Coastal systems can be divided into erosional shorelines and depositional shorelines based on dominant long-term processes. Erosional shorelines are dominated by erosive forces and typically have high-relief rocky coasts, while depositional shorelines are dominated by depositional processes and include environments like deltas, barrier islands, and reef coasts. Coasts experience various erosive and depositional processes from waves, such as refraction, longshore drift, and swash/backwash, which shape the shoreline over time. Stabilizing eroding coasts involves hard structures, beach nourishment, or relocation, but these approaches have limitations and tradeoffs.

1. Coastal Systems

2. Coastal Settings Open coasts can be divided into two general categories based on the dominant processes acting on the coast over long periods of time (1000’s of years or more) Erosional Shorelines dominated by processes that form erosional features along the shore Typically high-relief rocky coasts in tectonically active areas (e.g., the Pacific coast of North America) Typically high-relief rocky coasts Depositional Shorelines dominated by processes that form deposits along the shore Include a wide spectrum of environments Deltas, barrier islands, reef coasts, glaciated coasts, etc. More typical of passive, or trailing-edge, continental margins (e.g., the Atlantic coast of North America)

3. Features of erosional coasts 11.4-Thurman and Trujillo, 2004

4. Features of erosional coasts Cabo Rojo, PR Sea arch Wave-cut cliff

5. Features of depositional coasts 11.7-Thurman and Trujillo, 2004

6. Features of depositional coasts 21, 25-RPI Barrier islands along the South Carolina coast

7. A wave moving onto the shore 20.5-Tarbuck & Lutgens, 2005

8. Wave erosion

9. Wave erosion Breaking waves exert a great force Wave erosion is caused by Wave impact and pressure Abrasion by rock fragments

10. Wave erosion 20.6, 20.7-Tarbuck & Lutgens, 2005

11. Wave refraction Wave refraction Bending of a wave Causes waves to arrive nearly parallel to the shore Consequences of wave refraction Wave energy is concentrated against the sides and ends of headlands Wave energy is spread out in bays and wave attack is weakened Over time, wave erosion straightens an irregular shoreline

12. Wave energy focused on headland Wave energy dispersed over bay Wave refraction 9.19b-Thurman and Trujillo, 2004

13. Wave Reflection and Refraction

14. Wave Motion/Refraction

15. 10.20b-Garrison, 2005 Wave refraction, Maili Point, Oahu

16. Movement parallel to the ( ↔ ) shoreline Caused by wave refraction Along most shorelines, waves strike the shore at an angle Waves that reach the shoreline at an angle cause the sediment to move along a beach in a zigzag pattern called beach drift Sediment movement on the shore

17. Sediment movement on the shore Movement parallel to the ( ↔ ) shoreline Oblique waves also produce longshore currents Currents in the surf zone Flow parallel to the coast Easily moves fine suspended sand and rolls larger sand and gravel along the bottom

18. Movement of sand by longshore current 20.10-Tarbuck & Lutgens, 2005

19. Sediment movement along a beach 11.19-Segar, 2007

20. Beach Drift and Longshore Currents

21. Movement perpendicular ( ↕ ) to the shoreline Caused by breaking waves Swash ( ↑ ) Backwash ( ↓ ) Sediment movement on the shore

22. Swash -> ← Backwash Domes beach, Rincón, PR

23. T11.2-Thurman and Trujillo, 2004

24. 11.2a-Thurman and Trujillo, 2004

25. 11.2a-Thurman and Trujillo, 2004

26. Seasonal variation in beach profile 11.19-Segar, 2007

27. Barrier Systems Sandy Point, Cape Romain, South Carolina 38-RPI

28. Barrier Systems Thin strips of land built a few to several tens of meters above sea level Form due to the combined action of wind, waves, and longshore currents Act as a barrier – protect mainland coast from open-ocean wave energy, storm surge, etc. Protected environments form behind barriers – bays, lagoons, marshes, tidal creeks

29. Barrier Systems Most common along passive margins Economically important Vulnerable to storms, rising sea level, erosion One of the major forces impacting barriers today, as well as in the past, is rising sea level

30. 11.9c-Thurman and Trujillo, 2004 Heavily developed barrier islands Tom’s River, New Jersey Barrier islands north of Charleston, SC 21-RPI

31. Chesapeake Bay – a drowned river valley Pamlico Sound – a bar-built estuary 12.5-Garrison, 2005

32. Coastal Erosion and Beach Loss Coastal erosion is a natural process that redistributes sediments along coasts Coastal erosion becomes a problem when coastal development impedes or ignores the natural movement of sediment along the shore This problem is exacerbated by continued sea level rise

33. Coastal erosion is a natural process North Island, SC 32-RPI

34. Figure 20.16 Wave erosion caused by strong storms, Long Island, New York Coastal development makes erosion a problem

35. Sea-level rise makes the problem worse Studies show a 150x erosion multiplier for sea level rise on sandy shorelines. Hence, for a mean 0.24 m rise by 2050, beaches will recede 36 m (118 ft). ( Leatherman et al., 2000)

