1.4 Human Impacts

Question 1

Causes of Flooding?

Answer 1

Human - intensify
- Dams
- Deforestation - taliban kpk valley until 2009 - 2010 flood
- Land use/urbanisation - lower mersey, 25% increase - 25,000 homes

Drainage Basin Characteristics - intensify
- Size - 1million square kilometres
- Shape - River mole, teardrop
- Drainage density

Climate - cause
- Monsoon / high rainfall event - KP & Punjab 300to500mm in 5 days average in pakistan was double normal in july
- Glacial Melt - Rupal Glaciar - many in KP

Question 2

How to ameliorate & prevent floods?

Answer 2

Forecasts + Warnings;
- Prediction
- Forecasts

Hard Engineering
- Artificial Levees
- Channel Enlargement
- Resevoirs & Dams

Soft Engineering
- Flood Abatement
- Land Use Zoning
- Flood Proofing

Question 3

How does prediction of floods help prevent flooding?

Answer 3

Recurrence intervals - a statistical calculartion, to determine frequency of a flood, estimate size and likleyhood
- can then be used to reduce the impacts of flooding
-For example FEMA USA use these to determine flood insurance and where to place defences such as floodwalls or levees

Question 4

How does forecasting & warning help prevent flooding?

Answer 4

• Use satellites rains gauges and discharge monitors to see if a flood could happen
• then warnings can be sent downstream to those who may be effected by it

Example; Bangladesh Flood 2020
- FFWC used rainfall data, satellite imagery, and upstream river levels- - Which lead to up to 5 days of warning was provided.
- evacuations and temporary shelters in schools

Question 5

How does artificial levees help prevent flooding?

Answer 5

• Increased capacity so less likely to exceed bankfull and overtop

Example
- Mississippi, 4,500 km of levees along river -2011 flood helped a bit - New Orleans prevented submerging but breached in many places - lead to false state of secuity - some towns flooded by 80%
- 6,000km in Indus

Question 6

How does channel enlargement help prevent flooding?

Answer 6

• Large and wider by dredging - reduce channel roughness
• can carry more water + less friction
• long term issues downstream e.g. more sediment in water so greater deposition downstream

River Quaggy - London
- Prevented minor flooding in Lewisham due to channel enlargement in 2000s

Question 7

How do reservoirs & dams prevent flooding?

Answer 7

• Less overall discharge - by storing water
• Only work on small drainage basins

200 along Mississippi to regulate discharge - didn’t rly help 2011

Question 8

How does flood abatement prevent flooding?

Answer 8

Uses methods such as; afforestation, terracing, contour ploughing, to reduce the amount of surface runoff and increase infiltration

Example;
Scheme in Pickering Yorkshire
- peak river discharge decreased by 20% due 40,000 trees planted

Question 9

How does land use zoning prevent flooding?

Answer 9

Areas of high risk not developed on
- Soldier’s grove Wisconsin - whole cbd moved

Question 10

How does flooding proofing prevent flooding?

Answer 10

Building to amelirorate e.g. houses on stilts on Ganges river Bangledesh