Coastal Environments Final Exam

Delta

A coast formed from sediment that is deposited where a river flows into an ocean or lake.

Known for their presence on passive margins/depositional coasts

Less than 1% of the world's coasts, yet among the most economically important:

River Transportation, Source of Petroleum, etc.

River Dominated Delta

Bird Foot Shaped Delta

Long arms with marsh in between

Mississippi River Delta, Yangtze River Delta in China

Tide Dominated Delta

Cuspate (Very pointed) shaped, has defined sand bars/ridges

Ganges River Delta

Wave Dominated Delta

Shield/Bow shaped

Nile, Sao Francisco Deltas

Upper Delta Plain

Area of the delta that is still mostly river, but has a small amount of marine influence

Lower Delta Plain

Area of the delta where the water fans out.

Strong marine influence and is often controlled by the tides

Delta Apron

Area of the delta where sediment brought down from the river is deposited down slope off coast

Delta front

Location where the delta river channel meets a body of water and produces a sandy bar at the edge known as an apron.

Delta Migration

Deltas change in morphology over time due to sea level and sediment level changes

The river always tries to flow down the steepest path/gradient

When sediment builds down a path over time, it becomes less steep, making the path of the river change

Louisiana formation

Enough carried sediment to slow down the velocity of the river to the point almost all sediment is dropped at the mouth of the river, forming a delta.

What is required for a river opening to be considered a delta?

Old River Control Project

Louisiana project by Army corps of Engineers to prevent MS River from changing courses to Atchafalaya River to protect the city of New Orleans' water supply.

Worries of failure?

Reef

Positive relief on the seafloor

Rock, oysters, tube worms, cyanobacteria

What types of reefs are there Other than Coral?

Coral Reef

Marine version of a tropical rain forest

Most diverse ecosystem

>25% of Marine Life in Coral Reefs

More species per area than any other marine habitat

1000's of species, perhaps 1 - 8 million undiscovered species

$ Billion industry

<1% of ocean

Fringing Coral Reef

Formation of a new coral colony around a volcano above the water's surface

Reef forms around the margin of the new, young volcano

Barrier Coral Reef

As the volcano ages, its magma source diminishes and it shrinks

The growth of the coral grows and outpaces the rate of deposition, forming shelves underneath the water

Atoll

When the volcano becomes completely submarine, only rings of coral can be seen above the surface

This indicates the former outline of the volcano that was once present

Coral symbiotic relationship

Coral + Dinoflagellates

Algae inhabits coral tissue

Algae provide sugars (90% of coral diet), amino acids, fats

Help build calcium carbonate exoskeleton

Coral provide protection from grazers, fertilizers

Coral Bleaching occurs when algae leaves the coral

Indo-Pacific Ocean (Only a few in the Atlantic)

Where are most coral reefs located in the world?

Threats to Coral Reefs

Tectonic Uplifts

Coral Bleaching

Blackband and whiteband disease

Acidification

Death of keystone species in reefs

Overfishing

Invasive species (Clownfish)

Other:

Pollution, Eutrophication, Cruise Ship Disposal

Tidal Inlet

Small channels that divide barrier systems

Connect a lagoon to the sea

Must be maintained by the tides

More prominent in the East US Coast

Ex: Ocracoke

Macrotidal: Georgia/SC (Small wave energy)

Microtidal: NC (Large wave energy)

Tidal Inlet Sediment Movement

Constraint through inlet increases the velocity of tidal flow, causing it to move more sediment

During low tide, sediment comes into lagoon and is deposited

During high tide, sediment is rushed out of the lagoon and is deposited outside the tidal inlet

Flood Tide Delta

A tidal delta built on the sound side of a tidal inlet

Created by deposited sediment

Tide comes in through inlet throat and drops sediment here, creating a shield shaped floodtide ramp

Ramp creates an ebb shield that redirects flow during high tide

Ebb Tide Delta

A tidal delta built on the ocean side of a tidal inlet

Deposited sediment here is worn down by the waves, creating sand bar-like features

This area becomes pointed, which is called a swash platform

Area where sediment ends out to sea is called Terminal Lobe

Inlet Sediment Bypassing

Particle of sediment moves according to LST

Goes into tidal inlet during flood tide, gets caught on flood tide ramp

Gets knocked off during ebb tide and gets attached to swash platform

Eventually moves again down coast due to LST

Inlet Migration

Inlets shift south over time due to LST

Can make bridges difficult to build across them

Rate is not constant, so inlet size can vary

Erosion on north side, deposition on south side

Estuary

NOT a Delta

Semi-Enclosed

Terrestrial Run-Off = Seawater Dilution

Brackish water (mixing of salt/fresh water)

