Hello, I am writing a dissertation on Natural Flood Management (the use of natural features to mitigate flooding) and I’m creating a model of a river system using HEC-RAS. I want to model the effects of a Woody Debris Dam, which are soft-engineered barriers made of wood of varying sizes, that stretch across a stream. I am wondering if anyone could tell me the best way to model this? I would use an obstruction across a cross section but woody dams allow some amount of flow underneath, and the blockages automatically extend to the base. Woody dams are porous but I do not think there is any way to model that in HEC-RAS. I have also looked at the inline structure option but weirs/embankments also seem to extend to the base. Would changing the mannings number of a cross section be the best option?
Thanks in advance.
You could manipulate the n-value to represent losses due to turbulence and blockage of the channel, but you would be tweaking a calibration parameter. Can you cite other studies where n-values were empirically determined for in-channel wood debris? You could use such studies to modify your model, after you have it calibrated.
Have you accounted for why you would use a 1D model instead of a 2D or 3D model?
Hi thanks for the response! I’m using a 1D model due to lack of data on the site I’m modelling and due to time/resource constraints I’m aiming to keep the model as simple as possible. I have seen several studies that attempt to model these Dams but most did not use HEC-RAS. I will search and see if I can find a source for an n value, thanks!