The Coast: Beaches and Shoreline Processes North Carolina

Landforms and terminology in coastal regions Figure 10-1

Littoral Beach Profile

Movement of sand on the beach Movement perpendicular (↕) to shoreline Caused by breaking waves Light wave activity moves sand up the beach face toward the berm Heavy wave activity moves sand down the beach face to the longshore bars Produces seasonal changes in the beach

Summertime and wintertime beach conditions Summertime beach Wintertime beach Figure 10-2

Movement of sand on the beach Movement parallel (↔) to shoreline Caused by wave refraction (bending) Each wave transports sand either upcoast or downcoast Huge volumes of sand are moved within the surf zone The beach resembles a “river of sand”

Longshore current and longshore drift Longshore current = zigzag movement of water in the surf zone Longshore drift = movement of sediment caused by longshore current Figure 10-3b

Features of erosional shores Headland Wave-cut cliff Sea cave Sea arch Sea stack Marine terrace Figure 10-4

Sea stack, Sea arch, Sea stump Which Comes First????????

Features of depositional shores Spit Bay barrier Tombolo Barrier island Delta Figure 10-7

Barrier island, New Jersey

Barrier Islands North Carolina

Formation of barrier islands Sea level rose after the last Ice Age Caused barrier islands to roll toward shore like a tractor’s tread Figure 10-10

Barrier islands serve two main functions Barrier islands serve two main functions. First, they protect the coastlines from severe storm damage. Second, they harbor several habitats that are refuges for wildlife. Fantastic and diverse ecosystems

Changes in sea level Sea level has changed throughout time Tectonic and isostatic movements are localized and change the level of the land Eustatic changes cause sea level to rise or fall worldwide and are produced by: Changes in seawater volume Changes in ocean basin capacity

Sea level has risen since the last Ice Age Sea level was 120 meters (400 feet) lower during the last Ice Age About 18,000 years ago, sea level began to rise as the glacial ice melted Figure 10-14

U.S. coastal erosion and deposition Figure 10-16

Types of hard stabilization Hard stabilization perpendicular to the coast within the surf zone: Jetties—protect harbor entrances Groins—designed to trap sand Hard stabilization parallel to the coast: Breakwaters—built beyond the surf zone Seawalls—built to armor the coast

Jetties and Groins Jetties are always in pairs Groins can be singular or many (groin field) Both trap sand upstream and cause erosion downstream Figure 10-21

Breakwater at Santa Barbara Harbor, California Provides a boat anchorage Causes deposition in harbor and erosion downstream Sand must be dredged regularly Figure 10-22

Seawalls and beaches Seawalls are built to reduce erosion on beaches Seawalls can destroy recreational beaches Seawalls are costly and eventually fail Figure 10-24

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 Relocation of the Cape Hatteras lighthouse, North Carolina Figure 10C

Rip Tides

View From Beach