Sand mining along the Mangawhai-Pakiri coastline of New Zealand
Economic Development
Sand essential material resource in modern economy
wide range of uses e.g. construction, concrete making, glass manufacture and beach replenishment
high-quality sand resource occurs in nearshore zone at Mangawhai-Pakiri
This sand is high-quality and suitable for the construction industry
Located 50km North from Auckland
convenient for New Zealand's largest and economically most dynamic metropolitan region
Pop of over 1.5 million- Auckland region accounts for a 1/3 of New Zealand's total population and 35% of the countries GDP
the region is growing rapidly
business, finance and high-tech industry
Tourism centred on Auckland's outstanding coastal amenities- booming: in 2015 saw a record 2.3 million visitors
Offshore sand mining and the sediment budget
nearshore sand dredging on the 20 km long coastline between Mangawhai and Pakiri- operated over 70 yr.
between 1994-2004,165,000 m3/ year were extracted
2005 mining stopped in Mangawhai
continues in Pakiri
current stages of extraction are 75,000 m3/yr. until 2020- large proportion of this sand for replenished Auckland's tourist beaches
non-renewable resource
deposited during Holocene (past 9000 yrs)
few sizeable rivers in the area
most sand, therefore, is thought to derive from offshore
The coastal sediment budget is essentially a closed system
thus outputs are not replaced by inputs from:
rivers
offshore waves
Extraction rates at Pakiri exceed inputs by a factor of 5
Effect of mining is therefore to:
deplete the total sand supply
store in dunes
store on beach
store on the sea bed (up to 2km offshore)
As a result movements of sand between the major stores have diminished
Impact on coastal landforms
Beaches starved of sand is having become wider and flatter and are less effective in absorbing wave
foredune ridges are undercut by wave action, dev. steep, seaward-facing scarbs
higher energy wave this erode beach- landforms like dunes and spits become vulnerable