Coastal Processes and Landforms Flashcards
1
Q
Which country has the longest coastline?
A
- Canada, tops number 2 by almost 5x! (much of it is undeveloped and in the Arctic)
- Followed by Indonesia (number 2), Greenland, Russia, Philippines etc.
2
Q
How much of the worlds and North America’s population lives on the coast?
A
- 2.2 billion globally
- 75 percent NA
3
Q
How much coast does BC have?
A
- 22000km
4
Q
Dynamic environment of the coastal/littoral zone
A
- Interaction btwn terrestrial, atmospheric, and marine systems (solid, liquid, and gas processes)
- Energy from winds, waves, and tides (very dynamic)
- Rapid responses btwn process and form, continually changing
5
Q
Spatial and temporal variations of coastal/littoral zone
A
- Extensive zones spanning km’s from wave break to back shore (include inlets, fjords etc.)
- Forms and processes change w/ season, storms, tide range, sea-levels
6
Q
Coastal landforms change short-term with?
A
- Seasons
- Storms
- Tides
- Land characteristics
- Human alterations
7
Q
What are some examples of human alteration of coastal landforms on the short-term scale?
A
- Offshore: groins, sea walls
- Onshore: deforestation, etc.
8
Q
Coast landforms change longer-term with?
A
- Tectonics, subsidence, uplift
- Sea level change, transgression, regression
- Delta progradation
- Glaciation
- Land changes (river i/p, volcanic eruptions
9
Q
What percent of the worlds coastline is sandy?
A
- 34 percent
- popular for tourism, development, ecologically distinct
- Ever-changing, responsive to coastal processes
10
Q
What kind of coastline is highly responsive to coastal processes?
A
- Sandy
- Ever-changing
11
Q
What makes for a beach?
A
- Competent wind/wave/tidal processes and sediment supply and ‘accommodation space’
12
Q
Allochthonous
A
- Externally sourced
- 92 percent globally
- Mostly from rivers, aeolian, glacial, colluvial w/ some offshore sources
13
Q
Autochthonous
A
- Locally derived
- 8 percent globally
- Biogenic sediments, carbonate rich beaches, local shoreline erosion
14
Q
Coastal system landforms and zones
A
- Different parts of the littoral zone exhibit diff wave and current processes to create a suite of related landforms
- eg longshore currents: shore parallel current caused by wave action in the nearshore region w/in the breaker zone
15
Q
Schematic of longshore currents and beach
A
- Offshore, nearshore, shore, coast
- Beach composed of nearshore and shore
- Shore composed of foreshore (low to high tide) and back shore (where tide doesn’t reach)
- Breakers in nearhore
- Longshore bar, longshore trough, wave-cut bench, beachface, berm, notch, wave-cut cliff
16
Q
Where are beaches wider? Narrower?
A
- Further from erosional zone = wider, closer = narrower
- Broad, can also get dune systems from wind blowing seds back towards land
17
Q
Greenwich dunes, PEI
A
- Sed being limited by strong wind regime
- Fastest eroding shorelines in Canada (1-3m/yr)
- Isostatic collapse/ sea rising 30cm/100yrs
- Huge dune systems from strong wind regime liberating sediment
18
Q
Human made rock berms
A
- Meant to protect coast (e.g. highway in Haida Gwaii)
- Reflect energy back but can combine w/ incoming waves to generate positive feedback
- Feed back amplifies undercutting and erosion
- Also stronger rip and longshore currents
- Normal function: wave energy used in swash and sed transport
19
Q
What is another/maybe better way of protecting human infrastructure on the coast?
