Abstract
Overview of Sendai and its Water Problem▼
・Sendai, Japan, a city prone to natural disasters, faces significant water security challenges.
・The 2011 earthquake exposed the vulnerability of the centralized water system, highlighting the need for a more resilient approach.
Decentralized Intervention▼
・To enhance resilience and water security, a decentralized water reuse and recycling system is proposed for Sendai.
・This approach promotes community-level water management, reduces reliance on external sources, and conserves precious water resources.
Positive Outcomes and Assessment▼
・Decentralized systems offer cost-effectiveness, enhanced resilience, and increased community engagement compared to alternative solutions: centralized water recycle plant, desalination plant.
・Investing in these systems will help Sendai build a more sustainable and secure water future, minimizing the impact of future disasters.
Sendai – A City at Risk
Sendai, a bustling metropolis nestled along Japan’s picturesque coastline, is a city intimately acquainted with the capricious nature of its environment. Earthquakes, tsunamis, and floods are recurring threats, leaving an indelible mark on the city’s history and infrastructure. The Great East Japan Earthquake of 2011, a seismic event of catastrophic proportions, serves as a poignant reminder of Sendai’s vulnerability. The earthquake, and the subsequent tsunami that ravaged the city’s shores, exposed critical weaknesses in its lifeline systems, particularly its water infrastructure.
Fig. 1 Hydrology of Sendai Region
Fig. 2 Timeline of Earthquake & Tsunami Death Toll in Sendai Region over Time
Sendai’s Vulnerability – A Deeper Dive
While Sendai has implemented measures like reinforcing pipes and installing seismic-resistant joints to mitigate damage from earthquakes, the city’s water system still faces significant challenges in terms of resilience and disaster preparedness. The intricate network of pipes and treatment facilities, designed to deliver a constant flow of clean water to homes and businesses, remains vulnerable to disruptions caused by major seismic events. The 2011 earthquake, for instance, caused widespread damage to the water infrastructure, leading to significant water outages and highlighting the limitations of relying solely on a centralized system. [1][2][3]
In the wake of the 2011 disaster, it became evident that even with reinforced pipes and dual pipeline systems, the centralized nature of Sendai’s water infrastructure posed a significant risk. Damage to a critical component, such as a major pipeline or treatment plant, could disrupt the entire system, leaving large portions of the city without water. [2][3]
The experience of 2011 underscored the need for a more comprehensive approach to water resilience in Sendai, one that goes beyond simply reinforcing existing infrastructure. Diversifying water sources, promoting decentralized water management, and fostering community-level preparedness are crucial steps towards ensuring a more secure and sustainable water future for the city.
Fig. 3 Impact of the 2011 Earthquake on Sendai’s Water Supply
Chart 1 Trends in Emergency Water Distribution Following the 2011 Earthquake
Sendai’s Water Portfolio – Heavy Reliance on Reservoirs
An examination of Sendai’s water portfolio reveals a heavy reliance on reservoirs, which constitute approximately 75% of the city’s water supply. While reservoirs are a crucial component of water management, this over-dependence creates an inherent vulnerability, especially in a region prone to natural disasters. Reservoirs are susceptible to damage, contamination, or reduced capacity due to earthquakes, heavy rainfall, and landslides. This reliance on reservoirs, coupled with the inherent vulnerability of a centralized system, underscores the need for a more diversified and resilient approach to water management in Sendai.[4]
Fig. 4 Sendai’s Water Portfolio and Distribution Network
Decentralization: A Pathway to Water Resilience
To address the vulnerabilities of Sendai’s current water system, this project proposes a shift towards a decentralized approach. Decentralized water management involves distributing water treatment and storage capabilities across numerous points within the city, reducing reliance on a single, centralized infrastructure. This approach offers greater resilience to natural disasters, as damage to one part of the system does not necessarily cripple the entire water supply. In essence, it’s about creating a network of smaller, interconnected water systems that can operate independently or in conjunction with the main system, providing flexibility and redundancy in times of crisis.
