A new framework for assessing roughness elements in promoting fish passage at low-head instream structures

Abstract Increasing interest in fish passage solutions past low-head instream structures has led to the development and implementation of new designs with various types of roughness elements within these structures. We know that roughness elements increase the heterogeneity in water velocity by creating a continuous or discrete low velocity zone, which supports fish passage. However, the effectiveness of these roughness elements for various low-head structures and fish species differs and is often not assessed in detail. This paper highlights three important aspects of assessing roughness elements, namely fish behavior, flow hydrodynamics and passage efficiency. A novel multi-stage framework that can be used for assessing the effectiveness of fish passage solutions is proposed. Initially, we consider the uniqueness of behaviour between species and the hydrodynamics created by roughness elements, as a generalized solution for the size and arrangement of these elements might not work effectively for all species. Then, for effective performance, the link that is required between fish behaviour (both individual and for groups) and hydrodynamics and effectiveness of the roughness elements is discussed for ensuring effective use in low-head structure designs. The proposed framework synthesizes the information required for effective solutions to fish passage through low-head structures.