ERM Surfacewater Modeling Group CE-QUAL-W2;

CE-QUAL-W2

CE-QUAL-W2 ("W2") is a longitudinal-vertical hydrodynamic and transport model designed for long-term, time-varying water quality simulations of networks of rivers, lakes, reservoirs, and estuaries. W2 accurately reproduces vertical and longitudinal water quality gradients and is capable of multi-decade simulations. It can be used to infer changes in circulation and water quality as well as provide boundary condition data to 3-D models or to near-field models such as VPLUMES or CORMIX. W2 is the standard tool for simulation and analysis of water quality problems in US reservoirs. There have been hundreds of applications with the model world wide.

ERM's Edward M. Buchak is one of two primary authors of CE-QUAL-W2 (John Edinger being the other), having written the hydrodynamic and transport code LARM (now called CE-QUAL-W2) for the Ohio River Division of the U. S. Army Corps of Engineers in 1975. The Surfacewater Modeling Group at ERM has completed more than 60 W2 applications. SMG staff works at the source code level, which allows code enhancements needed for specific model applications.

ERM's Surfacewater Modeling Group (SMG) continues to apply and enhance CE-QUAL-W2. The SMG has supported academic users, electric utility clients, and various federal government agencies (USACE: WES, ORD, HEC, and district offices; Bureau of Reclamation; USGS, New York City DEP). In addition, the firm has conducted training workshops for commercial clients, the World Bank, the North American Lake Management Association, the US Bureau of Reclamation, and the US Geological Survey, among others.

CE-QUAL-W2 presently includes water quality routines for many nutrient and nutrient-related parameters as well as suspended solids, coliforms, total dissolved solids, and a numerical tracer. Other parameters and formulations are easily accommodated in the modular code. CE-QUAL-W2 is based on the laterally averaged equations of momentum, continuity, and transport. The formulation includes the vertically varying, longitudinal momentum balance, vertical momentum in the form of the hydrostatic approximation, local continuity, the free-water surface condition based on vertically integrated continuity, and longitudinal and vertical transport of any number of constituents. Constituents that determine density such as temperature and salinity are related to momentum through an equation of state. The vertically varying, longitudinal momentum balance includes local acceleration of horizontal velocity, horizontal and vertical advective momentum transfer, the horizontal pressure gradient, and horizontal and vertical shear stress. Included in the latter are the surface wind stress and the bottom stress due to friction. The horizontal pressure gradient includes the barotropic surface slope and the baroclinic vertical integral of the horizontal density gradient which is the dominant term in density-induced, convective circulation.

The time-varying solution technique of the model is based on an implicit, finite difference scheme that results from the simultaneous solution of the horizontal momentum equation and the free-water surface equation of vertically integrated continuity. This technique results in the surface long wave equation that is solved on each time step to give the water surface profile, from which the vertical pressure distribution can be determined. The horizontal momentum is then computed, followed by internal continuity and then constituent transport. The QUICKEST finite difference scheme is used for the advective processes in the constituent transport balances. Vertical turbulent transfer of momentum and constituents is determined from the vertical shear of horizontal velocity and a density gradient dependent Richardson number function.

The boundary conditions at the open ends of the branches can be any combination of either flux or elevation conditions. The fluxes or elevations are specified from boundary data. The elevation boundary condition enters the formulation through the implicit long wave surface equation. Fluxes at the elevation boundary are computed from a reduced form of the longitudinal and vertical momentum equations which include the baroclinic, barotropic, vertical shear, and local acceleration terms but do not include the longitudinal spatial acceleration.

CE-QUAL-W2 has been under development for the Corps of Engineers since 1974 and has had extensive review and testing by Johnson (1981). Previous verification studies using LARM, GLVHT (earlier versions of the code), and CE-QUAL-W2 have been presented by Gordon (1980, 1981 and 1983); Edinger, Buchak and Merritt (1983); Kim, Higgins and Bruggink (1983); Johnson, et al. (1981); and Martin (1988). Estuarine applications include Boatman and Buchak (1987); Buchak, et al. (1989); Buchak and Edinger (1989); Edinger, Buchak and Rives (1987); Johnson, et al. (1987); and, Johnson, et al. (1989). The model is described in Buchak and Edinger (1984) and Cole and Buchak (1993), which present formulations of the fundamental equations, the structure of the computations, and summaries of applications.

GEMSS^® (the Generalized Environmental Modeling System for Surfacewaters) fully-supports CE-QUAL-W2 applications, from grid generation through time-series data acquisition, field data accommodation in its geo-referenced database, and post-processing including graphical and statistical comparisons to observations and animations.

The Surfacewater Modeling Group provides the following CE-QUAL-W2 services:

Complete CE-QUAL-W2 Applications

Work with clients to jointly develop and calibrate the water budget, hydrodynamic, temperature, and water quality components of a study.
Provide complete CE-QUAL-W2 applications (includes problem definition and setup, boundary condition data, calibration, required simulations, report, and presentation).

Application Setup
Supply data sets for an application (includes acquisition and formatting of data for use by CE-QUAL-W2):

Bathymetric data from digitized map, soundings or other sources.
Meteorological data from the nearest first order station.
Complete inflow and outflow quantity data for a specific grid, derived from water balances.
Inflow temperatures from a Response Temperature Computation (RTC) model. This model can be used to develop hourly time series of inflow temperatures from a limited or non-existent tributary temperature observation record.

Productivity Tools
We offer GEMSS^®, a comprehensive suite of integrated pre-processing and post-processing tools. GEMSS^® allows input file construction from raw data, manage runs, and visualize output and observed data. Tools for model grid generation from map data, grid editing and meteorological data processing are also available included in GEMSS^®.

Technical Support

Telephone, fax, and e-mail support.
Application level (e.g., guidance on calibration strategy, etc.) and operational troubleshooting support by examining the application in our office.

Workshops

Generic training workshops for individuals or small groups; these are offered from time-to-time (Workshop 1: Reservoir Modeling Using CE-QUAL-W2).
Client-customized, model theory and application setup workshops for jump-starting an application.
QA-focused workshops

Application Review and Certification; QAPP Development
Review and certification of CE-QUAL-W2 applications; an in-house review of the application is performed at each of five stages:

after the construction of the model grid
after the water balance (for lakes and reservoirs only)
after the temperature calibration
after the water quality calibration
after one management scenario.

After each stage comments are issued. When the entire process is complete, a letter report is issued describing the application and our review. The review and certification can also be formalized as an EPA Quality Assurance Project Plan or as a nuclear-safety related calculation.