Basin-wide flood control, a flood control measure implemented through both hard and soft measures, involves various stakeholders in the river basin working together. "Basin-wide flood control projects" have also begun to clarify the overall picture of the efforts for each river system. However, with many stakeholders and a wide range of measures, there are concerns that it is difficult to see how to coordinate effectively, which measures should be prioritized, and what effects they will have. To overcome these challenges and move towards full-scale implementation, we spoke with four people at PACIFIC CONSULTANTS who are at the forefront of basin-wide flood control efforts: Ryoji HIRAKAWA, Chief Technical General Manager; Shogo NAGAO, Urban Management Sec., Transportation Planning Dept., Social Innovation Div. Haruka SUZUKI, Regional Flood Control Planning Office, Basin Planning Department, Land Infrastructure Div. Headquarters; and Hiroaki MAEDA, DS Promotion Office and Resilience Promotion Office, Disaster Prevention Dept. Department, Digital Service Div..
INDEX
- Why "river basin flood control" now?
- Why is river basin flood control so difficult to implement?
- Approaches to promoting river basin flood control
- Approach 1: Evaluate flood control measures and urban development as an integrated whole.
- Approach ② Supporting businesses by refining hazard maps
- Approach ③: Enhancement of countermeasures based on individual risk assessment and improvement of regional functions and value.
- What PACIFIC CONSULTANTS can do
Why "river basin flood control" now?
The shift away from traditional flood control methods, which are primarily driven by river administrators and focused on infrastructure, is driven by the increasing severity and frequency of floods due to climate change. According to data from the Japan Meteorological Agency, even just looking at rainfall patterns, the number of short-duration heavy rain events with hourly rainfall exceeding 50 mm averaged 226 times in the 10-year period from 1976 to 1985, but increased to 334 times in the 10-year period from 2015 to 2024, an increase of approximately 1.5 times. It is believed that in the future, increased rainfall due to rising sea surface temperatures associated with global warming and the expansion of damage due to larger typhoons are unavoidable.
Furthermore, flood damage is becoming more complex and severe. For example, heavy rainfall on slopes loosened by earthquakes can cause numerous landslides, leading to many debris flows. These flows send large amounts of soil and driftwood downstream, destroying bridges, levees, and even buildings. In some cases, this develops into secondary disasters, such as damage to power plants and water and sewage facilities, paralyzing urban functions.
In this context, the government has made a major shift in its approach to flood control. It has moved towards "basin-wide flood control," which considers flood control measures for the entire river basin, including not only the catchment area and river area, but also the downstream flood plain. Depending on the characteristics of each region, it is implementing a multi-layered approach, integrating both hard and soft measures, with three main objectives: (1) to prevent or reduce flooding as much as possible, (2) to reduce the number of people affected, and (3) to mitigate damage and facilitate early recovery and reconstruction.
source: "Basic Concepts of Basin-Based Flood Control" (Ministry of Land, Infrastructure, Transport and Tourism)
Why is river basin flood control so difficult to implement?
No one would disagree that future flood control measures will be a total war effort involving the entire river basin. However, there are many challenges, and progress is currently slow. One challenge is that the target field is extremely broad, and the stakeholders involved are diverse, including the national government, prefectures, municipalities, private companies, and residents, as well as a wide range of countermeasures. Another challenge is that it is difficult to see who will do what, how to coordinate the countermeasures, and what effects the countermeasures will have on the river basin. In particular, there is insufficient accumulated experience in countermeasures for damage reduction and early recovery and reconstruction in floodplains, which are newly required in addition to the conventional catchment areas and river areas. There is a lack of know-how in the development and implementation of elemental technologies, and the countermeasures that should be taken, their effects, and the specific effects and benefits for the municipalities, companies, and residents involved are not clear.
Approaches to promoting river basin flood control
Approach 1: Evaluate flood control measures and urban development as an integrated whole.
For example, "relocation to low-risk land" is said to be a promising option. However, for local governments, urban development challenges are not limited to flood control. While anticipating population decline and an aging society with a low birthrate, there are many challenges from the perspective of sustainable urban development, such as how to promote the revitalization of central urban areas, the development of industries, the maintenance of daily living environments, the stable provision of education, medical and nursing care services, and the securing of safe means of transportation. Prioritizing only flood control may make it more difficult to solve other problems. By implementing policies that combine flood control and urban development, a positive cycle that is effective for both flood control and urban development must be created. To achieve this, it is necessary to quantitatively evaluate the effects from a cross-sectoral perspective that includes not only flood control but also urban development.
Approach ② Supporting businesses by refining hazard maps
To advance watershed control in flood-prone areas, private real estate developers and housing companies have a significant role to play in developing land that is resilient to floods and providing housing. However, private companies have not made much progress in this area. This is because the business model is not yet established, and the benefits of investment are not clear. Currently, they only check whether the land is located in a landslide hazard zone on the hazard map, and if it is, they abandon development because they cannot sell houses. This is about the extent of understanding the information. They have not been able to translate this into unique corporate initiatives that increase the value of the land and buildings.
However, if, for example, a real estate developer can perform a detailed simulation of the risk of landslides on land they own, it will lead to a more precise representation of publicly available hazard maps. Knowing how much rainfall will cause slope collapses, where and how they will occur, and how the resulting debris flows will spread will allow for measures such as land development and zoning, the location and direction of fences, the creation of green spaces, and the design of evacuation routes. Even if a property is located within a warning zone on a hazard map, it is possible to mitigate risks and increase the value of the land through unique measures. Furthermore, in residential design, by utilizing engineering knowledge such as hydraulics to devise construction methods and strengthen specifications to create flood-resistant homes that take into account the risk of flooding and landslides on the land, it becomes possible to provide homes that are resistant to all hazards, including earthquakes, fires, floods, and landslides, offering higher value and leading to new business opportunities.
