1.4 The human impact Flashcards
What are the urbanising influences?
- 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
What is the possible hydrological response to removal of vegetation?
- Decreased evapotranspiration and interception
- Increased stream sedimentation
What is the possible hydrological response to Initial construction of houses, streets and culverts?
- Decreased infiltration and lowered groundwater table
- Increased storm flows and decreased base flows during dry periods
What is the possible hydrological response to development of residential, commercial and industrial areas?
- Decreased porosity, reducing time runoff concentration thereby increasing peak discharges and reduced time lag
- Increased volume of runoff and flood damage potential
What is the possible hydrological response to construction of storm drains and channel improvements?
- Local relief from flooding
- Concentration of floodwaters may aggravate flood problems downstream
Human impact on precipitation
- 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
Dams’ effects on hydrological cycle
- 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
Urbanisation’s effects on hydrological cycle
Overall:
- an increase in surface runoff
- reduction in evapotranspiration
- decline of surface storage (puddles)
- increased lag time
What are the effects of extracting groundwater?
- Surface water flooding
- Pollution of surface waters and spread of underground pollution
- Flooding of basemets
- Increased leakage into tunnels
Define flood
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
Physical causes of flood
- 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
Human causes of flood
- 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
Define recurrence interval
Refers to the regularity of a flood of a given size. Small floods may be expected to occur regularly. Larger floods occur less often
How to improve flood warnings?
- 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
Define disaster aid
Refers to any aid such as money, equipment, staff and technical assistance that is given to a community following a disaster
