Disaster Prevention Using Manholes on the Streets?! Preventing Flood Damage from Torrential Rains

New Flooding Countermeasures Needed for Frequent Torrential Rains

In recent years, torrential rains have occurred frequently. A torrential rain is defined as a locally concentrated downpour that unexpectedly occurs due to atmospheric instability. It is difficult to accurately predict torrential rains with weather forecasts. Since torrential rains may cause serious damage that exceeds that of current assumptions, the Flood Control Act was revised and the revision was put into force in July 2015 as a countermeasure against flooding.

For example, the revision to the Flood Control Act partially revised the flood risk warning system for administrators and owners of underground shopping malls based on sewage water-level information. Under the revised Act, prefectural and local governments are obliged to designate sewer inundation risk areas and urged to take flooding countermeasures such as those for river flooding. At the same time, various countermeasures have been taken to minimize damage, such as rebuilding and expanding drainage systems and collecting water-level data faster.

Using the conventional method to measure water levels, it is necessary to use fiber optic lines to lay dedicated cables to the drainage pipe measuring point. However, use of the method that involves installation of battery-powered water-level sensors on the bottoms of manhole covers requires frequent battery changes, which gives rise to the issue of high maintenance costs.

Reducing Operating Costs by Quickly Deploying a Cloud-based Solution

Fujitsu Laboratories has been conducting research and development on a sewer system flood detection technology for sewage works operators to reduce the damage caused by torrential rains and flash floods. Based on a field trial conducted in the City of Koriyama in 2015, Fujitsu resolved to put its solution on the market, and Fujitsu launched the Sewer System Flood Detection Solution on August 15, 2016.

Image of manhole cover installation

This solution employs energy harvesting technology* that converts small amounts of energy harvested from light, heat, and vibrations into electricity. It uses a sensor attached to an existing sewer manhole to collect water-level data, and wireless communications transmit this data up to the cloud every five minutes. As the solution does not require a power source or laying of fiber optic lines, it can be deployed quickly while keeping deployment costs down.

The water-level data collection sensor is powered by a thermoelectric converter that converts energy arising from temperature differentials in the manhole cover into electricity. This thermoelectric converter extends the battery replacement cycle, which is about 10 months for a sensor powered by batteries alone, to 5 years, which makes it possible to reduce operating costs. In addition, miniaturizing the converter and improving its efficiency has made it the first such unit in Japan that can be directly attached to a manhole cover**.

*: An epoch-making technology that enables long-term energy provision without charging/replacing batteries or refueling. Various applications are being considered with an eye toward the realization of a safe, secure society.
**: A technology developed by Fujitsu Kyushu Network Technologies.

Structure of the sewer system flood detection solution

Limiting the Damage due to Flooding from Torrential Rains

This solution regularly collects and aggregates data on drainage pipe water levels from manholes and transmits the data to the cloud in order to quickly detect sudden rises in drainage pipe water levels. Since it also enables this information to be grasped on a map in an easy-to-understand manner, those responsible for disaster prevention in local governments can immediately notify local residents of flood information in order to limit the damage resulting from flooding accompanying torrential rains. In addition, accumulated water-level data can be useful when evaluating sewer drainage plans and designing system renovation plans.

Fujitsu will continue to conduct research and development on solutions while maintaining its focus on regional safety and security.

Voices from the City of Koriyama where the field trial was conducted
  • By monitoring sewer system water levels in real time, we can quickly dispatch personnel to the relevant site, perform an emergency operation, and distribute evacuation information.
  • Quantifying changes in water levels makes it possible to verify sewer drainage performance. We can minimize flood damage by using this system to plan storm sewage measures.
  • The energy harvesting technology, which eliminates the need to replace batteries for long period of time, will improve worker safety and reduce maintenance costs.