If Controlled based on Upstream Elevation or Controlled based on Elevation Difference is selected, operational rules for structures can be defined. This has been implemented in an approach similar to the rule-based operations of sluice gate for hydraulic structures. One purpose of this enhancement is to allow the user to simulate rule-based pumps. It should be noted that at this stage, this feature only acts on the flow series and maintains the concentrations as constant i.e. there is no rise or fall for the WQ constituents.
The interface for the withdrawal/return boundary condition setup based on control rules rather than a time series is shown in Controlled based on Water ElevationA. The two control rule approaches require the user to configure rules for the structure. These rules are set in the W/R Flow and Concentration Rise/Fall Settings | Control Rules. Here the user may edit an existing rule or create new ones as well as set the initial conditions
Controlled based on Water ElevationA shows the settings for the rule-based withdrawal/return boundary. In this case, a pumping station has been configured using the withdrawal/return boundary conditions. The approach is similar to that described for rule-based sluice gate operations: the user configures the number of sets of rules and uses the up and down arrows to select the Current Rule set. Each set can have a number of different triggers. In this case, it is two. The triggers are determined by the control value. This is the upstream elevation, or the difference in the upstream and downstream head, depending on which option the user has selected.
EE uses the “state” of the structure to allow the user the high level of control required to simulate realistic scenarios. The logic of the process is that if the state of the structure is “1” then it is on, discharging the Flow Discharge set. This will continue from that trigger level until it reaches another trigger level. When a trigger is reached with a state of “0” the pump will stop, and flow changes to the new Flow Discharge. The prevent instability in the system with sudden turning on and off of large flow rates within the one-time step, EE allows the user to set a rate of increase and decrease of the flow discharge with the Rate variable, in cms/minute.
Figure 1. Withdrawal/Return form with rule-based boundary.
Figure 2. Boundary Data Series form.
Controlled based on Water ElevationA demonstrates the effect of the operation of the pumping station. In many cases, the user will configure a simple system as described here. In this case, it would seem the “state” setting is redundant as the pump is simply on or off. However, in some more complex systems, there may be two or more pumps at a particular location. These may be configured as lead and lag pumps, with the lead pump turning on at a low water level and the lag pump only turning on at a higher level. In these cases, the user may want both pumps to stay on even when the water level drops below the trigger level of the lead pump. For this reason, the “state” setting is required to fully simulate the complexity of the system.
Figure 3. W/R boundary condition pump example.