In ResSim, water quality (WQ) constituents, such as water temperature, dissolved oxygen, and nutrients, are the state variables simulated in the water quality model. These constituents are defined by the specific water quality modules integrated into the system. Three main water quality modules have been incorporated into the current version of ResSim software:

  1. WTSM (Water Temperature Simulation Module): Simulates heat energy balance and the sources and sinks of water temperature.
  2. NSMI (Nutrient Simulation Module I): Models the kinetics of 15 water quality state variables, including carbon, nitrogen, phosphorous species, dissolved oxygen, carbonaceous biological oxygen demand (CBOD), and algae. Nutrient simulation is dependent on water temperature, either simulated or set to a fixed reference value.
  3. GCSM (General Constituent Simulation Module): Handles simple kinetics of user-defined general constituents, including conservative tracers, coliform bacteria, and reactive particles.

These modules allow for the simulation of a variety of constituents within the water quality model. However, different modules simulate different sets of constituents, as detailed in the Water Quality Constituents by WQ Library.

Key steps to operate the water quality modules:

  1. Select Constituents: Choose constituents from the available Water Quality Modules (contained in a WQ Constituent Set).
  2. Specify Kinetics Parameters: Define the kinetics parameter values associated with the selected constituents, which are grouped in a WQ Parameter Set.

The user can create one or more WQ Constituent sets using the constituents from the three available water quality libraries. Additionally, users can define a reference value for each selected constituent. The reference value serves as a base comparison point for modeled results but is not used directly in the modeling process.

Process for defining simulated water quality constituents:

  1. Select Water Quality Libraries: Choose the appropriate water quality module(s).
  2. Select Constituents: Identify the relevant constituents from each library.

In ResSim, the user can create a simulated WQ Constituent Set at any time, as there are no prerequisites. However, certain datasets, such as WQ Parameter sets (Chapter 6), Boundary Condition sets (Chapter 8), Initial Condition sets (Chapter 9), and Mass Injection sets (Chapter 11), can only be created once a WQ Constituent Set has been defined.