Spring Water from the Source of the Hirose River, Miyagi Prefecture | Comprehensive Explanation of Clear Water from Sekiyama Pass to Sendai Bay, Selected as One of Japan’s Top 100 Waters
The Hirose River is a clear stream representing Sendai City, Miyagi Prefecture, and is an urban river selected for the Ministry of the Environment’s Top 100 Waters. With its water source near Sekiyama Pass close to the Yamagata Prefecture border, it flows through Sendai’s urban areas and merges with the Natori River before flowing into Sendai Bay. This article provides a comprehensive explanation of the Hirose River from its source spring water to its lower reaches, covering its geographical characteristics, history, water quality, ecosystem, water use, and relationship with citizens.
Geographic Overview of the Hirose River
Characteristics of the Source Area and Sekiyama Pass
The source of the Hirose River is located near Sekiyama Pass at the Yamagata Prefecture border in Sakuramachi, Aoba Ward, Sendai City, Miyagi Prefecture. Located on the southern slope of the Ou Mountain Range at an elevation of approximately 500 to 600 meters, this region is covered with abundant forests, and spring water that maintains stable water volume throughout the year is dotted across the area.
The point where Sakatate Stream flowing from Sekiyama Pass converges with Kazakura Stream flowing along National Route 48 is designated as the upper end of the Hirose River as a first-class river. This source area is spread with deciduous broadleaf forests such as Japanese beech and mizunara oak, and clear water is nurtured through the forest’s water-retention function.
The spring water in the source area is naturally filtered as it passes through the geological layers of the Ou Mountain Range, becoming high-quality water containing appropriate amounts of mineral content. This water quality excellence forms the foundation for the river’s selection as one of Japan’s Top 100 Waters.
Flow Route and River Characteristics
The Hirose River has a total length of approximately 45 kilometers, with its entire flow course being unusually located within Sendai City. The flow from source to Sendai Bay can be divided into the following characteristic sections:
Upper Reaches (Around Akiu Onsen)
The section from the source to Akiu Onsen forms steep gorges, carving V-shaped valleys as it flows. Clear stream features with alternating rapids and pools are continuous in this section, where the river can be observed cutting through bedrock.
Middle Reaches (Sendai Western Hill Region)
From the Aiko district to Aoba Mountain in the middle reaches, river terraces are well developed. These terraces were formed by past crustal movements and river erosion, significantly influencing the landform development of Sendai’s urban areas.
Lower Reaches (Sendai Urban Areas)
In the lower reaches flowing through Sendai’s urban areas, many bridges such as Hirose Bridge, Ohashi Bridge, and Miyazawa Bridge are constructed, intimately connecting with citizens’ lives. The river floodplain in this section is developed as parks, serving as a gathering place for citizens.
River Terraces and Development of Sendai Urban Areas
The river terraces formed by the Hirose River played an important role in Sendai’s urban development. Aoba Mountain, where Date Masamune built Sendai Castle, is also part of these river terraces. Terrace surfaces are less susceptible to flooding and blessed with water resources, making them long utilized as residential areas.
The current Sendai city center has developed on multiple river terraces formed by the Hirose River, serving as the foundation for the beautiful landscape called “City of Greenery.” The landforms woven by the river and terraces create Sendai’s unique urban landscape.
Selection as One of Japan’s Top 100 Waters and Water Quality Characteristics
Reasons for Selection for the Ministry of the Environment’s Top 100 Waters
The Hirose River was selected for the Ministry of the Environment’s (then the Environmental Agency) “Top 100 Waters” in 1985 (Showa 60). The selection was made based on the evaluation of the following points:
- Good water quality as an urban river: Maintaining relatively good water quality while flowing through the large city of Sendai
- Entire flow course within the city: Water source to river mouth are managed within one municipality, enabling integrated conservation
- Citizens’ environmental conservation awareness: Long-term conservation activities by civic groups including the Hirose River Citizens’ Conference
- Beautiful landscape: Harmony between seasonal natural landscapes and urban landscape
- Historical and cultural value: Close relationship with citizens’ lives since the Sendai Clan era
Current Water Quality and Changes
The water quality of the Hirose River deteriorated during the high-growth period due to inflow of domestic and industrial wastewater, but has shown improvement trends in recent years due to sewage system improvements and civic environmental conservation activities.
The BOD (Biochemical Oxygen Demand) value of the environmental standard is set at AA class (1 mg/L or less) in the upper reaches and A class (2 mg/L or less) in the middle reaches, with most points meeting the standard. The spring water in the source area is particularly clear with high transparency, maintaining an environment suitable for aquatic organism habitation.
