Mangawhai PAkiri - Sand mining New Zealand Flashcards
Why is sand so valuable and how is it used?
essential material in a modern economy - used for construction - concrete making - glass manufacture and beach replenishment - the sand in the near-zone of Mangawhai-Pakiri is high quality and suitable for the construction industry located 50km north of Aukland - large proportion used for replenishing Aukland’s tourist beaches.
How has Aukland changed?
Population of over 1.5 million - Aukland accounts for over a third of New Zealand’s population and 35% of its GDP - rapid growth in business, finance and high-tech industry - 2015 saw a record 2.3 million foreign visitors.
How land has sand dredging been occurring and how is it affecting the sediment budget?
Nearshore sand dredging on the 20k coastline has operate for over 70 years - between 1994 and 2004 - 165,000m3/year were extracted - Now at 75,000m3/year - mining has stopped at Mangawhai but continued at Pakiri.
Deposited in the Holocene sand is a non-renewable resource on the coastline - there a few sizeable rivers in the area - most sand is thought to have been driven from offshore - coastal sediment budget is essentially a closed system - output through nearshore mining is not replaced - extraction exceed a factor of 5 to replenishment - depleted the total store of sand - beaches and dunes and the sea-bed - movement between major stores have depleted.
What impact has it had on coastal landforms?
as the sediment cell is closed current rates of sand extraction are unsustainable - beaches starved of sediment are wider, flatter and less effective are absorbing wave energy - higher waves erode beaches and make spits and dunes vulnerable - loss of vegetation makes them susceptible to wind erosion .
1978 storms caused one 28m breach at the base of mangawhai spit - this and a second breach caused the sedimentation of Mangawhai-Pakiri’s harbour - shallow water threatened the waterfront community with flooding - dredging and groyne construction on the spit has helped restore some equilibrium.
How is it effecting coastal retreat?
Studies of the Mangawhai-Pakiri’s coastline by the Aukland regional council suggest that increased rates of coastal erosion are likely - natural protection is declining from extreme storm events - evident coastal retreat attributed to sand extraction - complicated by rising sea level and climate change - 35m by the end of the century - width of costal zone susceptible to erosion varies from 48-111m - higher than any other of Aukland’s 123 beaches.
