There are several types of navigation dam operations. The simplest is pool only control (as shown in Figure 14-30). In this case, the program tries to maintain the water surface immediately upstream of the dam within user specified targets. In the other operations (see below), the target water surface is located some distance upstream of the dam and there may or may not be limits on the water surface right at the dam.
In order to keep the water surface at the dam within the user specified limits, while only infrequently changing the gate settings (i.e., every six hours), the program needs to know what the approximate inflow at the dam will be some time into the future. This is done by monitoring the flow at an upstream cross section. The user must enter this location. In this example (Figure 14-30), the Flow Monitor tab has been activated and the flow monitor location has been entered as river station 315.5. The flow monitor location should be chosen so that the river travel time between the monitor location and the navigation dam is on the order of (or somewhat less than) the normal gate increment. In this example (Figure 14-30) the gate time increment is every six hours, so a location a few hours upstream would be appropriate.

For 1D, the navigation dam will automatically find and include additional inflows between the Flow Monitor location and the navigation dam.  Any 1D reach tributary inflows and any hydrograph inflows on the Unsteady Flow editor will be included.  So 1D tributaries do not need separate flow monitors.  A 1D navigation dam would generally only need a single flow monitor location for the pool.  If the navigation dam has a hinge, the hinge will need its own separate Flow Control location as described in the Hinge operation section.

Flow monitoring for 2D is more complicated.  Please see the section on 2D for more information.

The calibration of the navigation dam control data involves some empirical decisions and trial and error experimentation. This is true of the flow monitor location as well as most of the remaining data explained below.
For 1D, the flow monitor location must be a normal cross section in the model. This means that cross sections must be extended far enough upstream of the dam to account for this location. Note also that the monitor point can be located upstream of other hydraulic structures, including other navigation dams. As long as another upstream navigation dam does not have a significant storage capacity, it should not affect the results of the flow monitor. 
After the flow monitor location has been chosen, the Pool Control tab can be pressed bringing up the editor shown in Figure 14-31.

Figure 14 31. Navigation Dam Editor with Pool Control

The user enters a range of water surfaces and corresponding Flow Factors. In this example, the ideal target water surface has been entered as 459.35. The primary target range is from 459.2 (Target Low) to 459.5 (Target High). In general, if the water surface is between Target Low and Target High and it is time to change the gate settings, then the program will adjust the gates to get an average of the current flow at the dam and the monitor flow.
For instance, assume that at time 10:00 the current discharge from the navigation dam is 10,000 cfs, 11,000 cfs of flow is observed at the monitor location, and the water surface at the dam is 459.4 feet. Since 459.4 is in the primary target range, the program will compute the average of the flows, 10,500 cfs. By trial and error, the program will change the gates (and compute the corresponding flow) until there is 10,500 cfs (plus or minus the tolerance) of discharge at the dam. The tolerance is 1% of the flow, in this case 105 cfs. So the program will actually stop iterating whenever it first determines a gate setting that results in a flow that is between 10395 cfs and 10605 cfs. After the gates have been changed, they won't (normally) be adjusted for the next six hours. The flow from the dam willl vary as the water surface at the dam fluctuates.

As the water surface at the dam gets out of the primary target range, then the flow (that is, the discharge from the dam) is adjusted by the Flow Factors. In general, when the stage is between Target High and Maximum, then the flow is multiplied by Flow Factor Target High (in this case 1.03). Between Maximum and Maximum High, it is multiplied by at least 1.07. Between Maximum High and water surface Open River, the flow is rapidly increased up to at least Flow Open River (listed as 50,000). Flow Open River does not represent a cap. If the flow at the monitor location gets high enough, the discharge at the dam can go above Flow Open River based on the Flow Factors. Above water surface Open River, all the gates are opened all of the way.

The operations below the target zone work the same way. Flow Factor Target Low and Flow Factor Minimum are applied in the same way. Between Minimum Low and water surface Close Gates, the flow will be rapidly decreased to Flow Minimum, but again, this is not an absolute minimum. If the water surface remains low enough, the program will continue to close the gates and reduce flow. The only absolute minimum is that the program will not close the first gate group below the gate minimum opening.

The water surface targets are basically calibration knobs and no particular water surface targets have to exactly match the operationally prescribed limits on the pool surface. However, the best response will probably be obtained if the Maximum and Minimum are close to the prescribed limits.