A
- Build wider beaches so natural function of swash and sed transport can happen
- But building groins to do this starves beaches further down of sed
- Therefore more and more groins get built
20
Q
Time-space paradigms in coastal study
A
- Geological w/ Net shoreline
- Large-scale (engineering) w/ large size beach cycles, major storm erosion
- Events w/ seasonal beach cycles
- Instantaneous w/ ripple migration
21
Q
Geological time-space paradigm
A
- Geological: net shoreline, net shoreline movement
- on Millenia-century scale
- w/ climate change, tectonics, sea level, sediment supply
22
Q
Large-scale (engineering) time-space paradigm
A
- Large-scale (engineering): Net shoreline movement (horiz), large size beach cycles, major storm erosion, beach position
- on century-decade-year scale
- w/ Sed supply, wave-climate cycles, annual wave climate tidal regime
23
Q
Events time-space paradigm
A
- Events: beach position, seasonal beach cycles, beach migration beach face
- on yr-season-months-days scale
- w/ annual wave climate tidal regime, seasonal wave climate, tide cycles storm events, wave trains
24
Q
Instantaneous time-space paradigm
A
- Instantaneous: beach migration, beach face, ripple migration, ripples
- on day-hour-seconds scale
- w/ wave trains, tide, waves
25
What are the 5 main factors that influence coastal geomorphology?
- Climate (temp, evapotrans, precip)
- Sediment budget (sources of erosion and transport, sinks)
- Human activities (construction, alteration)
- Relative sea level (tectonic subsidence, compactional subsidence, eustatic changes, secular changes)
- Coastal processes (waves, currents, tides, wind, storms, river discharge, valley aggradation or incision
26
The coastal system and the time element?
- Shorface affected by shoaling, breaking waves, and swash
- At scales from millennia to instantaneous
- Each produces characteristic bed response and are linked through time and space by morphodynamic couplings
27
Coastal processes: forces w/in the liquid realm, Waves
- Formed by drag of wind over sea
- Dominant energy transfer process
- 2 types: Deep water waves of oscillation and Translational waves
28
Coastal processes: forces w/in the liquid realm, Tides
- Due to gravitational forces of moon and sun
- Locally interact w/ bathymetry
- Important where coastal configurations enhance tidal ranges and currents (e.g. bay of fundy)
29
Coastal processes: forces w/in the liquid realm, Nearshore currents
- Caused by winds and tides
| - Also driven by heat and density variations, Coriolis
30
Coastal processes: forces w/in the liquid realm, Winds
- Onshore transport of littoral sediments
31
Coastal processes: forces w/in the liquid realm, Long-term 'relative' sea level changes
- Function of eustatic, tectonic, temperature effects etc.
32
Wave development
- Formed by wind shear on water surfaces
- As waves grow, become higher, wider, faster
- Feedbacks btwn roughness, wind energy and wave growth
33
Wave growth
- Micro-ripples to ripples to chop to fully developed sea (fds)
34
Wave growth w/ increasing wind and fetch
- Micro-ripples to ripples to chop to fully developed sea (fds)
35
Max size of waves
- Function of wind speed, duration and fetch
- Need all 3 for giant waves
- Eg 111km/hr (60knots) wind of unlimited fetch produce 15m waves
36
Perfect storms
- Atlantic winds > 100km/hr for several days over 1000's of kms
- Produce the largest waves, >30m, highest record is 34m
37
Wave parameters
- Wavelength, dist btwn 2 peaks
- Height, btwn trough and crest
- Period, Time required for wave crest at one point to reach next point
38
Wave processes: deep water, waves of oscillation
- Water particles assume a circular orbital path w/ little forward motion
- Wavelength, L (m) = (gravitational acceleration x Period^2) /2pi
- Velocity/Celerity (m/s) = (g x Period)/2pi
39
Wave period
- T
- Time btwn passing wave crests
- Easily measured, proportional to both wavelength and velocity
40
Open Ocean waves
- Deep water, waves of oscillation
- Generated by strong steady winds blowing across long open fetches
- Wind stress causes water surface to deform into ripples, chop, then waves
- Waves from shifting winds combine to develop many frequencies in a typical wave spectrum (these show diff wavelengths and energies)
41
Wave dispersion
- Waves move from generation area, separate from one another due to travel speeds (big outrun small)
- Emerging waves more regularly spaced, low height to length ratios, low steepness, referred to as swell
42
Swell waves
- Emerging waves more regularly spaced, low height to length ratios, low steepness, referred to as swell
- Long periods, eg 100 seconds
- Follow directional pathways defined by dominant storm wind directions
43
Ocean swell cover's how much area?