36. Stabilizing the shore Shoreline erosion is influenced by several local factors including Proximity to sediment-laden rivers Degree of tectonic activity Topography and composition of the land Prevailing wind and weather patterns Configuration of the coastline and nearshore areas

37. Stabilizing the shore Three basic responses to erosion problems Building structures (Hard stabilization) Beach nourishment Relocation

38. Stabilizing the shore Hard stabilization perpendicular to the shore Jetties Usually built in pairs to develop and maintain harbors Extend into the ocean at the entrances to rivers and harbors

39. Jetties are built to prevent deposition Figure 20.17

40. Stabilizing the shore Hard stabilization perpendicular to the shore Groins Built to maintain or widen beaches Constructed at a right angle to the beach to trap sand Because of increased erosion on the downdrift side of the groin, additional groins may be built resulting in a groin field

41. 11.20-Thurman and Trujillo, 2004 Interference of sand movement Hard stabilization like the groin shown here interferes with the movement of sand along the beach, causing deposition of sand upstream of the groin and erosion immediately downstream, modifying the shape of the beach.

42. Figure 20.18 Groins along the New Jersey Shore at Cape May Longshore transport

43. Jetties and Groins Jetties are always in pairs Groins can be singular or many (groin field) Both trap sand upstream and cause erosion downstream 11.22-Thurman and Trujillo, 2004

44. Stabilizing the shore Hard stabilization parallel to the shore Breakwater Barrier built offshore and parallel to the coast Protects boats from the force of large breaking waves

45. Groins and Breakwaters 11.7-Jones and Jones, 2003

46. Figure 20.19

47. Coastal Stabilization Structures

48. Stabilizing the shore Hard stabilization parallel to the shore Seawall Barrier parallel to shore and close to the beach to protect property Stops waves from reaching the beach areas behind the wall Often the building of structures is not an effective means of protection

49. Seawalls and beaches Seawalls are built to reduce erosion on beaches Seawalls can destroy recreational beaches Seawalls are costly and eventually fail 11.25-Thurman and Trujillo, 2004

50. Seawalls are designed to protect beachfront property from erosion 13.21-Segar, 2007

51. Figure 20.20 Seawall in Seabright, New Jersey Where’s the beach?

52. Wine Island? 10.26-Merritts et al., 1998 Seawalls can’t compete with sea-level rise

53. Responses to Coastal Erosion and Beach Loss Hard stabilization “ Armoring” the shoreline

54. Responses to Coastal Erosion and Beach Loss Hard stabilization “ Armoring” the shoreline

55. Responses to Coastal Erosion and Beach Loss

56. USGS Illegal extraction of beach sand is one of the major causes of coastal erosion in Puerto Rico

57. Morelock et al. Illegal extraction of beach sand is one of the major causes of coastal erosion in Puerto Rico

58. Stabilizing the shore Alternatives to Hard Stabilization Beach nourishment The addition of large quantities of sand to the beach system Only an economically viable long-range solution in a few areas Abandonment and relocation of buildings away from the beach

59. Responses to Coastal Erosion and Beach Loss Beach nourishment Wrightsville Beach, NC 10.24-Merritts et al., 1998

60. Figure 20.21 Beach nourishment, Miami Beach

61. USGS Locations of three submerged sand deposit areas on the insular shelf of Puerto Rico Aerial photograph of the Escollo de Arenas, a subtidal sand and gravel deposit that extends some 6 kilometers north-northwestward of Punta Arenas on the northwest coast of Vieques Island, east of Puerto Rico.

62. Responses to Coastal Erosion and Beach Loss Caveats of beach nourishment Not permanent solution Expensive Need appropriate sand source

63. Responses to Coastal Erosion and Beach Loss Still, with appropriate financial and sand resources, nourishment can be a viable solution in some settings

64. Responses to Coastal Erosion and Beach Loss Abandonment and relocation

65. Alternatives to hard stabilization Restrict the building of structures too close to the shore Eliminate programs that encourage construction in unsafe locations Relocate structures as erosion threatens them Figure 10C Relocation of the Cape Hatteras lighthouse, North Carolina

66. Coastal Hazards Increasing coastal development and rising sea level puts more people and property at risk Combined wind and storm surge damage Iniki flooding reached >800 ft inland >25 ft above sea level

67. New Directions? Avoid development of eroding lands Discourage additional development in erosion hazard zones Enforce “setbacks” Acquire high-value coastal lands Construction guidelines for hazard areas Nourish eroding shorelines Natural resources are those that are derived from the Earth and that exist independent of human activity - Cutter and Renwick, 2004

68. New Directions? Without a sound understanding and appreciation of the dynamics of the coastal zone, and thoughtful environmental management of the shore We may lose one of our most precious natural resources