ADYN (Hydrodynamics)

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ADYN simulates discharge, water surface elevation, and other hydraulic variables over time at numerous model nodes throughout the simulated river system, based on a series of irregular channel cross-sections and user specified channel roughness, boundary conditions, and initial conditions.  Governing equations of conservation of mass and momentum are solved using a 4-point implicit finite difference scheme with a generalized Newton-Raphson iterative closure.  Hydraulic output available from ADYN results are numerous, but among them are velocity, depth, wetted area, travel time, Lagrangian particle tracking, wading safety index, stream power, etc.  Boundary conditions are flexible, but hourly dam discharges are typically used at the upstream boundary and an elevation-discharge rating or elevation hydrograph is used downstream.  Internal boundary conditions can be specified for multiple weirs and dams along the modeled river and its tributaries.  ADYN includes features for multiple dynamic tributaries, junctions, and distributed or point lateral inflows.   ADYN provides important hydrodynamic inputs to RQUAL, RHAB, and FISH.

RQUAL (Water Quality)

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RQUAL simulates temperature, DO, and carbonaceous and nitogenous forms of BOD over time at numerous model nodes throughout the simulated river system.  User-specified temperature and water quality for the main channel and tributaries serve as boundary conditions.  The mass transport governing equation is solved for each constituent using a choice of two numerical solution schemes:  4-point implicit finite-difference or Holly-Priessman characteristics scheme.  The model uses a full heat budget that includes atmospheric heat exchange, channel shading by trees and barriers, channel bottom heat exchange, heated discharges to the river, and other important factors.  DO is influenced by turbulent and wind-driven reaeration, weir aeration, photosynthesis-respiration of aquatic plants, sediment oxygen demand, and oxygen demands in the water column from waste loads, tributaries, and upstream sources.  RQUAL provides important temperature and water quality inputs to FISH.

RHAB (Physical Habitat)

RHAB simulates weighted-usable area (WUA) based on suitability (SI) curves for individual fish species and lifestages.  A separate model, CELVEL, uses ADYN discharges and produces a lateral distribution of cell velocities for RHAB based on local roughness at ADYN model nodes (transects).  Each cell has a specific wetted area, velocity, and depth.  These data are combined with the suitability scores for each type of habitat, producing WUA versus time at various sub-reaches along the modeled river.  Thus, WUA versus dam discharge and other investigations can be made with RHAB.  As an additional output, RHAB also produces “high value WUA”, which includes only those cells with combined suitability of 0.8 or higher (a user-defined threshold) on a scale from 0 to 1.  High-value WUA provides an important distinction from total WUA, because a single WUA magnitude can represent a great amount of “marginal” habitat or a small amount of “high-value” habitat.  As an alternative to WUA, RHAB can also quantify wetted areas sub-classed by depth.

FISH (Bioenergetics Fish Growth)

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FISH simulates fish biomass over time at modeled river locations resulting from bioenergetic exchanges during food consumption and respiration processes.  A team of TVA and EPA-Corvallis researchers developed this model in the early 1990s specifically for use hydropower tailwaters (Shiao, et. al. 1993).  In FISH, growth responds to fluctuations in temperature, DO, and food availability.  Temperature and DO are provided by RQUAL.  Food availability is not simulated in FISH; rather, it is back-calculated by calibrating the model to fish growth data from tagged cohorts that are stocked and retrieved over time to measure growth.