Unlinked Inflow slots of Reservoirs no longer default to zero for timesteps where they do not have user input values. This previous behavior had some undesirable effects on simulation and often caused confusion in the modeling approach. Existing models which rely on Inflow slot default values of zero for dispatching of upper-most reservoirs must be updated to produce the same results under RiverWare 1.2. For both Simulation and Rulebased Simulation, previously defaulted Inflow slots should be explicitly set to “0” for all simulation timesteps.

Models which perform water quality computations will also need to be updated. Water quality constituent Inflow quantities no longer default to zero when the Reservoir Inflow is unlinked. The following slots will now need user input of “0” for all simulation timesteps to produce the same results as previous RiverWare versions:

Exceeding the user-specified maximum iterations when setting a slot value now aborts the simulation run. This occurs when, during iteration, a slot’s value is set too many times. Normally, the iteration is terminated when the new slot value and the old slot value differ by less than the specified convergence value. Previously, when the maximum iterations was exceeded, a diagnostic warning message was posted, the new slot value was not set, and simulation proceeded. Since this could result in a violation of mass balance beyond the limits of the user-specified convergence value, the behavior was eliminated.

The iteration count of a slot is incremented every time a new value is set. There is a different iteration count for each timestep of the simulation and for each series slot of a model. Maximum iterations are set to 20 by default, but may be changed in each series slot’s Configuration menu. Exceeding maximum iterations is rare. Slow convergence of the solution can indicate a modeling problem. The cause of excessive iterations should be determined before arbitrarily increasing the maximum. In certain cases, the problem can also be solved by relaxing the slot’s convergence criteria.

This change applies both to Simulation and Rulebased Simulation. In Rulebased Simulation, however, iteration counting is turned off by default. To enable the checking of maximum iterations in Rulebased Simulation, turn on the Check Iterations checkbox in the Run Control Panel’s View Controller Specific Parameters Dialog. Rulebased slot iteration counters for all slots are reset each time a rule begins to execute.