Coasts - Case Study - Mangawhai-Pakiri - Coastline Used by People

Question 1

Where is the Mangawhai-Pakiri coastline?

Answer 1

New Zealand

Question 2

What is sand used for? (4)

Answer 2

1. Construction
2. Concrete making
3. Glass manufacturing
4. Beach replenishment

Question 3

Why is the sand in the nearshore zone at Manghawai-Pakiri useful? (3)

Answer 3

1. High quality
2. Suitable for the construction industry
3. Just 50km north of Auckland it is convenient for NZ’s largest and economically most dynamic metropolitan region

Question 4

What is the population of the Auckland region?

Answer 4

Over 1.5m (accounts for 2/3 NZ’s total pop & 35% of country’s GDP)

Question 5

How is the region growing rapidly?

Answer 5

Apart from business, finance and high-tech industry, tourism centred on Auckland’s outstanding coastal amenities is booming (2015 saw 2.3m foreign visitors)

Question 6

How long has sand dredging operated for & how much has been extracted?

Answer 6

1. Operated for over 70 years
2. 1994-2004, 165,000m3/year was extracted

Question 7

What are current rates of extraction?

Answer 7

Ended (2005) at Mangawhai but has continued at Pakiri Beach

Current rates of extraction = 75,000m3/year until 2020

Question 8

What is the sand extracted used for? (2)

Answer 8

1. Replenishing Auckland’s tourist beaches
2. Construction industry (many holiday homes & hotels being built in area)

Question 9

How has sand been deposited on the coastline? (3)

Answer 9

1. During Holocene (past 9,000 years) = non-renewable
2. Few sizeable rivers in area
3. Most thought to have been derived from offshore

Question 10

What type of system is the coastline essentially & why significant?

Answer 10

1. Essentially a closed system
2. Outputs of sand not replaced by inputs from rivers, and waves from offshore
3. Extraction rates at Pakiri Beach exceed input rates by a factor of 5
4. Effect = deplete total sand supply stored in dunes, beaches & on sea bed (up to 2km offshore) = movements of sand between major stores have diminished

Question 11

How is the depletion of sand impacting on coastal landforms? (4)

Answer 11

1. Beaches (starved of sediment) = wider and flatter = less effective in absorbing waves
2. Higher energy waves erode beaches and landforms (i.e. dunes and spits) become vulnerable
3. Foredune ridges undercut by wave action, developing steep, seaward-facing scarps
4. Loss of vegetation cover = susceptible to wind erosion

Question 12

What happened in the 1978 storms? (2 + although…)

Answer 12

1. 28-metre breach at the base of the Mangawhai spit- this (and second breach) altered tidal currents = sedimentation of Mangawhai’s harbour
2. Shallower water in the harbour threatened Mangawhai’s waterfront community with flooding

ALTHOUGH subsequent dredging of the harbour and groyne construction on the spit has helped restore some equilibrium

Question 13

What complicates the fact that coastal retreat is attributed partly to sand extraction?

Answer 13

Climate change & rising sea level

Question 14

What is long-term retreat by the end of the century estimated at? (2)

Answer 14

1. 35m
2. Width of coastal zone susceptible to erosion varies (48-111m) but this estimate is higher than any of Auckland region’s other 123 beaches