Lec #4 Esturaries and Deltas

Question 1

What are the effects astronomical tides have on the shore (3)

Answer 1

• the extent of the wave action and the flushing of estuaries
• the biological zonation of species
• chemical processes assciated with wetting and drying

Question 2

What causes astronomical tides?

Answer 2

the phases of the moon, as well as the sun

Question 3

What orientation of the moon and sun causes spring tides?

Answer 3

o O o (

Question 4

What orientation of the moon and sun causes neap tides

Answer 4

o
O (
o

Question 5

What are the key points on estuary characteristics (3)

Answer 5

Draining of river valleys
Tidally influenced
Mix of sea and fresh water

Question 6

What are the three zones of the estuary

Answer 6

Inner, central and outter

Question 7

What are the four types of estuaries?

Answer 7

fjord, canalaque, lagoons and rias

Question 8

Explanation of fjords

Answer 8

deep elonganated basin, U shaped and a ledge that seperates them from the ocean, there is high river input and little mixing

Question 9

Explanation of canalaques

Answer 9

high sided with limestone cliffs, found in the MED

Question 10

Explanation of a lagoon

Answer 10

Large area of water which is in part isolated from the sea, which may have tidal isolation

Question 11

What is the key process in estarine hydrodynamics

Answer 11

the mixing of salt and fresh water which mix through molecular diffusion

Question 12

What occurs if molecular diffusion is not effected

Answer 12

the estuary can become stratified and a salt wedge exists in the bottom part of the water column

Question 13

What is the area where mixing takes place, and explainataion of it

Answer 13

Turbidity maximum, it occurs on the extent of the salt marshes and entrain sediment which leads to chemical reactions

Question 14

What are river deltas

Answer 14

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

Question 15

What is specific about theses delta channels and why

Answer 15

The channels are constantly chaing due to river flow, wave action and solid flows

Question 16

What do deltas need for formation

Answer 16

Really high sedimentation

Question 17

What are the three types of deltas

Answer 17

Wave dominated
Fluvial Dominated
Tide dominated

Question 18

Explanation of a wave dominated delta

Answer 18

have exposure to ocean swell

Question 19

Explanation of fluvial dominated delta

Answer 19

large catchment area, river discharges into protected sea, low energy from waves with a small tidal prism

Question 20

Explanation of a tide dominated delta

Answer 20

Where the tide prism is larger than the river discharge

Question 21

What does the number of channels in a delta relate to?

Answer 21

The slope gradient and the size of sediment being desposited

Question 22

What is the delta front?

Answer 22

This is the most active part of the delta, most of the remaining sediment is deposited on the edge of the delta

Question 23

What is the delta plain?

Answer 23

The delta plain may have single or multiple channels which distribute sediment and water

Question 24

What is the prodelta?

Answer 24

Only the finest sediment will reach this zone does to large distance from the delta front

Question 25

Effect of turbidity currents on deltas?

Answer 25

These are negativity buoyant, highly concentrated, near bed suspensions that flow downhill under their own weight carving new channels

Question 26

What two things can occur at the delta mouth?

Answer 26

Jet plumes and density currents

Question 27

What determines if it will be a density current or a jet plume (3)

Answer 27

Current speed
Slope of the seabed
Density distribution in the water

Question 28

What are density currents

Answer 28

These are isopycnals out into the sea

Question 29

What are the three types of isopycnals and a quick explanation

Answer 29

Homophycals (mixed)
Hypo - river water is less dense and floats
Hyper - river water is more dense and sinks

Question 30

What are jet plumes?

Answer 30

These occur when water exists a basin at high speed into a deep water systems, also called axial jets

Question 31

Name two properties about axial jets

Answer 31

1. The have no interaction with the sea floor

2. Away from core water slows and sedimentation can occur

Question 32

What is delta switching?

Answer 32

This occurs with the delta when an active region of the delta switches into another area, lobe switching can also occur within delta switching