ENV 101 - Module 2

Coastal challenges

Coastal zone

The area of dry land and adjacent ocean space where terrestrial and oceanic processes impact one another.

How do inland activities impact the coast?

Connection between them by rivers.

Hydrodynamic

Relates to the movement of water.

Morphodynamic

Relates to the changes in Earth’s surface in response to fluid processes.

Fluid processes

Processes involving water or air.

Coastal hydrosystem

A coastal feature that spans a gradient from near-coast freshwater to marine.

Whta are the three types of coastal hydrosystem?

Open coasts, partially enclosed, closed coasts.

What are the four subclasses of partially enclosed systems?

Unrestricted, spit enclosed, barrier beach enclosed, intermittent with ribbon lagoon.

What features are used to classify a coastal hydrosystem?

Ocean exposure, tidal effects, geological characteristics, water body type.

Lacustrine

Relating to freshwater lakes.

Palustrine

Relating to inland wetlands.

Riverine

Relating to rivers.

Estuarine

Relating to the mixing of salt and freshwater.

Which NZ district has the most variety of coastline types?

Southland.

Which NZ district has the least variety in coastline types?

Gisborne.

What are the impacts of climate change on coastlines?

Sea level rise, flooding/inundation, erosion, warming oceans, ocean acidification.

Which planetary boundaries are most important to coastal systems?

Climate change, land use change, ocean acidification, biosphere integrity, biogeochemical fluxes.

During the 20th century, were partially enclosed systems more impacted by climate or non-climate drivers?

Non-climate drivers.

Mean sea level

The average position of the ocean without influence of tides.

Relative sea level

The level of the ocean relative to adjacent land - accounts for land uplift and subsidence.

How much has MSL increased over the last century?

21-24cm

On average, how much has MSL been increasing per year over the last century?

2-3mm/yr

How much is relative SLR in the western Pacific?

5-10mm/yr

How much is relative SLR along the Gulf Coast?

10-14mm/yr

What are the impacts of SLR on coasts?

More extreme and frequent flooding and erosion, larger waves and storm surge, increase in the water table, salinisation of groundwater, economic, social, and cultural impacts.

How has the rate of SLR changed over the past few decades?

It has increased.

How much excess heat is absorbed by the ocean?

90%

Where are oceans warming more and faster?

At higher latitudes.

How is sea level measured?

Tide gauges (local) and satellite altimetry (global).

How is ocean warming measured?

Conductivity-temperature-depth (CTD) sensors, remote sensing.

Sea surface temperature (SST)

The average temperature of the top layer of the ocean.

Why does ocean temperature continue to rise after CO2 emissions end?

Due to the stored heat.

How is remote sensing used to measure SST?

The infrared radiation emitted by the ocean is measured, with resolution of 1-50km.

What are the impacts of ocean warming?

Marine heatwaves, ecological impacts, economic, social, cultural impacts.

Do oceans or land warm faster?

Land.

How much of Earth’s surface do oceans cover?

70%

How much of the emitted CO2 do oceans absorb?

25%

How does absorbed CO2 increase the acidity of the ocean?

CO2 forms carbonic acid with water, which breaks down in bicarbonate and hydrogen ions, decreasing the pH.

How is ocean pH measured?

Using sensors.

What factors cause variations in ocean pH?

River outflow, biological activity, pollution.

What are the impacts of ocean acidification?

Dissolution of CaCO3 shells and reduced ability of organisms to produce shells.

How does SLR affect coral reefs?

Affecting islands, wave breaking, reef growth.

How do warming oceans affect coral reefs?

Coral bleaching.

How does ocean acidification affect coral reefs?

Dissolution and slowing growth of corals, sediment production.

What benefits do coral islands bring?

Providing land, sediment, and a breakwater.

What are the impacts of SLR on small islands?

Frequent/severe flooding, loss of livelihoods, forced migration, increased erosion, saltwater intrusion into groundwater, loss of habitat and biodiversity.

Why are coral atolls particularly vulnerable to SLR?

They are low lying (2-3m asl) and narrow.

Coastal flooding

The inundation of low-lying land near the coast with water.

Under 30cm of SLR, how common will extreme sea level events be by 2050?

Annual.

How does SLR contribute to coastal flooding?

It allows water to travel further inland and is changing the most out of all factors.

What factor is the main driver of increased coastal flooding?

Sea level rise.