Fig. 5 Proposed Solution for Sendai’s Water Resilience & Water Security
Decentralized water systems utilize a variety of on-site technologies to capture, treat, and reuse water, reducing dependence on external sources and promoting conservation. Rainwater harvesting systems collect and store rainwater from rooftops and other surfaces, providing a valuable source of water for non-potable uses like toilet flushing and irrigation. Greywater treatment systems, on the other hand, treat gently used water from sinks, showers, and laundry, allowing it to be safely reused for similar purposes. By implementing these technologies in homes, businesses, and public buildings, Sendai can diversify its water portfolio and reduce the overall demand on the centralized system.
The benefits of decentralized water management extend beyond increased resilience and water security. By promoting on-site water reuse and recycling, these systems contribute to environmental sustainability by conserving water resources and reducing wastewater discharge. Moreover, decentralized systems empower communities to take ownership of their water management, fostering a sense of responsibility and encouraging active participation in water conservation efforts. This community-based approach can lead to more efficient water use, greater awareness of water-related issues, and a stronger sense of collective resilience in the face of natural disasters.
Fig. 6 Comparison of Decentralized Water Management System with Alternative Options
Implementation: A Phased Approach
To effectively integrate decentralized water systems into Sendai’s urban fabric, a phased implementation plan is proposed. This plan outlines a gradual rollout of the systems, starting with a pilot project in a local elementary school. The school setting provides an ideal environment to demonstrate the feasibility and benefits of decentralized water management, educating students and the community about its importance. The pilot project will serve as a model for future installations, allowing for refinement of the system design and implementation strategies.
Following the successful completion of the pilot project, the implementation will expand to include a wider range of public facilities, such as hospitals, community centers, and government buildings. This phased approach allows for gradual adoption of the technology, ensuring proper integration with existing infrastructure and providing opportunities for learning and adaptation along the way. By 2040, the goal is to extend the implementation to commercial buildings, further diversifying Sendai’s water resources and enhancing its overall resilience. This long-term vision aims to create a city where water security is not solely reliant on a centralized system but is also supported by a network of decentralized, community-based solutions.
Fig. 7 Policy Intervention -Introduction of Decentralized Water Reuse/ Recycle System
Projected Building Coverage and Cost
The proposed policy envisions a phased adoption of decentralized water reuse and recycling systems in Sendai’s public and commercial buildings. This phased approach will gradually increase the number of buildings equipped with these systems over time. By 2040, it is projected that approximately 600 public facilities, including schools, hospitals, and community centers, will be covered by this policy. This represents a significant portion of Sendai’s building stock and highlights the potential for widespread impact in enhancing the city’s water resilience.
The estimated cost for implementing this intervention is 1.5 billion yen by 2040, with 1 billion yen for the initial setup and 0.5 billion yen for cumulative operation and maintenance (O&M) costs.
Chart 2 Estimaed Number of Covered Buildings and Its Cost: 2025-2040
Funding the Pilot Project (2025-2030)
This pilot project, introducing decentralized water systems in a school facility, will be a crucial step towards demonstrating the feasibility and benefits of this approach. To ensure the success of this initiative, a multi-faceted funding strategy will be employed, drawing on various sources[5][6]:
- Japanese Government’s Reconstruction Grant: This grant, specifically designed to support disaster resilience projects, will provide a significant portion of the funding for the pilot project.
- Sendai City Tax Revenue: A portion of the city’s tax revenue will be allocated to support this innovative water management initiative, demonstrating the city’s commitment to building a more resilient future.
- Miyagi Prefecture Allocation: The Miyagi Prefecture government will also contribute to the funding of the pilot project, recognizing the importance of this initiative for the entire region.
By securing funding from diverse sources, the pilot project gains greater financial stability and demonstrates a shared commitment to enhancing Sendai’s water resilience. This collaborative funding approach will help ensure the successful implementation of the pilot project and pave the way for broader adoption of decentralized water systems throughout the city.
