Spatiotemporal variation of sedimentation in an agricultural drainage canal with eco-friendly physical structures: a cas
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ARTICLE
Spatiotemporal variation of sedimentation in an agricultural drainage canal with eco‑friendly physical structures: a case study Shigeya Maeda1 · Shota Takagi2 · Koshi Yoshida1 · Hisao Kuroda1 Received: 15 January 2020 / Revised: 30 August 2020 / Accepted: 8 October 2020 © The International Society of Paddy and Water Environment Engineering 2020
Abstract Excessive sediment deposition in eco-friendly physical structures introduced in agricultural canals sometimes damages the function of these structures as fish habitats. This study reports the spatial and temporal changes in bed elevation in a canal section where a set of six fish nests and one fish pool were installed. Field observations and numerical simulation using the two-dimensional hydrodynamic model, Nays2DH, were conducted to describe the circumstances in which sediment deposition and scouring occur in the structures. The bed topography of the canal section was surveyed 12 times during 2016–2019, at 19 transverse cross sections of the area. The measured bed elevation was interpolated to estimate its spatiotemporal variation, sedimentation timing, and change in sediment volume. The results of this work clarified that deposition and scouring occurred in a 1-year cycle in the fish nests. The accumulation of sediment in the whole study area was found to be lower than expected. These results could provide insight for designing fish pools and fish nests that require less maintenance in an eco-friendly canal influenced by soil transport from surrounding paddy fields. Keywords Eco-friendly canal · Sediment · Drainage canal · Fish habitat · Paddy · Simulation
Introduction After the revision of the land improvement law in 2001 in Japan, eco-friendly physical structures have received much attention and have often been introduced to agricultural canals because they create conditions that help to conserve aquatic life. Typical eco-friendly physical structures include fish nests and pools. When a fish nest or a fish pool is installed in a concrete canal, it can generate low flowrate water regions, which serve as proper living environments for small-sized fish that prefer low-velocity currents. Lowvelocity currents promote the deposition of soil particles, mowed grass, and withered leaves in and around the structures, sometimes causing the need for additional maintenance activities to remove them. Although a suitable amount of deposited small-size grain particles is favorable for some * Shigeya Maeda [email protected] 1
College of Agriculture, Ibaraki University, 3‑21‑1 Chuuo, Ami, Inashiki, Ibaraki 300‑0393, Japan
Civil Engineering and Eco-Technology Consultants Co., Ltd, 2‑23‑2 Higashiikebukuro, Toshima‑ku, Tokyo 170‑0013, Japan
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fish habitats as well as for spawning sites, excessive amounts of sediment deposition in the eco-friendly physical structures decrease the area of fish habitats, which reduces the effectiveness of its conservation function (Tsuchiya et al. 1986; Minagawa et al. 2020). Therefore, maintaining the adequate amo
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