Thanks for you reply.
I recently got a reply from Chuck Downer. he sent me a cmt file. The cmt file produced by WMS 8.1 lack some parameters for soil erosion, TC_COEFF and TC_INDEX i think. I edited my cmt file and now GSSHA sediment is working.
Also, even if I select sediment flux and sediment deposition to be two of the grid outputs, WMS wont give extension filenames for these. Even if I manually specified, the saved prj file does not contain any card for these desired outputs. When I open the saved GSSHA prj file, the check box for the sediments becomes unchecked.
I contacted Aquaveo's tech support weeks before but got a reply that technical support is no longer available for GSSHA.