I built a 3d flow only model which had 20 vertical layers(kmax = 20). But the bottom shear stress  in his file and map file are different. 
In the his file, the bottom shear stress named Mean bottom shear stress, unit is pa. And in the map file, the bottom shear stress named Total bed shear stress, unit is N m-2. 
In the his file, the bottom shear stress is very big as shown in the right, it seems wrong. I compared map file result with observation data as shown in the left, it seems the result of map file is correct. But when i run 2d model (kmax = 0), his file and map file are same and correct.
I also built a3d  flow-wave coupled model, and in the coupled model the results of bottom shear stress in his and map file are same and correct.
Why the bottom shear stress in his file are wrong when run flow only model?