shorelines. coastal sediment budget the sediment budget determines whether a beach will shrink or...
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Coastal Sediment BudgetThe sediment budget determines whether a beach will shrink or grow.
• If sediment gain is greater than loss, a beach becomes wider (and visa versa).
Fig. 19.58
Coastal Sediment Budget
Gains include sediment:
• transported onshore by waves and longshore currents.
• newly eroded along a shoreline.
• delivered by rivers.
Fig. 19.26
Coastal Sediment Budget
Losses include sediment:
• transported offshore by waves and longshore currents.
• sand blown further onshore by wind.
Fig. 19.26
Coastal Sediment BudgetHuman activities can increase or decrease sediment supply.
• damming rivers decreases supply
• ag. erosion increases supply
Fig. 19.28
Barrier IslandsBarrier islands – long, narrow islands parallel to coast.
Wind and waves pile up sediment to form islands.
Fig. 19.29
Barrier Islands
Importance of barrier islands:• major cities (Atlantic City,
Miami, Galveston) built on them• protect mainland from
storm surge• recreation• lagoons behind islands are
marine nurseries
Barrier Islands
Constantly changing (human time scale).
Highest point only a few meters above sea level.
Waves wash over low points during storms.
Storms cut inlets through islands.
Barrier IslandsInlets serve as passages from protected marinas to open ocean.
Inlets will close over time unless they are stabilized by jetties.
Disrupt longshore sediment transport.
Fig. 19.30
deposition
erosion
Barrier Islands
Barrier islands will migrate as sea level rises.
Storms erode sand on ocean side and deposit it on bay side.
Fig. 19.48
Shoreline Features
Spits form by longshore currents depositing sediment off the end of a headland.
Fig. 19.22
Shoreline Features
Cape Cod is a glacial moraine that has been modified by longshore currents.
Fig. 19.22
Deltas
Delta – sediments deposited when river enters ocean/lake.
• water velocity decreases, sediment load deposited
Fig. 16.15
DeltasMain river channel splits into distributaries.
Sediments deposited over broad area.
Waves rework sediments (islands and bays).
Delta MigrationPosition of main channel on a delta periodically shifts.
• sediment deposition raises elevation near main channel• compaction lowers elevation away from main channel, • eventually main channel shifts to lower elevation