- Cover large areas of ocean
| - But has finite lateral boundaries, so strikes along short sections of coastline (10's of km)
44
How far can ocean swell travel?
- Can travel 100's of km w/o much energy loss
| - Most energy loss occurs in short period waves that dissipate in the generation zone into the longer period swells
45
Two sets of swell from different sources may combine to create?
- May combine into a systematic variation in wave height known as 'surf beat'
- Successive waves increase in height to a max, then systematically decrease
- Large waves may appear w/ predictable regularity (often every 6-8th wave but depends on wave periods and harmonics)
46
Shallow water shoaling and waves of translation
- Shoaling occurs as deep waves approach shoreline
- Begin to interact w/ ocean bottom
- Occurs when water depth is approx have the wave length
- Deep water become shallow water waves, transfer energy to the bed, particle orbits become flattened into ellipses
- Top oscillating water column starts tipping forward and flattening, eventually waves oversteepen and break
- Wavelength decreases and height increases
47
Waves of translation, what is the significance to sediment maintenance?
- Waves shoal, water particles develop forward motion critical to sediment maintenance on beaches and near shore areas
- W/o shoreward asymmetry, sands would move offshore and expose shoreline to erosion
48
Production of waves of translation and shoaling
- Water shallows, waves increase in height, decrease in wavelength and velocity
- Crest bunch up
- Wave period remains constant
- Waves break when wave height/length >1:7
- Oscillatory waves are replaced by a completely different wave type called 'Waves of Translation'
49
Waves of translation and geomorphology
- Transformation to shallow translational waves applies geomorphic work on bed
- Effective limit of wave influence on the bed is known as wave base (occurs when H/L = approx. 0.5)
- Greatest influence where waves break
50
What happens to wave parameters once waves become translational?
- Velocity and length are proportional to water depth (h)
- L = Period x sq. root g x h
- V = sq. root g x h
51
Types of breaking waves
- Spilling
- Plunging
- Collapsing
- Surging
52
Long durations and sustained winds =
Increase in wave amplitude
53
Spilling waves
- Breakers occur on gradual slopes w/ flat beaches
- Takes several wavelengths to break
- Turbulent whitewater spills down face of wave
- Minor energy impacts on bed
54
Plunging waves
- Breakers occur on steep slopes or at sudden depth changes (e.g. on reefs or sandbars)
- Break w/in a couple of wavelengths concentrating energy and causing significant scour
- Wave crest much steeper than spilling wave
- Curls over and drops onto wave trough releasing most of its energy at once in a relatively violent impact
- Active in shoreline erosion
55
Collapsing waves
- Breakers are intermediate btwn plunging and surging
- Crest never fully breaks
- Bottom face of wave gets steeper, collapses
- Results in foam
56
Surging waves
- Breakers occur on steep beaches but waves have low steepness
- Wave crests remain unbroken but wave base surges up the beach w/ smooth, sliding motion
- Causes crests to collapse and disappear
57
Shoaling zone
- Waves begin to feel bottom and increase in height
| - Offshore, coarser sediment trends, accretionary actions, better sorting, increasing energy
58
Breaker zone
- Waves break and forward translation begins
| - Wave collapse, coarsest grains, erosionary actions, poor sorting, high energy
59
Surf zone
- Forward translation (bores) continues
- Longshore currents, seaward return flow, rip currents
- varied sediment trend, transportation action, mixed sorting, energy gradient increasing to collision zone
60
Swash zone
- Swash and backwash in foreshore
- Collision and transition to swash zone
- Coarser sed towards bi-modal lag deposit in collision zone
- Accretion and erosion, poor to better sorting towards beach
- Highest energy in collision/transition zone, decreases to swash and beach zone
61
Wave energy spectrum
- Longest period to shortest: Tidal-Tsunami-Surf beat/seiches-wind waves-ripples
62
Wave energy is a function of?
