Tidal Inlets
Sediment/water/nutrient pathways through barrier systems
Tidal currents govern the inlet
Tidal Prism Area (behind the barrier) and tidal range determine the size and number of inlet
channels
Flood tide/Ebb tide current and resulting deltas
Deepest part of the inlet-“inlet throat” is typically in the narrowest part of the inlet (maximum
velocity of the water (discharge remains the same, so the speed has to increase in the smaller
volume of the narrowest part of the channel)
Flood tide delta is dependent on:
Wave energy
Tidal range
Sediment supply
Backbarrier setting
Areas with low tidal range don’t rework the sediment once it gets to the back barrier, so the delta
is fairly well developed
Delta size is related to the amount of open water in the backbarrier and the size of the inlet
Flood tide currents are maximum near high tide, when entire flood tide delta is submerged
Ebb tide deltas
Modified by waves in the “open” ocean
Tidal channels typically form during storms when they are breached by large waves
Most of the incising takes place during the draining of the backbarrier.
Channels are relatively stable in their position if they cut deep enough into relatively firm
substrate.
Channel inlets migrate when the longshore transport of sand is added predominantly to one side
of the inlet, causing constriction of the flow area. This speeds up the water which then erodes
away the downcurrent side of the channel.
O’Brien Relationship: Tidal prism area is related to channel throat cross sectional area