Flood Management
A flood, the most common form of natural disasters over the world, is an overflow of water out of its normal boundary, caused by heavy rain and/or snowmelt, submerges land, destroys private properties and public facilities, and sometimes claims human lives. Basic concept of flood management should be planned to apply "least damage approach" to flood of unknown magnitude, as we cannot tell the size of flood that will come in foreseeable future. Here, "flood of unknown magnitude" means both "flood within design safety level" and "exceeding flood". Generally, flood control facilities such as continuous dikes, flood control dams/retarding basins, etc. are planned with their dimensions to achieve safety level under targeted magnitude of flood (design flood). However, occurrence of precipitation of extreme intensity is increasingly experienced, supposedly caused by global warming. Therefore, occurrence of exceeding flood is also increasing, which hits the existing flood control facilities and causes extensive damages. There are two types of flood countermeasures: one is "countermeasures to discharge flood water within the river area" (hereinafter called "countermeasures in the river") and the other is "countermeasures to mitigate inundation damage in possibly submerged area" (hereinafter called "countermeasures in the basin"). Two types of countermeasures have both "hardware approach" and "software approach" as shown below: |
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| In "countermeasures in the river", hardware approach is divided into two categories: "qualitative countermeasure" and "quantitative countermeasure". | |
| Qualitative Countermeasure: | Attaining appropriate functions of dikes that are originally envisaged to meet the required conditions |
| Quantitative Countermeasure: | Decreasing disaster risk by discharging river water without permitting overflow |
| In particular, "quantitative countermeasure" should be studied carefully in the earliest stage of flood control planning, for example in "master plan", because it sometimes calls for a large civil works and large cost to implement. There are two approaches in "quantitative countermeasure" as shown below: |
| 1. Increase of river flow capacity by enlarging area of cross section by widening river course, heightening dikes, dredging the river bed, etc. |
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| River Improvement |
| 2. Reduction or control of the peak discharge of flood by using water storage facilities such as dam reservoirs/retarding basins. |
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| Reduction of Flood Peak Discharge by Dam/Retarding Basin |
| Further, even after the development of dikes/revetments is completed, these facilities may not fulfill the required functions if totally or partially damaged by erosion/scouring due to the lack of structural strength. For example, if there are no foot-protection works for revetment, foundation of revetment may be washed away during the flood and revetment may fail. To prevent this, it is important to stabilize the foundation of revetment by the installation of foot protection works. |
 
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| Mechanism of Riverbank Erosion and Revetment Failure |
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| Function of Foot Protection Works |
| NEWJEC has many experiences in river improvement and flood control countermeasures in domestic market. We are trying to expand our field in international market to contribute to building safer communities over the world, especially in developing countries. Our experiences include flood protection techniques that employ traditional methods developed in the long flood-fighting history of Japan. Please see our brochures. |
| Technical Brochures |
| ● Situation after Applying SODA Mattress on the Mekong Riverbank Protection Work (Page 1) |
| ● Situation after Applying SODA Mattress on the Mekong Riverbank Protection Work (Page 2) |