Fig. 8 Potential Financial Sources for the Test-pilot with School Facility – 2025-2030
Impact Assessment – Enhanced Water Security
By diversifying water sources and reducing reliance on the centralized system, this intervention will significantly enhance Sendai’s water security. The phased implementation plan will gradually increase the city’s capacity to store and treat water locally, providing a crucial buffer during emergencies. By 2031, decentralized systems are projected to provide backup water sources equivalent to 2% of Sendai’s daily demand, increasing to 5% by 2040. This means that even if the main water supply is disrupted, a significant portion of the city’s water needs can still be met through these decentralized systems.
Fig. 9 Long-Term Changes in Water Portfolio due to the Proposed Policy
Cost-Effectiveness – A Financially Sound Investment
The normalized initial cost, which is the cost per cubic meter of water produced, is significantly lower for decentralized systems. Specifically, the normalized initial cost for the decentralized system is projected to be 256 JPY/m3, while the centralized water reuse plant and desalination plant scenarios have normalized costs of 103,407 JPY/m3 and 75,936 JPY/m3, respectively.
Furthermore, the normalized annual O&M cost for decentralized systems is also projected to be lower than the alternatives. At 2040, the normalized annual O&M cost for the decentralized system is estimated to be 34 JPY/m3, compared to 365 JPY/m3 for the centralized reuse plant and 152 JPY/m3 for the desalination plant. This long-term cost advantage makes decentralized systems a sustainable and financially sound investment for Sendai’s water future. By reducing reliance on costly centralized infrastructure and minimizing water waste, decentralized systems can contribute to significant cost savings for the city over time.
Fig. 10 Decentralized Water Recycle/ Reuse Sytsem vs. Centralized Water Recycling vs. Desalination: A Cost-Effectiveness Analysis for Sendai City Show drafts
The Pilot Project – A School as a Model for Decentralization
The first phase of this intervention involves a pilot project in an elementary school. This pilot serves several purposes:
- Demonstrating feasibility: It will showcase the practical application of decentralized water systems in a real-world setting.
- Gathering data: The pilot will provide valuable data on system performance, water savings, and user experience.
The chosen school for this pilot project is strategically located in a densely populated area with over 1,000 households within a 200m radius. This ensures that the project has a significant impact on the community and provides a valuable opportunity for outreach and education. The school building itself will be equipped with a comprehensive decentralized water system, incorporating rainwater harvesting, greywater treatment, and other innovative technologies.
Fig. 11 The Location of Elementary School and Its Proximity to Tsunami Flood Risk Area in Sendai City
Decentralized Water Reuse in Schools – A Closer Look
The pilot project will showcase a real-world application of a decentralized water reuse and recycling system within a school. This section delves into the technical aspects of the system, highlighting its design and benefits.
The accompanying diagram illustrates the system’s operation within the school building. Greywater, indicated by the orange arrows, is collected from sinks, showers, and other sources. It is then treated in the rooftop system, highlighted in green. This strategic placement minimizes energy consumption by reducing the need to pump water up and down from ground level. The treated greywater is then stored and can be used for non-potable purposes such as toilet flushing and irrigation.
Furthermore, the integration of “blue infrastructure” elements, such as blue roofs, further enhances the system’s water reuse capabilities and contributes to overall sustainability. This model demonstrates how decentralized systems can be seamlessly integrated into existing buildings, maximizing efficiency and minimizing space requirements.
The estimated water savings from this system are significant. The model predicts that approximately 8.15 cubic meters of water can be recycled per day, enough to meet the daily water needs of roughly 34 people. This not only reduces the school’s reliance on the municipal water supply but also promotes water conservation and reduces the environmental impact associated with water treatment and distribution.