- Amplitude/magnitude and frequency
63
Tidal waves
- Longest period, hours to days
| - Due to Gravity force
64
Tsunami/Seismic sea waves
- Long period, not as long as tidal
- low in ocean
- Due to seismic disruption, landslides
65
Seiche waves
- Oscillating water levels in enclosed basins (e.g. lakes)
- Surf beat
- Restoring force = gravity
66
Capillary waves/ ripples
- Shortest period (up to 100/s)
| - Restoring force = surface tension
67
Instruments for measuring waves
- L, offshore buoy: wind, pressure data and wave parameters
- C, Acoustic doppler current profiler (upward radar): wave parameters
- R, Wave staff: water level
- Etc. Many more types
68
Frequency distribution of wave heights
- Skewed to left, more of smaller height, median less than mean
- Significant wave height then 90th percentile
69
Significant wave height, Hs
- Mean wave height of the highest 1/3 of waves
70
Nomograph
- Wave height-fetch relations
- Uses wind speed and duration to determine wave period (dashed line)
- Uses wind speed and fetch to determine significant wave height (solid line)
71
Coastal wave modification
- Along coasts, bottom topography and shoreline variations cause major changes to wave geometry and mechanics
- Product of transformations is geomorphic work applied to sea floor, beach and shoreline
72
Coastal wave modification transformation types
- Wave refraction
- Wave diffraction
- Wave reflection
- Wave shoaling
73
Wave Refraction
- Waves usually approach coast obliquely
- Shorten wavelength when encountering bottom, changes velocity, waves bend and refract towards shore
- Waves closer to shore slow down, outer waves move faster
- Results in bending of waves (refraction) and focusing wave energy more directly onshore
- Wave energy moves at right angles to wave crests
74
Wave Refraction results on geomorphology
- Focuses wave energy on headlands
- Dissipates energy in embayments (btwn headlands)
- Tends to flatten shorelines over time
- Resistant bedrock outcrops can inhibit even focused wave erosion
75
What is the result of seawalls and refraction?
- Seawalls aren't the best b/c they refract waves
- Focus energy
- Results in more erosion than prior to construction
76
Diffraction waves
- Transfer of energy along wave crest and occurs around obstacles
- Can lead to waves crossing directions, creating navigation hazards
- Waves on waves, continue patter w/o merging
- Either enhanced or diminished erosion
77
Breakwaters and Tombolos
- Breakwater diffracts waves and can help dissipate energy, reduce rip currents, prevent erosion, widen beaches
- Build tomoblos in low energy back section of breakwaters
- Breakwaters better when not very large/massive
78
Reflection Waves
- Waves impacting cliffs, steep beaches or vertical barriers (seawalls) often reflect waves back to sea
- Interactions btwn incoming and outgoing waves create constructive or destructive interference
- Significant effects on bedforms and bottom topography
- Coarse beaches can be reflective
79
Tides
- Essentially very long waves generated by gravitational attraction of mood and sun
- Magnitude varies w/ moon/sun alignment and proximity
- Regular/predictable periodicity
80
Tide periodicity
- Usually 2x daily
- High-high, high-low, low-high, low-low
- Moon phases generate spring-neap tidal cycle
81
What is the timing and amplitude of tides influenced by?
- Alignment of sun and moon
- Pattern of tides in deep ocean
- Shape of coastline and near-shore bathymetry
82
Where are the highest tides in the world found?
- Bay of Fundy
| - 16.3m
83
Beach type based on tidal range
- Microtidal to macrotidal
| - Most of BC is in macro tidal range, but varies considerably
84
Cause of tides
- Gravitational interactions w/ sun and moon
- Moon 2x as strong
- Opposing tidal bulges
- Spring when sun and moon in line, highest tides (full and new moon)
- Neap, lowest tides, when sun and moon 90 degrees from earth, opposing bulges (1st and 3rd quarter moon)
85
Tides as geomorphic agents
- Significant agent b/c involves enormous water quantities
- Tides change location of wave action, = geomorphic work
- Tides rise and fall faster in open ocean than coastal inlets, results in surface gradient, produces strong inward-flowing currents, transports sed
86
Geomorphic relevance of tides
- Tides alter focus of wave action, surf and swash, e.g. tidal terraces
- Flood/ebb tides influence sed transport direction and quantity, e.g. flood/ebb deltas
- Enhanced coastal erosion and sed transport if timing combines w/ storm surge and/or waves
87
What are the 3 basic types of tides?
