Initialisation of Tanks‏ in InfoWorks CS and InfoWorks ICM

One issue that is mentioned fairly regularly to the support desk is that tanks within an InfoWorks CS/ICM model appear to be full at the start of a simulation where they should in fact be empty.

The reason for the above is to do with initialisation flows. When a simulation is in the initialisation phase there are flows introduced from the initial timesteps of simulation events such as inflows or level files as well as the base flow at pipes. Initialisation will only complete once a steady state has been achieved within the network. The outcome of this is that it is only once tanks have been filled to outlet level (and therefore can have consistent inflows and outflows) that initialisation will be able to complete. This is obviously not the initial state that users would like to apply events to.

There is a common approach to deal with this situation within models which involves using a control link as well as RTC and a dummy outfall. In order to ensure that storage is empty at the start of a simulation the user should first create a dummy outfall close to the storage node location. Once the outfall has been placed this should be connected to the storage using an RTC controllable object. Normal practice is to use a variable sluice gate (the opening size should be sufficient to take all flows). Please note that the invert of the control object should be level with the lowest defined storage value. Once this connection has been established create an RTC object where the regulator is set as the control object which was introduced for the purpose of emptying storage. Now that the RTC object exists all that needs to be done is for a rule to be created with the default setting to “closed”. During initialisation the gate will remain open but as soon as the simulation starts the default rule is applied and the gate is shut. As a result from this point onwards the control object will play no further part in the simulation.

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