With heavy flooding currently affecting one million people in the southern provinces of Thailand, a more holistic approach to flood mitigation is needed. A paper in CIWEM’s Journal of Flood Risk Management highlights the critical issues and solutions in terms of flood management with regards to Southeast Asia.

Until recently, the approach to flood management in much of Southeast Asia has been piecemeal and localised. Works carried out consisted of control structures and flood embankments along riverbanks to protect habitation and agricultural land. This has isolated rivers from their floodplains, resulting in increased peak flood flow, bank erosion, riverbed sedimentation, loss of fertile sediment on the flood plain and destructive failures when banks are breached. In areas outside the engineered protection, floods have increased in depth and frequency. These problems are further compounded by low-lying areas and wetlands being reclaimed for urban development. And the considerable cost of flood control development is largely met through loan projects, often leaving operational and maintenance costs that cannot be met by local budgets so the works are only effective in the short term.

In all cases, there are tensions and trade-offs between economic, environmental and engineering issues, and between local inhabitants, basin managers and other stakeholders. It is here that the use of detailed mathematical modelling allows management decisions to be made that help formulate workable strategies that develop into sustainable basin plans. Mathematical models calibrated against observed field data allow such decisions to be made with confidence as to their future outcome when they are implemented.

The plans also have to be harmonised with the river basin management plans that cover other sectors and with the local government spatial plans. The flood management consultants’ best flood retention option might be another planner’s prime real estate site. Finalising the plans is normally an iterative process.

The study also stresses the need to adapt to learning to live with the floods and involving stakeholders in the decision-making process. Rather than a complete change to nonstructural improvements alone, a mix of structural and nonstructural initiatives provides the best technical, environmental and socially acceptable solution.

The authors state: “Perhaps the greatest lesson is the need to involve the stakeholders in a positive way throughout the planning process. They will be the end users and often have a deep understanding of the river basin. One may have to accept that the resulting plan could depend on the vagaries of human nature as much as optimisation and sustainability. Communication and education then become as important as engineering, modelling and economics.”

Source: The Chartered Institution of Water and Environmental Management (CIWEM)