Simulation of scour and deposition in the flow field and adaptability of fishes around eco-friendly notched groins

•A new groin structure with a notch in its middle part was proposed.•Fish habitat within the groin field can be further promoted by properly designing the notch width and depth.•In the main channel, the scour depth slightly decreased with increasing notch depth, which did not affect navigation. Over the past few decades, eco-friendly channel construction has gained wide attention around the world including China, as it considers both navigational and ecological functions. The Groin system is a hydraulic structure that can effectively increase the area of fish habitats. Groin shape has an influence on the local flow field and the scour and deposition pattern near the structure, thereby affecting the adaptability of fishes to the groin fields. In this study, a new groin structure with a notch in its middle part was proposed. A lab experiment was conducted on a physical model to investigate the characteristics of the flow field including patterns of water level distribution, flow velocity distribution, and scour and deposition on different submergence levels and incoming flows. This experiment used four notch depths: 0 (unnotched), 1/3 of groin height, 2/3 of groin height, and full groin height. Then the distribution of habitat suitability index (HSI) was calculated based on the assessment index system of the indicator fish species (Cyprinidae). The results showed that the notches created in the middle of localized overflow groins had a significant effect on the surrounding flow pattern. Due to localized overflow, both the flow velocity and the velocity gradient behind each groin increased. The flow velocity behind each groin was positively correlated with notch depth, while the flow velocity in the main channel was negatively correlated with notch depth. Under the complex flow conditions, depositional features did not occur along the edges of the groin fields, ensuring connectivity between groin fields and the main channel. An analysis of water depth and flow velocity suitability indexes of Cyprinidae suggests when notch depth is 2/3 of groin height, the notched groins have good ecological effects, especially in the groin fields.