flooding of low lying areas analysis
Answers
Answer:
At a national level, a government must make many decisions that require a balanced understanding of multiple issues, and therefore needs specific and reliable information on those issues. One issue which is integral to many planning decisions is that of flood risk. For example, a government may need to know what part of the population is exposed to potential flood hazard and where that risk is most serious. This can guide investment in disaster preparedness, in terms of shelter location and their capacity, as well as evacuation plans and event response procedures. Infrastructure at risk of flooding can also be identified and evaluating potential losses that may occur, can help decision making, in terms of protecting valuable or strategic assets, or upgrading structures. Indeed, “the value of vulnerability assessment and reduction” is recognized as one of the guiding principles of the National Hazard Mitigation Policy of Belize.
Even where good flood hazard information does not exist in a formal sense, it is likely that responsible persons within a government will use experience and historical knowledge to guide their plans to some extent. However, this knowledge is often lost when the experienced person retires and hence planning decisions may not include all potential risk, in an objective way. It is also difficult to integrate this informal knowledge into an increasingly data rich world, making flood risk analysis difficult and potentially inconsistent.
Many governments now use national flood hazard information which has been formally defined for different return periods (probability of occurrence), sometimes simplified into low, medium and high hazard categories (see definitions in the Methodology Book, for instance, sections 3 flood hazard assessment and section 5 Risk Assessment. Traditionally, this information is provided in map form, but is at its most useful in digital GIS format. A computerized digital format allows cross-analysis of the flood hazard information against the many other digital datasets that are now available. This analysis can be carried out rapidly and more accurately, and is consistent and repeatable.
Below is a schematic which illustrates the definition of flood risk (see section 5.1 of the methodology book for more detail). This Use Case focuses on using the flood hazard information defined in Use Case 8.6 national flood hazard method to identify exposure at a national scale. The vulnerability element is not explicitly included in the analysis due to a lack of data, although it is discussed so that appropriate data can be collected for future work.
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While this Use Case focuses on providing a pre-disaster assessment of flood risk, it should be noted that methods are similar to and closely tied to post-disaster assessments. In Belize, these assessments are coordinated by NEMO (National Emergency Management Organization) and are called DANA (Damage Assessment and Needs Analysis) reports. Many government agencies contribute to these reports and they provide a valuable analysis of losses arising from a natural disaster. An example for Hurricane Ernesto in 2012 can be found on the Belize NEMO website.
The main difference is that a pre-disaster assessment uses predicted hazard outputs from modeling exercises and a post-disaster assessment uses information for an actual event, collected in the field by survey teams or by satellite/airplane.
Objectives:
The overall objective of this Use Case is to demonstrate, using two example analysis categories, how to carry out a flood risk analysis at a national scale. It uses national indicative flood hazard maps and national level data to identify what and who may be at risk during floods, i.e. exposure. Population and roads are used as example categories in this Use Case analysis, but the method can be applied to other categories as well. The exposure information is then aggregated into enumeration areas to demonstrate how this can provide further value from the information in a planning context. Finally, it outlines how further analysis of the vulnerability of the flood exposure can be used to provide an estimate of the actual losses that might occur.
Explanation: