仿自然鱼道水力及过鱼性能物理模型试验

仿自然鱼道是具有一定自然特征的过鱼设施,适用于中低水头工程,是目前鱼道形式研究热点之一。为了获得一种具有综合生态功能的鱼道,该文提出了一种利用芦苇模块构建的植物型鱼道,并通过物理模型试验对其水力特性和过鱼性能进行了研究。结果表明:选取芦苇为基本单元构建植物型鱼道是合适的。植物模块交错布置的植物鱼道内可形成蜿蜒的水流,流态丰富,过鱼通道内流速均小于1.1 m/s,满足过鱼要求。过鱼试验表明,过鱼对象可以在该鱼道内顺利上溯,植物模块下游侧可形成低流速的鱼类休息区,验证了鱼道体型的合理性。该文提出的植物型鱼道丰富了鱼道的形式,具有一定创新性,对今后类似鱼道的设计和建设具有一定的指导意义。

Physical model test on hydraulic characteristics and fish passing performance of nature-like fishway

The natural-like fishway has a similar flow pattern to the natural river, and it has more ecological functions comparing to the traditional technical fishways. It is more conducive to fish migration. However, it is difficult to deviate from the design concept of the traditional technical fishway in China. In order to obtain a fishway with comprehensive ecological functions, a type of vegetative fishway constructed by plant modules was presented, and its hydraulic characteristics and fish passing performance were studied by experiments. Before we conducted the experiment, we need to select a proper type of plants to construct the fishway. The biological characteristics and growth cycle of the target plants should match with the migration season of the target fish. Four major domestic fish (green, grass, silver carp, bighead carp) were selected as the target fish, and the fishway was designed based on their swimming ability and migration season. Generally speaking, the four major domestic fish have similar biological index: the body length ranges from 0.2 to 0.9 m, the induced flow velocity is generally 0.1 to 0.2 m/s, the sustained swimming speed is 0.8 to 1.3 m/s, and the burst swimming speed is more than 1.3 m/s. According to the current fishway design practice in China, the control section velocity of the fishway was controlled at 1.1 m/s. The migration season of the four major domestic fish is also comparatively consistent, from April to August. Upon comprehensive consideration, reed was selected to build the fishway. Reed is widely distributed in China and has strong vitality. Its biological characteristics and growth cycle can match the migration season of the target fish. The physical model test was designed to verify the water-blocking effect of the emergent plants in the channel, so as to form a proper flow structure. In the model, the reed plants were simplified firstly, and then the individual plants were arranged to form the plant module. In this paper, the reed was simplified to single stem, and the water-blocking effect of the plants was weakened to some extent because of the removal of leaves. The physical model was designed according to the gravity similarity, and the length scale was 1:5. Firstly, the prototype reed was scale down according to the length scale. Two schemes were carried out to the physical model. The plant with full arrangement schemes was used to test the water-blocking effect of a reed plant module with 156 plants/m2 density. The staggered arrangement of plant modules was carried out for analyzing whether the flow structure can meet the requirements of fish from the view of hydraulics. The results showed that the reed plant module with 156 plants/m2 density had good water blocking effect, and the plant module could decelerate the flow velocity effectively. The staggered arrangement of plant modules could form a meandering flow in the fishway. The flow pattern was rich and changeable, and the flow velocity was effectively controlled to less than 1.1 m/s, which can meet the needs of fish migration. Fish passing test were carried out to check out the feasibility of the designed nature-like fishway in this paper. The juvenile grass carp was selected as the test fish. Considering the size of the fish path and the velocity of flow, juvenile grass carp with body length of (10±2) cm was selected. The critical swimming speed of juvenile grass carp in this experiment was about 0.95 m/s and the penetrating swimming speed was about 1.17 m/s. We carried the fish passing test in two cases, with different water depth in the fishway, the fish performance in the designed fishway was recorded. The results showed that, the success passing rate was 90% in the first case, with an average passing time of 66 s, and 100% in the second case, with an average passing time of 67 s. Through the fish passing test, it was proved that the fish can pass smoothly in the fishway with staggered arrangement of plant modules, and the plant modules can provide rest areas in the downstream side for the migration fish. The good performance of the migration fish verifies staggered arrangement of plant modules was reasonable. This paper had positive reference value to the design and reconstruction of the existing natural-like fishway. The nature-like fishway constructed by reed in this paper enriches the fishway form, which can guide the design and construction of similar fishways in the future.