5.5 Surpluses Within the Hydrological Cycle Flashcards
5.5a Meteorological causes of flooding
physical factors affecting flooding levels
vegetation:
greater vegetation cover generally produces higher level of interception, storage and evapotranspiration. This reduces rainfall and increases the lag time
soil depth:
deeper soil absorbs more water and results in less run-off
drainage density:
where the drainage density figure is low, there is a longer lag time and a reduced risk of flooding
slope:
steeper-angled slopes mean less water is absorbed and more runs off
rock type:
permeable rock allows greater infiltration and ground storage, leaving less water to run off
5.5a Meteorological causes of flooding
environments at risk
Low-lying parts of flood plains and river estuaries. These are subject to river flooding and groundwater flooding after the ground becomes saturated from prolonged heavy rainfall.
Partially urbanised low-lying areas with impermeable surfaces. There is a greater danger of temporary surface water flooding as intense rainfall has insufficient time to infiltrate the soil, so flows overland.
Small basins, especially in arid areas are subject to flash flooding. These are floods with an exceptionally short lag time that are usually associated with very intense convectional storms so infiltration is limited, allowing surface overland flow to develop very rapidly.
5.5a Meteorological causes of flooding
intense storms leading to flash flooding
a
5.5a Meteorological causes of flooding
unusually heavy or prolonged rainfall
a
5.5a Meteorological causes of flooding
extreme monsoonal rainfall
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5.5a Meteorological causes of flooding
snowmelt
a
5.5b Human actions exacerbating flood risk
channelling land use within the river catchment
straightening channels (realignment) to increase the flow, results in flooding downstream- this could be regarded as mismanagement in some ways
resectioning by dredging involves widening and deepening the channel to increase efficiency by increasing capacity and moving water away at a faster rate- but at a considerable environmental cost
5.5b Human actions exacerbating flood risk
mismanagement of rivers using hard engineering systems
a
5.5b Human actions exacerbating flood risk
urbanisation
urbanisation is the increase in the number of people living in towns and cities compared to the number of people living in the countryside
5.5b Human actions exacerbating flood risk
changing land use
deforestation, overgrazing, ploughing or drowning wetlands usually occurs upstream from urbanised flood plains, which has a knock-on-effect downstream with increased run-off and increased levels of sediment (which are washed into rivers and block river channels)
5.5c Impacts of flooding
environmental
In many natural ecosystems flood play an important role in maintaining key ecosystem functions and biodiversity, by linking the river with its land surroundings.
The floods can recharge groundwater systems, fill wetlands, increase connectivity between aquatic habitats, and move sediment and nutrients around the landscape into marine environments.
For many species, flood events trigger breeding, migration and dispersal.
Many natural ecosystems are resilient to the effects of moderate flooding, which can lead to increased productivity and maintenance of recreational environments
Intense flooding , caused by excessive overland flow, can lead to oversupplies of sediment and nutrients, with possible eutrophication and the destruction of aquatic plants, as well as introducing pollution from the nitrates, chemicals and heavy metals, which can degrade aquatic habitats.
Wildlife in the soil (such as earthworms, moles and hedgehogs) can be poisoned by polluted waters
5.5c Impacts of flooding
socio-economic impacts
Floods are the most frequent environmental disaster in Europe (fatalities low but costs high)
The threat of flood events depends on the depth and velocity of the water, the duration of the flood and the quality of water (sediment load, presence of raw sewage, toxic chemicals, pollution from oil, etc)
Flood depth has a clear link to mortality. In many developing countries people have not learned to swim and can be killed by poisonous snakes in the flood waters
Post-flood morbidity (ill health) is extremely likely in developing countries, mainly from water-borne diseases
In developed countries, psychological stress is very common among flood victims
Floods can affect people’s livelihoods in many ways
Direct structural damage to property in countries at all stages of development is the major cause of tangible flood losses
Concerns after flood events about getting flood insurance for future events
Coping with reduced property values when a flood-prone property is resold
crops, livestock and agriculture infrastructure suffer major damage in intensively farmed rural areas
Where farming is subsistence, there is a direct loss of food supplies and famine can occur
In developed countries, flood scan lead to escalating flood prices as shortages of key products occur
Infrastructure losses are often extremely high in mega cities as growth has outstripped flood defence systems
Negative images of flood-affected ares lead to tourists cancelling trips there, causing a substantial loss of income.
