Overview

The Iwaya Dam is a significant hydroelectric infrastructure project located in the city of Gero, Gifu Prefecture, Japan. It is situated on the Maze River, which serves as a key tributary within the broader Kiso River system. The structure functions as a multipurpose rockfill dam, designed to manage water resources for several critical regional needs. These include flood control, the supply of municipal and industrial water, irrigation for agricultural zones, and the generation of hydroelectric power. The dam's construction represents a strategic integration of civil engineering and energy production in central Japan.

Standing at a height of 127 meters, the Iwaya Dam creates a substantial reservoir that regulates the flow of the Maze River. This reservoir is the primary water source for the Mazegawa No.1 Power Plant, a hydroelectric power station operated by the Chubu Electric Power Company. The power plant has an installed capacity of 288 MW, contributing significantly to the regional energy grid. The facility was commissioned in 1976, marking the beginning of its operational history in the Chubu region. The dam's rockfill construction method provides structural stability while accommodating the varied geological conditions of the Gero area.

The integration of the Iwaya Dam into the Kiso River system enhances the efficiency of water management across the prefecture. By balancing flood control with power generation, the infrastructure supports both environmental stability and economic activity. The Chubu Electric Power Company continues to operate the facility, leveraging the consistent flow of the Maze River to maintain the 288 MW output. This operational model highlights the enduring value of multipurpose dams in modern energy infrastructure, combining reliability with multi-sector utility.

Why it matters

The Iwaya Dam serves as a critical node within the hydroelectric infrastructure of the Kiso River system in Japan. Located in Gero, Gifu Prefecture, this rockfill structure stands 127 meters high and functions as a multipurpose asset for flood control, municipal and industrial water supply, irrigation, and power generation. This integration highlights the strategic importance of the Kiso River basin in supporting regional energy demands through coordinated water management and power generation.

Strategic Role in Chubu Electric Power's Portfolio

The Mazegawa No.1 Power Plant, fed by the Iwaya Dam's reservoir, represents a significant component of the Chubu Electric Power Company's generation mix. With a capacity of 288 MW, the plant contributes to the stability and output of the Chubu region's grid. The dam's ability to regulate water flow ensures consistent power generation, which is vital for balancing variable energy sources and meeting peak demand in the region. This infrastructure underscores the continued relevance of large-scale hydroelectric projects in Japan's energy landscape, particularly in areas with substantial river systems like the Kiso.

Scale and Socio-Environmental Trade-offs

The construction of the Iwaya Dam involved significant socio-environmental trade-offs, characteristic of major hydroelectric developments in Japan. The creation of the reservoir required the flooding of 157 households, illustrating the human cost associated with securing water resources and energy production. This displacement highlights the complex balance between modernizing energy infrastructure and preserving local communities. The dam's multipurpose design aims to maximize utility, providing flood control and water supply benefits that extend beyond electricity generation, thereby justifying the extensive land use changes in the Gero area.

History and Construction

The Iwaya Dam was constructed as a multipurpose infrastructure project in Gero, Gifu Prefecture, Japan, on the Maze River, which is part of the broader Kiso River system. The development of the dam was initiated in 1966, with the structure entering service in 1976. This ten-year construction period reflects the scale of the engineering effort required to build a 127-meter-high rockfill dam in the mountainous terrain of central Japan. The project was designed to serve multiple functions, including flood control, municipal and industrial water supply, irrigation, and hydroelectric power generation.

Construction and Social Impact

Building the Iwaya Dam required significant land acquisition and social planning. The construction phase involved the displacement of 157 households, reflecting the substantial footprint of the reservoir and the surrounding infrastructure. The dam is a rockfill structure, a design choice that utilizes compacted rock and earth to create a stable barrier capable of withstanding the hydrostatic pressure of the Maze River. This type of construction is common in Japan for large-scale dams in seismic zones, offering flexibility and durability.

