Influence of Sediment Supply on River-bed Environment for Ayu-fish Spawning
| Autor: | SUZUKI, Takamasa, SUMI, Tetsuya, TAKEMON, Yasuhiro, NAKAJIMA, Kana |
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| Jazyk: | japonština |
| Rok vydání: | 2011 |
| Předmět: | |
| Zdroj: | 京都大学防災研究所年報. B. 54:711-718 |
| ISSN: | 0386-412X |
| Popis: | 静岡県に流れる天竜川では, 土砂吸引バイパスによる佐久間ダムから下流域への土砂供給が計画されている。本研究では, 土砂供給がアユの産卵環境にどのような影響をもたらすのか予測することを目的とした。まず, 既往研究と現地調査により, 礫底で比較的最近に土砂が堆積した瀬がアユの産卵に適していることが明らかとなった。次に, 平面2 次元河床変動計算によるアユ産卵適地の予測手法について検討を行った。現状の上流ダムからの土砂供給無しの条件では, 本流部の瀬ではなく, 増水時に砂州上に形成される副流部と本流部が合流する地点に産卵適地が形成された。また, 土砂供給に関しては, 砂分のみでは不十分であり, 産卵適地となり得る河道区間上流に礫を直接供給することが有効と考えられる。 Reduction of the Ayu-fish production has been recognized as an influence of dam constructions by decreasing sediment supply in the Tenryu River. Recently, comprehensive sediment management by introducing sediment bypass technique at Sakuma dam has been planned in order to recover this sediment routing system in the river basin. The present study focuses on the effect of sediment supply on the spawning bed conditions for Ayu-fish. Through the field survey, we found out that riffles with newly deposited gravel bed are soft enough for spawning. Based on the results, we have studied 2D flow and sediment transport model (CCHE2D) by simulating flow velocity, grain size distribution and bed softness, to predict high potential areas for Ayu-fish spawning bed. The results showed that riffles with newly deposited gravel bed suitable for the spawning are created at the confluence point of a main channel and a secondary channel running from the sand bar. In order to increase suitable riffles for Ayu-fish spawning bed, gravel replenishment with frequent high flow discharge is recommended by accelerating the gravel transport by cutting secondary channel near the confluence. |
| Databáze: | OpenAIRE |
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