Costal Erosion: “Approximately 25 percent of homes and other structures within 500 feet of the U.S. coastline and the shorelines of the Great Lakes will fall victim to the effects of erosion within the next 60 years, according to a study released by the Federal Emergency Management Agency (FEMA).”

Coastal erosion and sediment transport

Coastal Evolution Balance between: Balance between: Wave action (energy, geology)Wave action (energy, geology) Sediment supplySediment supply Sea levelSea level

Wave and Water Movement

Erosion and movement by WAVES Wave base: point at which wave action becomes negligible on the sea floor Wave base: point at which wave action becomes negligible on the sea floor It is the effective lower limit of wave action and erosion It is the effective lower limit of wave action and erosion /2 = wave base/2 = wave base

Waves So, surf is a powerful erosive agent So, surf is a powerful erosive agent Its energy is expressed by turbulence… Its energy is expressed by turbulence… …violent movements of parcels of water which are able to move and suspend sediment …violent movements of parcels of water which are able to move and suspend sediment

Oscillatory and Translational Motion

Sediment movement - redistribution by WAVES Longshore transport: waves hitting coast obliquely, depends on prevailing winds Longshore transport: waves hitting coast obliquely, depends on prevailing winds waves have both a perpendicular and parallel component relative to the coast waves have both a perpendicular and parallel component relative to the coast the parallel component represents longshore drift; transport of sediment along the beach the parallel component represents longshore drift; transport of sediment along the beach

Baymouth Bar - Russian River, CA

Wave Refraction Waves change path when they reach shallow water Waves change path when they reach shallow water Wave energy is concentrated on headlands and spread out in bays Wave energy is concentrated on headlands and spread out in bays

Wave Refraction off Cape Cod

Tombolo - Santa Cruz, CA

Rips When waves break parallel to a beach, rips occur When waves break parallel to a beach, rips occur

Rips, Lake Superior

Rip currents: water that flows straight out to sea from the surf zone. Travel at the surface and die out at depth. Carry fine grained particles out of surf zone to deeper water.

Winter Summer

Longshore transport or Beach drift: oblique waves which move sediment along the beach Longshore transport or Beach drift: oblique waves which move sediment along the beach Storm transport: very rapid erosion, much larger than normal, which tends to narrow beaches and move sediment offshore Storm transport: very rapid erosion, much larger than normal, which tends to narrow beaches and move sediment offshore Sediment movement - redistribution by WAVES

Sea Level Change 1. Glaciers Glaciers Lower Sea Level Slowly Glaciers Lower Sea Level Slowly They Melt quickly – sea level rises They Melt quickly – sea level rises 2. Mid Ocean Ridges Mid Ocean Ridge raises sea level if large and active Mid Ocean Ridge raises sea level if large and active Lowers sea level if activity slows - becomes smaller Lowers sea level if activity slows - becomes smaller

Sea level rise linked to global warming, either natural or human-induced linked to global warming, either natural or human-induced over next century, we anticipate sea level to rise by cm over next century, we anticipate sea level to rise by cm along the east coast where the coastal plain rises gently, this rise translates to a shoreline setback of feet. along the east coast where the coastal plain rises gently, this rise translates to a shoreline setback of feet.

Shoreline shift Impact of sea level rise is greatest in low coastal areas Impact of sea level rise is greatest in low coastal areas

Effects of the Pleistocene Sea level has risen at least 100 meters in the last 18,000 years Sea level has risen at least 100 meters in the last 18,000 years Most coastlines globally are submergent Most coastlines globally are submergent Primary coastlines are very common Primary coastlines are very common

(From Barnola, 2006)

Nonmarine Processes - Uplift Convergent Margins

Wave-Cut Platform, California

Sediment/Sand Budget

Artificial structures and beach erosion Dams Dams Groins Groins Breakwaters Breakwaters Seawalls Seawalls Inlets, dredging, and jetties Inlets, dredging, and jetties

Human intervention

Santa Cruz Harbor, California Direction of current

Our efforts to control nature can be a expensive struggle Santa Barbara Harbor in 1931 Source: Fairchild air photos & E-5780, UCLA Department of Geography Aerial Photo Archives

Santa Barbara Harbor in 1977 Source: John S. Shelton

Groins Designed to trap sediment… Designed to trap sediment… but they instead progressively starve beach of sediment in the direction of longshore-littoral current but they instead progressively starve beach of sediment in the direction of longshore-littoral current From Dean (1999)

