Coastal Dynamics Formuleblad
Coastal Dynamics I (Technische Universiteit Delft)
, H1 Coastal morphodynamics = Study of coastal evolution Linear propagation: (Linear waves No current)
Morphology: underwater topography Morphodynamics: defined as the Dispersion relation: Wave frequency: = ∗ tanh ℎ = , = H5 Coastal Hydrodynamics
mutual adjustments and morphology of hydrodynamic processes involved Water waves are dispersive Phase velocity of longer waves is larger.
sediment transport. Equilibrium concept: Negative feedback: stabilization “ Group: Waves disappear at the front and reappear at back, c>cg
process causing the system to return to the (stable) equilibrium in case of Phase speed: speed of phase point (crest): = / = /
perturbations Positive feedback: destabilization process causing the system Limits: Shallow=non-dispersive, Deep=dispersive.
to move away from (unstable) equilibrium in case of perturbations. Shallow (depth depend): tanh ℎ ≈ ℎ → = ℎ; =
Deep (c depends on frequency): tanh ℎ ≈ 1 → = ; = =
H2 Large scale coastal variations
Tsunamis: Extreme long waves. (T=5-60 min, h/L<0.5, low energy loss)
Introduction: Plaatje sheet 6
st
1 order features: thousands of km’s (Broadcast features of the coast.) Group velocity: <c, except for very long waves: = , = +
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∆
Controlled by continental shelf width, varying from 10m to 1500 km. =∆ = − , =∆ , = − , =∆ , =∆
nd rd
2 order: hundreds of km’s (outer banks of N. Carolina) 3 : few km’s. Transformation: Storm ( Direction)
Medeo-tide: Wind has more influence than tide (very shallow water). Area of generation, Combined, -long+intermediate, Long period waves
Ocean: where depth > 1km, Continental shelf: Shallow area, connected Generation of tide:
to continent Shelf width: Wide and flat: sediment accumulation, Tide: Sinusoidal semi-diurnal water level variation modified with:
Permit more rapid coastal progradation, Reduce wave energy to a large - A fortnightly spring- and neap-tide amplitude variation.
extent, Amplify tidal amplitude, higher potential storm surge elevations. - Daily inequality that varies with latitude and with monthly cycle.
Geographical variation of Coastal material: Attractional forces:
Coastal diversity: Nature of material. ) )
&' = ( ,* and &! = ( ,- plaatje Sheet 52
Continental sediments: Sand, Mud, Gravel&Rock. Plaatje sheet 10 +* +-
Coral Differential pull generates the tide.
.
Shell On earths near side: ∆&! = &! = 0.46 ∆&'
+
Rebound: Holland is lowering due to no ice on Scandinavia anymore. Equilibrium theory: immediate response of the oceans to tidal forces.
Supply of sand and fines: to coast largest from 40N-40S - No inertia
Higher mud content in tropics: Chemical weathering and… - Negligible friction and Coriolis plaatje Sheet 54
Biotic factors: Coral reefs, Mangrove swamps (small latitudes), - Entirely ocean covered with uniform depth
Salt marshes (larger latitudes), Dune vegetation. Solar day: Time for earth to return to same position to sun = 24 hrs.
Techtonic plate settling: Lunar day: 24hrs, 50 min. Moon takes 29,5 days to return (=L. month)
Continental drift: Continent cluster Continents moving away fr. eo. Principal lunar tide M2: amp = 0.24 m; -Solar tide S2=0.46*0.24=0.11m
Leading edge Trailing edge Spring tide: S&L reinforce each other. Neap tide: S&L cancel each other.
Rugged, cliffed coastline Far from plate boundaries Tidal propagation
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Mountain ranges near coast Temperate climate Dynamic theory: (Only around 65 S an Equilibrium tide can exist, >=N)
Vulcanic ranges furder from coast Broad coastal plains, delta’s barri’s - Continents prevent tidal wave from covering circumference of earth.
Tectonic unstable Tectonically stable - Land masses move water masses along with them, instead of tide.
Narrow continental shelf; steep Wide shelf: Balance equations: Local storage = Net import + Local productions
Large waves Limited wave action, Depth restriction: Smaller h’s Amplitudes increase, velocity more.
Rapidly flowing, short streams Larger tidal amplitudes Coriolis effect: Diverts a moving to the right on NH, left at SH.
Relatively coarse sediment supply And storm surge heights. Coriolis force: Pseudo-force to make Newton’s Eq’s of motion valid.
Acceleration: &3 = 45 = 2 7 ∗ sin : ∗ 5, V=current velocity. Max: poles
Tectonic classification: Coastal character is influenced by proximity to
Forces: ;<,=>?">@"! = 2 ∗ sin : ∗ A = 4A, ;B,=>?">@"! = −4C, SH:sin : < 0
and plate boundary. Leading/collision/convergent; Trailing/passive.
Co phase: connect all places with same phase at same time.
Afro-trailing coast: opposite coast is also trailing (slow development of
Co range: connect all places with same tidal range. ” Run around A.Ps
coast, no extensive deltas and little river sediment supply)
Amphidromic points: zero-tidal range Co-phase lines radiate away.
Amero-trailing coast: Far away from plate boundary, stable, wide shelf,
“systems: Resonance influenced by size and shape of basin.
large supply of sand, temperate cimate, delta. Ria: drowned river valley.
Coastally trapped Kelvin Wave: Linearised equations of motion.
Increasing maturity: Neo Afro Amero (+sed deposit +widest shelf)
- Cross-shore M-balance is Geostrophic: p-gradient balances Fcoriolis
Marginal sea: bordering a sea enclosed between the landmass and isle.
- Alongshore “: inertia balances p-gradient, c in phase with h.
