Diversion Tailwater

The methods in this category calculate the elevation of the tailwater on the diversion from a reservoir. This category is dependent on the selection of a method other than the default method, None, in the Diversion Power category. If a method other than the default is selected for Diversion Power, then a method other than the default, None, must be selected for Diversion Tailwater.

None

This is the default method for the Diversion Tailwater category. No calculations are performed in this method.

There are no slots specific to this method.

Diversion Base Value Plus Lookup

The Diversion Base Value Plus Lookup method computes the Diversion Tailwater Elevation by adding the average Diversion Tailwater Base Value (over the timestep) to a function of Diversion defined in the Diversion Tailwater Table slot. This method is similar to the Base Value Plus Lookup Table method in the Tailwater category but uses the Diversion and Diversion Tailwater Base Value slots instead of Outflow and Tailwater Base Value. The Diversion Tailwater Base Value may be input by the user or linked to another slot, such as the Pool Elevation of another Reservoir. If the Tailwater Base Value is neither input nor linked, it is automatically set to zero.

Slots Specific to This Method

Diversion Tailwater Table

Type: Table Slot

Units: Flow vs Length

Description: This slot defines the relationship between Diversion and the Diversion Tailwater Elevation; Diversion vs either the diversion tailwater elevation or the tailwater elevation increment

Information: If the Diversion Tailwater Base Value is non-zero, the Diversion Tailwater Table gives values of incremental increase in Tailwater Elevation over th base value. Otherwise, the table gives the Diversion Tailwater Elevation values. The first row of the table should be for a Diversion flow of zero.

I/O: Required input

Links: Not linkable

Diversion Tailwater Base Value

Type: Series Slot

Units: Length

Description: The base elevation of the diversion tailwater, such as a downstream stage

Information: If the slot is not input or linked, it defaults to 0.

I/O: Optional, can be input or linked

Links: Linkable

Diversion Tailwater Elevation

Type: Series Slot

Units: Length

Description: The water surface elevation of the tailwater from the reservoir diversion

Information: This slot is used to compute Diversion Operating Head in Diversion Power calculations

I/O: Output only

Links: Not linkable

Method Details

When this method is executed, the Diversion value will already be known. If the Diversion Tailwater Base Value is neither linked, input nor set by rules, then it will default to zero.

The following steps are performed to calculate Diversion Tailwater Elevation.

1. TWTemp is obtained from a table interpolation on the Diversion Tailwater Table using Diversion.

If both Diversion Tailwater Base Value[t] and Diversion Tailwater Base Value[t-1] are known, then the Diversion Tailwater Elevation is calculated as follows:

2. If Diversion Tailwater Base Value[t] is known, but Diversion Tailwater Base Value[t-1] is not known, then the Diversion Tailwater Elevation is calculated as follows:

3. If Diversion Tailwater Base Value[t-1] is known, but Diversion Tailwater Base Value[t] is not known, then the Diversion Tailwater Elevation is calculated as follows:

4. If neither Diversion Tailwater Base Value[t] nor Diversion Tailwater Base Value[t-1] are known but Diversion Tailwater Elevation[t-1] is known, the current timestep’s Diversion Tailwater Elevation is set equal to Diversion Tailwater Elevation[t-1].

5. If neither Diversion Tailwater Base Value[t], Diversion Tailwater Base Value[t-1], nor Diversion Tailwater Elevation[t-1] are known, or if Diversion is not known, the method will exit and wait for more information.

Revised: 08/02/2021