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WASP5 / DYNHYD5

Detailed Description

WASP5 / DYNHYD5

WASP5 / DYNHYD5





Introduction

WASP5, Water Quality Analysis Simulation Program, is a U.S. EPA generalized modeling framework that simulates contaminant fate in surface waters. Based on the flexible compartment modeling approach, WASP5 can by applied in one, two, or three dimensions. WASP5 is designed to permit easy substitution of user-written routines into the program structure. Problems that have been studied include biochemical oxygen demand, dissolved oxygen dynamics, nutrients, bacterial contamination and toxic chemical movement. The DYNHYD5 model is a simple hydrodynamic model that simulates variable tidal cycles, wind, and unsteady inflows. It produces an output file that can be linked with WASP5 to supply the flows and volumes to the water quality model.

WASP Modeling System

The WASP modeling system is a generalized modeling framework for contaminant fate and transport in surface waters. Based on flexible compartment modeling, WASP can be applied in one, two, or three dimensions. WASP is designed to permit easy substitution of user-written routines into the program structure. Problems that have been studied using WASP include biochemical oxygen demand, dissolved oxygen dynamics, nutrients/eutrophication, bacterial contamination, and toxic chemical movement. The WASP system consists of two stand-alone computer programs, DYNHYD and WASP, that can be run in conjunction or separately. DYNHYD is a hydrodynamics program which simulates the movement of water while the water quality program, WASP, simulates the movement and interaction of pollutants within the water. WASP is supplied with two kinetic submodels to simulate two of the major classes of water quality problems: conventional pollution (involving dissolved oxygen, biochemical oxygen demand, nutrients and eutrophication) and toxic pollution (involving organic chemicals, metals, and sediment). The linkage of either submodel with the WASP program gives the models EUTRO and TOXI, respectively.

The basic principle of both the hydrodynamics and water quality program is the conservation of mass. The water volume and water quality constituent masses being studied are tracked and accounted for over time and space using a series of mass balancing equations. The hydrodynamics program also conserves momentum, or energy, throughout time and space.

The Hydrodynamic Program (DYNHYD) is a simple link-node hydrodynamic program capable of simulating variable tidal cycles, wind, and unsteady flows. It produces an output file that supplies flows, volumes, velocities, and depths (time averaged) for the WASP modeling system.

The Eutrophication Model (EUTRO) combines a kinetic structure adapted from the Potomac Eutrophication Model with the WASP transport structure. This model predicts dissolved oxygen, carbonaceous biochemical oxygen demand, phytoplankton, carbon, chlorophyll-a, ammonia, nitrate, organic nitrogen, and orthophosphate in bed and overlying waters.

The Toxic Chemical Model (TOXI) combines a kinetic structure adapted from the Exposure Analysis Modeling System (EXAMS) with the WASP transport structure and simple sediment balance algorithms. TOXI predicts dissolved and sorbed chemical concentrations in the bed and overlying waters.

The WASP package also includes three other programs: PREDYN, W5DSPLY and PLOT. PREDYN is an interactive preprocessor program for DYNHYD. W5DSPLY is a tabular post processor program for TOXI, EUTRO and DYNHYD. PLOT is a graphical post processor for TOXI, EUTRO and DYNHYD.

DYNHYD

The WASP hydrodynamics model DYNHYD is an enhancement of the Potomac Estuary hydrodynamic model which was a component of the Dynamic Estuary Model. DYNHYD solves the one-dimensional equations of continuity and momentum for a branching or channel-junction (link-node ), computational network. Driven by variable upstream flows and downstream heads, simulations typically proceed at one- to five-minute intervals. The resulting unsteady hydrodynamics are averaged over larger time intervals and stored for later use by the water quality program.

The hydrodynamic model solves one-dimensional equations describing the propagation of a long wave through a shallow water system while conserving both momentum (energy) and volume (mass). The equation of motion, based on the conservation of momentum, predicts water velocities and flows. The equation of continuity, based on the conservation of volume, predicts water heights (heads) and volumes. This approach assumes that flow is predominantly one-dimensional, Coriolis and other accelerations normal to the direction of flow are negligible, channels can be adequately represented by a constant top width with a variable hydraulic depth, i.e., rectangular, the wave length is significantly greater than the depth, and bottom slopes are moderate. Although no strict criteria are available for the latter two assumptions, most natural flow conditions in large rivers and estuaries would be acceptable. Dam-break situations could not be simulated with DYNHYD nor could small mountain streams.

