A study on construction of tidal biological channels connecting land and sea and its impact on inland water bodies: taking the North Branch of the Yangtze River Estuary and the North Lake as an example

The establishment of effective biological corridors in the land-sea transitional zone can enhance the biodiversity of the area, elevate the ecological quality and overall service capabilities of the coastal realm, and foster the high-quality advancement of integrated sea-land development. This study takes Chongming North Lake, located on the north side of Chongming Island, as a case of study to examine the viability of developing tidal fishways utilizing existing trenches and culverts. Based on a 2D hydrodynamic numerical model and salinity model, the hydrodynamic characteristics of different tidal fishway sizes and their impact on inland water bodies are analysed, and the plant configuration and operation management measures of biological channels explored. Results indicate that, firstly, by selecting the appropriate length of the biological corridor the distance between dams, and the width of the gaps, it is possible to achieve an optimal flow velocity within the corridor for the passage of fish and other organisms during specific period of tidal flux. Secondly, constructing a suitable scale of land sea connected biological pathway can satisfy the functional requirements while mitigating the risks associated with storm surge disasters. Thirdly, under typical tidal conditions with a 10-year recurrence interval, the water level in Chongming North Lake fluctuates by about 20 cm. Even under a 100 year storm surge scenario, the water level can be managed to remain below the designed limit. Fourthly, considering the daily influx of saline water, turbid water and polluted water bodies in the northern branch of the Yangtze River Estuary, it is recommended to undertake habitat creation within the biological corridor and to restore habitats in the North Lake area. The arrangement of vegetation should take into account the dynamics of flow velocity, water level variations, and the mixed zones of brackish-water.