Beaches & Shoreline Processes

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Beaches & Shoreline Processes. Landforms and terminology in coastal regions. 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. - PowerPoint PPT Presentation

Transcript of Beaches & Shoreline Processes

Page 1: Beaches & Shoreline Processes
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• 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

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Landforms and terminology in coastal regions

BermBeach face

Notch

Wave-cutbench

Longshore bar

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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

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Summertime and wintertime beach conditions

Summertime beach Wintertime beach

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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”

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• Erosion• Deposition• Human Development

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Longshore current and longshore drift

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

• Longshore drift = movement of sediment caused by longshore current

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Features of erosional shores

• Headland• Wave-cut

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

terrace

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Headland

Eastern tip of Oahu

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Wave-cut Cliff

Ka‘ula

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Sea Cave w/collapsed roof

Na Pali Coast, Kauai

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Sea stack (collapse of sea arch)

Sea arch

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

Chain of Craters Rd., HI

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Sea Arch and Sea Stack

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Marine Terrace

Haunama Bay

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Features of depositional shores

• Spit

• Bay barrier

• Tombolo

• Barrier island

• Delta

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Spit

                                                                        

                                                                                                           

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Barrier Bay

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Tombolo

                                                            

Poipu Beach ParkKauai

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Formation of barrier islands

• Sea level rose after the last Ice Age

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

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Barrier IslandsFeatures:

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

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Barrier Beaches

                                                                                                                                                    

Red Sands Beach, Maui

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Barrier Islands

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DeltasFeature:

• Triangle deposit of sediment

Mississippi Delta Nile River Delta

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Features of Submerging Shorelines

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

• Ice ages• Global warming

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

• Shells

• Sponge spicules

• Calcareous algae

• Volcanic particles

• Shark teeth

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White Sand Beach

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Black Sand BeachBig Island

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Green Sand BeachBig Island

Mahana Bay, HI

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Red Sand BeachMaui

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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

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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.

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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

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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

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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

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Shoreline Hardening: Groin

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Shoreline Hardening: Groin

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Shoreline Hardening: Jetty

                                          

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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.

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Shoreline Hardening: Seawall

                                                                               

Waikiki Beach from the Halekulani Hotel.

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Lanikai

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Lanikai

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Beach ReplenishmentKohio Beach

10,000 cubic yards of sand pumped from off shore

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Beach ReplenishmentKohio Beach

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Beach ReplenishmentKohio Beach

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Before After

Beach ReplenishmentKohio Beach

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Beach ReplenishmentKohio Beach

Before

After

2006-2007

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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.

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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?