47. Flooding types

Groundwater flooding

Groundwater flooding occurs when the water table rises to the surface or saturates the soil, resulting in water pooling on the ground's surface or infiltrating into basements, cellars, or underground structures. Groundwater flooding typically occurs gradually over time, influenced by factors such as rainfall, geological conditions, soil permeability, and land use practices. 

Sewer flooding

Sewer flooding occurs when sewage systems, including sewers, drains, and wastewater treatment infrastructure, become overwhelmed or blocked, causing sewage to back up and flood properties, streets, or public spaces. Sewer flooding may result from heavy rainfall, inadequate drainage capacity, blockages from debris or waste, or infrastructure failures in the sewage network. 

Surface water flooding

Surface water flooding, also known as pluvial flooding or urban flooding, occurs when rainfall exceeds the capacity of natural or man-made drainage systems, leading to the accumulation of water on roads, pavements, fields, and other surfaces. Surface water flooding can occur rapidly during intense rainfall events, causing flash floods, inundating properties, and disrupting transportation and infrastructure. 

Coastal flooding

Coastal flooding occurs when rising sea levels, storm surges, high tides, or coastal erosion inundate coastal areas, beaches, estuaries, and low-lying coastal communities. Coastal flooding is often associated with severe weather events, such as tropical cyclones, hurricanes, or nor'easters, and poses significant risks to coastal properties, infrastructure, and ecosystems. 

River flooding

River flooding, also known as fluvial flooding, occurs when rivers, streams, or watercourses overflow their banks and inundate adjacent floodplains, valleys, and riparian areas. River flooding can result from heavy rainfall, snowmelt, upstream runoff, or ice jams, causing prolonged flooding, riverine erosion, and damage to properties, agriculture, and infrastructure along river corridors.

Other types of flooding

Other types of flooding may include: 

• Flash flooding: Rapid-onset flooding occurring within a short duration, often characterised by high flow velocities and debris-laden floodwaters, posing significant risks to life and property. 
• Backwater flooding: Flooding caused by the obstruction or blockage of water flow in rivers, streams, or drainage channels, leading to upstream flooding and inundation of upstream areas. 
• Tidal flooding: Flooding occurring due to tidal fluctuations, storm surges, or tidal wave events along coastal areas, estuaries, or tidal rivers, resulting in saltwater intrusion and coastal inundation.