Boundary Fluctuation

Protected from Wave Action

Coastal Plain Estuary (Drowned River Valley)

An estuary formed by rising sea level flooding a coastal river valley

Hudson River, Thames River (UK)

Fjord Estuary (Glacial Valley)

An estuary in a fjord, a steep, submerged, U-shaped valley

VERY HIGHLY Stratified

Juan de Fuca Strait (WA/Canada), Loch Ness (Scotland)

Tectonic Estuary

An estuary formed when a depression along a fault line fills with water

San Francisco Bay (California)

Bar Built Estuary

A shallow lagoon separated from the open ocean by a bar deposit such as a barrier island

Mississippi Sound (MS/Gulf)

Salt Wedge Estuary (River Dominated)

An estuary in which rapid river flow and small tidal range cause an inclined wedge of seawater to form at the mouth.

Salinity changes more with depth than across horizontal

Quadrant 1 concentric radial graph-like appearance

Partially Mixed Estuary (River Dominated)

An estuary in which an influx of seawater occurs beneath a surface layer of fresh water flowing seaward. Mixing occurs along the junction.

Negative Tangent graph-like appearance in stratification

Well Mixed Estuary (River Dominated)

An estuary in which slow river flow and tidal turbulence mix fresh and salt water in a regular pattern through most of its length.

Straight line/no stratification (no wedge)

Wave Dominated Estuary

Narrow entrance to estuary

River flow and wave energy is high

Low turbidity (Clear water)

Wind mixing

Low Lying areas (Central Basin)

Most mixing occurs in Central Basin (Below sea level)

Tide Dominated Estuary

Diverse range of estuary habitats

Larger entrances

Alternating beds of mud and sand

Wood boring trace fossils

River Dominated Estuary

Drain directly into the ocean/sea, estuary not a bay

Low lying areas inundated due to sea level rise

Strong river overrides tides

Importance of Estuaries

Buffer from ocean (waves/storm surge)

Protects other environments/ecosystems from sea

High biodiversity, but low variation

Sustainable fishing (Shellfish)

Filter toxins and sediments (High nitrogen)

Mangroves (Mangrove Coasts)

Can survive in marine environments

Indicator of high water salinity in low marsh regions (Red variant)

Black variants are further back, roots are exposed by tides. Needs tides to bring in salt and nutrients. Medium to high marsh

White variants are furthest back and least cold/saline tolerant (Button Bush)

Coastal Engineering

Needed to due to threat of Sea Level Rise/Transgression

Protects Structures/Buildings

Protects Infrastructure(Roads/Airports/Pipelines)

Protects Economic Resources:

- Beach/Ocean Based Tourism Economies/Commercial Shipping/Fishing Harbor Access

- Recreational Boating/Fishing Harbor Access

Environmental Management (Protection of Eroding Wetlands)

Sea Wall

Steel/concrete wall that protects property temporarily, but also increases beach erosion by deflecting wave energy onto the sand in front of and beside it.

High waves can also wash over these and destroy them and property.

Not aesthetic

Stone version (rip-rap)

Galveston, TX

Groin

Structures that extend from the beach into the water (perpendicular to coastline) and block LST. They help counter erosion by trapping sand from the current.

These accumulate sand on their updrift side, but erosion is worse on the downdrift side, which is deprived of sand.

Jetties (Jetty)

A pair of structures extending into the ocean at the entrance to a harbor or river that are built for the purpose of protection against storm waves and sediment deposition.

Interrupt the movement of sand, causing deposition on the upcurrent side

Erosion by sand starved currents occurs downcurrent from these structures

Breakwater

A barrier that protects a harbor or shore from the full impact of waves

Similar to a sea wall, but nearshore rather than on the shore

Causes deposition closer to shore where the structure is present

Erosion where the structure is not present, not aesthetically pleasing

Salt Marsh

Salinity determined through vegetation

Very productive

Predominantly grasses

Sediment consists of peat (organic material), muddy silt from upstream, and sands from ocean tides

Beach Nourishment

Artificial placement of sand on a beach

Popular on Gulf and East coasts of US

Most aesthetically pleasing approach, but only temporary

Less harsh than hard stabilization methods

Helps protect property from sea level rise

Very expensive

Benthic Ecosystem Destruction

Managed Retreat

The organized migration of human population/certain structures away from the coast to avoid sea level rise

Economic Disruption

Refusal - Counters Population Trends

Lose of Property Value

Threats to Human Coastal Habitation

Sea Level Rise, Storm Surge/Waves destroying structures, severe flooding, costly disaster repairs

Federal/state tax money, FEMA (Flood insurance)

Who currently pays for beach structures being built and insurance for those who live on the coast?