Flow Characteristics around a freshwater mussel in a gravel bed flume

Abstract

Mussels are a defined as “ecosystem engineers” capable of affecting the hydrodynamics, passively and actively (Navaratnam et al., 2018; Termini et al., 2023; Modesto et al., 2023). The generation of larger-scale turbulence around the mussels living on the river bed may also affect the quality of the habitat. Thus, it is extremerly important to know the effects determined to the presence of mussels on flow characteristics. In the present study reports preliminary results on flow and turbulence characteristics around an isolated mussel over a gravel-bed. The presence of mussel enhances the effects determined by the rough-bed on the kinematic characteristics of flow. The analysis is performed on the basis of data collected in a straight laboratory gravelbed flume both in absence and in presence of an isolated and partially buried mussel (Unio elongatulus), aligned with the incoming flow. In order to take into account spatial heterogeneities, the double-averaged velocities are considered for the analysis in the absence of mussel on the bed. Results show that, because of the presence of gravels, in the absence of the mussel, the streamwise velocity profiles show an inflection point with the formation of a mixing layer whose thickness varies passing from the banks to the channel axis. The presence of mussel modifies the shape of the velocity profile with the formation of turbulent flow structures around it. Different effects on the velocity and turbulence fields have been identified in relation with the mussel’s filtrating capacity