Fig. 12 Integrated Decentralized Water Management System for a School Facility: Greywater Recycling, Blackwater Treatment, and Rainwater Harvesting Show drafts
Emergency Preparedness
This decentralized water management system is not only sustainable but also designed to provide essential water services even during emergencies such as natural disasters. To ensure functionality during power outages, which are common after earthquakes or severe storms, each building can be equipped with independent power sources. These could include:
Solar panels with battery storage: This allows for the collection and storage of solar energy, providing a reliable backup power source during daylight hours and beyond.
Connection to a microgrid with backup generators: This approach allows buildings to share energy resources and potentially benefit from a larger-scale backup generator, further enhancing resilience.
Fig. 13 Integrated Decentralized Water and Energy System for a School Facility
By incorporating these backup power solutions, the decentralized water system ensures the continued operation of critical services, such as greywater recycling for toilet flushing and rainwater harvesting for drinking, even when the main power grid is down. This not only supports the school’s daily operations but also enhances its ability to function as a community shelter during emergencies, providing a safe and resilient haven for those in need.
Benefits Beyond Water Savings – Education, Engagement, and Community Ownership
The integration of decentralized water systems in schools offers a multitude of benefits that extend beyond mere water savings. It provides a unique opportunity to educate students and the community about the importance of water conservation and sustainable water management practices. By having a tangible example of water reuse and recycling within their own school environment, students gain a deeper understanding of the water cycle and the interconnectedness of water resources.
Moreover, these systems foster community engagement by creating a shared responsibility for water management. Schools can become hubs for water education and outreach, organizing workshops, tours, and awareness campaigns to involve the broader community. This participatory approach not only promotes water conservation but also strengthens social cohesion and encourages collective action towards a more sustainable future.
Furthermore, decentralized systems equipped with IoT and digital monitoring tools provide real-time data on water usage, system performance, and potential issues. This information can be shared with residents, empowering them to make informed decisions about their water consumption and contribute to the overall efficiency of the system. By fostering transparency and community ownership, decentralized water systems can catalyze a broader shift towards more sustainable water practices in Sendai.
Fig. 14 Fostering Education, Community Engagement, and Local Ownership for a Sustainable Future
Considerations and Challenges
While decentralized water systems offer a promising pathway towards a more resilient and sustainable water future for Sendai, it is essential to acknowledge and address the potential challenges associated with their implementation. These challenges can be categorized into two main areas: policy and operation & maintenance.
Policy:
Existing regulations may need to be adapted to accommodate the widespread use of greywater recycling systems. This includes establishing clear guidelines for greywater quality, treatment standards, and safe reuse practices.
Implementing decentralized systems requires significant financial investment. Securing long-term funding mechanisms, such as public-private partnerships, subsidies, or innovative financing models, is crucial for the widespread adoption and maintenance of these systems.
Operation & Maintenance:
Depending on the specific building and site constraints, space optimization may be necessary to accommodate the various components of a decentralized water system. Modular systems offer greater flexibility in this regard, allowing for customized designs that fit within existing infrastructure.
Decentralized water systems, particularly those involving treatment and pumping processes, require a reliable power supply. Ensuring continuous operation, especially during emergencies, may necessitate the integration of renewable energy sources like solar panels or battery backup systems.
Addressing these challenges proactively will be crucial for the successful implementation and long-term sustainability of decentralized water systems in Sendai. By fostering collaboration among policymakers, technology providers, and community stakeholders, these challenges can be transformed into opportunities for innovation and community empowerment.
Conclusion – A Vision for a Water-Resilient Sendai
The devastating impact of the 2011 Great East Japan Earthquake served as a stark reminder of the vulnerability of centralized water systems in the face of natural disasters. Sendai, with its history of seismic activity and its heavy reliance on reservoirs, needs a new approach to water management—one that prioritizes resilience, sustainability, and community engagement.
This project proposes a solution: the implementation of decentralized water reuse and recycling systems throughout the city. By diversifying water sources, empowering communities, and promoting water conservation, Sendai can build a more robust and adaptable water infrastructure. The phased implementation plan, starting with a pilot project in a school and expanding to public and commercial buildings, will gradually transform Sendai’s water landscape.