Multipurpose Development Context

The Iwaya Dam exemplifies the multipurpose dam development strategy pursued in Japan during the mid-20th century. This era saw a surge in infrastructure projects aimed at maximizing the utility of water resources. By integrating flood control, water supply, irrigation, and power generation, the Iwaya Dam provided a comprehensive solution to the regional needs of Gifu Prefecture. The reservoir created by the dam plays a critical role in supplying the Chubu Electric Power Company's Mazegawa No.1 Power plant, which has a capacity of 288 MW. This integration of water management and energy production highlights the strategic importance of the Iwaya Dam in the regional energy and water infrastructure network. The dam remains operational, continuing to provide essential services to the region since its commissioning in 1976.

Technical Specifications

It is situated on the Maze River, which is part of the broader Kiso River system. The dam was constructed as a multipurpose infrastructure project designed to manage water resources for several key functions. The engineering design prioritizes stability and water retention capacity to serve the surrounding region effectively.

Structural and Hydrological Details

The dam has a height of 127 meters. This significant elevation allows for the creation of a substantial reservoir. The reservoir plays a critical role in the local energy infrastructure by supplying water to the Mazegawa No.1 Power Plant. This hydroelectric power station is operated by the Chubu Electric Power Company. The water from the Iwaya Dam reservoir is directed to the power station to drive turbines and generate electricity. The dam's location is defined by the coordinates 35.76105556, 137.15716667. These coordinates place the structure within the mountainous terrain of Gifu Prefecture. The rockfill construction method provides robust support against the hydrostatic pressure of the reservoir. This method involves compacted layers of rock and earth, which offer flexibility and durability. The dam's design ensures efficient water flow management for both power generation and downstream needs.

Parameter Value
Dam Type Rockfill
Height 127 meters
Location Gero, Gifu Prefecture, Japan
River Maze River (Kiso River system)
Coordinates 35.76105556, 137.15716667
Primary Function Multipurpose (Flood control, water supply, irrigation, hydroelectric power)
Associated Power Plant Mazegawa No.1 Power Plant
Power Plant Capacity 288 MW
Operator Chubu Electric Power Company

The integration of the Iwaya Dam with the Mazegawa No.1 Power Plant highlights the synergy between civil engineering and energy production. The reservoir's water volume is managed to optimize power output while maintaining flood control capabilities. This balance is crucial for the region's water security and energy reliability. The dam's operational status remains active, continuing to serve its designated purposes. The rockfill construction ensures long-term structural integrity. The dam's height and location allow for efficient gravitational flow to the power plant. This setup minimizes energy loss during water transmission. The Chubu Electric Power Company manages the operations to ensure consistent power generation. The dam also supports agricultural activities through irrigation water supply. Municipal and industrial water needs are met through the reservoir's storage capacity. This multifaceted utility makes the Iwaya Dam a vital asset in Gifu Prefecture.

Hydroelectric Power Generation

The Iwaya Dam serves as the primary hydraulic infrastructure supporting the Mazegawa No.1 Power Plant, a key component of the hydroelectric network within the Kiso River system. Located in the city of Gero, Gifu Prefecture, Japan, the dam is situated on the Maze River, which feeds directly into the broader Kiso watershed. The reservoir created by the rockfill dam provides the necessary water storage and head required for consistent power generation, integrating flood control, municipal water supply, and industrial irrigation into a multipurpose utility framework. This integration ensures that the hydroelectric output is not solely dependent on immediate river flow but is stabilized by the reservoir's capacity, allowing for more flexible energy dispatch within the regional grid.

Plant Capacity and Operator

The Mazegawa No.1 Power Plant, supplied by the Iwaya Dam reservoir, has an installed capacity of 288 MW. This output is managed by the Chubu Electric Power Company, which operates the facility as part of its broader hydroelectric portfolio in central Japan. The 288 MW capacity represents a significant contribution to the regional energy mix, providing reliable baseload or peaking power depending on the seasonal water levels in the Maze River. The Chubu Electric Power Company leverages the strategic location of the dam to optimize energy production, utilizing the natural elevation difference and water volume stored behind the 127-meter-high rockfill structure. The operational status of the plant remains active, continuing to deliver electricity generated from the kinetic energy of water released from the Iwaya Dam reservoir.

