Developing an Upgrade Strategy for Major Water Treatment Plants in Ōita

Climate change impacts

Power outages and damage from river flooding are frequent occurrences in the city of Ōita, such as the torrential rain disaster that hit western Japan in July 2018. The number of short-term heavy rain events with precipitation ⩾ 50 mm per hour at the end of the 21^st century is expected to increase, relative to the end of the 20^th century, in various parts of Ōita Prefecture.

Adaptation activity

To date, Ōita City has worked to ensure a safe and secure supply of potable tap water and reliable water management, using three main treatment facilities: the Furugō and Enokuma Water Purification Plants, which use the surface water of the Ōita River as their source, and the Yoko-o Water Purification Plant, which uses the Ōno River. However, the conditions affecting water supply systems have changed dramatically, such as recent large-scale disasters. In order to cope with these environmental changes, the “Strategy for Rebuilding Major Water Treatment Plants in Ōita City: Ōita Water Supply System to Support Life for the Next 100 Years” was confirmed in March 2020.

One of the five main policies (see Note) is "Optimizing the Upgrade of Three Major Water Treatment Plants," which proposes the construction of disaster-resistant water supply facilities by constructing a pipeline system to connect the plants, floodproofing the facilities, and increasing their resilience to power outages in order to enhance disaster mitigation and allow for rapid post-disaster recovery. For example, an emergency backup system for the three plants has been developed. This minimizes interruption of the water supply by allowing water resources to be diverted between facilities in the event that any of the plants is incapacitated. Two sections of emergency pipeline between the Furugō and Yoko-o plants, and the Furugō and Enokuma Plants are expected to be in service by FY2023 (Fig. 1).

In mapping of Ōita flood hazards, flooding of up to 5m to 10m has been anticipated at the Furugō and Enokuma plants. Therefore, flood control measures are being taken for electrical equipment and machinery at each site. In terms of physical changes, waterproof doors are being installed, and the elevation of windows and ducts is being raised, in addition to the construction of the emergency pipeline systems. In terms of administration, organizational business continuity plans (BCPs) are being developed (Fig. 2). In addition, mobile water purification systems (Mobile Siphon Tank, MST (Fig. 3)) are being introduced, which can be used in the event of emergencies. MSTs would allow treatment of water with high turbidity from local torrential rains, that would not normally be possible at the water treatment plant, or can be transported to sites where water delivery systems have been disrupted.

Another strategic goal, the "systematic renewal of water supply facilities," promotes preventive maintenance and functional enhancement of utilities, such as the renovation and development of pipelines for key reservoirs and also high-priority pipelines for important facilities such as major hospitals and administration services.

Outputs / Expected benefits

The Upgrade Strategy for Major Water Treatment Plants in Ōita City enables appropriate solutions to the challenges facing water supply. In response to changes in society and the environment, a sustainable water supply system will be developed that looks 100 years ahead without postponing issues for future generations.

Footnote
(NOTE)The five main objectives of the "Upgrade Strategy for Major Water Treatment Plants in Ōita City" are: ① optimal renovation of three major water treatment plants; ② utilization of the latest technology such as IoT; ③ systematic renewal of water supply facilities; ④ ensuring the supply of potable tap water; and ⑤ strengthening of operational infrastructure.