Groins off Cape May, New Jersey Source: John S. Shelton

Further effects of groins Rockaway beach, New York Eroded beach…compare buildings on either side of groin Highly eroded beach

Breakwaters Designed to allow sediment to settle Designed to allow sediment to settle Smaller waves behind, less sediment is transported Smaller waves behind, less sediment is transported From Dean (1999)

Seawalls Various types: revetments, rip- rap, concrete walls, piles of rubble, etc. Various types: revetments, rip- rap, concrete walls, piles of rubble, etc. Nearly 100% of the time they damage or destroy a beach which is eroding to begin with Nearly 100% of the time they damage or destroy a beach which is eroding to begin with From Dean (1999) Loss of beach Flooding of beach Destruction of seawall

Beach-Protection Structures - Riprap Source: Jack Dermid /Photo Researchers, Inc.

Beach-Protection Structures – Seawall Along the Gulf Coast of Louisiana Source: Martin Miller

The consequences of NO BEACH Hugely costly measures are required to restore beach, e.g., pumping sand, and this is only a temporary solution Hugely costly measures are required to restore beach, e.g., pumping sand, and this is only a temporary solution Also, houses are now closer to the water and more vulnerable Also, houses are now closer to the water and more vulnerable On either end of the seawall, the beach erodes and is displaced toward the land naturally…so the walled part of the beach is exposed to the ocean and vulnerable to storms On either end of the seawall, the beach erodes and is displaced toward the land naturally…so the walled part of the beach is exposed to the ocean and vulnerable to storms

Sand bypassing to replenish beach on down-current side of jetty From Dean (1999) Replenishing sand the old- fashioned way

Inlets Inlets are created naturally by large storms…they are breaks in a barrier beach Inlets are created naturally by large storms…they are breaks in a barrier beach Over time, the inlet will heal naturally Over time, the inlet will heal naturally The inlet can heal rapidly, or can linger for years or decades The inlet can heal rapidly, or can linger for years or decades From Dean (1999)

Raccoon Island, Louisiana

Closing of an inlet The healing time of an inlet depends on: The healing time of an inlet depends on: -amount of sand transported by littoral drift -amount of sand transported by littoral drift -amount of water flowing through with tide -amount of water flowing through with tide Thus, if the tidal flow is low and littoral currents carry abundant sand, the inlet can heal quickly Thus, if the tidal flow is low and littoral currents carry abundant sand, the inlet can heal quickly Flood tide deltas represent a large amount of sand carried inside the inlet’s mouth Flood tide deltas represent a large amount of sand carried inside the inlet’s mouth This is a natural sink for sand, and the sand remains relatively undisturbed This is a natural sink for sand, and the sand remains relatively undisturbed

Inlets and dredging Inlets are kept open artificially sometimes, e.g., for a harbour, fishing fleet, etc. Inlets are kept open artificially sometimes, e.g., for a harbour, fishing fleet, etc. If so, inlet needs to be dredged periodically If so, inlet needs to be dredged periodically The dredged sand is often dumped in deep water offshore…the sand is therefore lost The dredged sand is often dumped in deep water offshore…the sand is therefore lost If sand were dumped on the beach down- current, beach might be stabilized…but not an easy task due to the high-energy surf zone If sand were dumped on the beach down- current, beach might be stabilized…but not an easy task due to the high-energy surf zone

Inlets and jetties Another way to keep inlets open artificially is by building jetties Another way to keep inlets open artificially is by building jetties The jetties serve to “jet” out sand into deeper water…again, a loss The jetties serve to “jet” out sand into deeper water…again, a loss The longer the jetty, the worse the erosion down-current The longer the jetty, the worse the erosion down-current

Jetty in Miami Beach, Florida Source: Townsend P. Dickinson

Artificial modification of inlets One problem is political…stakeholders may have diametrically opposite viewpoints… One problem is political…stakeholders may have diametrically opposite viewpoints… …e.g., tourism operators who need a beach vs. fishing fleets who want easy access to the ocean through the inlet …e.g., tourism operators who need a beach vs. fishing fleets who want easy access to the ocean through the inlet One solution is sand-bypassing, but this is expensive and inefficient compared to Mother Nature One solution is sand-bypassing, but this is expensive and inefficient compared to Mother Nature