This decentralized approach offers numerous benefits, including enhanced water security, reduced environmental impact, and increased community engagement. The cost-effectiveness of decentralized systems, compared to centralized alternatives, makes it a financially sound investment for Sendai’s future.
By embracing innovation and community participation, Sendai can create a model for water resilience in disaster-prone regions. This vision of a water-secure future, where communities are empowered to manage their water resources sustainably, is within reach. Let us work together to make this vision a reality for Sendai and inspire other cities to follow suit.
Reference
[1] Sendai City Waterworks Bureau. 2011. “Damage and Restoration Status of Water Supply Facilities in the Great East Japan Earthquake” [東日本大震災における水道施設等の被害及び復旧状況]. Accessed December 7, 2024. https://www.mlit.go.jp/common/000207872.pdf
[2] Sendai City. 2011. “Damage Situation of the Great East Japan Earthquake in Sendai” [東日本大震災における本市の被害状況等]. Accessed December 7, 2024. https://www.city.sendai.jp/okyutaisaku/shise/daishinsai/higai.html
[3] Ministry of Health, Labour and Welfare. 2011. “Overview of the Damage to Water Supply Facilities Caused by the Great East Japan Earthquake” [東日本大震災水道施設被害状況調査の概要]. Accessed December 7, 2024. https://www.mhlw.go.jp/stf/shingi/2r9852000002qek5-att/2r9852000002qep4.pdf
[4] Sendai City Waterworks Bureau. 2020. “Current Status and Issues of Sendai City Waterworks in 2020, Priority Measures” [令和2年度 仙台市水道事業の現状と課題 重点施策]. Accessed December 7, 2024. https://www.suidou.city.sendai.jp/nx_image/01-jigyou/01-309-kihon-15juten2.pdf
[5] “About the Framework for Reconstruction, Reconstruction Agency, April 30, Reiwa 6.” [復興の枠組みについて]. Accessed December 4, 2024. https://www.reconstruction.go.jp/topics/main-cat7/sub-cat7-2/20240430_03_shiryo03-01.pdf.
[6] Sendai City Hall. “Reconstruction Grant Project Plan.”[復興交付金事業計画]. Accessed December 4, 2024. https://www.city.sendai.jp/shinsaifukko/shise/daishinsai/fukko/kofukin/index.html.
Figures/ Charts
Fig. 1 Data from Ministry of Land, Infrastructure, Transport and Tourism. n.d. “Geological Cross Section” [地質断面図]. Accessed October 14, 2024. https://nlftp.mlit.go.jp/kokjo/inspect/landclassification/land/detail/verticality/F4/kouiki.html.
Fig. 2 Data from: Japan Meteorological Agency. n.d. “Major Earthquakes and Tsunamis that Damaged Miyagi Prefecture” [宮城県に被害を及ぼした主な地震・津波]. Accessed December 5, 2024. https://www.jma-net.go.jp/sendai/knowledge/earthquake/higai.html.
Image from: Tanaka, Akira. 2023. “Seismic Intensity 6 Upper, 1695 People Stranded at the Airport: Survived with Strangers” [震度6強、空港に取り残された1695人 見知らぬ相手と生き延びた]. Asahi Shimbun, Accessed March 9, 2023. https://www.asahi.com/articles/ASPB76TRZPB5UNHB00W.html.
Fig. 3, Chart 1 Data from: [1]
Fig. 4 Data from: [4]
Fig. 8 Data from: [5], [6]
Fig. 11 Data from: Miyagi Prefecture. 2023. “Shapefile Data Pertaining to Miyagi Prefecture Flood Inundation Estimated Area Map.”[宮城県洪水浸水想定区域図に係るシェープデータ]. Miyagi Prefecture and Municipalities Joint Open Data Portal Site. February 20, 2023. https://miyagi.dataeye.jp/datasets/283.
Fig. 14. Base-image Generated by Google Imagen. December 3, 2024