Water quality may be modeled in RiverWare along with simulated water quantity calculations. Currently water quality modeling is available on reservoirs, reaches, confluences, bifurcations, canal, gages, aggregate reaches, aggregate diversion site, aggregate distribution canals, water users, and groundwater storage objects. Constituents include Salinity (TDS), Temperature, Dissolved Oxygen (DO), and Total Dissolved Gas (TDG).

The development of the water quality methods were initially completed in 1996, but were not used extensively. They were updated in 2012 to better model salinity but still may require some minor modifications with more extensive testing and use.

Following is an overview of the available water quality methods.

Salinity, Temperature and Dissolved oxygen can be modeled using a layered approach on reservoirs and groundwater objects and a discretized approach on reaches. Other objects pass the constituents along using methods that are indicated with the propagate terminology.

The layered/discretized approach models reservoirs as having two layers, an epilimnion and a hypolimnion. Reaches are modeled based on the selected routing method but can be discretized such that 1 dimensional dispersion can be included. In this approach, mass, concentration, and/or heat are calculated and propagate downstream. As a result, the user should link each constituents mass, concentration, and/or heat slots between objects. For salinity modeling, salt concentrations (instead of mass) should be linked between objects.

Following are features of the Reservoir methods:

Features of the reach water quality methods include the following:

Features of the Groundwater salinity methods include the following:

Salinity can be modeled using simple well mixed methods. These assume that water in each of the objects is completely mixed. In this approach, mass and concentration are calculated.Concentrations propagate upstream or downstream. As a result, the user should link each salt concentrations between objects.

Following are features of the simple well-mixed salt approach:

High Total Dissolved Gas (TDG) concentrations can reduce the population of some fish species. These effects are most pronounced in the tailwater of reservoirs during spill operations. The TDG concentrations are increased by spills; the turbulent nature of the spill creates air bubbles that are then forced deep into the tailwater. The deep water has higher pressure which cause gases in the bubbles to dissolve in the water. Once dissolved, the gas propagates downstream.

To alleviate the problems of high TDG concentrations, certain reservoir operations are constrained by maximum allowable TDG tailwater concentrations. RiverWare models TDG in both simulation and optimization on the following objects:

This document describes how to enable and define a water quality simulation. Then the water quality methods and solution approach is presented for each type of object.

Water quality is modeled by first enabling water quality for the entire system and specifying the timing of the computations, either inline or post process. Select the constituents and methods on each object and populate slots with data. Run the model as usual; the water quality results are stored in slots on the individual objects. Following is a brief description of the steps to set up a water quality model.

Enable water quality modeling on the Run Control parameters dialog. From Run Control, select either View, then Simulation Run Parameters or View, then Rulebased Simulation Run Parameters, depending on the selected controller. Check the Water Quality box to enable the methods.

Select one of the Water Quality processes. The following section gives more information on how each process works.

When water quality modeling is enabled and the methods are selected, the water quality slots are instantiated. The water mass balance simulation proceeds as usual with objects dispatching when dispatch conditions are met. Similarly, there are separate dispatch methods for the water quality used to solve how the constituents move through the objects. Water quality dispatch methods are described for each of the objects. Each dispatch method calls a number of utility methods that typically do the work.

Like the mass balance dispatch method, water quality dispatch methods have dispatch conditions. Whenever the water quality dispatch conditions are met for a given method, the object is added to the queue. Water quality dispatch conditions also include water quantity slots. For example, for a reservoir to dispatch for water quality it needs to know Inflow, Outflow, and Storage as well as the inflow salt concentrations, temperature, etc (depending on constituents modeled). The water quality dispatch condition are always solved top down, i.e. after the water balance has been executed for that object. It is not possible to specify or “request” a particular salinity at the lower end of the river and have the system solve for the flow with that salinity. It must first solve for the water quantity, before it can solve for water quality.

The water quality dispatch methods are processed based on the selected process, either Inline or Post, as follows:

Following is the order of operations for a water quality calculation as part of a regular simulation.

Combining water quality with Rulebased Simulation allows the rules to reference water quality slots in making operating decisions. The Inline Process water quality dispatching happens during the timestep when the required dispatch conditions are met. This means that water quality can dispatch multiple times during a timestep based on the values that the rules set and whether the dispatch slots are reset.

In a rulebased simulation run with the Post Process water quality selected, dispatching happens at the end of the run. Rules cannot reference water quality information as it has not been solved yet.

The Model Run Analysis tool is used to show dispatching information. See “Simulation” in Debugging and Analysis for a general description. This utility by default shows object dispatching information for the water quantity solution. When Water Quality is enabled as described above, a Water Quality checkbox is shown on the main Model Run Analysis dialog. When checked, the dialog shows dispatch information for the water quality solution. Double clicking on a cell opens the Dispatch Behavior Details dialog. This dialog has an analogous WQ check box. This details dialog shows the required knowns and unknowns for each dispatch method and the known and unknown status of each slot.

The Water Quality check boxes represent a single state shared among the Model Run Analysis and all instances of the Dispatch Behaviors Detail dialog; clicking the check box in any of these dialogs also changes the check box in all open dialogs of either type.

The remainder of this document is organized as follows: for each object, we describe the water quality approach including slots and user methods, then present solution and dispatch methods, then utility methods if defined.