If the pool elevation is below the guide curve (set as top of conservation in the model), ResSim will hold as much inflow as possible to rise up to the guide curve as quickly as possible.
If the pool elevation is above the guide curve, ResSim will release as much as needed to get down to top of conservation as quickly as possible.
If there are no rules of operation, its only limitation will be the amount of inflow and the physical capacity of the outlets. To illustrate this, I have developed a simple model with one reservoir.
Next, we can look at how ResSim behaves when the pool is above top of conservation. To do this, I start the simulation with the pool at 52 ft (2 feet into the flood pool). At this point, I have no rules of operation in the flood pool. The pool is drawn down to the top of conservation in about 2 days. The release is set to 1,000 cfs (physical capacity of outlet) once the simulation begins. Recall that the first three days are the lookback period where a constant elevation was specified.