Lateral Link Direction
The Lateral Link Direction category is dependent upon selection of the Head Based Groundwater Grid or the Link to MODFLOW GW method. When the Head Based Groundwater Grid method is selected, you need to specify the number and location of the connected objects with respect to the current object. This category includes 15 user methods, which are the combinations of Upstream, Downstream, Left, and Right. For example, a groundwater object may be connected to only one other groundwater object which is upstream. Or it may be connected to four other groundwater objects which are upstream, downstream, left, and right.
These methods are used to control the slots added and the dispatch conditions used (the dispatch conditions will depend on the Elevation Upstream/Downstream/Left/Right Previous slots).
When the Link to MODFLOW GW method is selected, you need to specify the number and location of the connected objects with respect to the current object. This category includes three user methods: Upstream, Downstream, and Upstream and Downstream. For example, a groundwater object may be connected to only one other groundwater object which is upstream; or it may be connected to both an upstream and downstream object.
These methods are used to control the slots added and the dispatch conditions used (the dispatch conditions will depend on the Elevation Upstream and Downstream Previous slots).
See the following topics for details:
No Linked ObjectsA No Linked Objects method is also available. This method can be used without specifying connections to other groundwater objects.
Upstream, Downstream, Left, and/or RightNote: Throughout this section, the term Elevation U/D/L/R Previous slots refers to any or all combinations of the following slots:
• Elevation Upstream Previous
• Elevation Downstream Previous
• Elevation Left Previous
• Elevation Right Previous
Slots Specific to This Method
Elevation Upstream, Downstream, Left, and Right Previous
Type: Series Slot
Units: length
Description: The previous elevation of a connected groundwater object
Information: These are four separate slots. You can choose the number and the location of the connected groundwater objects, with respect to the current object. There is a slot for each connected object. These slots were previously called Previous Adjacent Elevation Left/Right/Upstream/Downstream.
I/O: Output only
Links: These slots are linked to the Elevation Previous slots on each of the connected groundwater objects
Conductance Upstream, Downstream, Left, and Right
Type: Scalar Slot
Units: Area per time
Description: The conductance values that correspond to the area between this groundwater object and each of the connected groundwater objects
Information: These are four separate slots. You can choose the number and location of the connected groundwater objects. There is a slot for each connected object.
I/O: Input or computed; see Groundwater Conductance.
Links: Not linkable
Flow Upstream, Downstream, Left, Right
Type: Series Slot
Units: flow
Description: The flow between the current object and each of the connected groundwater objects
Information: These are four separate slots. You can choose the number and location of the connected groundwater objects. There is a slot for each connected object. A positive value represents an inflow to the groundwater object.
I/O: Output only
Links: Not linkable
Flow Factor Upstream, Downstream, Left Right
Type: Series Slot
Units: Fraction
Description: Proportion of the flow initially calculated from the previous elevations that will actually occur
Information: This value is between 0 and 1. It can remain NaN, and the value is assumed to be 1.0. If the slot is not linked, it is unused (assumed to be 1). If the slot is linked, and the calculated lateral flow would result in a negative storage, the dispatch method sets this slot to a value less than 1 in order to reduce the lateral flow and prevent negative storage.
I/O: Output only
Links: Linkable to other Flow Factor Left/Right/Upstream/Downstream slots. For example, the Flow Factor Right will be linked to the Flow Factor Left on an adjacent object.
RiverWare requires either all Flow Factor slots in use in a groundwater network to be linked, or none linked; otherwise, a gain or loss of mass could occur. Linking some Flow Factor slots and not others within a groundwater network causes the run to terminate with an error message.
Method Details
In the code, one method deals with all 15 user methods in the Lateral Link Direction category. This method is called by the dispatch method and computes temporary values for the Flow slots. These temporary values may be adjusted in the dispatch method by applying the corresponding Flow Factor (see Solve given Inflow from Surface Water). Depending on the number of connected objects, the method performs one or all of the following calculations:
The results are passed back to the dispatch method and used in the mass balance equation to solve for storage. The actual slot values are set from the dispatch method.
Note: The Flow terms are computed based on the previous timestep elevation differences. This is done to avoid iteration problems that would result if the groundwater flows were computed based on current timestep elevations.
Note: Mass may be lost from the system if the conductance values are not identical on either side of a given link. For example in a two groundwater object system where an upstream GW Object 1 is linked to a downstream GW Object 2, the upstream conductance on GW Object 2 must be identical to the downstream conductance on GW Object 1 to conserve mass. If you use the Compute Conductance method, on each groundwater object, then adjacent conductances are guaranteed to be identical; see Compute Conductance.
Revised: 12/01/2020