Dry Bed (Low Flow)

For the dry flow condition, the numerical model applies a very small initial steady flow (virtual flow) at the start the simulation. This virtual flow is applied system-wide and has negligible effect on the computational results over the full simulation. The engine distributes and manages the virtual flow allocation and de-allocation dynamically across all the network branches and loops over the full course of the simulation, and sophisticated algorithms are developed to distribute the virtual flows in the way that they will not be accumulative and they have only local impacts on the very low flow conditions. These virtual flow assignments are based on a tiny threshold value that is dynamically adjusted over the duration of the analysis. A virtual flow filter algorithm adjusts the results for the virtual flow quantities and depths by subtracting the virtual flow effects from the hydraulic results at each time step at each solution point over the network.

To users, these virtual flows are invisible and there is no practical impact on the computational results.