- Semi diurnal w/ 2 highs and 2 lows, often 1 higher high and 1 lower low
- Mixed tides w/ mix of semi-diurnal and diurnal
- Diurnal w/ 1 high and low
88
Why do some places have higher tides than others?
- Tides are waves, when encounter shoreline, get higher
- eg Oak bay is protected inlet, energy peak not high, therefore lower tides
- Inlets w/ tidal waters funnelled (Port Alberni, Bay of Fundy), tidal waves greatly amplified
89
Tidal range
- High tide to low tide
| - Local ranges highly variable depending on ocean size, water depth, bathymetry, shoreline shape, currents, timing
90
Tides and storm surges
- Enhanced water levels occur in storm surges, can be deadly
- Due to combined effects of wind stress, pressure drop, and/or temperature
- 1mb drop results in 1cm rise in SL
- Enhanced during el nino seasons (warmer = stormier)
91
Tidal influence on coastal landforms
- Considerable effect
- Macrotidal = higher tide ranges, shore-normal currents, wide salt marshes and tidal flats, large ebb and flood sed inputs
- Microtidal and lower mesotidal = barrier islands, tidal deltas, high energy and the sediments get remobilized
92
Esquimalt lagoon - Coburg peninsula
- Barrier spit complex
| - Microtidal range
93
Tidal dunes
- Evidence found near Victoria
- Indicates very high energy
- Very large amplitude dunes
94
What are the 2 main types of nearshore currents
- Cross-shore, ie rips
- Longshore, unidirectional
- Both affected by tidal stage
- Combine to form nearshore circulation cells that span m to kms of coast
95
Cross-shore rip currents
- Controlled by bottom topography in surf zone, especially bars, and troughs parallel or sub-parallel to shoreline
96
Longshore currents
- Uprush/swash in thin sheet moving sediment onshore in direction of wave, oblique to shore
- Some water sinks, some washes down beach face, moving sed as slope-normal backwash (90 degree to shore)
- Net result is beach drift
97
Beach drift
- Result of longshore current
| - Primary mechanism for movement of sediment along the shore face
98
What are the best results for quantifying nearshore currents?
- Best results use momentum analysis
- Momentum, unlike energy, is preserved as waves break and separates into shoreline parallel and shoreline normal components
- Good estimate of longshore current velocity at midsurf is V = 2.7um sin alpha cos alpha
- Where um is max orbital velocity at breaker zone, alpha = breaker angle of incidence w/ shoreline
99
Bed shear stress
- Like fluvial
- Bottom boundary layer, friction generates small turbulent vortices
- Set up stresses between fluid and grains
- = Fluid density x Horizontal turbulent velocity x Vertical turbulent velocity
- Not used until recently, older methods exist
100
Alternative method for quantifying nearshore sed transport
- Use friction factor and free stream velocity above boundary layer
- = 1/2 fw x u^2
- ks is bed grain roughness, used to calculate fw
- D is mean sed size, A is orbital amplitude defined by wave period
- Parameterizations done in lab settings w/ fixed beds, not great analogues
101
2 dominant approaches to swash zone sediment transport
- Meyer-Peter and Muller
- Bagnold (1963)
- Needs calibration coefficients, mean flow velocity during 1/2 swash cycle, duration of 1/2 swash cycle, friction angle of sed, beach gradient etc.
