I'd like to model the hydraulic effect of the implementation of beaver dam analogs (BDA) in a stream using HEC-RAS. For that, I need to establish a relationship between the water level upstream the structure and the outflow downstream the structure (based on Darcy's law). The missing element here is the permeability coefficient (k) of the composite of sediments and organic materials that forms that kind of structure. I wonder if the evaluation of that coefficient has ever been made in the past for beaver dams or BDAs. Would it even be ok (for restoration purposes) to establish a mean value for that coefficient and use it widely in order not to repeat such measurement for each project?