Session FT 5.20

Flash Floods

 

 

 

 

Conveners

• World Meteorological Organisation
• Swiss Federal Office for the Environment (FOEN)
• National Weather Service – USA
  

Flash floods are the deadliest type of floods. Advances in forecasting cannot overcome the physical limitations inherent in the type of event. However, realizing the limitations of forecasting, the way the communities affected by flash floods should prepare themselves for mitigating their adverse impacts was addressed. Mudslides were also considered. The question “Are we prepared to deal (technically and institutionally) with them and their consequences?”  was posed.

 

Lessons learned

 

 

 

Key messages

 

1. A good knowledge of the hazard is a vital prerequisite
   You cannot fight against the unknown, therefore the first step to the establishment of a risk management policy is to learn the characteristics of the different types of hazards likely to impact one region.
2. Think of the unthinkable and see how your system behave
   Even if one cannot prevent any major event, it costs next to nothing to make trial runs and see how your system behaves against the “Big” event. What you could learn from this exercise could improve enormously your system. In other words, you should prepare a robust system that could resist stronger events than those used to design it. 
3. Integrate potentially affected people in the planning
   The most effective systems are those where people respond with discipline and in time. For that to happen communities must be convinced and they must feel a sense of ownership. There is no better way to obtain that than involving them from the planning stages, which, by the way, will also improve the overall effectiveness of the system, as it will incorporate their traditional knowledge of the issues at hand.
   

 

Orientations for action

 

 

 

Local Actions presented

 

Prevention measures for flash floods. Recent events of 2005 in Switzerland.

Hans-Peter Willi,Water Risks Section Federal Office for the Environment (FOEN), Switzerland

On 21/22 August 2005 most of Switzerland was hit by severe floods, setting a new record in damages. The task of the FOEN was to obtain an overview of the damages, the resources needed, and the technical know-how for reconstruction and improvement of prevention. As federal agency, the FOEN was not directly involved in the immediate intervention, but plays an important role in the necessary prevention measures. Investigations to establish "lessons learnt" have already started.

 

Proyecto para el control de torrentes en la cuenca del río Blanco, Veracruz, México.

Alfredo Jimenez, Comisión Federal de Electricidad, México

The government of Vera Cruz and Petroleos Mexicanos worked together on the project of mitigation of the mud floods in the rio Blanco basin. Infrastructures together with environmental impact studies and an early-warning system were designed. Finally, 14 infrastructure projects were considered to be a priority, embankments, fllod expansion areas, and the canalisation of one part of the river in urban area.

 

Countermeasures for debris flow & flash floods, Quezón Province, Philippines

Jerry A. Fano,  Flood Control and Sabo Engineering Center,  Philippines

There seems to be an increasing trend in the occurrence of sediment-related disasters in the Philippines. In November 2004 debris flow and flash floods greatly devastated several towns of Quezon and Aurora Provinces, resulting in hundreds of lives lost and damages to infrastructure and homes. The FCSEC conducted a survey and assessment and now develops proposals for countermeasures.