Hi, 

The same time step is applied in both morphodynamics and hydrodynamics for all flow solvers. Hence, also when the backwater curve is solved (i.e.,. steady flow). Ever time step, a new backwater curve is solved using the boundary conditions (discharge and water level) at that time. Hence, the water discharge can vary with time. 

The documentation of Elv is basically stored in my mind, sorry for that . On the other hand, the code is sufficiently accessible for easily inspect the routines to check what exactly is going on. Quasi-steady means that the flow is not fully steady (i.e., backwater curve) nor fully unsteady (i.e., Saint-Venant (1871) equations). The time derivative of the continuity equation is considered, but the time derivative of the momentum equation is neglected. The best book explaining this is (in my view) that of Battjes and Labeur. Check the lecture notes of TUDelft in case you do not have the book. The solver is in function 'preissmann'. It is not the simplest to understand. All possible tricks to speed it up where used . 

Hi Hermjan, 

Indeed, you call diffusive to what I call quasi-stedy. Still, it is not the same. The diffusive wave equation is found further assuming small water slope after assuming quasi-steady. In Elv you solve the quasi-steady set of equations and not the diffusive wave equation. 

[From Hermjan]Hi Victor,
Thanks for your answer
I donot understand yet. Does Elv solve the equation given in Batjes and Labeur? That would in my opinion be the same as what I adopted. Anyway I did not succeed to run a quasi-steady simulation. 

Thanks again and with best regard.

Hermjan

Hi Hermjan, 

In Battjes and Labeur, both the quasi-steady system of equations (Equations 8.1 and 8.2) and the diffusive equation (Equation 8.17) are presented. Elv solves the quasi-steady system of equations. You can see this in the terms present in function 'preissman'.