Beaches and Coasts 11-15
How large are tidal amplitudes in the Bay of Fundy?
50 ft
What does the O'Brien Relationship describe?
A prism equals the function of the inlet cross sectional area
What is a tidal inlet?
A region where the water penetrates the land and connects the oceans to bays, lagoons, marshes, and tidal creeks
Where are tidal currents strongest? Why?
At the throat and other constrictions
Name three ways tidal inlets are formed?
Breaching of barrier islands and spits, Spit building (constricts the opening to the sea), Drowned River Valleys
Tidal inlets can interrupt the longshore transport down a coast. How do we deal with this interruption so that the tidal inlet does not fill up or cause erosion in the down drift direction?
Building jetties and dredging
Where is the "throat" of an inlet?
Constriction/narrow part
What are tidal channels? Do they form primarily on flood or ebb tides?
Deep channels that allow water to flow in and out of intertidal flats mostly off drainage patterns and ebb tides
What distinguishes estuaries from deltas?
Deltas don't extend into land and deltas are on the outside of the outlet
What does the Walton-Adams Relationship describe?
Ebb tidal sediment volume is a function of the Tidal Prism
Describe the following types of organisms found in mud flats, epifauna, infauna, and give examples?
Epifauna: mud snails, worms, amphipods Infauna: clams
What is a flood tide, ebb tide?
Flood Tide: incoming/rising tide that inundates the land area Ebb Tide: outgoing/falling tide that drains the land area
What are flood tidal deltas, ebb tidal deltas, and where can they be found?
Flood tidal deltas: pile of sand inside the inlet Ebb tidal deltas: deposit of sand outside of the inlet
What are the two driving forces for tides?
Gravitational and centrifugal forces
What are typical periods for lunar tides and solar tides?
Lunar tides: 12 hours 25 minutes Solar tides: 12 hours
What are two characteristics that are needed to characterize an inlet as a "tidal inlet"?
Maintained by tidal currents and sediment transport is required
What is MHHW, MHW, MTL, MLW, MLLW?
Mean higher high water, mean high water, mean tide level, mean low water, mean lower low water
Most navigational charts reference water depths to what level?
Mean lower low water
What type of sediment are found within salt marshes?
Mud, plant debris, fine sediments, bioturbation extensive, and infauna
Mud sediment (less than 62.5 microns) is cohesive. How does this property of mud affect the slopes of tidal channels bordered by mud (relative to those bordered by sand) ?
Mud= steep channel walls Sand= gently slopping walls
List three reasons why tidal inlets are important?
Navigation for boats, nutrient exchange into oceans, and ecosystem ecology in back bay areas
Can mangrove forests tolerate large temperature changes? Where can mangroves be found geographically on the planet?
No because it needs to be at places near the equator above 16.5 degrees Celsius
Are mud flats vegetated, associated with high wave energy, usually associated with tides?
Not vegetated, low wave energy, and are associated with tides
What is an intertidal flat? Where can they be found?
Region of the back bay that gets covered and uncovered by tides. Along margins of coastal embayments with tides
Are rivers or oceans modulated by runoff and precipitation, regular variations due to tides?
Rivers are modulated by runoff and precipitation Oceans are modulated by regular variation of the tides
What demarcates the extent of salt marshes and mangroves?
Salt marshes- low is tidal flats and high is spring tides Mangrove swamps- low is woody shrubs and high is fresh water
What distinguishes salt marshes from mangrove swamps?
Salt marshes- mainly composed of grasses Mangrove swamps- composed of woody plants
What sediments are usually found in tidal channels?
Sand sized sediments
What factors may limit the success of organisms that live on intertidal mud flats?
Sediment in the water column and erosion of habitat
What is meant by semi-diurnal tides, unequal semi-diurnal tides, diurnal tides, and mixed tides?
Semi diurnal: 2 tides per day, 2 highs and 2 lows Unequal semi diurnal: 1 high or low tide bigger than the other Diurnal: 1 tide per day, 1 low and 1 high Mixed: change between diurnal and semi diurnal
Are tidal flats similar or different in character to drainage basins that feed riverine systems?
Similar
Are estuaries sources or sinks for sediments?
Sinks, the property that limits their geologic lifespan
What is meant by stratified, partially mixed, and well mixed estuarine environments?
