1.4. The human impact

Question 1

Removal of trees and vegetation (Potential hydrological effects of urbanistation.)

Answer 1

Decreased evapotranspiration and interception; increase stream sedimentation

Question 2

Initial construction of houses, streets and waterpipes (culverts) (Potential hydrological effects of urbanistation.)

Answer 2

Decreased infiltration and lowered groundwater table; increased storm flows and decreased base flows during dry periods.

Question 3

Complete development of residential, commercial and industrial areas. (Potential hydrological effects of urbanistation.)

Answer 3

Decreased porosity, reducing time of runoff concentration, thereby increasing peak discharges and compressing the time destruction of the flow; greatly increased volume of runoff and flood damage potential

Question 4

Construction of storm drains and channel improvements. (Potential hydrological effects of urbanistation.)

Answer 4

Local relief from flooding; concentration of floodwater may aggravate flood problems downstream.

Question 5

Dams (Human impact on evaporation and transpiration)

Answer 5

Increase in evaporation due to the construction of large dams

Question 6

Urbanisation (Human impact on evaporation and transpiration)

Answer 6

Leads to a huge reduction in evapotranspiration due to the lack of vegetation. There may also be a slight increase in evaporation because of higher temperatures and increased surface storage.

Question 7

Urbanisation (Human impact on infiltration and soil water)

Answer 7

Urbanisation creates an impermeable surface, with compacted soil. This reduces infiltration and increases overland runoff and flood peaks.

Question 8

Deforestation (Human impact on interception)

Answer 8

Deforestation leads to:

1) a reduction in evapotranspiration
2) an increase in surface runoff
3) a decline of surface storage
4) a decline in lag time

Question 9

Abstraction and water storage

Answer 9

The removal of ground water has reduced the extent of the aquifer by 50% in large parts of certain countries.

In contrast some industrial areas, reductions in industrial activity have led to less groundwater being taken out leading to the rise of ground water, adding to the problem caused by leakage from ancient, deteriorating pipe and sewerage systems.
Resulting in:
1) surface water flooding
2) pollution of surface waters and spread of underground pollution
3) flooding of basements
4) increased leakage into tunnels

Question 10

Recurrence interval

Answer 10

Refers to the regularity of a flood of a given size.

Question 11

Disaster aid

Answer 11

Refers to any aid, such as money, equipment, staff and technical assistance that is given to a community following a disaster.

Question 12

CASE STUDY: Cause of Thailand floods 2011 (WoULDITCH)

Answer 12

Physical Factors
- Heavy rainfall - 23% above normal
- Tropical storms - remains of 4 tropical storms brought high rainfall
- Influence of tides - Effect of high tide from the gulf of Thailand causes water level to spill over Chao Phraya banks
Human Factors
- Rapid Urban Development - most of Bangkok’s surface areas are covered with houses, roads or paved surfaces
- Deforestation - rapid surface run-off
- Land subsidence - due to pumping of large amounts of underground water
- Release of water stored in dams - wrong calculations of water release and so excess was released - Bhumibol and sirikit dams
- Ineffective use of canals - left choked with silt

Question 13

CASE STUDY: Thailand Flood prevention (DARKU)

Answer 13

1) Klongs - excess water from river is drained into the canals
2) Artificial Levees - soil embankments to prevent flooding
3) Retention Bains - “Kaem Ling” - stores water temporarily in some areas (ponds) at high tide
4) Dams - Help control he flow through the Chao Phraya Basin
5) Underground drainage tunnels - double the efficiency of the city’s water drainage system

Question 14

CASE STUDY: Impacts of Thailand floods 2011

Answer 14

• World Bank ranked the 2011 Floods of Thailand as the world’s 4th costliest disaster in history
• Interrupted the global supply chain of automobile and electronic industries in Japan and Europe
• 5 million people effected
• Around 750 deaths
• Reduction in tourist numbers

Question 15

Flood prediction-data collection, technology (flood defence method)

Answer 15

Highly accurate forecasts and warnings % images shows wind and precipitation percentages across country

Daily forecasts issued with details about precipitation levels e.g. 60mm predicted, risk areas highlighted and multiple updates during the day

+ Heavy rain well forecast, well updated in day, warnings used to aid evacuation

• never 100% accurate

Models may not be specific enough- towns could be told wrong info

Question 16

Hard Engineering

Answer 16

projects are ones that involve the construction of artificial structures

1) Levees
2) Retention Pools
3) Dams and reservoirs

Question 17

Retention Pools (Hard engineering)

Answer 17

Areas surrounded by embankment - floodwater diverted during heavy rainfall ( Gloucester )

+Reduce flood waters downstream
-Can limit land use around pools

Question 18

Dams and reservoirs (Hard engineering)

Answer 18

Large barrier which holds back water - built upstream store floodwater if not already full

+ Can be used to generate electricity , store of water
- Can increase flooding upstream
More infiltration-more water lost

Question 19

Planting woodland (Soft engineering)

Answer 19

Vegetation-increases interception of water, trees encourage evapotranspiration ( Malvern Hills)

+Reduces surface runoff, natural look, inexpensive , reduce flood risk
-Takes time

Question 20

Soft Engineering

Answer 20

projects are ones that do not involve the construction of artificial structures

1) Planting Woodland
2) Floodplain zoning
3) Silt traps

Question 21

Silt traps (Soft engineering)

Answer 21

Basin that holds back silt-prevent silt, soil, sediment entering a drainage system (Purton)

+Increase river capacity
-Need to be emptied-traps will refill

Question 22

Floodplain zoning (Soft engineering)

Answer 22

Only use floodplain land for things that are not affected much by floods e.g. sports pitches

Floodwaters infiltrates onto floodplain -no infrastructure obstructing water

+Houses not flooded-less cost in damages
-Limits land use for developers

Question 23

Flood Risk Analyiss

Answer 23

• A scatter graph is produced using historical flood data from a place
• The magnitude of the flood is plotted against the recurrence interval of the flood (how often, on average, that size of flood is likely to occur
• Using a best fit line, the size of the floods can be calculated

Question 24

Flood risk maps

Answer 24

• The flood risk maps are very reassuring for most people live in the area shown. Very few buildings are at risk