1. Coastal Processes

2. Wavelength and Amplitude Wave height (amplitude) = f(vel of wind, duration of wind, and fetch) Wave speed (celerity) = f(wavelength and water depth) –Period = 1/frequency If depth >> wavelength –Deepwater wave If wavelength > depth –Shallow water wave First (storm) waves to hit shore are the fastest! e.g., c=30m/s, travel 2400km in one day!

3. Wave Energy Energy per unit length of wave –KE + PE Wave power: rate at which work is done –Shallow wavespeed (C) x energy –Mostly a function of H, amplitude (wave height) –Big waves do the most geomorphic work on coasts

4. Shallow waves moving onshore Shoaling: waves interact with bottom topography Edge of wave closest to shore encounters shallower water (vel = f(depth)) –Slows down Wave front and wave rays bend Wave refracts, impacting shore at obtuse angle

5. Breeze Point (Yellowstone Lk.) Note refracted wave crests

6. 3. Nearshore Currents Two Types of Wave-Induced Currents: Rip Current Longshore Return flow from longshore currents Copyright © Rob Brander 2002 Wave Energy Longshore Current Rip Current forms at low spots

7. Rip Current Forms at low spot or break in sand bars Water looks smoother (or choppier) in rip current zone Zone extends from shoreline, through surf zone, past breaking waves

8. Flows parallel and normal to shoreline Shape topography on beach and nearshore zones Move sediment (apart from waves and tides) On-beach (“beach drift”) and off-shore (“longshore drift”) movement is huge –X00,000 m 3 /year

9. Beach drift Longshore drift Littoral drift If wave angle is not normal (90 o ), moves sand down (parallel) the coast Water also moves parallel: longshore current Latin, litus for “shore”

10. Beach Drifting and Longshore Currents

11. Littoral Drift Littoral sediment flux= Velocity, U x Transport layer thickness,  x Distance over which waves influence bed, L Drift rate = f(wave angle, and wave height)

12. Littoral Cell “A self-contained unit of coastline within which sand sources and sinks are contained” (Anderson, 2008) At steady state, volume of sand in each cell is constant –Inputs = outputs Sources: cliff retreat, rivers Sinks: suspension, submarine canyons

13. Littoral sand cells (open) http://walrus.wr.usgs.gov/outreach/mbay/mbay_map.gif

14. dump truck capacity = 10 cy Consider ramifications for coastal engineering! 356 275 191 306 255 Rates of littoral drift

16. Coastal Landforms

17. Types of Coastlines Depositional Erosional

18. Seasonal beach morphology Late summer Winter storms Early spring Early summer Late summer

19. Seasonal Beaches Example: Australia (sand stored off-shore)

20. Beach Morphology Ridge Runnel CurrentsWavesStormsWind Tide Range

21. Example Ocean Park, WA quad Features –Runnel –Ridge –Trough –Bar Runnel Ridge Trough Bar

22. Beach Cusps crescent-shaped scallops, parallel to shore offshore horns bounding small bays feedbacks between topography and fluid flow

23. Convergence of water by refraction => erosion of bays Off-shore deposition in front of bay Deceleration in front of horns Flow “trips” on bar, accelerates near horn Topography-wave-sediment transport loop Spacing controlled by extent of swash

24. Bayhead beach Rocks Sand

25. Baymouth bar

26. Capes and Spits Created by longshore sediment transport –= f(angle of wave approach) –0 o incidence angle: no onshore momentum –90 o : no momentum in alongshore direction –Max. transport at ~45 o – erosion –>45 o : decreases transport => deposition

27. White, 1966 “These capes are not deltas under present conditions; however, at the beginning of a glacial stage, the river gradients were markedly increased by sea-level lowering and deltas developed. As the sea retreated, the deltas formed farther seaward on the continental shelf, resulting in the deposition of deltaic ridges of sediment perpendicular to the coast. During the subsequent submergence which accompanied glacial melting, the deltas became the loci of barrier islands and prominent capes. Submergence was accompanied by erosion and retreat of the barrier capes resulting in the present capes, shoals, and embayments.”

28. Depositional Coastal Landforms

29. Spits and Bars: Dungeness, WA Olympic Mountains Puget Sound Pacific Ocean

30. Schwartz et al., 1987

31. Dungeness Spit Primary driver: littoral drift powered by long fetch and large sediment source Modified by –tidal ebb/flow –river delta deposition –near shore current

32. Spit Provincetown, MA NOTE: –Refraction –Multiple breakers –Dunes N

34. Geologic map of Cape Cod (generalized from detailed mapping by K. F. Mather, R. P. Goldthwait, L. R. Theismeyer, J. H. Hartshorn, Carl Koteff, and R. N. Oldale).

36. Tombolo (wave shadow zone) Copyright © Ann Dittmer 2002

37. Incipient tombolo