If the boundary conditions at one of your boundaries are inaccurate and you therefore have stability problems (blow-ups) at this boundary, you can specify a small band (2 to 4 grid lines) with a very high resistance. Manning numbers in the range 5 -10 m1/3/s have been applied successfully. However, this method should only be used if it is impossible to improve the boundary conditions. Furthermore, the simulation results in the area around the small resistance numbers should be used with caution.
When carrying out a tidal calibration you can use the bed resistance to increase or decrease the tidal amplitude. The tidal phase is adjusted by changing the water depth. When the depths have been read from a sea chart, increasing the depth is all the more justifiable as these charts often give the minimum depths, which are more important to shipping than the maximum depths.
Because h1/6 is calculated for each grid point and at each time step when the Manning formulation is selected rather than the Chezy formulation, the computational time is increased. Please see CPU Time (p. 99) for an estimate of the additional CPU time required.