Introduction of the "Terraced Rice Field Fishway" case: Fishway design/construction on the Iruma River in Saitama Prefecture.
[Case Study] Improving upstream migration efficiency with a unique design! The terraced fishway solves the issues of traditional fishways.
In conventional fishways, there were challenges such as difficulties 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: Improvement of Fish Migration Environment at Terayama Weir and Asama Weir, No. 201 Iruma River ■Construction Location: Iruma River (Saitama Prefecture) ■Construction Photos: Please see the construction photos on this page. 【Reasons to Choose the "Terraced Rice Field Fishway"】 ■Fish can migrate 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. ■Thanks to its unique structure, it can respond to changes in water levels, allowing water to flow from the collection ditch below the floor during low water periods. ■By realizing the concrete secondary productization as terraced rice field fishway blocks, it achieves stable quality and simple construction as a 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 for upstream passage from both sides, featuring a high upstream effect. It is a unique slit-type fishway with pools made of cobblestones, allowing fish to navigate upstream along a route that suits their stamina amidst various flow conditions. Additionally, due to its distinctive pool depth of 20 cm, maintenance such as the removal of accumulated sediment inside the fishway is unnecessary, and it has been confirmed that there is no sediment accumulation even after investigations following floods, while the functionality of the fishway is adequately maintained. We have developed fishway blocks with dimensions of 1m in depth, 1.5m in width, and thickness ranging from 20cm to 35cm 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 producing these as secondary products in the form of fishway blocks, we can ensure the quality of the fishway after construction and also shorten the construction period. They 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 date 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 adoption cases in various government agencies, including the Ministry of Land, Infrastructure, Transport and Tourism, as well as in 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 with a 180° opening, it prevents fish from lingering. 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 about 70% of the aquatic organisms (swimming fish, bottom-dwelling fish, aquatic insects, etc.) that ascended through the entire fishway did so from the left and right fan-shaped sections, and it was also confirmed that fish ascend without lingering.
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A maintenance-free structure that does not accumulate sediment. The water depth of the pool during normal water levels is set to about 20 cm, with a width of about 80 cm, making it shallow and narrow. Both sediment and debris are carried 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. Even 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) compared to the longitudinal direction (in the direction of the river flow) to encourage the flow to gather. This design ensures that even when the flow decreases, the water does not spread out shallowly, but instead collects and flows into the "collection ditch" beneath the riverbed, serving as "calling water" that attracts fish to migrate upstream.
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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 lowering 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 the quality of the fish passage. The terraced fish passage blocks come in various 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.