History of CE-QUAL-W2
CE-QUAL-W2 has been under continuous development since 1975. The original model was known as LARM (Laterally Averaged Reservoir Model) developed by Edinger and Buchak (1975). The first LARM application was on a reservoir with no branches. Subsequent modifications to allow for multiple branches and estuarine boundary conditions resulted in the code known as GLVHT (Generalized Longitudinal-Vertical Hydrodynamics and Transport Model). Addition of the water quality algorithms by the Water Quality Modeling Group at the US Army Engineer Waterways Experiment Station (WES) resulted in CE-QUAL-W2 Version 1.0 (Environmental and Hydraulic Laboratories, 1986).
Version 2.0 was a result of major modifications to the code to improve the mathematical description of the prototype and increase computational accuracy and efficiency. Numerous new capabilities were included in Version 2.0, including:
- An algorithm that calculates the maximum allowable timestep and adjusts the timestep to ensure hydrodynamic stability requirements are not violated (autostepping)
- A selective withdrawal algorithm that calculates a withdrawal zone based on outflow, outlet geometry, and upstream density gradients
- A higher-order transport scheme (QUICKEST) that reduces numerical diffusion (Leonard, 1979)
- Time-weighted vertical advection and fully implicit vertical diffusion
- Step function or linear interpolation of inputs
- Improved ice-cover algorithm
- Internal calculation of equilibrium temperatures and coefficients of surface heat exchange or a term-by-term accounting of surface heat exchange
- Variable layer heights and segment lengths
- Surface layer extending through multiple layers
- Generalized time-varying data input subroutine with input data accepted at any frequency
- Volume and mass balances to machine accuracy
- Sediment/water heat exchange
Version 3.0 is a result of additional improvements to the numerical solution scheme and water quality algorithms, as well as extending the utility of the model to provide state-of-the-art capabilities for modeling entire waterbasins in two-dimensions. The new capabilities included in Version 3 include:
- An implicit solution for the effects of vertical eddy viscosity in the horizontal momentum equation
- Addition of Leonard’s ULTIMATE algorithm that eliminates over/undershoots in the numerical solution scheme
- Inclusion of momentum transfer between branches
- The ability to model multiple waterbodies in the same computational grid including multiple reservoirs, steeply sloping riverine sections between reservoirs, and estuaries
- Additional vertical turbulence algorithms more appropriate for rivers
- Additional reaeration algorithms more appropriate for rivers
- Variable vertical grid spacing between waterbodies
- Numerical algorithms for pipe, weir, and pump flow
- Internal weir algorithm for submerged or skimmer weirs
- Three algal groups
- Arbitrary constituents defined by a decay rate, settling rate, and temperature rate multiplier
- Nine inorganic suspended solids groups
- Dissolved and particulate biogenic silica
- Age of water
- Derived constituents such as total DOC, organic nitrogen, organic phosphorus, etc. that are not state variables
- A graphical pre/postprocessor
- Converted to FORTRAN 90/95 with Dynamic Array Allocation eliminating the need to recompile the code for each application
- User defined evaporation models including the Ryan-Harleman model
Version 3.1 is a result of additional improvements to the water quality algorithms including:
- User defined number of
- Generic constituents
- Inorganic suspended solids
- CBOD groups
- Algal groups
- Epiphyton/periphyton groups
- Computation of kinetic fluxes (sources/sinks) for ease in water quality calibration
- Ability to animate any state variable, such as dissolved oxygen, or derived variable, such as total organic carbon, as well as terms in the solution of the momentum equation
- Redesign of control file inputs for easier use and code for easier understanding
- GUI preprocessor
- Salt water correction for DO saturation
- Dynamic light extinction inputs
- Dynamic topographic and vegetative shading algorithm
- Spatially varying wind sheltering coefficients
- CBOD nutrient recycling
- Kinetic flux algorithms
Version 3.2 is a result of additional improvements to the model. These new capabilities include:
- Internal code rewrite to reduce code size, simplify code maintenance, and improve model execution speed
- New screen display during model run-time. The new screen display allows for controlling the processor usage, examining output variables, and stop-ping, starting and restarting a model run on the fly. This allows the model user to stop a code, then make changes in the control file or any input file, and then restart the model at the point that it was stopped.
- Addition of a new algorithm to estimate suspended solids resuspension as a result of wind-wave action.
- Reorganization of the graph.npt file to allow more output control formatting possibilities.
- New turbulent kinetic energy-turbulent dissipation turbulence closure model was added to the model.
→ Version 3.2 Last supported code from WES Corps of Engineers
Version 3.5 is a result of significant enhancements to the model. These new capabilities include:
- Addition of the macrophyte model of Berger and Wells (in-review) with a user-defined # of species
- Addition of a zooplankton model with a user-defined # of species based on an updated version of the CE-QUAL-R1 model (Environmental Laboratory, 1995)
- Addition of a new focusing or settling velocity for sediments that accumu-late in the first order sediment model. In earlier versions, sediment focusing occurred at the velocity given for POM. In this version, a user can specify that focusing velocity. This means that sediments can still migrate toward the bottom of the channel over time even after they have hit the sidewalls of the channel.
- User-defined time-variable input of P and N associated with organic matter inputs. In earlier versions, the P or N associated with organic matter was based on a static stoichiometric coefficient specified in the control file. Now, the user provides in the input files the dynamic P and N associated with organic matter inputs from tributaries or inflows. This is essentially allowing for variable stoichiometry in the input boundary conditions.
- Based on the above refinement, the organic matter fractions within the model now have variable stoichiometry for P and N. This preserves P and N mass balances. The stoichiometry given in the input files is merely the initial value of the C-N-P stoichiometry of POM and DOM compartments. Hence, organic P and organic N are tracked correctly in the code.
- The first order sediment model also tracks C-N-P correctly and has a dynamic stoichiometry as it accumulates organic matter in the sediment. Prior versions of W2 had a user-defined value of fixed stoichiometry for the 1st order sediment model.
- CBOD groups now have a user-defined settling velocity. Hence, the user can define organic matter groups as particulate and dissolved based on specification of the settling velocity. As in prior versions, CBOD has associated stoichiometry and if there is settling, it will accumulate in the 1st order sediment compartment.
- A sediment burial rate was added to the 1st order sediment model.
- A Monod kinetic approach to the onset of anoxia rather than an ON/OFF approach.