The shallow groundwater is not always well mixed in terms of salinity. In some areas, the upper portion of the aquifer interacts quickly with the surface, but further down, the interaction is slower. This process can be modeled as two fully mixed layers within the groundwater object.

The current implementation of the ground water quality model allows you to model salinity with the Layered Salt method.

Figure 11.1 shows the groundwater object with two layers in terms of flow and volume slots. Figure 11.2 shows the two layers in terms of salinity slots. All slots and links shown in (see “solveGWMB_givenPreviousElevations” in Objects and Methods) are still present; the object just has additional slots and links for salinity modeling.

In this approach, the thickness of the upper layer is constant. Each mass balance component except Evaporation and Evapotranspiration have an equivalent Salt Concentration component. They are shown in red in Figure 11.1. On the groundwater object, the Flow Upstream/Downstream/Left/Right, Inflow From Surface Water, Pumped Flow and Percolation could be either negative or positive.When the flow is coming into the groundwater object, the salt concentration comes from the linked slot or be specified (input or rules). If the flow is out of the groundwater object, the concentration is computed by the groundwater object. When the groundwater object is defining the concentration, the previous values are used to avoid iteration problems.

Following are assumptions used in this computation:

Following is a conceptual overview of the computation to determine storage and salt concentration in each layer. See “Dispatch Method - Solve 2 Layer Salt” for details on this computation.