1.4 The Human Impact Flashcards
How can human activity modify EVT?
EVT: Dams can create reservoirs prone to evaporation which can be reduced with chemicals and covers.
Urbanisation has reduced EVT due to less vegetation. May increase evaporation as higher temperatures and surface storage - less porous, low runoff times, high peak discharge
How does human activity affect precipitation?
Air pollution adds condensation nuclei and the heat island affect creates more rainfall in city areas. Likewise, global warming has a similar effect.
How does human activity affect water storage and interception?
Dams provide water for irrigation, recreation, industry, power and control flooding. They even out the river flow, cause lots of evaporation, low discharge, peaks, flooding - more evaporation and storage
Deforestation causes less EVT, more runoff, more surface storage. On the other hand afforestation does the opposite and can cause more sediment which is bad due to overland runoff, less ground vegetation, young trees and bare ground.
How does human activity effect infiltration?
Urbanisation reduces infiltration as implies compact soil. In forests it is much higher as roots and stems channel water, grazing reduces compactness causing more infiltration and ploughing causes less.
How does human activity affect groundwater levels?
Artificial recharge is used to fill aquifers via boreholes to maintain water table height and stop streams drying up. Some boreholes are used to extract water, which can cause saline intrusion stopping the amount of consumable water.
Rising groundwater levels resurfacing leads to springs, river flow, underground pollution of water, reemergence of springs, leakage into tunnels, reduced stability, reduced capacity of foundations, swelling clay, chemical attack
Centre-pivot irrigation schemes occur when boreholes are drilled into the ground in aquifers which is then pumped and sprayed onto crops.
Where is flooding the most hazardous?
Most vulnerable areas are low lying floodplains, estuaries, small basins subject to harsh floods, below unsafe dams and low lying shorelines.
In HICs there has been a decline in deaths - it is more hazardous in LICs as often settle in low lying areas for economic implications with weaker protection.
What are some of the causes of flooding?
Natural: precipitation (rain/snow/ice), estuary interactions, storm surges, earthquakes, mass movements, landslides, dam failures, monsoons
Human: urbanisation, land use, floodplain development, bridges, dams, vegetation, engineering, climate change
Cold weather reduces evapotranspiration and mechanised farming can increase runoffs.
Causes relate back to hydrographs: topography, vegetation, soil type, rock type, characteristics of drainage basin, velocity, urbanisation (paths, gutters, sewers, obstacles such as bridges), deforestation.
How are floods categorised?
The frequency is given by the number of events/magnitude over a given time period.
The magnitude is inversely proportional to frequency in a 1/x graph, meaning that as magnitude rises frequency falls
This is then used to find the recurrence interval to statistically determine the probability of flooding and its likely size, using (number of years on record+1/ranking of flood)
How are floods forecasted?
Weather satellites and radar forecasts, rainfall length estimates, snowpack melting, land use changes, information exchange between forecasters and countries, technology sharing.
Met office collaborate with EA to give warnings using stations and satellites into computer simulations and give warning codes according to risk.
Community preparedness - EA preparation in evacuation, sandbagging and emergency planning, moving furniture and belonging to upper floors, boats, storing emergency supplies.
EA advise gather essentials, get water, move family and pets upstairs, turn off gas and electricity, do not touch electricity sources, listen to radio, stay calm, avoid walking or driving in it.
Flood maps are made to determine areas at risk to zone areas and build in awareness of the risk - insurance
sand proofing - tiling, drains, blocked entrances/windows, sandbags, etc. It shows the extent to which areas are at risk to to flood from overflowing rivers, is updated every 15 minutes, taking into account defences and magnitude
This can then be used to naturally allow flood waters to submerge river floodplains through planning and control.
Catchement models used the CHZM modeller - software which predicts effects and flows.
What are the methods of hard engineering?
Dams: large concrete structures storing discharge in reservoirs to manage downstream. Provides electricity, reduces flood risk, provides tourism, irrigation, industry, agriculture and recreation however they are expensive, hold silt and cause deposition, destroy ecosystems, relocate settlements from flooding.
Channelization: straightening/dredging the river to allow for more flow away from the area, increasing capacity and speed - may be done by smoothing banks to reduce friction. Often very expensive and can cause downstream flooding and erosion.
Embankments: raise banks to increase capacity and discharge, provide habitats if natural, safer however expensive, permanent, high maintenance and ugly
Raising buildings
Washlands/retention zones: areas allowed to flood naturally so it doesn’t damage property and less downstream damage. The land cannot be used and habitats may be lost during floods but also provides wide area for wildlife and recreation and is also cheap.
Flood relief channels are diverting water into channels away from the main course, increasing capacity of waterways able to hold the discharge and reduce the main river discharge. It creates new rivers, recreation and wildlife, reduces risk and causes less flooding. However, they are expensive, disturb wildlife, ugly and cause downstream flooding and erosion.
What are some soft engineering methods?
Floodplain zoning: no development on floodplains at risk so reduced damage to property. However, areas are usually already built on before knowing at risk.
Afforestation increases interception, infiltration, EVT and reduced runoff - takes time to mature and may need to be large scale projects
Wash lands aside river using floodplain zoning
Conservation - protecting existing channels and valleys so habitats and species are maintained as natural river giving place to go in flood and diversifying the area
Contouring flood plain to reduce surface runoff - mainly on farmland
Restoration - return rivers to original state before, providing there is environmental gain and consideration to the socioeconomic impact - improved river quality, sustainable management schemes working with nature.
Wetland and river conservation schemes - protect existing river channels and valleys
Forecasting floods and warnings
What are the impacts of flooding?
Death of people and animals
Damage to buildings, industry, farmland and infrastructure
Disruption of lives, homelessness or economics - jobs lost, unemployment. HICs tend to have higher costs of damages but less deaths.
