1.4 The human impact

Question 1

What are the urbanising influences?

Answer 1

• Removal of trees and vegetation
• Initial construction of houses, streets and culverts
• Complete development of residential, commercial and industrial areas
• Construction of storm drains and channel improvements

Question 2

What is the possible hydrological response to removal of vegetation?

Answer 2

• Decreased evapotranspiration and interception

- Increased stream sedimentation

Question 3

What is the possible hydrological response to Initial construction of houses, streets and culverts?

Answer 3

• Decreased infiltration and lowered groundwater table

- Increased storm flows and decreased base flows during dry periods

Question 4

What is the possible hydrological response to development of residential, commercial and industrial areas?

Answer 4

• Decreased porosity, reducing time runoff concentration thereby increasing peak discharges and reduced time lag
• Increased volume of runoff and flood damage potential

Question 5

What is the possible hydrological response to construction of storm drains and channel improvements?

Answer 5

• Local relief from flooding

- Concentration of floodwaters may aggravate flood problems downstream

Question 6

Human impact on precipitation

Answer 6

• Cloud seeding
• As rain requires particles such as dust and ice on which to form, seeding produces silver iodide, solid CO2 (dry ice) or ammonium nitrate to attract water droplets
  => increase precipitation

Question 7

Dams’ effects on hydrological cycle

Answer 7

• Impoundment of water behind the dam causes the velocity of water to drop => increase potential for evaporation from the river => increased precipitation => soil will be saturated => little infiltration and percolation
• Volumes of channels increase, might exceed peak discharge => increased surface runoff => little baseflow, throughflow and groundwater flow
• An increase in precipitation means that water will be absorbed by plant => increased evapotranspiration

Question 8

Urbanisation’s effects on hydrological cycle

Answer 8

Overall:

• an increase in surface runoff
• reduction in evapotranspiration
• decline of surface storage (puddles)
• increased lag time

Question 9

What are the effects of extracting groundwater?

Answer 9

• Surface water flooding
• Pollution of surface waters and spread of underground pollution
• Flooding of basemets
• Increased leakage into tunnels

Question 10

Define flood

Answer 10

A high flow of water which overtops the bank of a river. Occurs when the river’s discharge exceeds the capacity of its channel to carry that discharge

Question 11

Physical causes of flood

Answer 11

• Excessive level of precipitation occurring over a long period of time
• Intensive precipitation over a short period of time
• Snow melt
• Climatic hazards such as cyclones and storms
• The nature of the drainage basin - relief, soil type, shape, vegetation

Question 12

Human causes of flood

Answer 12

• Urbanisation - construction of concrete buildings and roads => increases impermeability of surface => increased overland flow
• Deforestation => less interception => more groundwater flow and overland flow
• Climate change/ global warming => ice melt
• River management on 1 part of the drainage basin that increases flood risk in other areas - dam

Question 13

Define recurrence interval

Answer 13

Refers to the regularity of a flood of a given size. Small floods may be expected to occur regularly. Larger floods occur less often

Question 14

How to improve flood warnings?

Answer 14

• Improved rainfall and snowpack estimates, better and longer forecasts of rainfall
• Better gauging of rivers, collection of meteorological info and mapping of channels
• Better and current info about human populations, infrastructure, elevation and stream channels to improve flood risk assessment models
• Share info to the general public

Question 15

Define disaster aid

Answer 15

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

Question 16

Define loss sharing

Answer 16

Adjustments including disaster aid and insurance

Question 17

Define event modification

Answer 17

Adjustments including environmental control and hazard-resistant design

Question 18

How well a flood is dealt depends on:

Answer 18

• The level of preparedness at the location of the expected hazard
• Amount of warning
• Level of economic development

Question 19

Define flood management

Answer 19

• Seeks to reduce the frequency and magnitude of flooding and therefore, limit the damage a flood causes
• Can be achieved by 2 methods: hard and soft engineering

Question 20

Define hard engineering

Answer 20

Controlled disruption of natural processes by using man-made structures. Has the most definite outcome. Occurs where flood protection is vital. e.g. dam construction

Question 21

Define soft engineering

Answer 21

Uses natural processes and natural systems to slow down and store water. Not as well developed, therefore outcomes occasionally uncertain. e.g. afforestation

Question 22

Define drought

Answer 22

An extended period of dry weather leading to conditions of extreme dryness

Question 23

Causes of drought

Answer 23

• Due to global atmospheric circulation around 20-30 degrees N and S (subtropical high pressure belt)
• Distance from sea and continentality
• Rain shadow effects
• Human activities such as cash crop farming, overgrazing, slash and burn gives a rise in desertification

Question 24

Effects of drought

Answer 24

• Hunger and malnutrition
• Declining crop yields
• Reduced water supplies
• Stress on natural ecosystems
• Economic activities may be affected

Question 25

Methods of preventing and lessening drought

Answer 25

- Public education and education campaigns - Water service restrictions - Improvements in water systems - Management of available water resources