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Objects and Methods : Reach : User Methods : Stage
Stage
This category controls the calculation of river stage or elevation. Depending on the method selected, the upstream, downstream, and average stage may be calculated.
Note:  If stage values are linked or used together with other elevation values (as in surface water / ground water interfacing applications), RiverWare assumes that they all share the same datum.
* None
This method is the default for this category. It performs no calculations.
There are no slots specific to this method.
* Inflow Stage Table Look Up
This method finds the stage in the river from a table interpolation using the inflow. You can select this method if Head Based Diversion is selected in the Diversion From Reach category. This method is only available when the Reach solves in the downstream direction only. As a result, for No Routing and Time Lag, this method is available only if the Specify Local Inflow, Solve Outflow or No Local Inflow, Solve Outflow method is selected. For the other Routing methods, the method is always available as these only solve downstream. See the following topics for details:
Slots Specific to This Method
 Inflow Stage
Type: Series
Units: LENGTH
Description: Stage of reach
Information:  
I/O: Output only
 Inflow Stage Table
Type: Table
Units: FLOW versus LENGTH
Description: table to find reach stage from inflow
Information: In reality, this should represent the average stage in the reach
I/O: Required input
 Stage
Type: Series
Units: Length
Description: the average reach water surface elevation
Information: Values in this slot are output only, except in the case of a time lag in the Reach/Drain Elev Interp method of the Drain Water Surface Elevation method category. This requires that values for Stage are input for pre-dispatching timesteps needed by the time lag.
I/O: Output only
Method Details  
Inflow Stage is calculated by using the Inflow with the Inflow Stage Table. The Stage slot, which is used in certain seepage calculations, is set equal to the Inflow Stage.
* Stage Table Look Up
This method finds the stage in the river from a table interpolation. You must select this method if Head Based Diversion is selected in the Diversion From Reach category.
Slots Specific to This Method
 Inflow Stage
Type: Series
Units: LENGTH
Description: Stage of reach at upstream end
Information:  
I/O: Output only
 Inflow Stage Table
Type: Table
Units: FLOW versus LENGTH
Description: table to find reach stage from flow at upstream end of reach
Information:  
I/O: Required input
 Outflow Stage
Type: Series
Units: LENGTH
Description: Stage of reach at downstream end
Information:  
I/O: Output only
 Outflow Stage Table
Type: Table
Units: FLOW versus LENGTH
Description: table to find reach stage from flow at downstream end of reach
Information:  
I/O: Required input
 Stage
Type: Series
Units: Length
Description: the average reach water surface elevation
Information: Values in this slot are output only, except in the case of a time lag in the Reach/Drain Elev Interp method of the Drain Water Surface Elevation method category. This requires that values for Stage are input for pre-dispatching timesteps needed by the time lag.
I/O: Output only
Method Details  
Inflow Stage and Outflow Stage are calculated by using the Inflow with the Inflow Stage Table and the Outflow with the Outflow Stage Table, respectively. The Stage slot, which is used in certain seepage calculations, is set equal to an average value whenever possible. If inflow and outflow stage values are known for the current time step, the stage is set as the average of these two values. If one of the values is not known for the current time step, a value is sought at the previous time step. The stage is then set as the average of a current time step stage value (either inflow or outflow) and the previous time step stage value (either inflow or outflow, corresponding to whichever is not available at the current time step). If a value from the previous time step is sought for but is not available--at the first time step of a model run, for example--no averaging is done. The stage slot value is set equal to whichever value is known at the current time step.
Note:  When the reach is dispatched with Solve given Outflow, No Routing; Solve given Inflow, No Routing; or Solve given Inflow, the Stage Table Look Up user method is solved twice: once near the very beginning of dispatch and once near the very end. When the object dispatches the first time (for a given time step), the following process occurs.
1. The stage is calculated averaging a current flow value and a previous flow value.
2. Other user methods are solved, including seepage methods that may depend on the stage value.
3. The flow at the other end of the reach is determined (Inflow for Solve given Outflow, No Routing or Outflow for Solve given Inflow, No Routing and Solve given Inflow).
4. The stage is recalculated averaging available values for the current time step for both inflow and outflow.
Under this arrangement, the intermediate user methods will use an appropriately averaged value of stage for solution, but the final value in the stage slot is unlikely to represent the value used by those user methods. Also, any subsequent re-dispatch of the objects will cause Stage Table Look Up to average existing current inflow and outflow values at the beginning of dispatch. That value still may not equal the value found in the stage slot at the end of dispatch.
Note:  The stage method Inflow Stage Table Look Up does not have this same dispatching pattern and should be considered if you want to avoid this. See Inflow Stage Table Look Up for details.
Double solution of the Stage Table Look Up user method as described above does not occur in Solve given Inflow, Outflow, No Routing; Solve given Outflow, Time Lag; Solve given Inflow, Time Lag; Solve given Inflow, Outflow, Time Lag; Solve given Inflow, Time Lag, Downstream Only; or Solve given Inflow, Storage Routing dispatch methods.
* Input Stage
The Input Stage method allows you to input the average water surface elevation of the Reach for use in certain Seepage calculations.
Slots Specific to This Method
 Stage
Type: Series
Units: Length
Description: The average reach water surface elevation
Information:  
I/O: Required input
* Gage Based Stage
The Gage Based Stage method is used when a reach must be discretized, as may be the case with Gradient Seepage methods. When gages are not available on the Reach element more distant gages must be used to determine the stage.
Slots Specific to This Method
 Stage
Type: Series
Units: Length
Description: The average reach water surface elevation
Information:  
I/O: Output only
 Upstream Gage Elev
Type: Series
Units: Length
Description: The elevation of the upstream gauge
Information: This is the elevation of a gauge that is not immediately adjacent to the Reach. It is some distance upstream.
I/O: Required input
 Downstream Gage Elev
Type: Series
Units: Length
Description: The elevation of the downstream gauge
Information: This is the elevation of a gauge that is not immediately adjacent to the Reach. It is some distance downstream.
I/O: Required input
 Distance Between Gages
Type: Table
Units: length
Description: The horizontal distance between upstream and downstream gauges
Information:  
I/O: Required input
 Downstream Distance to Reach
Type: Table
Units: length
Description: The horizontal distance from the upstream gauge to the point on the Reach for which elevation is desired
Information:  
I/O: Required input
Method Details  
The difference between the upstream and downstream gage readings (the rise) divided by the distance between the gages (the run) provides the Reach gradient. When this is multiplied by the distance downstream from the upstream gage to the Reach element, it provides the change in elevation. This is subtracted from the upstream elevation for the Avg Stage.
Revised: 07/17/2020