## 2 Risk Redistribution under the Kaldor-Hicks Compensation Principle
### Classifying Suitable Measures  
A detailed risk assessment of all possible flood management measures is not economically feasible. Using available data, a competent professional with knowledge of the flood management domain can discard certain flood management options without analyzing each of them in depth [40]. Similarly, there are certain measures that are preferable under certain prevailing conditions [41]. For example, floodproofing of individual areas within the floodplain has proved economically more feasible than flood protection by constructing dikes under conditions where the floodplain is not densely  
Figure 1: The proposed basic framework for risk-based flood management fitted into the context of ISO Guide 31000 [39].  
populated [36]. A few measures are highly counterproductive in certain situations. One example is constructing a dike in mountainous areas, where flood levels fluctuate more rapidly and the chances of dike failure are high. In this case, the dike prevents the floodwaters from receding once the flood peak has passed. Which flood measures are selected depends on the available resources, technical limitations, and the effectiveness of an individual measure. The following are common examples of flood management measures, with a brief description:  
* **Reservoirs** reduce the flood peaks holding the surplus flows.
* **Rain harvesting** also works in the same way as reservoirs but on a smaller scale. The stored water is used mainly for domestic purposes.
* **Dikes, levees, floodwalls, and other barriers** suppress the flood hazard from reaching settlements, thus avoiding the risk.
* **Channel improvements** facilitate the convenience of flow within a channel and reduce the stage against a high discharge by widening, deepening, smoothing, or removing curves from a channel.
* **A diversion (or bypass)** of the flow capacity of a channel is increased by diverting a part of the flow to follow a different flow path and rejoining the main stream at a downstream point, where appropriate.
* **Insurance and relief** are approaches to make the system more robust by increasing the recovery speed and extent of recovery. These options also play an indirect role in controlling exposure and susceptibility within a floodplain.
* **Flood warnings, rescue, and pre-emptive evacuation** are capacity-building measures within the floodplain that enhances the capacity of settlements to react against floods by moving out or removing the assets from a floodplain in time.
* **Public awareness** is a multidimensional tool that helps us to react against floods in many ways because of the flexibility and effectiveness of allowing settlements to understand flood issues, management options, and response options.
* **Flood zoning, encroachment control, and implementing building codes** are effective tools to control the vulnerability of floodplains in an effective way.  
The selection of a suitable measure is carried out by considering the appraisal requirements and the contribution of the measures in achieving the appraisal objectives. Different flood management options should be evaluated one by one by approximation. Developing options correctly can save time and resources. The following steps are recommended to develop the most suitable combination for appraisal needs.  
1. Identification of a wide range of options by considering the topographical, environmental, social, cost-effective constraints.
2. Screening out of impractical and infeasible options.
3. Shortlisting of options that will most probably achieve the best use of resources.
4. Development of a wide range of options by combining different measures.  
Table 1 provides a rule of thumb guideline example to shortlist the measures under the predominant conditions of the floodplain. The data are compiled based on an extensive literature review and field experts' opinions. This guidance is tentative and based on a range of typical benefits, including reduced costs and additional socioenvironmental benefits.