2b.9a

Question 1

What local factors can increase flood risk on some low-lying and estaurine coasts

Answer 1

(height, degree of subsidence (2.151 and -3.076 mm/yr), vegetation removal);
- note global sea level rise further increases the risk
- CS = ny city
- $52bn nvestment into sea gates across mouths of major bays and inlets along New York Harbor, including Jamaica Bay

Question 2

Why is flood risk an issue in NY

Answer 2

US Eastern sea-board (coastline)
One of the most populated coastlines, and particularly low-lying
12% of the US live there

Question 3

Why is NY low lying (first local flood risk factor)

Answer 3

• Coastal plains – beaches, tourism, access
• Estuaries – good for trade, e.g. Thames
• Deltas – fertile land, e.g. Nile / Mississippi
• high level of exposure to sea level rise due to its coastal location on the Hudson estuary and its barrier shoreline on the Atlantic Ocean,e

Question 4

What human activities increase flood risk

Answer 4

• Mangrove deforestation (e.g. woods / charcoal), which could reduce wave height (40% for first 100m) and stabilised sediment, and storm surge heigth (0.5m per 1km
• Groundwater extraction, which causes subsidence
• River straightening (e.g. for navigation), so sediment is propelled offshore faster

Question 5

How do people affect the height of land

Answer 5

Can cause isostatic sinking
The height of land: Reclaimed land can exist below sea-level (protected by sea walls)

Question 6

Why does hieght affect local flood risk

Answer 6

• Low lying coastlines are only 1-2 m high above (high tide) sea level so at risk from flooding
• Temporary flood risk from storm surges, permanent flooding from global sea level rise

Question 7

Give an example of height increasinf flood risk

Answer 7

The Maldives archipelago in the Indian Ocean has a population of 340,000 spread across 1,200 islands
1) The highest point in the Maldives is only 2.3 m above sea level
2) Malé, the main island and capital, is protected by a 3 m sea walT

Question 8

How does subsidence affect local flood risk

Answer 8

• Low lying coastlines in estauries, deltas or outbuilding zones are subject to natural subsidence through the settling and compaction of recently deposited sediment
• However, subsidence is usually outpaced by fresh deposition and the bioaccretion of organic matter
• Deltas experience periodic isostatic subsidence when the weight of the delta sediment reaches the threshold sufficient to cause the crust to depress - leading to marine transgression and flooding

Question 9

example of subsidence increasing locsal fllood risk

Answer 9

• 50 large islands in the Ganges-Brahmaputra delta subsided by 1.5 m since 1960
• Partly due to isostatic crustal depression and partly due to water abstraction by occupying populations, partly due to natural settling of sediment while the earth bund flood protection prevents compensation fresh sediment deposition

Question 10

Give an example of vegetation removal

Answer 10

• An estimated 50% world’s mangrove forest removed since 1950 - 1/4 of the loss for the creation of shrimp farms, and lots removed for tourist beaches
• Bangladesh contains the 180 km Sundarbans, the largest mangrove forest in the world. However, 71% is experiencing some vegetation removal. Some parts are eroding at 200 m p.a

Question 11

Why is vegetaion removal bad

Answer 11

• Vegetation stabilises existing sediment and traps new sediment, raising the height of the land above sea level
• Vegetation absorbs wave energy, reducing wave impact and erosion, and reduces the distance waves travel onshore before the energy is exhausted
  An 100 m belt of mangrove forest is estimated to reduce wave height by 40%
  A 1 km belt of mangrove forest reduces the height of a storm surge by 0.5 m

Question 12

How does gloval sea level rise increase local flood risk

Answer 12

• IPCC predicts a further 18-59 cm rise in sea level by 2100
• Bangladesh - a 40 cm sea level rise would permanently submerge 11% of Bangladesh, creating 7-10 million environmental refugees
• Maldives - 50 cm sea level rise would permanently flood 77% of the Maldive Islands’ land area

Question 12

How does gloval sea level rise increase local flood risk

Answer 12

• IPCC predicts a further 18-59 cm rise in sea level by 2100
• Bangladesh - a 40 cm sea level rise would permanently submerge 11% of Bangladesh, creating 7-10 million environmental refugees
• Maldives - 50 cm sea level rise would permanently flood 77% of the Maldive Islands’ land area