Integration with the Kiso River System

The Kiso River system is one of Japan's major river networks, and the Iwaya Dam plays a crucial role in its hydrological management. By regulating the flow of the Maze River, the dam helps balance water distribution for downstream users while maintaining optimal conditions for hydroelectric generation. The reservoir's ability to store water during periods of high inflow, such as seasonal rains or snowmelt, allows the Chubu Electric Power Company to release water through the turbines at times of peak electricity demand. This multipurpose design enhances the efficiency of the Kiso River system, ensuring that water resources are utilized effectively for both energy production and regional water supply. The coordination between the dam's water management and the power plant's operational schedule exemplifies the integrated approach to hydroelectric infrastructure in Japan's mountainous terrain.

Multipurpose Functions

The Iwaya Dam is explicitly designed and operated as a multipurpose infrastructure asset, extending its utility far beyond the generation of 288 MW of hydroelectric power for the Chubu Electric Power Company. According to the, the rockfill structure, standing 127 meters high on the Maze River in Gero, Gifu Prefecture, was constructed to simultaneously manage flood control, municipal water supply, industrial water supply, and irrigation. This integrated approach ensures that the reservoir created by the dam serves as a critical resource hub for the regional development of Gero and the broader Kiso River system.

Flood Control and Water Resource Management

Flood control is a primary function of the Iwaya Dam, mitigating the natural variability of the Maze River, which is part of the larger Kiso River system. By regulating water flow through its 127-meter rockfill structure, the dam reduces the risk of downstream flooding in Gero, Gifu Prefecture. This flood mitigation is essential for protecting municipal infrastructure and agricultural lands in the region. The reservoir’s capacity to store excess water during peak flow periods allows for a more stable water release, which supports consistent municipal and industrial water supply. This reliability is crucial for the economic stability of Gero, ensuring that water availability does not fluctuate drastically with seasonal changes or extreme weather events.

Municipal and Industrial Water Supply

The reservoir created by the Iwaya Dam provides a steady source of water for municipal and industrial use in Gero, Gifu Prefecture. Municipal water supply ensures that the local population has access to clean, reliable water for daily consumption, supporting public health and quality of life. Industrial water supply is equally important, enabling local industries to maintain consistent production levels. The availability of a reliable water source attracts and sustains industrial activity in the region, contributing to the economic growth of Gero. The integration of these water supply functions with hydroelectric power generation maximizes the efficiency of the dam, allowing the Chubu Electric Power Company to leverage the same water resource for multiple economic benefits.

Irrigation and Agricultural Support

Irrigation is another key function of the Iwaya Dam, supporting agricultural activities in Gero, Gifu Prefecture. The reservoir provides a controlled water supply for irrigation, ensuring that crops receive adequate water throughout the growing season. This support is vital for maintaining agricultural productivity in the region, which contributes to the local economy and food security. The ability to regulate water flow for irrigation helps farmers manage water resources more effectively, reducing the impact of droughts and floods on crop yields. By integrating irrigation with flood control, municipal, and industrial water supply, the Iwaya Dam plays a comprehensive role in sustaining the agricultural sector in Gero.

Regional Development Impact

The multipurpose functions of the Iwaya Dam collectively contribute to the regional development of Gero, Gifu Prefecture. By providing flood control, the dam protects infrastructure and reduces economic losses from water-related disasters. The reliable municipal and industrial water supply supports public health, industrial growth, and economic stability. Irrigation support enhances agricultural productivity, contributing to the local economy and food security. These functions, combined with the generation of 288 MW of hydroelectric power, make the Iwaya Dam a cornerstone of regional development. The integrated management of water resources ensures that Gero benefits from a balanced approach to infrastructure, supporting both economic growth and environmental sustainability in the Kiso River system.

