Introduction of the "Terraced Rice Field Fishway": Fishway design/construction on the Asukagawa River in Gifu Prefecture.
[Case Study] Improving upstream efficiency with a unique design! The terraced fishway solves the issues of traditional fishways.
In traditional fishways, there were challenges such as difficulty in guiding fish to upstream routes and sediment accumulation within the fishway, which reduces its functionality. These issues are addressed by Yamatazumi's "Terraced Rice Field Fishway," which features a unique shape utilizing natural stones. We also provide explanations about the terraced rice field fishway, consultations on fishway design (such as drawing creation and quantity calculation), proposals, and assistance, so please feel free to contact us. 【Case Study】 ■ Project Name: No. 1 Public Comprehensive River Basin Disaster Prevention (River Environment Project) ■ Construction Location: Asukagawa (Gifu Prefecture) ■ Construction Photos: Please see the construction photos on this page. 【Points for Choosing the "Terraced Rice Field Fishway"】 ■ Fish can ascend from any direction due to the 180-degree design, preventing fish stagnation. ■ It has a maintenance-free structure that prevents sediment accumulation inside the fishway. ■ Its unique structure can respond to changes in water levels, allowing water to flow from the collection ditch below the floor during low water periods. ■ By realizing concrete secondary products as terraced rice field fishway blocks, we achieved stable quality and simplified construction for the fishway. *For more details, please contact us or download the catalog to view.
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basic information
This is a fishway with a 180-degree opening that allows fish to ascend from both sides, featuring a highly effective ascending shape. It is a unique slit-type fishway with pools made of cobblestones, enabling fish to navigate easily through various flow conditions according to their own stamina. Additionally, due to its distinctive pool water depth of 20 cm, maintenance such as the removal of accumulated sediment inside the fishway is unnecessary, and investigations after flooding have shown no sediment accumulation, confirming that the fishway's functionality is well maintained. We have developed fishway blocks with a depth of 1 m, width of 1.5 m, and thickness ranging from 20 cm to 35 cm for use. In the case of on-site construction, there are issues such as insufficient fixation of cobblestones during compaction, variations in cobblestone arrangement, and inconsistencies in quality depending on the contractor. By manufacturing fishway blocks as secondary products, we can ensure the quality of the fishway after construction and also shorten the construction period. These have been adopted by the Ministry of Land, Infrastructure, Transport and Tourism, various prefectures, and municipalities, with numerous construction achievements. We are available to assist with design and proposals, so please feel free to contact us.
Price information
Please contact us. *Prices may vary depending on the transportation location, so feel free to reach out to us.
Delivery Time
※The delivery time may vary depending on the quantity, so please feel free to contact us.
Applications/Examples of results
【Purpose】 It alleviates a drop of about 2 meters at river dams and is effective for fish migration. Additionally, by installing it next to existing fish passages, it can further promote fish ascension and the movement of aquatic organisms as a supplementary fish passage. 【Track Record】 There are many cases of adoption by various government agencies, including the Ministry of Land, Infrastructure, Transport and Tourism, as well as Gifu Prefecture, Hokkaido, Saitama Prefecture, Yamanashi Prefecture, Nara Prefecture, and Kumamoto Prefecture.
Detailed information
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Fish can ascend from anywhere. Since fish can ascend from any point within the 180° opening, it prevents fish from stagnating. The terraced fishway has a 180-degree entrance, allowing fish to ascend from anywhere within the fishway. In the ascent survey conducted after the installation of the fishway, it was confirmed that approximately 70% of the aquatic organisms (swimming fish, bottom-dwelling fish, aquatic insects, etc.) that ascended through the entire fishway came from the left and right fan-shaped sections, and it was also confirmed that fish can ascend without stagnating.
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Maintenance-free structure that prevents sediment accumulation The water depth of the pool during normal water levels is set to about 20 cm, with a width of approximately 80 cm, making it shallow and narrow. Both sediment and debris are swept away by the turbulent flow, leaving no space for sediment to accumulate. The water depth of the terraced fishway pool is set to about 20 cm, which is very shallow compared to other fishways that have depths of 35 to 80 cm. During floods, the sediment that flows out is flushed downstream, preventing any accumulation of sediment. Therefore, the removal of accumulated sediment is unnecessary.
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Responding to changes in river flow During low water periods, water is drawn from the collection ditch beneath the riverbed. Natural rivers constantly experience changes in flow. The stepped fishway is designed with a steeper gradient in the transverse direction (across the flow of the river) than in the longitudinal direction (the direction of the river flow) to concentrate the flow. This prevents the water from spreading shallowly when the flow decreases, allowing water to gather and flow into the "collection ditch" beneath the riverbed, which serves as "calling water" to attract fish for upstream migration.
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Concrete secondary products are created to ensure the quality of fish passages. When placing cobblestones and other materials on-site, the use of a vibrator can cause the cobblestones to sink, making it difficult to set them at the desired height, which poses a risk of degrading the quality of the fish passage. The terraced fish passage has been developed using natural cobblestones as concrete secondary products, known as terraced fish passage blocks, ensuring quick construction and maintaining quality as a fish passage. The terraced fish passage blocks come in several shapes, and the combination of these products forms the terraced fish passage.
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Company information
Yamachin Group is supported by the understanding and guidance of many people, and with the corporate philosophy of "creativity, ingenuity, and tireless effort," we are committed to contributing to the local community alongside the development of our company. By engaging in civil engineering projects that involve nature, we consider how to conduct construction with respect for the natural environment, learn many lessons from it, and aim to create a "distinctive company" among numerous construction contractors. In 1991, we established the Environmental Division and began "environmental conservation activities unique to the construction industry," developing and proposing various environmental products such as natural stone block series for river environment conservation, various fishway series tailored to installation locations, and the "Hybrid Eco Pump," an underwater pump that operates without electricity. We have worked on promoting and raising awareness of environmentally friendly construction methods. Thanks to this, we have been adopted in numerous projects, and we are grateful to be contributing to environmental conservation. Yamachin Group will continue to take on challenges through the construction industry, working on "proposals dedicated to the natural environment of our hometown" and contributing to global environmental conservation.