Temperature Modeling with HEC - RAS

Abstract

The Hydrologic Engineering Center – River Analysis System (HEC - RAS) is a onedimensional unsteady flow hydraulics program capable of simulating a full network of open channels and hydraulic structures such as bridges, culverts, and weirs, with variable spatial discretization. HEC - RAS is widely used, is in the public domain, and has been applied to a variety of e cosystem function problems such as simulation of floodplain inundation and evaluation of fish passage through culverts; but no capability has been provided for water quality until now. An advection-dispersion module for water quality and temperature simul ation has recently been added to HEC - RAS. It employs the QUICKEST-ULTIMATE explicit numerical scheme. Water temperature simulation has been implemented using a full energy budget approach. Model input requirements include hydrodynamic information and system geometry both of which are passed from the HEC - RAS unsteady flow model, as well as temperature at hydrodynamic boundaries, and meteorological data. Output from the water temperature model includes results of intermediate calculations such as computation of individual energy budget terms, as well as computed water temperatures. Results from the water temperature model may be combined with output from the hydrodynamic model to facilitate graphical output such as combined time series and profile plots of simulated water temperature, discharge and velocity. A plan view of the river schematic may be color coded to describe spatial distribution of model results. HEC - GeoRAS is an ArcView (and ArcGIS in development) extension that facilitates export of geo-referenced information from and import of model simulation results to a GIS. For example, GeoRAS produces flood inundation maps that identify the intersection of water surface and land surface grids , and color coded overlays of simulated water temperatures so that model results may be viewed in context of important spatial information such as areas of critical habitat.