r&b: tidal flats, marshes, and mangrove forests, sediment budgets, and human structures

where are intertidal beaches found?

commonly at estuarine/deltaic lagoonal environments (intertidal around lagoon; lagoon gets filled with sediment to form flat)

sand flats

characteristic ripples; found low on beach because of strong currents (waves are stronger there)

mud flats

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?

not really

salt marsh

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?

tropical regions

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

mangroves

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)

healthy beach

seaward expansion; can hold its position

unhealthy beach

landward expansion

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

groin

huge rocks protruding seaward; erodes beach downstream (deflects longshore transport further down); make lose sediment to submarine canyons

jettys

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?

S/SW

how have humans impacted erosion rates?

x10-100 increase in erosion

how have humans impacted sedimentation rates?

x1/2 decrease in sedimentation

breakwaters

structures that are parallel/subparallel to beach; has same issues as jettys/groins