102
Calibration coefficient for swash zone sed transport
- Not well understood
- 'Fudge factor'
- Take empirical data to calculate but doesn't work
- Needs a calibration factor to make work
- Main consistency is that k is larger for uprush vs. backwash, which matches empirical data
103
Longshore sediment transport, littoral drift
- Shore-parallel movement of sediment on upper shore face
- Rates generally much larger than cross-shore/rip transport rates
- Typically unidirectional, mainly current driven
- Straight, uninterupted shorelines have very high longshore transport
- On the order of 1 million cubic m/yr
104
Littoral drift eqn
- Inman and Bagnold, 1963
- Q mu K'Hb^2V
- Where Q = longshore volumetric transport rate (m^3/a), K' = constant of proportionality (0.08 - 2.2), Hb = breaking wave height (m), V = longshore current velocity (m/s)
105
Factors affecting nearshore transport (5)
- Fluid velocity
- Grain size and sorting
- Bedforms
- Wave groups
- Wave breaking
106
Fluid velocity (nearshore transport)
Typically higher u" from waves and/or currents
107
Grain size and sorting (nearshore transport)
- Sediment fall velocity
108
Bedforms (nearshore transport)
- eg turbulence from ripples enhances bed shear and vertical mixing
- Bars create feedback
109
Wave groups (nearshore transport)
- 'pumping up' of sed concentrations toward end of larger wave groups
110
Wave breaking (nearshore transport)
- Additional turbulence and vertical mixing w/ bed
- Turbulence can enhance bed shear, reduces velocity, makes shallower
- eg vortices under plunging breakers vs. spilling breakers
111
Beach state, 2 end members
- Fully Dissipative
| - Highly Reflective
112
Fully dissipative beach state
- Flat, shallow beaches w/ relatively large subaqueous sand storage
- Spilling breakers occur
113
Highly reflective beach state
- Steep (> 6 deg) beaches w/ little subaqueous sand storage
| - Waves plunge and dissipate energy
114
How do tidal cycles influence wave state?
- Tides shift position of swash, surf, and shoaling waves zones
- Pronounced effects on water circulation, rips and undergo are stronger at low tide
- Rule of thumb: as wave height increases, Dimensionless fall velocity and Surf-scaling parameter increase, Relative Tide Range (RTR) decreases
115
What are the 3 ways that beach state is defined?
- Dimensionless fall velocity
- Surf-scaling parameter
- Relative tide range RTR
116
Dimensionless fall velocity, omega
= Hb/sed fall velocity x T
- Hb breaking wave height, sediment fall velocity, Wave period (T)
- < 1 reflective, >6 dissipative
- Function of grain size and wave characteristics
- Decreases w/ smaller grain sizes
117
Surf-scaling parameter, epsilon
- Differentiates effects of different kinds of waves
- requires Hb - breaker height, Wave period, Beach gradient
- < 2.5 = reflective, >20 = dissipative
118
Relative Tide Range, RTR
= TR/Hb
- TR = mean spring tide range
- Hb = breaking wave height
119
Wave dominated beaches
- RTR < 3
- Dissipative: Dimensionless fall vel >6, Surf-scaling >20
- Intermediate: fall vel 2-5, surf-scaling 2.5 - 20
Reflective: fall vel <1, surf-scaling <2.5
120
Tide-modified beaches
- Typically RTR = 3-10
- All: RTR = 10-50, fall vel <2
- Reflective and low-tide terrace: fall vel <2
- Reflective and low-tide terrace and bars and rips: fall vel 2-5
- Ultra-dissipative: Fall vel >5
- Mud flats: RTR >50
121
Dissipative beaches
- High waves, wide surf zone, wide flat beach, low mobility
- Max aeolian and wave induced sediment transport
- Large, high foredune
- Extensive holocene barrier development
- Commonly extensive parabolic or transgressive dune fields
- Flat to concave beach face, parallel bars and troughs, spilling breakers
122
Intermediate Beaches
- Low to high waves, narrow to wide surf zones, berms wide, flat beach, high mobility
- Moderate aeolian and wave induced sediment transport
- Small to large, low to high foredune
- Small to extensive holocene barrier development
- Narrow foredune plain to extensive parabolic dune fields
- Wrack line, berms and megacusps, crescentic bars and rips, plunging breakers
123
Reflective Beaches
- Low waves, narrow surf zone, steep beach, low mobility
- Minimal aeolian and wave induced sed transport
- Small, low foredune
- Limited holocene barrier development
