Qual2k

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 Barnwell1987). 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 simulatedon 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 andInterface. Q2K is imple-
mented within the Microsoft Windows environment. It
is programmed in the Windows macro language: Visual
Basic for Applications (VBA). Excel is used as the graphi-
caluser interface.
• Model segmentation. Q2E segments the system into river
reaches comprised of equally spaced elements. In contrast,
Q2K uses unequally-spaced reaches. In addition, multipleloadings 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 oxidizingform (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 oxida-
tion reactions to zero at low oxygen levels. In addition,
denitrification is modeled asa first-order reaction that
becomes pronounced at low oxygen concentrations.
• Sediment-water interactions. Sediment-water fluxes of dissolved oxygen and nutrients are simulated internally...