Abstract: In the regulation of shoal waterways in mountainous rivers, spur dikes are usually built on the side beach, or the river channel during medium-low water periods is narrowed along the dike, increasing the scouring capacity of the water flow to maintain the stability of the waterway. However, the beach slow-flow area in the shallow reach is often an important habitat for migratory fish such as grass carp, and the waterway regulation buildings have changed the shape of the beach, forming complex flow patterns such as rapids and large-scale eddies, thus affecting the migration of fish. To address this issue, a method combining high-precision flume experiments and three-dimensional flow mathematical models was adopted to study the hydrodynamic conditions of beach and the variation characteristics of grass carp upstream migration behavior before and after the construction of spur dike in shallow river. The results show that after constructing a spur dike on the beach, the river channel cross-section contracts, and its impact on water flow and the upstream migration of grass carp decreases with the increase of the submergence depth of the spur dike. When the spur dike is not submerged, the head of the spur dike is in the high velocity area, so it is extremely difficult for grass carp to pass through, and the shelter area behind the spur dike becomes a gathering habitat. When the spur dike is submerged shallowly (H/D=1.125), the success rate of grass carp upstream migration decreases by about 20%. When the spur dike is submerged deeply (H/D=1.875), the success rate of grass carp upstream migration decreases by about 4%. Generally, spur dikes used in waterway regulation projects are all short spur dikes (the length is less than 1/3 of the river width), and the flooding degree of spur dikes during grass carp migration is generally 1.200~1.500, so the impact of spur dike on the success rate of grass carp upstream migration is below 20%.

Key words: waterway engineering; mountainous waterway; shoal; spur dike; flow of beach; grass carp migration

摘要： 山区河流浅滩航道治理通常在边滩修筑丁坝或者顺坝束窄中枯水河槽，通过增加水流冲刷能力以保持航槽稳定。然而，浅滩河段的边滩缓流区往往是草鱼等洄游性鱼类的重要生境区，航道整治建筑物改变了边滩形态，形成急流与大尺度漩涡等复杂流态，从而对鱼类的洄游产生影响。针对这一问题，采用高精度水槽试验和三维水流数学模型相结合的方法，研究了浅滩河段丁坝修筑前后边滩水动力条件和草鱼上溯行为的变化特征。结果表明，边滩修筑丁坝后河道断面收缩，其对水流和草鱼上溯的影响程度随丁坝淹没深度的增加而减弱；当丁坝未淹没时，坝头处于高流速区，草鱼上溯极为困难，而丁坝后的掩护区成为聚集栖息场所；丁坝淹没较浅时(H/D=1.125)，草鱼上溯成功率下降约20%；丁坝淹没较深时(H/D=1.875)，草鱼上溯成功率下降约4%。总体看，航道整治工程常使用短丁坝(长度小于1/3河宽)，草鱼洄游期丁坝淹没程度一般在1.200~1.500，因而其对草鱼上溯成功率的影响通常在20%以下。

关键词: 航道工程；山区航道；浅滩；丁坝；边滩水流；草鱼洄游