If we can combine civil engineering and architecture based on detailed disaster risk simulations to improve land use and increase the added value of buildings, we can link flood control measures to business enhancements and greatly encourage private companies to participate in basin-wide flood control.
Created by our company based on existing materials (provided by Professor Takebayashi of the RiSM Research Dept., Kyoto University).
Approach ③: Enhancement of countermeasures based on individual risk assessment and improvement of regional functions and value.
In basin-wide flood control efforts in flood-prone areas, it is necessary to reduce flood risk throughout the entire region, including the flood-prone areas themselves. Protecting key factories and large-scale businesses within this context is a crucial issue. The impact of floods is not limited to a single company; if operations are suspended for an extended period, it can spread through the supply chain to surrounding small and medium-sized enterprises and the local economy, potentially causing widespread damage. However, despite the nationwide development of hazard maps and other publicly available information by the government, these are not adequately translating into concrete countermeasures. One reason for this is that hazards are not being evaluated as "risks," which prevents them from being linked to specific countermeasures and investment decisions.
For example, in a complex of buildings with different roles and equipment, it's necessary to identify where the equipment vulnerabilities lie. Furthermore, understanding how these vulnerabilities will affect the production line as flooding progresses allows for the clarification of realistic priorities and investment scales for countermeasures. Conducting such risk assessments at the individual site level makes it possible to set goals such as "what scale of flooding to cope with" and "to what extent to ensure business continuity," and to concretize the measures necessary to achieve them. Implementing countermeasures based on this will not only enhance the company's business continuity but also contribute to reducing damage throughout the region, becoming a crucial element in improving the effectiveness of river basin flood control.
Furthermore, developers redeveloping specific areas in urban centers also have a significant role to play as key players in basin-wide flood control. Addressing basin-wide flood control is not just a disaster response issue; it is a management challenge that affects the profitability and competitiveness of development projects. In recent years, flood risk has increasingly influenced real estate valuations, tenant selection, and investment decisions, and the ability to appropriately incorporate future risks will determine the competitiveness of development projects. Therefore, if these risks can be properly understood and visualized, the prioritization of countermeasures and the accuracy of investment decisions will greatly improve. By analyzing the progression of flooding over time and clearly identifying "where flooding will occur at what rainfall level" and "which facilities and spaces will become bottlenecks," rational countermeasures that are neither excessive nor insufficient can be implemented. Specifically, this can lead to the following business benefits.
- Advanced preventative measures during the design phase (optimization of equipment placement, water stoppage plans, etc.)
- Strengthening tenant attraction by adding safety as a value proposition
- Improving our ability to explain our policies to investors through compliance with ESG and SSBJ standards *
- Maintaining and improving asset value while incorporating future risks.
* ESG standards established to strengthen sustainability information disclosure by Japanese companies.
Furthermore, sharing countermeasures that take into account the risks across the entire district with stakeholders facilitates cost-effectiveness-based consensus building, directly leading to faster and more sophisticated decision-making in large-scale redevelopment projects.
The accumulation of sophisticated countermeasures based on such micro-level risk assessments will ultimately lead to the formation of disaster-resilient urban infrastructure, thereby improving the overall functionality and value of the district.
What PACIFIC CONSULTANTS can do
Promoting basin-wide flood control is a total effort; otherwise, it cannot be effective. There are two important points for its realization. First, measures must be promoted in a way that is consistent with the long-term goal of realizing compact cities as sustainable urban development. Second, the responsibility for basin-wide flood control must be expanded from being solely government-led to including the private sector. Without these two points, basin-wide flood control cannot be achieved. What is most needed now is the establishment and utilization of a method for quantitatively evaluating the effectiveness of various measures from multiple perspectives and selecting the future direction of the city, as well as the establishment of a business model that encourages the active participation of private companies in basin-wide flood control.
PACIFIC CONSULTANTS has a 75-year history as a comprehensive construction consulting firm, and in its new efforts in basin-wide flood control, it has been quick to develop a "quantitative evaluation method for the multifaceted effects of countermeasures" utilizing applied urban economic models accumulated through its work in the field of transportation planning. Applied urban economic models are models for analyzing, predicting, and evaluating the impact of urban and transportation policies on urban structure. By applying this model, we aim to quantitatively evaluate what effects will result not only in reducing flood risk, but also in various aspects such as urban development, economy, industry, and the environment, when urban development (such as guiding residential and industrial development) is carried out in conjunction with flood control measures. This will clarify what value flood control measures have in terms of urban development, and will lead to EBPM (Evidence-Based Policy Making), that is, policy making for urban development based on objective data.
Furthermore, by applying the detailed flood simulation technology cultivated in the river management field to flood-prone areas, we are now able to conduct detailed inundation analyses of residential areas, factories, and buildings. We are already conducting concrete discussions with many local governments, companies operating large-scale factories, real estate companies developing land, and developers working on urban development in prime locations in the city center, on how to minimize damage in flood-prone areas.
Furthermore, we are considering partnering with home builders to develop and brand homes that are resistant to all kinds of disasters, including not only earthquakes and fires but also floods.
River basin flood control can only be achieved through collaboration across multiple fields. PACIFIC CONSULTANTS believes that its comprehensive capabilities, encompassing a wide range of technical fields, allow it to act as a hub. Already, young, next-generation engineers are passionately and proactively utilizing cutting-edge technologies with flexible thinking, advancing activities that go beyond the scope of a construction consultant. Moving forward, we will continue to collaborate with all stakeholders working in the river basin to further advance river basin flood control.