According to water quality surveys, the water temperature in the source area remains relatively stable throughout the year, and is cold at approximately 15 degrees even in summer, demonstrating the characteristics of spring water. The pH is neutral to slightly alkaline, containing appropriate amounts of mineral content such as calcium and magnesium.
Water Source Retention Function and Forest Conservation
The good water quality of the Hirose River is supported by abundant forests in the source area. The forests of the Ou Mountain Range function as natural water purification facilities, infiltrating rainfall into the ground and supplying it to the river slowly over time.
To maintain this water source retention function, Sendai City, Miyagi Prefecture, and the Forestry Agency cooperate in forest conservation efforts. Forest management activities such as thinning and tree planting help maintain healthy forest ecosystems, which in turn protects the clear spring water.
History of the Hirose River
From Ancient to Medieval Times
Traces of human habitation from the Jomon period have been found in the Hirose River basin. Many archaeological sites on river terraces indicate that this area blessed with water and greenery has long been a place of human habitation.
In ancient times, the Hirose River was recognized as “a tributary of the Natori River,” but in the medieval period, the place name “Hirose” began to appear in written records. Various theories exist regarding the origin of this name, but the theory that it was named from “wide rapids,” referring to the wide, shallow rapids in the river, is most plausible.
Water Utilization and Flood Control During the Sendai Clan Era
In 1601, when Date Masamune built Sendai Castle, the Hirose River became increasingly important in the development of the castle town. Masamune utilized the river’s water to construct moats around the castle, enhancing its defensive functions. The river’s water was also used as domestic water for the castle town and irrigation water for agriculture.
Throughout the Edo period, many irrigation channels were drawn from the Hirose River and used for paddy field irrigation and water supply to merchant districts. Many irrigation channels such as Yotsutsuya irrigation, Shin-hori irrigation, and Shichigou-bori, some of which still remain today, were developed during this period.
On the other hand, the Hirose River frequently caused floods, and the Sendai Clan invested heavily in flood control works. The construction of embankments and river course modifications were carried out, forming the foundation of the current Hirose River’s flow course.
Changes in the Modern Era and Beyond
With the Meiji era, modern flood control techniques were introduced, and more comprehensive river improvements were undertaken. From the Taisho to early Showa periods, hydroelectric power generation development also progressed, with several small power plants built in the upper reaches.
During Japan’s postwar high-growth period, water pollution became severe due to urbanization. In the 1970s, the “Protect the Hirose River” movement began among citizens, which later led to the establishment of the Hirose River Citizens’ Conference.
In 1988, the “Ordinance for Creating the Environment of a City of Greenery” was enacted, legally establishing Hirose River environmental conservation. Since then, with the progress of sewage system development and increased public environmental awareness, water quality has gradually improved.
Biodiversity and Ecosystem
Fish Species
Diverse fish species inhabit the Hirose River. From the source to the upper reaches, stream fish such as char and yamame trout are found. These fish prefer clear, cold water, so their presence serves as an indicator of good water quality.
From the middle to lower reaches, abundant cyprinid fish such as dace, rosy bitterling, and Japanese dark chub inhabit the river. Ayu fish migration upstream is also confirmed, and in autumn, the sight of fish heading upstream for spawning can be observed.
In recent years, the intrusion of non-native fish such as largemouth bass and bluegill has been confirmed, raising concerns about competition with native fish. Removal activities for non-native fish are conducted by civic groups and government agencies.
Birds and Waterside Organisms
The Hirose River’s waterside is inhabited by many bird species including kingfishers, wagtails, and ducks. The kingfisher in particular is beloved by citizens as a symbol of clear streams, and many photography enthusiasts visit to photograph its beautiful form.
In winter, duck species such as mallard, spot-billed duck, and northern pintail migrate for overwintering, making the river floodplain a hot spot for birdwatching. Heron species also frequently visit to hunt fish.
Aquatic insects are also abundant, with larvae of mayfly, caddisfly, and stonefly inhabiting areas beneath stones. These serve as important water quality indicator organisms and are utilized as teaching materials for environmental education.
Vegetation and Riparian Forests
Riparian forests centered on willow species have developed along the Hirose River. Japanese pussy willow, weeping willow, and other willow species are seen, creating a beautiful spring landscape as catkin fluff dances in the air.
Herbaceous plants such as Japanese pampas grass, common reed, and tall goldenrod grow abundantly in the river floodplain, serving as habitats for diverse insects and small animals. In spring, dandelions and milk vetches can be seen, and in summer, garden balsam and Chinese bellflower.
The forests in the upper reaches are predominantly composed of deciduous broadleaf trees such as Japanese beech, mizunara oak, and Japanese oak, offering beautiful autumn foliage. These forests are important not only for water source retention but also as habitats for diverse wildlife.
