Erosion control - Sabo

Controlling the production, runoff, and movement of sediment in mountains, streams, and rivers to prevent landslides. Heavy rain and snowmelt can cause mountainside collapses and landslides in mountainous areas, while heavy rain can cause debris flows in mountain streams, causing damage to human lives, houses, fields, roads, and more. When rivers transport sediment produced in mountains and streams and deposit it in reservoirs, the reservoir's capacity decreases and its function is impaired. When sediment accumulates in downstream river channels, the riverbed rises, increasing the risk of flooding and making it difficult to drain land along the river. To prevent landslides caused by the production, runoff, and movement of such sediment, erosion control methods such as sabo dams, bed compaction works, revetments, mountainside works, and landslide prevention works are used. Erosion control dams store sediment that runs off from upstream, control and adjust sediment outflow downstream, prevent riverbed and streambank erosion, control sediment production, and stop and reduce the force of debris flows. Bed consolidation works prevent riverbed and streambank erosion, control sediment production, and prevent the riverbed and streambank from lowering, thereby controlling riverbank erosion and sediment production due to collapse. Bank protection works protect riverbanks and streambanks, and control sediment production due to riverbank erosion. Mountainside works plant seedlings and other trees on bald mountains and degraded land to green the area, prevent erosion due to rainfall, and control sediment outflow. Landslide prevention works are divided into control works and deterrent works. Restraint works include groundwater drainage works that drain groundwater that causes landslides, surface water drainage works that prevent the infiltration of rainwater and melting snow, earth removal works that remove soil from the head of the landslide to mitigate landslide movement, and restraint embankment works that pile up soil at the end of the landslide slope to restrain landslide movement, etc. Restraint works include pile works that drive steel pipe piles into the landslide slope to restrain landslide movement, shaft works that excavate large-diameter vertical shafts into the landslide slope and pour reinforced concrete into them to restrain landslide movement, and anchor works that drive steel rods through the landslide slope to the bedrock to restrain landslide movement, etc.

[Noboru Ikawa]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

土砂災害を防止するために山地、渓流、河川における土砂の生産、流出、移動を制御すること。山地では豪雨や融雪により山腹崩壊、地すべりが発生し、渓流では豪雨により土石流が発生し、人命、家屋、田畑、道路などに被害をもたらす。山地や渓流で生産された土砂を河川が運搬し、貯水池に堆積(たいせき)すると、貯水池容量が減少し、貯水池の機能を低下させる。下流河道で堆積すると、河床が上昇し、洪水氾濫(はんらん)の危険性を高め、また河川沿岸の土地の排水を困難にする。このような土砂の生産、流出、移動に起因する土砂災害を防止するために、砂防ダム、床固め工、護岸、山腹工、地すべり防止工などの砂防工法が用いられる。砂防ダムは上流からの流出土砂を貯留し、下流への土砂流出を抑制、調節したり、渓床・河床浸食、渓岸・河岸浸食を防止して土砂生産を抑制したり、土石流を抑止、減勢する。床固め工は渓床・河床浸食を防止して土砂生産を抑制し、渓床・河床の低下を防いで渓岸・河岸の浸食、崩壊による土砂生産を抑制する。護岸は渓岸・河岸を防護して渓岸・河岸浸食による土砂生産を抑制する。山腹工ははげ山や荒廃地に苗木などを植えて緑化し、降雨による浸食を防止し、土砂流出を抑制する。地すべり防止工には抑制工と抑止工がある。抑制工には地すべりの要因となる地下水を排水する地下水排除工、雨水・融雪水の浸透を防ぐ地表水排除工、地すべり頭部の土を除去して地すべり運動を緩和させる排土工、地すべり斜面の末端部に盛土して地すべり運動を抑える抑え盛土工などがある。抑止工には地すべり斜面に鋼管杭を打ち込んで地すべり運動を抑える杭工、地すべり斜面に大口径の縦坑（シャフト）を掘削し鉄筋コンクリートを打設して地すべり運動を抑えるシャフト工、鋼棒を地すべり斜面を通して岩盤まで打ち込んで地すべり運動を抑えるアンカー工などがある。

［鮏川　登］

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