QUAL2EU, Enhanced Stream Water Quality Model with Uncertainty Analysis, is a U.S. EPA steady-state model for conventional pollutants in branching streams and well mixed lakes. QUAL2EU can be operated as either a steady-state or dynamic model. It is intended for use as a water quality planning tool. The model can be used to study the impact of waste loads on instream water quality. QUAL2EU can also be used to identify the magnitude and quality characteristics of non-point waste loads as part of a field sampling program.
QUAL2EU is the U.S. EPA Enhanced Stream Water Quality Model with Uncertainty Analysis. The QUAL2EU package consists of four modules:
- QUAL2E - Enhanced Stream Water Quality Model
- QUAL2EU - Enhanced Stream Water Quality Model with Uncertainty Analysis
- AQUAL2 - Interactive Data Preprocessor Program for QUAL2E and QUAL2EU
- Q2PLOT - Interactive Graphics Postprocessor Program for QUAL2E and QUAL2EU
The Enhanced Stream Water Quality Model (QUAL2E) is a steady-state model for conventional pollutants in branching streams and well mixed lakes. It can be operated either as a steady-state or dynamic model. The model is intended for use as a water quality planning tool.
The model can be used to study the impact of waste loads on instream water quality. It can also be used to identify the magnitude and quality characteristics of non-point waste loads as part of a field sampling program. The user can:
- Model effects of diurnal variations in meteorological data on water quality, primarily dissolved oxygen and temperature.
- Examine diurnal dissolved oxygen variation caused by algae growth and respiration.
The Enhanced Stream Water Quality Model with Uncertainty Analysis (QUAL2EU) is an enhancement to the QUAL2E model that allows the user to perform uncertainty analysis. Three uncertainty options are available:
- Sensitivity analysis
- First-order error analysis
- Monte Carlo simulation
With this capability, the user can assess the effect of model sensitivities and uncertain input data on model forecasts.
AQUAL2 is an interactive data preprocessor program for the QUAL2E and QUAL2EU models. AQUAL2 can be used to build input data files for either of these models.
Q2PLOT is an interactive data postprocessor program for the QUAL2E and QUAL2EU models. This program can read output from either model and display text and/or two-dimensional graphs on the monitor screen of the following information:
- Nitrate and ammonia
- SUM-N and organic N
- Dissolved P and organic P
- CHLA and extinction coefficient
- User-specified curves
QUAL2EU is a comprehensive and versatile stream water quality model that can simulate up to 15 water quality constituents in any combination desired by the user. Constituents which can be simulated are:
- Dissolved Oxygen
- Biochemical Oxygen Demand
- Algae as Chlorophyll a
- Organic Nitrogen as N
- Ammonia as N
- Nitrite as N
- Nitrate as N
- Organic Phosphorus as P
- Dissolved Phosphorus as P
- Arbitrary Nonconservative Constituent
- Three Conservative Constituents
QUAL2EU is applicable to dendritic streams that are well mixed. It assumes that the major transport mechanisms, advection and dispersion, are significant only along the main direction of flow (longitudinal axis of the stream or canal). It allows for multiple waste discharges, withdrawals, tributary flows, and incremental inflow and outflow. It also has the capability to compute required dilution flows for flow augmentation to meet any prespecified dissolved oxygen level.
Hydraulically, QUAL2EU is limited to the simulation of time periods during which both the stream flow in river basins and input waste loads are essentially constant. QUAL2EU can operate either as a steady-state or as a dynamic model, making it a very helpful water quality planning tool. When operated as a steady-state model, it can be used to study the impact of waste loads (magnitude, quality and location) on instream water quality and also can be used in conjunction with a field sampling program to identify the magnitude and quality characteristics of non point source waste loads. By operating the model dynamically, the user can study the effects of diurnal variations in meteorological data on water quality (primarily dissolved oxygen and temperature) and also can study diurnal dissolved oxygen variations due to algae growth and respiration. However, the effects of dynamic forcing functions such as headwater flows or point loads cannot be modeled in QUAL2EU.
QUAL2EU allows the modeler to perform uncertainty analysis on the steady-state water quality simulations. With this capability, the user can assess the effect of model sensitivities and of uncertain input data on model forecasts. Quantifications of the uncertainty in model forecasts will allow assessment of the risk (probability of a water quality variable being above or below an acceptable level. The uncertainty methodologies provide the means whereby variance estimates and uncertainty prediction can become as much a part of water quality modeling as estimating expected values are today. An evaluation of the input factors that contribute most to the level of uncertainty will lead modelers in the direction of most efficient data gathering and research. In this manner the modeler can assess the risk of imprecise forecasts and recommend measures for reducing the magnitude of that imprecision.
QUAL2E or QUAL2EU permit simulation of any branching, one-dimensional stream system. The first step in modeling a system is to subdivide the stream system into reaches, which are stretches of stream that have uniform hydraulic characteristics. Each reach is then divided into computational elements of equal length. Thus, all reaches must consist of an integer number of computational elements.
There are seven different types of computational elements:
- Headwater element
- Standard element
- Element just upstream from a junction
- Junction element
- Last element in system
- Input element
Headwater elements begin every tributary as well as the main river system, and as such, they must always be the first element in a headwater reach. A standard element is one that does not qualify as one of the remaining six element types. Because incremental flow is permitted in all element types, the only input permitted in a standard element is incremental flow. A type 3 element is used to designate an element on the main stem just upstream of a junction. A junction element (type 4) has a simulated tributary entering it. Element type 5 identifies the last computational element in the river system; there should be only one type 5 element. Element types 6 and 7 represent inputs (waste loads and unsimulated tributaries) and water withdrawals, respectively. River reaches which are aggregates of computational elements are the basis of most data input. Hydraulic data, reaction rate coefficients, initial conditions, and incremental flows data are constant for all computational elements within a reach.
QUAL2E and QUAL2EU have been designed to be a relatively general program; however, certain dimensional limitations have been imposed during program development. These limitations are:
- Reaches: a maximum of 25
- Computational elements: no more than of 250
- Headwater elements: a maximum of 7
- Junction elements: a maximum of 6
- Input and withdrawal elements: a maximum of 25
QUAL2EU includes the source code, executable version, user's manual, and technical support as well as test files.
QUAL2EU Requirements: IBM-PC or compatible with 640K RAM, math coprocessor, and hard disk.