r&b: tidal flats, marshes, and mangrove forests, sediment budgets, and human structures
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where are intertidal beaches found?
commonly at estuarine/deltaic lagoonal environments (intertidal around lagoon; lagoon gets filled with sediment to form flat)
characteristic ripples; found low on beach because of strong currents (waves are stronger there)
very smooth; found high on beach because of weak currents (swash is weaker the further away from sea it ends up)
what controls upward growth of tidal flats?
rate of sea level rise
why is there an accumulation of sediment onto tidal flats/lagoons?
flood tides are stronger than ebb tides due to frictional interactions; more sediment transported landward than seaward
do tidal flats have vegetation?
where intertidal is speckled with vegetation; home to many species of salt grasses
where are salt marshes found?
temperate, subpolar, and polar regions
where are mangroves found?
why are so many species of salt grasses found in salt marshes?
there are many niches to be filled; zonation occurs in accordance to these niches
how does the presence of vegetation affect the morphology of salt marshes?
buffers flow, reduces tidal current velocity, and enhances sediment accumulation
when intertidal at tropics are full of vegetation; home to many species of trees
why are there so many species of trees in mangroves?
same reason there are so many grasses in marshes: many niches to be filled; zonation occurs as well
why do mangroves have very unique root systems?
because mud they grow in is anoxic; roots find unique ways to get oxygen
how does the presence of mangroves affect the morphology of the intertidal?
reduces water flow and accumulates sediment due to dense roots and trunks
where can sedimentation occur only as fast as sea level rises in mangroves?
along the flat part of the forests; edge of the forests and edge of shore
where can sedimentation occur faster than how sea level rises in mangroves?
along the fringe (area closer to shore)
why are mangroves so important for blue carbon?
most of their biomass is underground, meaning the carbon they store is underground, and thus can't be transferred into atmosphere
why do coasts migrate?
in accordance to sea level changes, sedimentation changes, and shoreline erosion
how are coasts and their barriers migrating overall today?
landward (sea level is rising)
what is the current rate of sea level rise?
2-3 mm per year
where do maritime forests occur?
along back of dunes, on barrier flats
in terms of beach-scale, where are tidal marshes, mangroves, and tidal flats found?
near sea level on lagoon side of beach; get their water by washover during storm surge
where are mud and peat found?
tidal flats, marshes, and mangroves; when beach migrates landward, deposits can be found poking out on ocean side of beach
what are the three mechanisms for landward migration? (not sea level rise)
wind transport through/to dunes, tidal transport through inlets, and washover
can inlets themselves migrate?
yes, in accordance to longshore transport
do inlets close?
yes, old inlets close and new ones form all the time
how are flood-tide deltas formed?
when tides move past inlets and deposit into lagoons, where velocity is low, depositing sand; forms land with distributary channels
how are ebb-tide deltas formed?
when some sand reaches the lagoon during ebb tide and some sand leaves lagoon by ebbing currents; these are very small
what two ways remove sand from longshore transport?
accumulation upstream and entrapment in flood-tide delta
what happens when a longshore transport system is starved?
erodes downstream sides of land (this is why tidal inlets migrate for example)
seaward expansion; can hold its position
what are five sediment sources for beaches?
longshore drift, cliff erosion, rivers, biogenic shells, continental shelf (from flood current)
what are five sediment losses for beaches?
longshore drift, dunes, washover, tidal inlets, submarine canyons
what kind of beaches are easier to erode?
finer grained beaches
what are two human structures that have attempted to slow landward migration?
groins and jettys
huge rocks protruding seaward; erodes beach downstream (deflects longshore transport further down); make lose sediment to submarine canyons
huge features that jut out sometimes for miles into sea; basically bigger groins; used to stabilize inlets
what direction do winter winds blow during storm conditions in washington?
how have humans impacted erosion rates?
x10-100 increase in erosion
how have humans impacted sedimentation rates?
x1/2 decrease in sedimentation
structures that are parallel/subparallel to beach; has same issues as jettys/groins