Sandy coasts: Dominate subtropics and lower mid-latitudes: Humidit
Tidal analysis and prediction
climates, passive margin coasts, more energetic waves+tidal environme.
Discrete and known frequencies!
Sea level changes: Worldwide rise, shapes coast at local level.
Determine amplitudes and phases
Quaternary climate variations: Inheritance from ice-ages, glaciers.
Careful with: Nodal factor fn, astronomical argument βn
Holocene: interglacial, sea-level rise. (from 10.000 years ago till now)
Tidal levels (low): LAT, MLW, MLWS, MLWN, MLLW.
Pleistocene: period of repeated glaciations sea level fall during glacial
Tidal ranges: MHW-MLW (normal), MHWS-MLWS (Spring),-Neap
Global/Eustatic changes: Amount+expansion water, volume+shape Ocs.
Klickers:
Local effects: Seismic activity, regional subsidence by fluid withdraw,
1. Wave height represents total energy content of irregular wave: Hrms
Regional effects: Isostatic: Glacio=(un)loading by ice, Hydro=-by water.
2. Propagation speed of tsunami wave train (L=500km, h=6km): 873 km/h
Bruun rule: Equilibrium shoreface response to sea-level rise.
3. Swell traveling 1100 km, T=8s, h>50m. Trave time: 50 hours
Balance between sea-level change and sediment supply.
4. The tide needs a day to travel shallow North Sea basin to the Dutch coast
Regression: seaward shift of the shoreline (water regresses).
time between full moon and spring tide is about 2 days.
Transgression: landward shift of shoreline: flooding
Progradation: sediment deposited, shoreline moves seaward.
Retrogradation: sediment deposited but shoreline moves landward. H4 Global wave and tidal environments
Emergence: land emerges out of water due to relative sea-level fall. Zonal wind systems:
Submergence: inland regions flooded due to relative sea-level rise. Uneven heating of the sun: equator more than poles:
Classification Result: Heat advection by ocean currents and winds.
Valentin: Coast advances (emerge/depot),-retreats (submerge/erosion) Colt air sinks at the poles, warm air rises at equator. Plaatje S7
Shepard: Primary= shaped by non-marine agency, Secondary= -marine. Pressure belts: (due to coriolis)
Dutch coast character: retreat/advance periods, terrestrial+marine shpe Moderate easterlies polar high
o
Basis: Material(soft/origin), tectonic controls(Inman), Valentin, Shepard. Strong+variable westerlies 60
Galloway: relative Moderate persistent trade winds Plaatje S10 30o
influence of : Plaatjes sheet 66 Calm doldrums 0o
Wave: High and low pressure systems
Regional effects: Seasonally reversing monsoon, cyclones, L+sea breezes
River: Global wave environments: + Shape ’n orientation of oceans ‘n coastlines.
Closely related to: Wave generating systems, wind ‘n cyclonic regimes
Tide: Wave classes: low: Hs<0.6; medium: 0.6<Hs<1.5m; high energy Hs>1.5m.
Boyd: Storm wave climate West coast swell wave climate
Prograding coast: Tidal flats, delta, strand plains. Most energetic wave environment Year round in SH, winter in NH
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Transgressive coast: “, estuary, Lagoons, barriers. Between 40 and 60 N and S Between 0 and 40o N and S
Ternary Shoreline diagram: Year round in SH, winter in NH Americas, Africa, Australia, NewZ
Prograding fluvial source Plaatje Locally generated by westerlies Origin:NH & SH storm wave belts
Fluvial power Embayed mix source Steep, shortcrested, irregular and “also trade winds for tropic swell
Marine source multi directional waves (sea). Arriving: NW in NH and SW in SH
Westerly to SW directions Typical wave heights 1-2 m
DW: H’s: 2-3m [90%], 5-6m [10%] Decreasing towards equator
H3 Ocean wind, waves and tide: Wave/tide power Periods ≈ 5 s, longer during storms Persistent and long waves T≈ 10s
Definitions: East coast swell climate: as west coast but more moderate.
Deep water: speed depends on frequency (dispersive) c = gT/2pi Global tidal environments:
Shallow water: speed depends on depth (non-dispersive) c = sqrt(gh) Tidal environments: Semi-diurnal, mixed (Tropics), diurnal (S-Pole)
Dispersive wave group: waves disappear at the frond and reappear at Form factor expresses tidal character: F=(K1+O1)/(M2+S2)
the back, and individual waves travel faster than the group wave front. Variations in “: Controlled by large scale coastal configurations.
Coriolis force: a pseudo-force to make Newton’s equations of motion Coastal impact:
valid in our non-inertial frame of reference. Storm wave climate Swell wave climate
Amphidromic points have a zero tidal range. Co-range lines (lines of =High, short waves, highly variable =Low long waves (relatively const)
constant tidal range) run around the amphidromic points, co-phase lines Wide+Flat, multiple bars, dunes… Break close to shore, S onshore
(connect all places with high water at same time) radiate away from
Dynamic coastal profile Narrow sany profile, steep.
amphidromic points.
Dimensionless fall velocity: Ω = Hb/(ws*T) to indicate beach profiles.
Introduction:
Dissipative beach: Ω>6; Reflective beach Ω<1. ws= Sediment fall velocity.
Wave classification: based on disturbing-, restoring force, wave period.
Wave dominated features Tide dominated features
Sea: locally generated wind waves, Swell: Generated far away.
Short term statistics: Dynamic sandy coastal profile with Tides smear beach morphology
Sea state, Spectral variance/density bars and dunes. Wide, low-gradient, muddy t.-flats
Beach slope depends on waves Salt marshes, mangroves, ridges
