34

In what climate environment can evaporation exceed river input?

Answer 34

Arid climate

Question 35

What is a salt plug estuary?

Answer 35

intermediate situation where evaporation marginally exceeds fresh water supply from rivers, making R/V only just negative.

Question 36

Where are salt plug estuaries found?

Answer 36

common in regions w/ seasonally variable rainfall in tropics, where evaporation is permanently high and observed during dry season.

Question 37

What is the circulation pattern of a salt plug estuary?

Answer 37

Combination of positive and negative estuary circulation

Question 38

What happens to the salinity in a salt plug estuary as water moves towards the sea?

Answer 38

Salinity increases due to strong evaporation, becoming hypersaline

Question 39

How does the circulation in the lower reaches of a hypersaline salt plug estuary differ from the upper reaches?

Answer 39

Inverse estuary circulation in lower reaches