Author(s): P. Sammarco; M. Di Risio

Linked Author(s):

Keywords: Floaters; River flows; Hydraulic roughness; Resistance coefficient; Drag force

Abstract: The presence of floaters (i.e. moored boats or floating objects) must be taken into account when dealing with hydraulic analyses of river flows. This research aims to propose a simplified method to compute the value of the resistance coefficient able to reproduce the effects of floaters upon the flow levels. The banks of large rivers can often host up to a few thousand moored boats. Moreover, the presence of large wood debris may influence the flow levels. This is tremendously important when dealing with hydraulic analyses aimed to reproduce the floods propagation (e.g. within the frame of hydraulic risk analysis). Then, an additional flow resistance occur that is not usually included in the model equations used to perform hydraulic analyses. Indeed, numerical models aimed to describe in details the effects of floaters have a high increase of computational costs. The main goal of this research is to propose a general method that can be simply applied to standard hydraulic analyses while taking into account the presence of floaters along the computational domain. The rationale of the method relies on the hypothesis that any floaters (boats moored along the banks or wood debris gathered at existing fixed structures) are subjected to a drag force exerted by the current. In turn, this action is counteracted by the mooring lines or by the fixed structure and an equal and opposite force is exerted by the floaters on the river flow. The forces may be expressed as an average tangential stress on the flow, i.e. by an increase of the hydraulic roughness. Of course, any claim to describe the flow features locally cannot be made, however here we are interested in the larger spatial scale of field evolution. The proposed method provides a general formulation able to estimate the increase of the hydraulic roughness as a function of the floaters dimensions and arrangements along the river stretch.

DOI: https://doi.org/10.3850/978-981-11-2731-1_133-cd

Year: 2018