Water Utilization and History of Water Use
Use as Agricultural Water
The Hirose River’s water has long been used as agricultural water. Most of the irrigation channels supplying the grain belt of the Sendai Plain are fed by water from the Hirose River.
The Shichigou-bori is a representative irrigation channel excavated during the Sendai Clan era, currently supplying water to paddy fields in Wakabayashi Ward. This irrigation channel, stretching approximately 14 kilometers, draws water from the middle reaches of the Hirose River and irrigates approximately 1,000 hectares of paddy fields.
The Yotsutsuya irrigation is another historically significant channel excavated in the early Edo period, supplying water to paddy fields and residential areas in Aoba Ward. Its current role as agricultural water has diminished, but portions have been developed as water-friendly spaces, becoming gathering places for citizens.
Industrial Water and Tap Water Source
From the Meiji era onward, Hirose River water came to be used as industrial water. Paper mills and dyeing factories became located there, taking advantage of the abundant water volume.
Currently, Sendai City’s tap water is primarily sourced from the Kamafusa Dam and Shichiritada Dam in the Natori River system, but the Hirose River is also positioned as a supplementary water source. Particularly during water shortages, the good water quality of the Hirose River plays an important role in supporting citizens’ lives.
Hydroelectric Power Generation
Hydroelectric power generation has been conducted in the upper reaches of the Hirose River since the Taisho era. Several small hydroelectric power stations such as Akiu Power Station and Jogi Power Station operate, supplying clean energy electricity to the region.
In recent years, with growing interest in renewable energy, the potential of small-scale hydroelectric power has been re-evaluated. As a sustainable water use approach that considers the environment, future developments are anticipated.
Tributaries and Basin Characteristics
Major Tributaries
Many tributaries flow into the Hirose River, each forming its own unique basin environment.
Shin River
The largest tributary of the Hirose River, flowing through the northern part of Aoba Ward. Although an urban river flowing through residential areas, waterfront development has progressed in recent years with pedestrian paths and parks being developed.
Ryunokuchi Gorge
A small gorge flowing along the northern side of Aoba Mountain, with beautiful natural scenery preserved. Situated adjacent to Tohoku University’s campus, it serves as a gathering place for students and researchers.
Okura River
A tributary flowing through Taihaku Ward, winding between residential and agricultural areas. River improvement has enhanced its flood control function, though environmental conservation remains a concern.
Umeda River
A tributary flowing through southern Aoba Ward, which experienced severe water pollution in the past but has improved with sewage system development. Currently, regular cleaning activities are conducted by local residents.
Land Use in the Basin
Land use in the Hirose River basin changes significantly from upstream to downstream.
The upper reaches are predominantly forested with well-preserved natural environments. Tourist destinations such as Akiu Onsen exist, with land use harmonized with nature.
The middle reaches are mixed residential and agricultural areas. While land development has progressed in recent years, paddy fields and farmland remain along the river, with suburban agriculture being conducted.
In the downstream Sendai urban area, commercial and residential districts are densely packed, but the river floodplain is preserved as parks and green spaces, serving as valuable open spaces in the city.
Bridges and Landscape
Historic Bridges
Many bridges span the Hirose River, each telling stories of Sendai’s history and culture.
Ohashi Bridge
A representative bridge of central Sendai, it was an important transportation route since the Edo era. The current bridge was rebuilt in 1965 and sees many people crossing during the Sendai Tanabata Festival.
Hirose Bridge
Connecting Aoba Mountain and the urban areas, the bridge serves as an access route to Sendai Castle ruins. From the bridge, one can enjoy a panoramic view of the beautiful flow of the Hirose River and the greenery of Aoba Mountain.
Miyazawa Bridge
Located in the lower reaches, the surrounding area is developed as “Miyazawa Green Space.” The riverbed features “Miyazawa’s Depths,” a deep pool that once served as a swimming area.
Hyogijo-Kawara Bridge
The bridge derives its name from Hyogijo-Kawara in the Sendai castle town, preserving this historic place name. The surrounding area is also known as a cherry blossom viewing spot.
Landscape of Depths and Rapids
Characteristic depths and rapids are scattered throughout the Hirose River, each bearing its own name.
Ushikoshi Bridge Rapids
Beautiful rapids in the upper reaches where clear water can be observed flowing over bedrock. Known as a spot for sweetfish fishing.
Yodo Bridge Depths
A deep pool once used as a boat landing. Currently serves as a bird observation spot.
Hyogijo-Kawara
Said to be where Date Masamune’s retainers held council meetings during his era. Characterized by wide riverbed and beautiful scenery, it now serves as a gathering place for citizens.
