The Hydraulic Characteristics Of Typical Baffles In Culvert Fishways Based On The Upstream Behavior Of Small Fishes

Baffle is a reverse distribution of weir along a culvert(or channel),which are used to reduce the flow rate,increase the depth of flow and establish resting areas for fish.In order to design a culvert fishway suitable for fish to pass through,the hydraulic characteristics of different types and sizes of baffles must be deeply analyzed and studied.In this research,based on the upstream behavior of typical small fishes,the hydraulic characteristics of typical baffles in culvert fishways and their passing effect under the water depth of 18 cm,28cm and 38 cm were studied.Grass carp living in the middle and lower strata,silver carp living in the upper strata,and Opsariichthys bidens were selected for research object,in order to study the upstream effect of them in these two typical baffle systems by placing a baffle in an open channel.By comparing the simulated flow field with the measured flow field,the fine flow field in the test area is obtained.The preference degree of fish to different water conservancy environmental factors is analyzed,and the coupling relationship between baffle effect,hydraulic characteristics and fish upstream preference is studied.This study can provide some theoretical basis and reference value for baffle design in practical culvert engineering.The main conclusions are as follows:(1)For non-baffle culvert,the success rate of the three species of fish used in the study was 0 under the water depth of 28 cm and 38 cm.The evaluation results of the fish passage obstacle of Fish Xing showed that the water depth and velocity in the smooth culvert were important factors that affect the successful upstream of the target fishes.While,reduce the inlet water depth to 18 cm,the success rate is only 15.4%;(2)Under the condition of water depth of 18 cm,the slotted-weir baffle with the size3(b=20cm,H =25cm,L=125cm)has the best hydraulic characteristics,and its stable velocity at the measuring point and average velocity in the chamber are the lowest;(3)Slotted-weir baffle weir baffle and weir baffle can greatly increase the success rate of fish upstream and.the upstream success rate of fish in both baffle systems is water depth28>38 >18.In addition,slotted-weir baffle is higher than weir baffle;(4)In the weir baffle system,the three species of fishes tend to pass through the lower part of the weir when passing from one chamber to the next,while in the weir baffle system,the target fishes tend to pass through the lower part of the weir;Only the grass carp showed obvious the behavior of sticking wall or bottom;(5)The shorter the upstream time,the higher the success rate,and the upstream timemostly concentrated in 0-5min;The test results show that under these three kinds of baffles and three kinds of water depth,grass carp's preferred velocity was 0.2-0.4m/s and turbulent kinetic energy was 0.029-0.059J/kg,silver carp and Opsariichthys bidens were 0.3-0.5m/s and turbulent kinetic energy was 0.044-0.076 J /kg,there difference is not obvious.