• the foreshore - the area most influenced by the high and low water marks and breaking waves.

• the backshore - submerged only during the highest tides and severest storms.

• the berm – the high point on the beach; the backshore-foreshore boundary. It changes seasonally.

Landforms and terminology in coastal regions

Landforms and terminology in coastal regions

BermBeach face

Notch

Wave-cutbench

Longshore bar

Light versus heavy wave activity

Light wave activity Heavy wave activity

Berm/long-shore bar

Berm grows and longshore bars shrink

Longshore bars grow and berm shrinks

Wave energy Low High

Time span Long Short

Characteristics Summertime beach: sandy, wide berm, steep beach face

Wintertime beach: rocky, thin berm, flattened beach face

Summertime and wintertime beach conditions

Summertime beach Wintertime beach

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”

• Erosion• Deposition• Human Development

Longshore current and longshore drift

• Longshore current = zigzag movement of water in the surf zone

• Longshore drift = movement of sediment caused by longshore current

Features of erosional shores

• Headland• Wave-cut

cliff• Sea cave• Sea arch• Sea stack• Marine

terrace

Headland

Eastern tip of Oahu

Wave-cut Cliff

Ka‘ula

Sea Cave w/collapsed roof

Na Pali Coast, Kauai

Sea stack (collapse of sea arch)

Sea arch

Puu Pehe (Sweetheart Rock) on the island of Lanai.

Chain of Craters Rd., HI

Sea Arch and Sea Stack

Marine Terrace

Haunama Bay

Features of depositional shores

• Spit

• Bay barrier

• Tombolo

• Barrier island

• Delta

Spit

                                                                        

                                                                                                           

Barrier Bay

Tombolo

                                                            

Poipu Beach ParkKauai

Formation of barrier islands

• Sea level rose after the last Ice Age

• Caused barrier islands to roll toward shore like a tractor’s tread

Barrier IslandsFeatures:

1. Ocean beach2. Dunes3. Barrier flat4. High salt marsh5. Low salt marsh6. Lagoon

Barrier Beaches

                                                                                                                                                    

Red Sands Beach, Maui

Barrier Islands

DeltasFeature:

• Triangle deposit of sediment

Mississippi Delta Nile River Delta

Features of Submerging Shorelines

Changes in Sea Level:• Tectonic movement• Isostatic adjustment• Worldwide (eustatic) changes in sea level

• Ice ages• Global warming

Composition of Beach sand in Composition of Beach sand in Hawaii:Hawaii:• Coral

• Shells

• Sponge spicules

• Calcareous algae

• Volcanic particles

• Shark teeth

                                        

      

White Sand Beach

Black Sand BeachBig Island

Green Sand BeachBig Island

Mahana Bay, HI

Red Sand BeachMaui

1. An abundant supply of loose sand in a region devoid of vegetation

2. A wind energy source sufficient to move sand grains

3. A topography whereby sand particles lose their momentum and settle out

Vegetated dune, Kanaha, Maui. Naupaka shrub and 'aki'aki and pohuehue (with purple flowers) ground cover at center, 'aki'aki (sparse ground cover) in background.

Close up of 'aki'aki. Photo from JOHNSTONE, 1997.

Close up of 'akulikuli. Photo from JOHNSTONE, 1997.

Close up of pohuehue, Honokahua, Maui Common name: beach morning glory

Sea-Level RiseSea-Level Rise Wave/Current ActionWave/Current Action

Coastal ErosionCoastal Erosion

Sediment DeficienciesSediment Deficiencies

• Sand mining• Dune grading• Sand impounding (behind shoreline structures)• Water quality degradation• Harbor/navigational channel construction

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

Shoreline Hardening: Groin

Shoreline Hardening: Groin

Shoreline Hardening: Jetty

                                          

Shoreline Hardening: Breakwater

                                          

Magic Island is a peninsula shooting off from Ala Moana Park. The beach is protected by a man-made breakwater that cuts off the action of the surf while allowing enough water circulation to keep the salt water fresh and clean.

Shoreline Hardening: Seawall

                                                                               

Waikiki Beach from the Halekulani Hotel.

Lanikai

Lanikai

Beach ReplenishmentKohio Beach

10,000 cubic yards of sand pumped from off shore

Beach ReplenishmentKohio Beach

Beach ReplenishmentKohio Beach

Before After

Beach ReplenishmentKohio Beach

Beach ReplenishmentKohio Beach

Before

After

2006-2007

Reasons to Protect Hawaii's Beaches

• Multi-billion dollar visitor economy • They are critical in flood and erosion

prevention • They are a part of Hawaii's culture and

heritage. • Beaches and dunes are important

elements of our shoreline environment and are critical to the health of the coastal marine ecosystem.

Inquiry

1. Types of hard stabilization include:_____.

2. Is there a way to slow down erosion without using hard stabilization?

3. Beach sand from Hawaii is composed of _____.

4. How is a sea stack formed?5. What are some key characteristics of

plants living on dunes?