A case study for optimal position of fishway at low-head obstructions in tributaries of Han River in Korea

The biggest problem involved in installing fishways at obstacles across natural streams is to engineer the optimal position of the fishway entrance. The four criteria that were used in this study to construct a fishway at low-head submerged weirs located in the Han River of Korea are established based on previous studies. The criteria include, the farthest point toward upstream, the vicinity of the thalweg, the vicinity of the primary velocity, and a point of less erosion and deposition. Among these, the third and fourth criteria are revealed by means of flow and sediment transport analysis. In particular, the entrance and exit of a fishway have often been closed due to the action of erosion and deposition resulting from extreme flood events that occur in the monsoon season of Korea. Numerical models of two-dimensional flow and sediment transport are used to reveal the structure of the flow field and characteristics of erosion and deposition. The propriety of location of the fishway is verified based on the four criteria using the numerical simulation at the Gapyeng Stream, which has many fishways. The efficiency of the fishway is evaluated indirectly by monitoring the fish. The criteria are also used to locate the best position of a fishway at a weir located in the Wangsuk Stream, which is a tributary of the Han River and does not have any fishway.