Questions about sediment transport model

I use the 4.1.0 version of HEC-RAS with SI units to perform a sediment analysis. I try to reproduce Newton degradation experiment.

DATA

The channel is 9.14m long, 0.305m wide and 0.5m depth. Cross section was placed each 0.2m.

I used the following quasi-unsteady flow file for the simulation: normal depth (slope of 0.00416) for the downstream boundary condition and flow series for the upstream condition (time step of 1 min), The simulation is performed for one day.

I used the following data for the sediment transport calculation:

rating curve boundary condition

properties of sediments

transport parameters

options

Questions

Question 1

First of all, with a supply of 2 tons/day, I obtained a critical depth at the entrance of the channel. I don't really understand how HEC-RAS calculated data for the first cross section. Could you explain it to me?

Question 2Moreover, I don't understand how HEC-RAS converts mass into volume. I have attached an excel file in order to show you the results I have, just by changing mass or volume in sediment output option (yellow cells).

The mass/volume ratio is perform in this excel file (on the right of the file). could you explain to me why the ratio is not equal to the density?

Question 3

This question is about initial conditions. I put 2 tons/day in the rating curve condition. Nevertheless, the result file indicates that the cumulated mass in in the first cross section is 2.4 tons/day whereas I put 2 tons per day. Why initial condition and results are different? (see blue cell in the attached excel file)?

Question 4

The last question is about sediment computation options and tolerances. If I choose min bed change before updating cross section of 0.00067 ft, the tolerance in SI units is not 2.10^(-4) as I expected (0.00067*0.3048) but the tolerance is 2.10^(-7). It seems that unit conversion is not correct?