Qual2K: a modeling Framework for Simulating River and Stream Water Quality (Version 11)

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A Modeling Framework for Simulating River and Stream Water Quality

(Version 2.11)

The Mystic River at Medford, MA

Steve Chapra, Greg Pelletier and Hua Tao

December 16, 2008
Chapra, S.C., Pelletier, G.J. and Tao, H. 2008. QUAL2K: A Modeling Framework for Simulating River and Stream Water Quality, Version 2.11: Documentation and Users Manual. Civil and Environmental Engineering Dept., Tufts University, Medford, MA., Steven.Chapra@tufts.edu

The information in this document has been funded partly by the United States Environmental Protection Agency. It is currently being subjected to the Agency's peer and administrative review and has yet to be approved for publication as an EPA document. Mention of trade names or commercial products does not constitute endorsement or recommendation for use by the U.S. Environmental Protection Agency.
The QUAL2K model (Q2K) described in this manual must be used at the user's own risk. Neither the U.S. Environmental Protection Agency, Tufts University, the Washington Dept. of Ecology, nor the program authors can assume responsibility for model operation, output, interpretation or usage.
The creators of this program have used their best efforts in preparing this code. It is not absolutely guaranteed to be error free. The author/programmer makes no warrantees, expressed or implied, including without limitation warrantees of merchantability or fitness for any particular purpose. No liability is accepted in any event for any damages, including accidental or consequential damages, lost of profits, costs of lost data or programming materials, or otherwise in connection with or arising out of the use of this program.


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.

  • Branching. The system can consist of a mainstem river with branched tributaries.

  • Steady state hydraulics. Non-uniform, steady flow is simulated.

  • Diel heat budget. The heat budget and temperature are simulated as a function of meteorology on a diel time scale.

  • Diel water-quality kinetics. All water quality variables are simulated on a diel time scale.

  • Heat and mass inputs. Point and non-point loads and withdrawals are simulated.

The QUAL2K framework includes the following new elements:

  • Software Environment and Interface. Q2K is implemented within the Microsoft Windows environment. Numerical computations are programmed in Fortran 90. Excel is used as the graphical user interface. All interface operations are programmed in the Microsoft Office macro language: Visual Basic for Applications (VBA).

  • Model segmentation. Q2E segments the system into river reaches comprised of equally spaced elements. Q2K also divides the system into reaches and elements. However, in contrast to Q2E, the element size for Q2K can vary from reach to reach. In addition, multiple loadings and withdrawals can be input to any element.

  • 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).

  • 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 can be 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. These algae have variable stoichiometry.

  • 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 computed based on these two quantities.

  • Pathogens. A generic pathogen is simulated. Pathogen removal is determined as a function of temperature, light, and settling.

  • Reach specific kinetic parameters. Q2K allows you to specify many of the kinetic parameters on a reach-specific basis.

  • Weirs and waterfalls. The hydraulics of weirs as well as the effect of weirs and waterfalls on gas transfer are explicitly included.

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