Mangawhai pakiri

Question 1

Uses of holocene sand mined

Answer 1

Beach replenishment
Glass and concrete manufacturing
Construction industry

Question 2

Why this area?

Answer 2

Auckland nearby
1/3 population of NZ so high demand for industry and tourism and good trains and economy

Holocene sand

Question 3

Near- shore sand extraction rates

Answer 3

75000m3year-1
Used to be 165000m3year-1
Stopped at Mangawhai but still mined at Pakiri (spacial variation)
Most sand used to replenish Auckland

Question 4

Problems

Answer 4

Sand from Holocene era 9000 years ago so non renewable bc no major rivers or off shore waves to input sediment (closed system)
Extraction 5X input so shrinks supply and influences stores and processes
1978 28m spit breached in Storm
High energy waves lack sand for protection

Question 5

Impact on tidal currents

Answer 5

Breach altered tidal currents
Increased sedimentation in Mangawhai harbour
Shallower and higher flood risk for Mangawhai community
Dredging harbour helps

Question 6

Impact on beaches

Answer 6

Flatter so less good at absorbing high energy waves.
So, sand banks collapse in mass movement chasing steep Seward facing scarps
Less vegetation due t steep slopes so move at risk from sub-ariel erosion

Question 7

Future change

Answer 7

Out if equilibrium
Rising sea level and mining causes king term retreat
Higher rates of erosion
Predicted 35m retreat by end of centuary
Greater differential erosion when compared to nearby coastlines