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Water Quality - Salinity
Water Quality was enhanced to provide additional functionality when modeling Salinity. Following are the improvements. Additional Information can be found Water Quality Overview in Water Quality.
Additional Salt Mass Slots
The following salinity slots were added for completeness when checking mass balance of salt across many objects. Now each variable has a concentration and mass salinity slot:
• AggDiversionSite.Diversion Salt Mass
• Bifurcation.Inflow Salt Mass
• Bifurcation.Outflow1 Salt Mass
• Bifurcation.Outflow2 Salt Mass
• Reservoir.Reservoir Salt Mass
• Reservoir.Return Flow Salt Concentration
• Reach.Return Flow Salt Concentration
Linking on Aggregate Objects
On aggregate objects (Agg Reach, Distribution Canal, and Aggregate Diversion Site), salt slots are now automatically linked like the flow slots. For the Aggregate Diversion Site, the linking is based on the specified Linking Structure and the selected method on the aggregate. Warning and error messages are posted on model load if there is a problem linking the water quality slots.
Layered / Discretized Salinity only
A “Salinity” only option was added to the Layered / Discretized solution approach. Many objects were improved or enhanced with methods to model salinity with this approach.
In addition, for all Layered/Discretized salt methods, now the Salt Concentration should be linked instead of Salt Mass. Any models will need to be updated.
Following is a summary of the changes made to each object:
Groundwater Object
Water quality methods were added to model the head based groundwater object as two-layers, with a constant upper layer. Slots and solution equations were added to track the flow and storage of water and salt in both layers. Water and salt can flow to/from the upper or lower layer in four lateral directions: left, right, upstream and downstream. In addition, water and salt can enter/exit the object through Pumping, Deep Percolation, and Inflow from Surface Water. Evaporation and Evapotranspiration remove water but not salt. The following diagram shows a two layer groundwater object with the water and salinity components.
Flow into the object can be either negative or positive. When the flow is entering the groundwater object, the salt concentration propagates from the linked slot or must be specified. If the flow is out of the groundwater object, the concentration is set to the previous timestep’s value to create an explicit solution.
For more information on this solution, see Solution / Dispatching in Water Quality.
The two outflow salt concentrations are set equal to the inflow salt concentration.
Methods combine the two inflows and compute the flow weighted average Outflow Salt Concentration.
Distribution Canal and Agg Distribution Canal
Methods route salt through the canal and divert water and salt to linked objects.
Diversion Object and Stream Gage
Methods propagate concentration via a linkable Salt Concentration slot. If you previously modeled water quality on the Stream Gage, you will need to re-link slots and you may need to re-specify any input data and/or modify rules. You can link the constituent to both the upstream and downstream slot(s).
The water quality routing and seepage method is automatically selected based on the flow and seepage routing method, respectively. A variable lag time salt routing method was added. Methods were also added to model salt when using head based seepage.
Previously in Layered/Discretized, the temperature determined how inflows were distributed to hypolimnion and epilimnion. Since there is no Temperature in the Salinity only option, the following two methods were developed to distribute inflows:
• Specify Distribution - Specify flow into one of the layers as input, rules, or links. The other is computed.
• Specify Fraction - Input the fractional split on a series slot.
Water User and AggDiversion Site
Methods were added to compute the return flow salt concentration based on the diversion, diversion salt concentration, and any specified salt additions.
Revised: 08/02/2021