6 Human Activity - Mangawhai-Pakiri

Question 1

Background

Answer 1

• Both beaches located on New Zealand’s North Island
• Pacific coast of Northlands Peninsula, 50km north of Auckland
• Sand high quality and suitable for the construction industry
• Haukari Gulf is site of the biggest seabed mining operations in NW waters
• Rules on seabed mining less restrictive eg illegal in UK to extract landward of the 19m depth or within 600m of shore

Question 2

Need for sand: What is sand an essential mineral source for?

Answer 2

Construction, concrete, glass manufacture, beach replenishment

Question 3

Need for sand: How much is the sand sold for?

Answer 3

approv NZ$50/m3, or which the NZ government takes NZ$1.70/m3 in royalties

Question 4

Need for sand: What was announced in the 2016 Unitary Plan?

Answer 4

In the 2016 Unitary Plan, Auckland City Council announced plans to build 422000 extra houses over the next 25 year - same number built over the previous 160 years
Needs 2.5x greater construction rate than achieved in the previous 25 years

Question 5

Need for sand: How much did Auckland’s population increase by?

Answer 5

1995-2016
Increased by 20000/year - fastest ever period of growth

Question 6

Need for sand: How much did Auckland’s GDP grow by?

Answer 6

2000-2018
NZ$52 billion to NZ$93 billion

Question 7

Need for sand: What has the sand mined from Mangawhai-Pakiri used for?

Answer 7

Replenishing Auckland’s tourist beaches (Mission Bay, Kohimarama and St Heliers)

Question 8

Need for sand: What is Aucklands and what is its significance?

Answer 8

• New Zealand’s largest urban area (pop 1.5 million - 1/3 of the population)
• Accounts for 37% of GDP and 35% of its workforce
• 235% larger than the next largest urban area (Wellington)
• Home to thriving financial and high tech industries as well as tourism, centred around the outstanding coastal amenities
• 2015, 2.3million foreign visitors

Question 9

Offshore sand mining/sediment budget: What system could the coastal sediment budget be classed as?

Answer 9

Essentially a closed system
Outputs from sand mining exceed the inputs from rivers and offshore sources by a factor 5

Question 10

Offshore sand mining/sediment budget: How long has the nearshore sand dredging been occurring?

Answer 10

• On the 20km coastline between Mangawhai and Pakiri beaches has been taking place for over 70 years
• Between 1994 and 2004, 165000m3/year was extracted using suction dredging from water 5-20m deep
• Extraction at Mangawhai ended in 2005, but continues at Pakiri at rates of 76000m3/year

Question 11

Offshore sand mining/sediment budget: What did the NZ’s Environment Court grant in 2006?

Answer 11

2 extraction permits for Pakiri, lasting until 2020, despite strong opposition on environmental grounds from Auckland Regional Council and Friends of Pakiri

Question 12

Offshore sand mining/sediment budget: Why is there little fluvial sediment input and what does this mean?

Answer 12

Few sizeable rivers
With input<outputs, the effect of mining is to deplete the sand stores (dunes, beaches and sea bed up to 2km offshore)

Question 13

Offshore sand mining/sediment budget: Where does the beach and nearshore sediment at Mangawhai-Pakiri originate from?

Answer 13

Dates from the last 9000 years (the Holocene)
Pushed up from offshore sources by rising sea levels (the Flandrian Transgression) was Warth’s climate warmed in the late Pleistocene/early Holocene
This process and sediment input ended c.6000BP, when sea levels stabilised

Question 14

Offshore sand mining/sediment budget: Where does the Holocene sand lie?

Answer 14

6-10m deep in the dunes at the back of the beaches, 2-6m deep on the beach and only 0.3m deep in the offshore zone
Underlain by older Pleistocene sand, but this is of less value due to iron impurities

Question 15

Offshore sand mining/sediment budget: Why is the sand extraction unsustainable?

Answer 15

Sand is non-renewable resource along this coastline and extraction at current rates is unsustainable

Question 16

Offshore sand mining/sediment budget: Why is the rate of erosion increasing along the beaches and dunes?

Answer 16

The deeper water created by dredging allows higher energy waves to approach the shoreline

Question 17

Impact on coastal landforms: What is the impact on beaches?

Answer 17

Beaches starved of sediment. come wider and flatter and are less effective at absorbing wave energy

Question 18

Impact on coastal landforms: Why is there more erosion of landforms?

Answer 18

Higher energy waves can erode landforms such as dunes and spits

Question 19

Impact on coastal landforms: What is the prediction for erosion rates?

Answer 19

ARC predict rates will increase due to declining natural protection, eustatic sea level rise and more frequent storm events

By 2100, 35m of retreat along the Mangawhai-Pakiri coastline is expected, vulnerable to erosion between 48-111m. Higher than any of the other Auckland regions other 123 beaches

Question 20

Impact on coastal landforms: How has dredging and groin construction been used to restore some equilibrium?

Answer 20

In 1978, storms caused a 28m breach at the base of Mangawhai spit
Altering tidal currents and increased sedimentation in Mangawhai Harbour
Shallower water in the harbour –>threat to boat navigation and seafront properties with flooding
Restored some equilibrium after this

Question 21

Impact on coastal landforms: What is undercut by wave action and what does this lead to?

Answer 21

Foredone ridge
Creates steep seaward-facing scarps and loss of vegetation cover makes them vulnerable to wind erosion

Question 22

Other impacts: What is the impact on fisheries?

Answer 22

Reduction in quality of local surf and harmful impact on fisheries