Detect Sewer Overflow from Torrential Rain Using Manhole Sensors

Prevent sewer systems from overflowing as a result of frequent torrential rain

In recent years Japan has often experienced unexpected intense rain due to the development of cumulonimbus clouds; these are frequently occurring torrential downpours. According to the Meteorological Agency, in 2014 short period heavy rainfall exceeding 50 millimeters per hour occurred 237 times (at 1,000 observation points). The long-term statistics from 1976 clearly shows this as an increasing trend.

Due to such torrential downpours, sewer systems have overflowed and numerous instances of flood damage have been incurred mainly in cities. Equipping manholes in sewer line infrastructures with sensors can measure water levels and accurately detect early signs of overflow . However, the operating cost for each sensor is expensive, making it difficult to install sensors across a wide area.

For this reason the number of sensors installed needs to be minimized. However, the effective installation of sensors was largely dependent on intuition and experience of the workers and now there are growing expectations on ICT to achieve this.

Reducing the number of manholes equipped with sensors to cut operational costs by 90%

By analyzing the time required for water to flow from upstream pipes to downstream locations (based on land topography and sewer pipe shape and length) Fujitsu Laboratories developed a technology to determine the optimal the locations and number of manholes for sensors to be installed.


How sensor locations are identified based on time required for water to flow


Comparison between existing methods for locating sensors and the newly developed method

The time required for water to flow from upstream pipes to downstream locations is calculated, and the correlation between changes in upstream water levels and changes in downstream water levels is computed by taking this time into account. This makes it possible to avoid installing sensors in areas with low correlation, and enables identification of the locations and the number of manholes to be installed with sensors.

These technologies make it possible to reduce the number of sensor installations to approximately one-fifth, while at the same time provide the same sewer water flow tracking at approximately one-fifth of the cost.

The technologies help control power consumption while selectively controlling sensors to match typical rainfall patterns. This ensures accurate measurements can be maintained while reducing power consumption by a maximum of 70%. Assuming that sensors are operated using solar cells or other renewable-energy sources, the per-unit operating costs of a sensor could be reduced by roughly 90%.


Sensing power control technology that adjusts to circumstances

Preparation for sudden torrential downpours

Predicting the potential overflow of sewer systems makes it possible to take counter measures in advance, such as piling up sandbags where rainwater will potentially overflow. By acting on these countermeasures in advance, flood damage is minimized and there is greater possibility to significantly prevent extensive destruction.

Fujitsu Laboratories plans to further reduce the power consumption and costs of sensor devices, and is aiming to commercially launch these devices during fiscal 2015. Going forward, Fujitsu Laboratories will consider ways to use sensor data as well the installation of sensors to contribute to the development of disaster resilient communities.