How does the Iwaya Dam fit into the Kiso River system?

The Iwaya Dam is a critical infrastructure component within the broader Kiso River system, located specifically on the Maze River in the city of Gero, Gifu Prefecture, Japan. The Maze River serves as a significant tributary within this extensive river network, and the dam’s strategic placement allows for the effective management of water resources across multiple sectors. As a rockfill dam with a height of 127 meters, the Iwaya Dam was constructed to serve as a multipurpose facility, addressing the diverse needs of the region through flood control, municipal and industrial water supply, irrigation, and hydroelectric power generation.

Integration with Regional Water Management

The Kiso River system is vital for the Chubu region, and the Iwaya Dam plays a key role in its overall water management strategy. The reservoir created by the dam provides a consistent water supply for municipal and industrial use, ensuring stability for local communities and businesses. Additionally, the dam supports agricultural activities by providing essential irrigation water, which is crucial for the region's agricultural output. The flood control capabilities of the Iwaya Dam further enhance the resilience of the Kiso River basin, mitigating the impact of seasonal floods and ensuring a more predictable water flow throughout the year.

Hydroelectric Power Generation

A significant aspect of the Iwaya Dam’s contribution to the Kiso River system is its role in hydroelectric power generation. This hydroelectric power station is an important source of renewable energy for the region, helping to meet the growing energy demands of the Chubu area. The integration of the Iwaya Dam with the Mazegawa No.1 Power Plant exemplifies the efficient use of water resources for energy production, contributing to the overall energy mix and sustainability efforts in the region.

The operational status of the Iwaya Dam, which has been active since its commissioning in 1976, underscores its long-term reliability and importance in the Kiso River system. The dam continues to serve as a multifaceted asset, balancing the needs for water supply, flood control, and energy generation, thereby supporting the economic and environmental health of the region. The collaboration between the Chubu Electric Power Company and the local authorities ensures that the Iwaya Dam remains a cornerstone of the region’s infrastructure, effectively managing the resources of the Maze River and the wider Kiso River system.

What are the environmental and social impacts of the Iwaya Dam?

The construction of the Iwaya Dam in Gero, Gifu Prefecture, represents a significant intervention in the local landscape of the Maze River, a tributary within the broader Kiso River system. As a rockfill dam standing 127 meters high, its primary function is multipurpose, encompassing flood control, municipal and industrial water supply, irrigation, and hydroelectric power generation for the Chubu Electric Power Company’s Mazegawa No. 1 Power plant. While the infrastructure delivers 288 MW of capacity, the development necessitated substantial social adjustments for the local community.

Social Displacement and Community Impact

The most direct social consequence of the Iwaya Dam’s construction was the displacement of local residents. The creation of the reservoir required the flooding of 157 households, fundamentally altering the demographic and social fabric of the immediate area. This level of displacement is typical for large-scale rockfill dams in Japan, where valley floors are often densely populated before inundation. The relocation of these households involved not only the physical movement of homes but also the reconfiguration of local community networks, agricultural patterns, and access to traditional land. The balance between regional infrastructure development and local community stability is a central theme in the dam’s history, reflecting the trade-offs inherent in securing reliable water and energy resources for the Chubu region.

Environmental Effects on the Maze River

Environmentally, the Iwaya Dam alters the natural hydrological regime of the Maze River. By creating a large reservoir, the dam regulates water flow, which is critical for the downstream Mazegawa No. 1 Power plant and for flood control measures in Gero. However, this regulation impacts the river’s natural sediment transport, water temperature profiles, and aquatic ecosystems. The conversion of terrestrial land into a reservoir also affects local biodiversity, potentially fragmenting habitats for flora and fauna native to the Gifu Prefecture mountainous terrain. The rockfill construction method itself involves significant earthworks, which can influence local soil stability and vegetation cover in the surrounding area. These environmental modifications are managed as part of the dam’s ongoing operational status, aiming to balance ecological health with the demands of municipal water supply and hydroelectric generation.

See also