services - floods studies and management services

Flooding is a natural phenomenon caused by large rainfall events, where the amount of surface runoff caused by the event far exceeds the amount that can infiltrate. This causes land that is not normally covered by water to be inundated for various lengths of time.

Land use changes (particularly in semi- and impervious urban areas) have increased the frequency and severity of flood events, where climate change is predicted to further increase the severity thereof. Built-up areas close to rivers are particularly vulnerable, since there is a higher probability of flood exposure, which could cause loss of life and building damages. This affects various sectors, for example insurance companies, where personal injuries (or loss of life), building or car damage could result in large sums of money to be paid from insurance claims.

EkoSource has been involved with several flood assessments. The outcomes of these assessments could result in various mitigation measures that could be implemented in order to reduce the flood exposure in areas more prone to inundation (such as flood dykes/levees).

EkoSource performs flood exposure, vulnerability, hazard and risk assessments. These individual assessments are explained in further detail below.

Floods Exposure

Flood exposure is essentially determining the extent of flood waters for a particular event or flood return period. The outcomes of a flood exposure exercise would be a map showing the various water depths in the affected areas, along with an optional boundary line showing the overall inundation areas for various flood return periods and scenarios.

Example of a flood exposure map, showing the various water depth classes

Flood Vulnerability

A flood vulnerability assessment identifies various areas that are more vulnerable to floods than others. This procedure is generally based on the area's physical, social and economic resilience to floods, where a multi-criteria decision analysis (MCDA) is performed to produce an overall vulnerability map. These areas are generally categorized from low to high classifications of vulnerability.

Example of an overall vulnerability map (often based on landuse types)

Flood Hazard

A flood hazard analysis involves a detailed floodplain assessment, providing information about the flood extent, water depths (water level), flow velocity and flood hazard/danger level. The measure of hazard is obtained when combining current velocity with water depth estimates.

Example of a flood hazard map (note extreme areas due to deep, fast flowing waters)

Flood Risk

Determining the Flood Risk Exposure involves simulating the flooded extent resulting from a particular flooding event, or a specific flood return period. The outcomes of a Flood Risk Exposure assessment is typically a map showing different water depths and flood lines associated with the flooded areas. If several different return periods and scenarios are required, different maps and flood lines are produced for each scenario.

Example of a flood risk map (where flood hazard and flood vulnerability intersect)

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