Miyazawa’s Depths
A deep pool in the lower reaches where large rocks once called “Seven Stones” lay across. The water’s color is beautiful, making it a popular spot for photography.
Civic Activities and Environmental Conservation
Hirose River Citizens’ Conference Initiatives
The Hirose River Citizens’ Conference, established in 1989, is a civic group that promotes environmental conservation and utilization of the Hirose River. It conducts diverse activities including regular cleaning operations, water quality surveys, and environmental education programs.
Each June, it hosts the “Play in the Hirose River” event, conveying the importance of nature to children through river play and biological observation. The “Hirose River 10,000 People Project” has basin residents conduct simultaneous cleanup activities, deepening their affection for the river.
As a Site for Environmental Education
The Hirose River serves as an important field for environmental education in Sendai schools. Using comprehensive learning time, students conduct water quality surveys and biological observations, learning about environmental issues.
Research institutions such as Tohoku University also use the Hirose River as a research subject, accumulating valuable data on urban river environmental conservation. These research findings are applied to river management and environmental policy.
Development of Water-Friendly Spaces
Sendai City is developing the Hirose River’s floodplain as water-friendly space, advancing environmental creation where citizens can enjoy the river. Pedestrian paths and cycling roads have been developed, with citizens seen jogging and taking walks.
Stepped embankments have been installed on riverbanks, making it easier to access the waterside. In summer, children enjoy water play, and families enjoy barbecuing. However, balancing safety considerations with environmental conservation remains an issue.
Hirose River as a Tourism Resource
Charm Throughout the Seasons
The Hirose River presents different faces throughout the year, captivating visitors.
Spring
During cherry blossom season, the cherry tree rows on the river floodplain bloom beautifully, drawing crowds of flower viewers. The Hyogijo-Kawara area is particularly known as a cherry blossom viewing spot.
Summer
The contrast between verdant greenery and clear water is beautiful, with many enjoying river play. Fireflies can be seen in some areas at night.
Autumn
The fall foliage in the upper reaches is spectacular, with many tourists visiting in conjunction with Akiu Onsen. The pampas grass on the riverbank evokes autumn sentiment.
Winter
The snow-covered Aoba Mountain and Hirose River landscape resembles ink wash painting. Winter bird observation is also suitable during this season.
Access and Tourism Spots
Many tourism spots exist in the Hirose River basin.
Sendai Castle Ruins (Aoba Castle Ruins)
Located on a high ground overlooking the Hirose River, the Date Masamune equestrian statue and stone walls convey the appearance of former times.
Akiu Onsen
A hot spring in the upper reaches where one can enjoy gorge scenery and hot springs. Close to the Hirose River’s source, visitors can bathe while listening to the murmur of clear water.
Akiu Waterfall
A famous waterfall in the Natori River system, a tributary of the Hirose River, numbered among Japan’s top three waterfalls.
Yagiyama Zoo
Located on high ground overlooking the Hirose River, the zoo offers views of Sendai’s urban landscape and the Hirose River.
Future Challenges and Prospects
Response to Climate Change
In recent years, increased frequency of heavy rains due to climate change has raised concerns, and Sendai faces strengthened flood control measures for the Hirose River. Beyond hard infrastructure such as river improvements and detention ponds, improving rainwater storage and infiltration functions throughout the basin is important.
Meanwhile, increasing drought risk demands water source forest conservation and efficient water use.
Biodiversity Conservation
Native organism habitation is threatened by invasive species and changing habitats. Citizen-participated removal of invasive species and habitat preservation and restoration are necessary.
In particular, improvement of dams and weirs blocking fish migration and construction of fish passages are required.
Sustainable Utilization
To pass the Hirose River to future generations as a citizens’ asset, balance between environmental conservation and utilization is essential. Excessive use increases environmental burden, while appropriate utilization heightens interest and affection for the river.
Constructing a framework for sustainable river management through cooperation among citizens, government, and experts is required.
Summary
The spring water from the Hirose River’s source represents precious water resources embodying Sendai, Miyagi Prefecture. Clear water gushing from abundant forests near Sekiyama Pass nourishes the city, supporting diverse ecosystems. This clear stream selected as one of Japan’s Top 100 Waters has nurtured Sendai’s history and culture, becoming an indispensable presence in citizens’ lives.
Preservation of natural environments in the source area, maintenance and improvement of water quality, protection of biological diversity, and sustainable river management through citizen cooperation remain important ongoing tasks. Beginning with what each individual can do is essential to passing on the blessings of the Hirose River to future generations.
The Hirose River, a symbol of the City of Greenery Sendai. The story of nature and culture woven by this clear stream from its source to the river mouth will continue to provide inspiration and healing to countless people.
