IMS W3 Coasts, waves & tides Flashcards
Types of coast dynamic landscapes
Natural induced: water, wind, vegetation
Human induced: zandmotor
First classification of coasts
Primary coasts: determined by terrestrial processes (Terrestrial erosion and submergence/terrestrial deposition)
Secondary coasts: determined by present-day marine or biotic processes
Primary coasts: Terrestrial erosion and submergence
Fluvial erosion and drowned river valleys (ria coast/ Maine)
Glacial erosion coasts (fjord)
Drowned karst topography (Florida, Thailand)
Primary coasts: Terrestrial deposition(4)
Glacial deposition coasts: under the ice cap landforms formed creating a specific coastal types (Denmark)
Aeolian deposits: induced by wind (Saudi Arabia)
Deltaic deposits: bird foot delta created by rivers that drag sediments outwards (Mississippi)
Landslide coasts (California)
Secondary coasts (3)
o Wave erosion coast: wave straightened cliffs
o Marine deposition coast: barrier island, lagoon, salt marshes (most common type)
o Biotic coast: fully dominated by animals (coral reefs, sea grass meadows)
Boundary conditions of coasts (1/1 + 1/4)
Factors from the land
o Geological setting (sediment type, resistance to erosion)
Factors from the sea
o Wave climate
o Tide and other sea level changes
o Ice effects
o Biological effects
Storm waves and swells
Storm waves: dominated by wind (4/5/6 meters)
West coast swell/east coast swell: low energy waves unless there is a cyclone (1-1.5/15 meters) Created over a big region.
Tide environments, old classification
<2m non tidal: non to micro tidal: wave dominated coast
2-4 mesotidal: drumstick barrier island. Beach is wave dominated and the inlet tidal dominated.
4-6 macro tidal: funnel chaped: Maine. Tidal dominated
> 6 mega tidal
New classification wave/tide environment
Relative imprtance of wave and tidal energy. Looking at tidal prism.
Coastal change
Bio-morpho dynamics: sediment will change due to biological cycles.
Geomorphologic: physical is dominating.
Bio-geomorphologic: mangroves, reefs
Ecological: dunes that create no real change
Waves factors
Wind velocity
Wind duration
Fetch
Vertical motion waves
Deep water: orbital paths: d/L = > 1/4
Intermediate water: ellipse: 1/4 > d/L > 1/20
Shallow water: no vertical motion: d/L < 1/20
Storm waves Netherlands
Between 4-6 meters.
Wave period: 8-10 s.
From the North West high waves: long fetch.
From the South West low waves: UK is in the fetch.
Dispersion relationship
Unique relationship between wave length, wave period and water depth.
Wave breaking
Spilling: white foam
Plunging: surfer wave
Surf break: collapsing wave: water spills over itself.
Subtidal bars
- 1 or 5 alongshore sand ridges below the low-tide line
- 10 – 100 km in the alongshore direction
- life time: up to 20 years
- alongshore variability: rips and crescentic shapes
Very dynamic:
– Cross-shore migration
– Changes in alongshore variability
Australian beach model Wright and Short
Dissipative beach
Intermediate beach
- Longshore bar and trough
- Rhythmic bar and beach
- Transverse bar and rip
- Low tide terrace
Reflective beach
Storm response tidal bars
During: bar moves offshore due to undertow. 3D features are wiped out.
After: bar moves onshore due to mass transport. 3D features develop and grow.
Different time periods tides
semidiurnal
mixed
diurnal
Tide characteristics
Wavelength depend on tidal period.
Shallow water wave: wave length and period are very long compared to depth.
Moves faster in the ocean.
Standing wave
tide generating force
Gravitational force - Centrifugal force
Only seen in fast water areas.
Diurnal tides
Eath axis is titled which creates two bulges do to the centrifugal force of the moon. M2.
Kelvin wave
Created by Coriolis force. Balances the force of the coastline. Not created by wind as coriolis force is not visible due to small lenght scales.
Amphidromic points
Bulge where the tide moves around. A Kelvin wave also moves around the point. The tide and kelvin can cancel eachother out. There is no tide in the point.
Tides and kelvin wave on shelf sea
- Largest amplitudes near the coast.
- A place with no tidal variations (amphidromic point)
- Tides that rotate around amphidromic point.
- This resembles observed tidal patterns in enclosed shelf seas
Consequences tidal wave into estuaries
- Strong influence of morphology and shape of basin/estuary on tidal characteristics.
- In estuaries interaction of river and tides.
- Decrease or increase of tidal amplitude due to friction, resonance and funneling.
- Tidal waves become asymmetric and can thereby cause net sediment transport.
Factors tide
Water level variations: tidal range
Flow velocities: tidal prism
Tidal inlets
Created by tide dominated energy. All different inlets are seen as different tidal basins –> tidal divide. The basins are filled in motion.
Different basins
Short basin <1/10 wavelength. Tidal range is constant. (standing wave)
Resonance: ~ 1/4 wavelength. Tidal range at end of basin larger than in inlet.
Tidal wave losses energy in basins as they are shallow.
Different tidal inlets
Tide dominated
Mixed energy straight
Mixed energy offset
Wave dominated
Relations tidal prism - basin
Channel volume is related to tidal prism by the power of 1.55.
Area of inlet cross section is related to tidal prism.
Volume of ebb tidal delta is related to tidal prism to the power of 1.23.
Ebb tidal delta
Sediments are deposited in the ebb tidal delta as the flow expands out of the inlet can no longer hold the sediments anymore. The ebb tidal delta can be eroded by the tidal current parallel and littoral drift.