WASP

WASP is a dynamic compartment model that can be used to analyze a variety of water quality problems in such diverse water bodies as ponds, streams, lakes, reservoirs, rivers, estuaries, and coastal waters. This section presents the basic water quality model used to simulate dissolved, conservative chemicals such as chlorides or dye tracer.

The equations solved by WASP are based on the key principle of the conservation of mass. This principle requires that the mass of each water quality constituent being investigated must be accounted for in one way or another. WASP traces each water quality constituent from the point of spatial ant temporal input to its final point of export, conserving mass in space and time.

To perform these mass balance computations, the user must supply WASP with input data defining seven important characteristics:

  • Simulation and output control
  • Model segmentation
  • Advective and dispersive transport
  • Boundary concentrations
  • Point and diffuse source waste loads
  • Kinetic parameters, constants, and time functions
  • Initial concentrations

These input data, together with the general WASP mass balance equations and the specific chemical kinetics equations, uniquely define a special set of water quality equations. These are numerically integrated by WASP as the simulation proceeds in time. At user-specified print intervals, WASP saves the values of all display variables for subsequent retrieval by the postprocessor W5DSPLY. This program interactively produces tables of variables specified by the user.

EUTRO

Several physical-chemical processes can affect the transport and interaction among the nutrients, phytoplankton, carbonaceous material, and dissolved oxygen in the aquatic environment. EUTRO can be operated by the user at various levels of complexity to simulate some or all of these variables and interactions. To simulate only BOD and DO, for example, the user may bypass calculations for the nitrogen, phosphorus, and phytoplankton variables (the bypass option is documented in the User Manual). Six levels of complexity are identified and documented at the end of this section:
  1. Streeter-Phelps
  2. Modified Streeter-Phelps
  3. Full linear DO balance
  4. Simple eutrophication kinetics
  5. Intermediate eutrophication kinetics
  6. Intermediate eutrophication kinetics with benthos

EUTRO simulates the transport and transformation reactions of up to eight state variables. They can be considered as four interacting systems: phytoplankton kinetics, the phosphorus cycle, the nitrogen cycle and the dissolved oxygen balance. The general WASP mass balance equation is solved for each state variable. To this general equation, the EUTRO subroutines add specific transformation processes to customize the WASP transport equation for the eight state variables in the water column and benthos.

TOXI

TOXI is a dynamic compartment model of the transport and fate of organic chemicals and metals in all types of aquatic systems. It combines the hydrodynamic capabilities and the transport capabilities with the sediment balance and chemical transformation capabilities discussed. Several physical-chemical processes can affect the transport and fate of toxic chemicals in the aquatic environment. TOXI explicitly handles most of these excluding only reduction and precipitation-dissolution. If the kinetics of these reactions are described by the user, they can also be included as an extra reaction.

TOXI simulates the transport and transformation of one to three chemicals and one to three types of particulate material (solid classes). The three chemicals may be independent or they may be linked with reaction yields, such as a parent compound-daughter product sequence. Each chemical exists as a neutral compound and up to four ionic species. The neutral and ionic species can exist in five phases: dissolved, sorbed to dissolved organic carbon (DOC), and sorbed to each of the up to three types of solids. Local equilibrium is assumed so that the distribution of the chemical between each of the species and phases is defined by distribution or partition coefficients. In this fashion, the concentration of any species in any phase can be calculated from the total chemical concentration. Therefore, only a single state variable (WASP system) representing total concentration is required for each chemical. The model then is composed of up to six systems, three chemical and three solids, for which the general WASP mass balance equation is solved.

The WASP package includes both source and executable codes. Technical support is provided.

WASP5/DYNHYD5 Requirements: IBM-PC or compatible with 640K RAM, math coprocessor, and hard disk.



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