Practical help to identify the type of flood your building may face
Source: Andreas Solaro, AFP
All floods present unique characteristics, shaped by local geography, weather, and land use. However, most can be grouped into four main types:
- Runoff floods (Pluvial) – Caused by intense rainfall that overwhelms the ground’s ability to absorb water, leading to surface water accumulation.
- River overflow floods (Fluvial) – Occur when rivers or streams exceed their banks due to heavy rain or snowmelt.
- Rising groundwater floods – Result from the water table rising above the surface after prolonged wet periods.
- Coastal floods – Caused by storm surges, high tides, or sea-level rise affecting coastal areas.
How we integrate flood types in our model
Inond’Act only takes into consideration the first three floods. Indeed, coastal flooding adds a parameter we have yet to modelize – salt water.
Below, you’ll find a brief explanation of each flood type in Inond’Act. It will help you determine which scenario you should select when using our model.
Although multiple flood types usually occur simultaneously, Inond’Act requires that you specify the one your house is most likely to face.
More explaination on each flood type
Runoff floods
Runoff floods occur when the ground can no longer absorb water, leading to temporary surface streams capable of damaging infrastructure or farmland.
Therefore, your house could be at risk if it’s located in a low-lying area and subject to heavy rainfall. Poor soil health or impervious surfaces (like pavement) worsen runoff effects, as water can no longer be absorbed into the ground.
River overflow floods
River overflow floods occur when a river or stream exceeds its capacity and spills over its banks, flooding the surrounding land. This typically happens after prolonged or intense rainfall, snowmelt, or when upstream water flows faster than the river can carry it downstream. Inond’Act distinguishes between quick and slow overflowing, as certain rivers are much faster flowing than others.
Thus, homes and infrastructure near rivers are especially at risk. Poor land management, deforestation, or urban development along riverbanks can make overflow floods worse by reducing the land’s ability to slow and absorb excess water.
Rising groundwater floods
Rising groundwater floods occur when the water table rises above the surface, leading to flooding from below. This usually happens after long periods of heavy rainfall that saturate the ground and raise underground water levels. Unlike other floods, groundwater flooding can be slow to appear and even slower to recede, and it may damage basements, foundations, or underground infrastructure.
Areas with shallow water tables or poorly draining soils are especially vulnerable, even if they are far from rivers or coasts. If you live in a known floodplain or low-lying basin, you’re more likely to be at risk.