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River and Stream Water Quality Model (QUAL2K)

QUAL2K (or Q2K) is a river and stream water quality model that is intended to represent a modernized version of the QUAL2E (or Q2E) model (Brown and Barnwell 1987). Q2K is similar to Q2E in the following respects:

One dimensional. The channel is well-mixed vertically and laterally.

  • Steady state hydraulics. Non-uniform, steady flow is simulated.
  • Diurnal heat budget. The heat budget and temperature are simulated as a function of meteorology on a diurnal time scale.
  • Diurnal water-quality kinetics. All water quality variables are simulated on a diurnal time scale.
  • Heat and mass inputs. Point and non-point loads and abstractions are simulated.

The QUAL2K framework includes the following new elements:

Software Environment and Interface. Q2K is implemented within the Microsoft Windows environment. It is programmed in the Windows macro language: Visual Basic for Applications (VBA). Excel is used as the graphical user interface.

  • Model segmentation. Q2E segments the system into river reaches comprised of equally spaced elements. In contrast, Q2K uses unequally-spaced reaches. In addition, multiple loadings and abstractions can be input to any reach.
  • Carbonaceous BOD speciation. Q2K uses two forms of carbonaceous BOD to represent organic carbon. These forms are a slowly oxidizing form (slow CBOD) and a rapidly oxidizing form (fast CBOD). In addition, non-living particulate organic matter (detritus) is simulated. This detrital material is composed of particulate carbon, nitrogen and phosphorus in a fixed stoichiometry.
  • Anoxia. Q2K accommodates anoxia by reducing oxidation reactions to zero at low oxygen levels. In addition, denitrification is modeled as a first-order reaction that becomes pronounced at low oxygen concentrations.
  • Sediment-water interactions. Sediment-water fluxes of dissolved oxygen and nutrients are simulated internally rather than being prescribed. That is, oxygen (SOD) and nutrient fluxes are simulated as a function of settling particulate organic matter, reactions within the sediments, and the concentrations of soluble forms in the overlying waters.
  • Bottom algae. The model explicitly simulates attached bottom algae.
  • Light extinction. Light extinction is calculated as a function of algae, detritus and inorganic solids.
  • pH. Both alkalinity and total inorganic carbon are simulated. The river's pH is then simulated based on these two quantities.
  • Pathogens. A generic pathogen is simulated. Pathogen removal is determined as a function of temperature, light, and settling.
QUAL2K Model Information
Current Version
Release Date
January 2009
Operating System
Windows ME/2000/XP / MS Office 2000 or Higher
Intended Audience
Environmental Engineers/Scientists, Regulatory Agencies
Key Words
aquatic biology, assessment, compliance, discharge, environmental effects, hydrology, NPS related, NPDES, point source(s), surface water, test/analysis, TMDL related
Surface Water
Pollutant Types
Conventional Pollutants (Nitrogen, Phosphorus, Dissolved Oxygen, BOD, Sediment Oxygen Demand, Algae), pH, Periphyton, Pathogens
File Type/Priority Filename/Format/Size File Description
File Download Information

-- Zip File

Containing Spreadsheet Interface, Model Executable and Users Manual

4.0 MB

This file contains the QUAL2K model and Users Manual. Note that Microsoft Excel 2000 or higher is REQUIRED to use this model.

QUAL2K Fact Sheet (PDF) (1 pp., 213KB, about PDF)

This file contains a Fact Sheet about the QUAL2K Modeling System in PDF Format.

Technical Support Center fact sheet (PDF) (2 pp., 733 KB, about PDF)

TMDL fact sheet (PDF) (2 pp., 697 KB, about PDF)

Contact the Athens, GA Ecosystems Research Web editor to ask a question, provide feedback, or report a problem.

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