Flood Damage Assessment
One of the approaches for mitigating the ill-effects of floods is to exercise some degree of control over these natural phenomena in order to minimize losses. Effective ﬂood management in any region depends on the evaluation of different types of ﬂood losses. Losses in respect of residential, commercial, agricultural and industrial land use categories are to be assessed. Two main approaches are adopted:
1. Empirical approach – based on damage caused during past flooding events, and
2. Synthetic approach – which uses damage data collected by interview survey or questionnaire.
Flood damage assessment takes into consideration the value of social, economic and ecological damage that has been caused or would be caused in the event of a flood. There are many factors which determine the degree of repairable or irreparable damage to buildings, infrastructure, goods and environment. Some of them are listed below. The extent of potential damage is considerably affected by:
Extent of flooded area
Assets within the inundated area
Duration of a flood event
Type of land use
To assess flood damage, the following aspects are required to be considered:
1. Direct or indirect damages
2. Tangible or intangible damages
3. Primary and secondary damages.
Direct and Indirect Damages: Direct flood damages result from the actions of floodwaters, inundation and flow, on property and structures. Indirect damages arise from the disruptions to physical and economic activities caused by flooding. Indirect damages are for example, the loss of sales or the reduced productivity.
Tangible and Intangible Damages: Tangible damages are monetary losses directly attributable to flooding. They may occur as direct or indirect flood damages. Intangible damages arise from adverse social and environmental effects caused by flooding. Examples of intangible damages are loss of life, emigration, stress and anxiety, damage caused to people’s health etc. These intangible damages are not easily quantifiable and have not been included in the monetary assessment of flood damages.
Primary and Secondary Damages: Primary and secondary losses are distinguished in the sense that the primary damage result directly from the flood event, while secondary damage includes impairment of the functions of a material or asset due to prolonged indirect exposure to water or contamination resulting from inundation. The damage could be reversible or irreversible. An example of reversible secondary damage would be swelling or cupping and/or bowing of a wooden floor. An example of irreversible damage would be wood rot. Another common example of secondary damage is fungal growth or mold.
Method of Damage Assessment
A very important part of damage calculation process is the determination of the asset values within the damaged/vulnerable area. The asset values are calculated using one of the following methods:
Value at Purchase Price: Values of assets are calculated considering the cost price at the assets at the time of their purchase. There are two ways in which the value may be assessed – a constant value during the entire lifecycle of the asset (the gross concept), or taking into account the depreciation of the asset (the net concept).
Value at Actual Price: Estimated damages include all prices for rebuilding flood affected units. There are two ways in which damage is estimated – by taking the difference between the cost of rebuilding and gross values of assets (the gross concept), or by taking the difference between the cost of rebuilding and depreciated value of assets (the net concept).
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Department of Geology
Aligarh Muslim University, Aligarh - 202 002 (India)