4.b. CASE STUDY: Mangawahi-Pakiri

Question 1

what is Mangawhai-Pakiri?

Answer 1

Mangawhai-Pakiri is a high quality reserve of sand suitable for the construction industry located 50km north of Aukland - large proportion used for replenishing Aukland’s tourist beaches

Question 2

why is this resource so valuble to Auckland?

Answer 2

Auckland is New Zealands largest metroploitan centre with a Population of over 1.5 million - Aukland accounts for over a third of New Zealand’s population and 35% of its GDP -

Question 3

how has Auckland economically developed? and why?

Answer 3

• rapid growth in business, finance and high-tech industry - 2015 saw a record 2.3 million foreign visitors. = huge amounts of tourist resort development
• Auckland’s economic growth is significant, driven by factors like a thriving port and airport, a diverse range of industries, and a strong skilled workforce. The region experiences rapid growth, fueled by exports and the demand for skilled labor.

Question 4

what is the dredged sand used for?

Answer 4

• replenishing aucklands tourist beaches
• building new holiday homes and resorts for tourists

Question 5

unintentional impacts casued by the dredging

Answer 5

• beaches are starved of sediment and have become wide and flatter = less effective at absorbing waves = higher energy waves are eroding beaches quickly = depletion of spits and dunes.
• fordune ridges are undercut by wave action = developing steep seaward facing scarps.
• loss of vegetation = beaches and dunes vunerable to wind erosion.
• total depletion of sandunes, beaches and sea beds
  = diminishing movement between major stores.

Question 6

what did the 1978 storms cause?

Answer 6

1978 storms caused a 28 m breach at the base of the mangawhai spit.
this + a second breach altered tidal currents leading to sedimentation of mangawhais harbour.
shallower water in harbour threatened the waterfront community with flooding.

Question 7

where is this sand thought to have come from?
what are current rates of depletion?
what is the effect of this?

Answer 7

• offshore sources due to relativley closed system + few sizable rivers in the area
• deposited during holocene [past 9000 yrs]
• non - renewable resource
• extracted at 5x inputs at pakiri beach
  = total depletion of sandunes, beaches and sea beds
  = diminishing movement between major stores.

Question 8

what is expected to happen to the coasts in the future?

Answer 8

• Studies by aucklands regional council suggest a likely increase in coastal erosion, with declining natural protection from storm evernts
• coastal retreat is already evident and attributed to both sand extraction and limate change/ rising sea levels.
• longterm retreat in a streatch of 11-48m is expected to be 35m by the end of the century.

Question 9

past + Current rates of extraction

Answer 9

past 70 years;
- 1994-2004 165,000 m3/yr extracted
- mining ended at magawhai in 2005 [ongoing at pakiri beach]
- rates at pakiri = 75,000m3/yr untill 2020