Flood risk mapping as part of flood risk assessment is an important part of a floodplain management system.
A little about floodplain management. Already in 1996 Miller et al., stated that majority of damages appeared to result from unwise use of floodplain areas, it became increasingly clear that careful land use planning, in combination with engineering, architectural and hydrologic measures, could be employed to avert local flood damage. Floodplain management is defined as “… a decision-making process whose goal is to achieve appropriate use of the nation’s floodplains. Appropriate use is any activity or set of activities compatible with the risk to natural resources (natural and beneficial functions of floodplains) and human resources (life and property) …”. The basic challenge of the flood problem is the development of a set of management strategies which can permit more intensive use of floodplains and yet minimise potential damages (Milliman, 1984).
Floodplain management system
Floodplain Management System is a system that exists of different actions that together form a structure to manage a flood plain (“Floodplain Development Manual” which was published by the New South Wales Government in 1986 and updated in 2005).
The system is shown in the following figure.
Floodplain Risk Management Committee
The main aim of such a committee is to assist a municipality in the development and implementation of a flood plain management plan. The floodplain management committee can be a sub-committee of the municipalities Disaster Management Advisory Forum.
Flood studies define the nature and extent of possible flood events. The first action is the demarcation of the flood plain through hydrological and hydraulic studies.
Demarcation of areas in the floodplain
It is necessary to divide the floodplain into categories descriptive of the impact that development may have on floodwater and the impact that floodwater may have on development. This will include land use and land cover assessments.
Flood plain management studies
Flood plain management studies are undertaken to identify and evaluate the effectiveness of suitable measures. Measures can be classified as structural and the latter as non-structural measures.
Flood risk assessment must be completed to evaluate measures. The figure below shows the results of flood damage estimation for Upington, Northern Cape. The possible damage can now be used in cost benefit analysis to determine the most appropriate measures.
Flood plain management plans
Before a floodplain management plan can be drawn up, it must be assured that the plan measures up to specific criteria. Objectives can include:
- The use of land that is prone to floods must be planned and managed in such a way that it is compatible with the calculated frequency and extent of floods.
- Land that is prone to floods must be managed in such a way that social, economic and ecological costs and benefits are considered.
A project implementation plan must be developed and executed. In South Africa this must be done through the IDP process.