Stratified- split between salt and fresh water Partially mixed- some salt and fresh water mixed Well mixed- vertical uniform mixing top to bottom
In tidal forcing, what situation is described by syzygy and quadratic?
Syzygy occurs when the sun and moon are directly in line with the earth and their gravitational pulls reinforce each other to make the highest tides. Quadratic occurs when the sun, earth, and moon form a right angle and the sun's gravitational pull counteracts the moon's pull making a weaker high tide.
How does the mixture of mud and sand change as you move across the tidal flat?
The higher you get on the intertidal zone, the mud cracks
What is the tidal prism? How would we determine its magnitude?
The volume of water that flows in and out, the cross sectional area of the inlet determines how much tidal flow enters an inlet
How are coasts important to shoreline processes on open coast beaches?
Tides affect the water level because tidal elevation swings have major impacts during storms
Why are there (generally, or most commonly) two high tides and two low tides each day?
Tides are pulled to earth at close points and pushes away at far points and it create a tidal wave as earth spins
What are bedforms? Give three examples and their approximate size in terms of wavelength or height?
Undulations of the sea bed Examples: Ripples- wavelength: 10's of cm amplitude: cm's Megaripples- wavelength: 10 meters amplitude: 1 meter Dunes- wavelength: 10's of meters amplitude- 1-10 meters
What are vagrant and sessile organisms?
Vagrant- can move around, like worms Sessile- can't move horizontally, like oysters
Tidal inlets can migrate to new locations. Briefly explain how this might happen. How do we stabilize an inlet location?
When currents become unstable and cause a new channel. Jetties stabilize inlet locations
What is a "maestrom"?
Whirlpool caused by a tidal current
Is there much organic material associated with sedimentary material found in salt marshes? Is this important to carbon fluxes and climate change?
Yes and yes this is important to carbon fluxes and climate change because of blue carbon
What are the three main ways that salt marshes are classified?
Young, intermediate, old
What is an estuary?
a coastal bay influenced by fresh water, associated with tidal flows
What is a amphidromic point, co-tidal line, co-range line?
amphidromic point: point tides rotate around co-tidal line: times in hours relative to a starting point where high tides occur co-range line: tide range is the same
Are tidal inlets commonly or rarely found in nature?
commonly
What is a bayhead delta?
delta found within the estuary at the mouth of the river
How do we keep tidal inlets safe for navigation?
dredging
Is fresher water lighter or heavier than saltier water?
fresher water is lighter than saltier water
Name three ways estuaries might be formed?
generated by fault, drowned river valleys, fjords
Where are tidal currents important?
inlets and constrictions
List three characteristics of wave dominated estuaries?
large wave, sediment dominated, less strong tidal currents
What sediments are usually found in tidal channels?
limited sediments because tidal channels have higher flowing rates, they have coarser sediments, and settling is discouraged
Name two types of plants, one found in low marshes and one high marshes?
low marshes- spartina high marshes- juncus
What relative elevations are typical of low salt marshes, high salt marshes, mangroves?
low salt marshes- lower high salt marshes- medium high mangroves- highest elevation
For tidal forcing in the gravitational equation, what are m1 and m2, and what is r2?
m1 and m2 are the masses of the two objects and r2 is the square of the distance between the two
What is brackish water?
mixture of fresh and salt water
Do river-dominated estuaries typically have more or less mud than tidal dominated estuaries?
more
Where are the muddier sediments found in most estuaries?
near banks where the flow is weak
What do the perihelion and aphelion and perigee and apogee have to do with tides?
perihelion and aphelion: earth/sun elliptical system perigee and apogee: earth/moon elliptical systems
List three characteristics that determine that nature of salt marsh environments?
protection of wave energy, sediment supply, and rate of sea level rise
What are coastal wetlands?
salt marshes and mangrove swamps
List three characteristics of tide dominated estuaries?
sand dominated with bedforms, funnel shape, strong tidal currents
What are spring and neap tides?
the highest and lowest tides of the lunar cycle
What is bioturbation?
the reworking of the soil by organisms like acorn worms
Where along the coast does the greatest changes to shorelines occur?
tidal inlets
What are typical values for tidal wavelengths, tidal amplitudes on open coasts away from inlets and embayments?
wavelengths: 10,000 km amplitudes: 0.5 m
Do the plants in salt marshes promote or discourage sedimentation?
yes through the settling of suspended material