- Commonly narrow relict foredune plain
- Cusps, steps, linear near shore zone, surging breakers
124
Seasonality and beach form
- Low waves in summer can bring sed onshore
| - Winter storms w/ larger waves move sed offshore, results in more gravelly coarse beach
125
Erosional landform features: 3 categories
- Headlands and bays
- Caves, arches, stacks
- Cliffs, wave cut platforms
126
Erosion of a headland
- 1. Weak areas attacked by waves, opened to form cave due to erosion and hydraulic action
- 2. Cave widened and deepened by erosion, forms an arch
- 3. Roof of arch is undercut, eventually collapses, leaves isolated Stack
- 4. Stack eroded, becomes a Stump
127
Depositional landforms
- Spits
- Barrier islands
- Tombolos
- Nearshore bars
- Bay barriers, lagoons (behind barriers)
128
Spits
- Long, shore parallel extension of land
- Attached at one end to mainland coast
- Build by waves and longshore currents
- Can form in any tidal range
- Can be hooked or 'recurved'
- Deflection along longshore drift zone, sends out from shore and deposits sed in long bars
129
Barrier Islands
- Long, shore parallel island
- Not attached to mainland coast
- Build by waves and longshore currents
- Micro-meso tidal envrs
- Separated by shallow bays, lagoons, or sounds
- Often in chains that extend for 100 plus km
- Extensive in E Canada down to Florida
- Beaches can lead to flood and ebb deltas
130
Tombolos
- Wave diffraction around an island
- Sediment builds up behind island, can connect island to mainland shore
- Typically moderate to low wave energy
131
Nearshore bars
- Nearshore and intertidal shore parallel, asymmetric features
- 0.25-4m high, 25-150m wide, 50m-km long
- Formed by convergence of onshore transport due to shoaling and breaking waves, w/ undertow near bed
- Bars migrate during storms (dynamic envr)
- Straight bars, transverse bars, inner bars, outer bars, crescentic bars
132
4 Characteristic profile forms
- Nonbarred
- Barred
- Alternating
- Tidal influenced
133
Nonbarred profile form
- Smooth, planar to curvilinear
134
Barred profile form
- 1 or more bars
- Associated troughs
- Year round
135
Alternating profile form
- Alternating barred and nonbarred
| - Often seasonally
136
Tidal influenced profile form
- Semi-permanent bars in intertidal and subtidal zones
137
Summary of Coastal processes
- Coastal zone is interface btwn water bodies, atm, and lithosphere, therefore highly dynamic
- Coastal processes consist of waves, tides, currents, and sediment transport processes and models
- Depositional forms consist of spits, bars, barriers, tombolos etc.
- Beach energy regimes consists of RTR, surf similarity, fall velocity and result in wave-to-tide-dominated beaches
- Erosional landforms consist of arches, stacks, caves, platforms, stumps, etc.
138
Coastal zone consists of?
- Interface w/ lithosphere, atm, and water
- Offshore, nearshore, foreshore, and backshore
- Extends several km from point of wave break to back shore
- Forms and processes vary over tides, events (storms), seasons, interannually, longer term RSL
139
What does the growth of a bar form lead to?
- Narrowing of the breaker zone
| - Increased breaker intensity
140
Sediment transport patterns of bar initiation
- Convergence near breaker zone of onshore transport under shoaling and breaking waves with offshore transport in the undertow
141
Dimensionless fall velocity between 0-2
- Reflective Type beaches
- Low RTR = Reflective, cusps, steps, short profile length
- Intermediate RTR, 3-7: Low tide terrace plus rip, cusps, reflective beach face
- High RTR, 7-15: Low tide terrace, long beach profile, reflective high tide beach, dissipative low tide terrace
142
Dimensionless fall velocity between 2-5
- Intermediate type beaches
- Low RTR: Barred beach, steep beach face w/ deep trough and pronounced bar or subdued bar-morphology
- RTR 3-7: Low tide bar/rip, low tide transverse bar and rip morphology, steeper beach face, swash bar
- RTR 7-15: Ultra dissipative, flat and featureless, very long profile
143
Dimensionless fall velocity >5
- Dissipative type beaches
- Low RTR: Barred dissipative w/ multiple subdued bar-trough morphology
- RTR 3-7: Non-barred dissipative, flat and featureless
- RTR 7-15: Ultra-dissipative, flat and featureless w/ very long profile
