Modeling the Hydromechanical Solution for Maintaining Fish Migration Continuity at Coastal Structures

Abstract

To promote water control in coastal areas developed for agriculture, tidal hydraulic structures (doors and flap gates) are used for the hydraulic management of irrigation and drainage networks. By closing when the water level increases due to the tide, they prevent sea water inflow. However, fish using the tidal wave to move forward (e.g., glass eels) are also blocked from accessing the hydrologic network. There are hydromechanical solutions to mitigate these problems, such as adding a wooden block to leave an opening at high tide or adding a spring to delay the closing of the structure. The latter solution allows the structure to remain open only during a part of high tide. Designed empirically, these solutions can either alter the hydraulic control performance or be insufficiently effective for fish passage. This study proposes an operating model approach for hydromechanical structures that takes these passage solutions into account. This approach makes it possible to evaluate the performance of the passage solutions for fish passage and hydraulic regulation. With the help of these models, it is possible to design solutions that ensure a compromise between the passability of fish species and agricultural uses.