Coastal processes Flashcards
Surf zone facts
linear wave theory is not applicable after wave breaking
waves progressively dissipate as they travel towards the shoreline
wave height and celerity are controlled by water depth
region between wave breaking point and the still water shoreline
Swash zone
the region between maximum wave-up rush and down-rush
waves traverse in zigzag
swash depend on incident waves and beach slope
Wave breaking
wave becomes steeper in shallow water (height increases, length reduces)
they break when the wave form is unstable
wave energy dissipated when wave form is unstable
part of dissipated energy is transferred to turbulence. aeration and sound
types of breaking waves
spilling
plunging
surging
Spilling breaker
beach is usually flat
Plunging breaker
beach usually steep
Surging breaker
beach is usually very steep
wave breaking criteria
incident wave steepness: H/L > 1/7
wave height to water depth ratio
Wave set-up and set-down
the change in mean sea water surface due to wave breaking
Longshore currents
when waves incident obliquely to the shoreline, wave breaking generates a gradient in momentum flux
gradient in momentum flux is balanced by a water surface gradient
water surface gradient in the longshore direction alongshore current
types of cross shore currents
mass transport
undertow
rip currents
mass transport
an on-shore directed net water movement due to wave asymmetry in the nearshore zone
- causes a net forward water moment called ‘mass transport’
Undertow
a current flowing in the offshore direction, near the sea bed
they compensate the shore-directed water mass (mass transport) by broken incoming waves
Rip currents
directed offshore
bring surplus water carried over the bars in the breaking process back to offshore
