When using Bentley Hydrology, there are certain memory limitations that apply in certain cases.

First, there is a limit of 32k ordinates per computed hydrograph.

Second, based on the number of catchments, the simulation duration and the output increment you are also limited in how many points may be used per hydrograph and it can be below the 32k internal maximum.

If you get the message about out of memory (and this can appear in several different ways including but not limited to a user notification) you should try increasing your output increment and/or decreasing your simulation duration.

The fewer catchments you use in a model, the longer total simulation time you can use before reaching the memory threshold of the Bentley Hydrology engine.

It is difficult to predict the exact threshold of the Bentley Hydrology Engine as there are many dependent variables involved. Some of these variables include but are not limited to the operating system (32-bit vs. 64-bit) , the amount of system memory available, the size of the model (primarily the number of catchments in said model), the output increment and total simulation time.

Also note that Long Term Continuous Simulation is not recommended with the Bentley Hydrology methods as using longer simulations can easily exceed the 32k per computed hydrograph limitation. It is highly recommended that you use the Explicit (SWMM5) engine in the calculation options and use the EPA-SWMM Runoff Method for your catchments. In this approach you will get the full benefit of the built-in support for Long Term Continuous Simulation using the SWMM 5 engine.