Flooding
What are the causes of flooding?
The main causes of floods are typically climatic forces, which have become more erratic and severe with climate change. Other contributing factors are specific to drainage basins and have been increasingly influenced by human activities.
Rainfall Intensity
In the UK, floods are often linked to deep depressions (low-pressure systems) during autumn and winter, typically lasting long periods and covering large areas.
Seasonal Variations in Discharge
In countries like India, up to 70% of annual rainfall can occur in a hundred summer days during the southwest monsoon. Additionally, melting snow from mountains like the Himalayas, Rockies, and Alps can lead to widespread flooding during spring.
Relief
Steep slopes can prompt swift run-off. Flood damage potential multiplies with velocity, and speeds exceeding 3m per second can be highly destructive.
Urbanisation
Urban developments contribute to flooding by creating impermeable surfaces and dense drainage networks, which increase run-off and drainage density, respectively. Moreover, infrastructure often constrains natural river channels, diminishing their carrying capacity. Inadequate sewerage systems can’t handle the heightened storm run-off. Impermeable rocks, high drainage density, lack of vegetation, and soils with low infiltration capacities also promote fast run-off. Human-induced deforestation and poor farming practices can boost run-off by reducing interception.
The prediction and prevention of flooding
Prediction
Flood forecasting and warning accuracy have improved over recent years, particularly in developed nations. As per the US Geological Survey (USGS), flood prediction needs data on rainfall, storm type, river/channel network discharge rate changes, and drainage basin characteristics. Swift communication about impending flood threats and their severity is crucial. For instance, the UK government website enables users to assess their flood risks and provides flood preparedness, response, and recovery guidelines.
Prevention
Historically, ‘hard engineering’ methods like dams, reservoirs, levees, channel straightening, and flood-relief channels were used to manage floods. Recently, ‘soft engineering’ measures focusing on working with nature rather than controlling it have gained prominence. These include catchment management plans, river restoration, and wetland conservation. Land-use zoning can limit flood risk to premises and individuals. Hazard-resistant design (flood-proofing) involves modifying buildings and interiors to minimize flood losses.