How do tides contribute to coastal flooding?

Larger tides bring more water further inland.

King tide

A perigean spring tide.

How often do king tides occur?

3-4 times a year.

Storm surge

A bulging up of water in a low-pressure system.

How does storm surge contibute to coastal flooding?

It is pushed towards the coast by winds and brings more water here.

How do storms/cyclones contribute to coastal flooding?

They contribute to storm surge.

How will storms/cyclones change in the future?

Becoming less frequent, more intense, and moving towards the poles.

Wave setup

The increased water level near the coast.

How do waves contribute to coastal flooding?

Breaking waves transfer energy to the water column, elevating the sea level.

How does tolerance contribute to coastal flooding?

People’s response to more frequent and severe flooding will impact the coastline.

Megacities

Cities with a population over 10 million.

Where are most megacities located?

Along coastlines.

Why is Jakarta more vulnerable to coastal flooding?

Sea level rise and land subsidence (10cm/yr).

Why is New York more vulnerable to coastal flooding?

More intense hurricanes that move further north and threaten the barrier islands.

Why is Shanghai more vulnerable to coastal flooding?

Rapid urbanisation.

Why is Dhaka more vulnerable to costal flooding?

Low-lying land, meltwater from the Himalayas.

By 2050, how many people in coastal cities will be affected by regular flooding?

Over 800 million.

Coastal erosion

Landward movement of the coast and shoreline retreat due to removal of sediment and bedrock.

What are the three types of drivers of coastal erosion?

Hydrodynamic, extremes, anthropogenic.

Hydrodynamic drivers of erosion

Extreme drivers of erosion

Include tsunamis, storm surge, cyclones. These events accelerate erosion and transport it to different areas, which can create islands and storm ridges.

Anthropogenic drivers of coastal erosion

Human-made drivers, including climate change, SLR, and construction on/near coastlines.

How does construction of sea walls impact coastal erosion?

It prevents movement of the coastline in one area, meaning that erosion is concentrated in adjacent areas.

How much land on the Louisiana coast has been lost due to erosion?

5000km²

What factors have contributed to the erosion in Louisiana?

SLR, land subsidence, loss of barrier islands and wetlands, dams, hurricanes, storm surge, saltwater intrusion due to canals.

Climate prediction

Probabilistic estimates of future natural conditions.

Climate projection

Scenario-based estimates of future climates under assumptions of human-related activities.

Hindcast

Prediction of the past. 

Forecast

Prediction of the future.

What processes are involved in understanding coastal flooding and erosion?

Sea level rise, waves, tides, storm surge, tectonics, sediment supply, human modifications.

Wave climate projections in New Zealand show that there will be an ____ in wave height in the south and west. 

increase

Wave climate projections in New Zealand show that there will be a ____ in wave height in the north and east.

decrease

What direction do waves travel along the east coast of New Zealand?

Clockwise

What direction do waves travel along the west coast of New Zealand? 

Anticlockwise

Significant wave height

The average height of the top third of the tallest waves.

Hs

Significant wave height.

How much is storm surge typically in New Zealand? 

30-50cm

In New Zealand, storm surge is projected to increase in the ____.

south

In New Zealand, storm surge is projected to decrease in the ____.

north

What do projections of sea level rise show? 

The rate of SLR is increasing. 

Vertical land movement (VLM)

Looking at whether the land is uplifting or subsiding.

What infrastructure in New Zealand is most vulnerable to coastal flooding?

Roads, railways, Auckland and Wellington airports, DoC land, culturally and archaeologically important sites.

Where is exposure to the risk of coastal flooding increasing at a constant rate? 

Auckland, Bay of Plenty, Waikato. 

Where is exposure to the risk of coastal flooding accelerating rapidly with SLR?

Hawkes Bay, Wellington, Canterbury.

What areas in New Zealand are most significantly affected by coastal flooding?

Firth of Thames, South Dunedin.

Why is the Firth of Thames vulnerable to coastal flooding?

The land is subsiding and it is built on low-lying reclaimed land.

Why is South Dunedin vulnerable to coastal flooding? 

It is a low-lying area with poor drainage, a high water table, and rising groundwater. 

How much damage did the June 2015 floods do in south Dunedin?

$138 million and 1200 homes damaged.

What places in New Zealand are most affected by coastal erosion?

Port Waikato, Kapiti Coast, Orewa Beach.