The effects of flooding on people, property and land

Overview

Effects of a major river flood on people, effects of a flood on property and infrastructure and effects of a flood on the land.

What you need to know

Answer each one before you reveal it.

Questions from this subtopic

Each one with the model answer underneath.

1. 1

   What are the effects of a major river flood on people?

   Model answer

   Deaths and injuries occur through drowning, being swept away by fast-moving water, building collapse and electrocution. Large numbers are displaced from their homes into temporary shelter, sometimes for many months. Contamination of drinking water by sewage and animal carcasses spreads waterborne disease such as cholera, typhoid and dysentery, and standing water encourages mosquito-borne disease, effects that are far more severe where sanitation and health care are weak. Livelihoods are lost when crops, livestock, tools, stock and workplaces are destroyed. Education and health services are disrupted, and the experience of losing a home and possessions causes lasting anxiety, depression and stress, which is often reported as the longest-lasting effect of all.

2. 2

   What are the effects of a flood on property and infrastructure?

   Model answer

   Homes are inundated, with contents, furnishings, electrics and vehicles ruined and structures damaged by water, silt and, in fast flows, by undermining of foundations and collapse. Where construction is of mud, timber or corrugated iron the buildings may be destroyed outright, whereas brick and concrete buildings usually survive but need months of drying and refitting. Roads and railways are cut, bridges and culverts washed out and embankments scoured, isolating settlements and hampering rescue. Electricity substations, water treatment works, telephone networks and sewers are put out of action. Businesses close, sometimes permanently, with lost output and lost jobs. Where insurance exists, claims are enormous and premiums subsequently rise or cover is withdrawn; where it does not, the whole loss falls on the household.

3. 3

   What are the effects of a flood on the land?

   Model answer

   Standing crops are destroyed and the harvest lost, and livestock drown. Fast-flowing water strips topsoil and scours gullies, while the retreating water may leave a sheet of infertile sand and gravel over productive fields, or bury pasture in silt. Where a coastal surge is involved, salt water causes salinisation that can take years to leach out. Waterlogging persists after the flood, damaging soil structure and delaying replanting into the following season, and pollutants from sewage, fuel, chemicals and industrial sites are spread across the land. Habitats are destroyed and river banks collapse. Against this, the deposition of fine silt across a floodplain replenishes its fertility, and wetlands and groundwater are recharged, so not all effects on the land are negative.

4. 4

   Distinguish between the primary and secondary effects of a flood.

   Model answer

   Primary effects are the immediate, direct results of the water itself: drowning and injury, buildings inundated and damaged, vehicles and possessions destroyed, crops submerged and livestock drowned, roads and bridges washed away and power cut. Secondary effects follow on afterwards as consequences of those: outbreaks of waterborne disease from contaminated supplies, homelessness and long stays in temporary accommodation, food shortages and price rises after the harvest is lost, unemployment and business failure, disruption to schooling, mental health problems, rising insurance costs and falling property values. Secondary effects usually last far longer than the flood itself and are often the greater part of the total loss.

5. 5

   Why are short-term and long-term effects of a flood often quite different in character?

   Model answer

   The short-term effects are dominated by the emergency: casualties, rescue, evacuation, loss of power and water, blocked roads and immediate destruction, all measured in days and weeks. The long-term effects are economic, social and environmental, measured in months and years: the cost of rebuilding, businesses that never reopen, families still out of their homes, agricultural land out of production for one or more seasons, debt, higher insurance, falling property values and population loss where people choose not to return, alongside slow ecological recovery. A flood can therefore look manageable on the day and still leave a community permanently poorer.

6. 6

   How would you go about assessing the impact of a flood on a community, and what data would you look for?

   Model answer

   You would look at the number of deaths and injuries, the number of people evacuated and made homeless and for how long, the number of properties flooded and the depth of water in them, the estimated cost of damage and of lost economic output, the area of farmland inundated and the value of crops and livestock lost, the length of road, rail and utility network affected and how long services were interrupted, and the reported incidence of disease and of mental ill-health afterwards. You would compare all of these against the pre-flood situation and against the design standard of any defences, and you would look at how the losses were distributed between social groups, because the poorest are usually the worst affected and the slowest to recover.

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