TREX: Two-Dimensional Runoff Erosion and Export

Spatially Distributed Model To Assess Watershed Hydrology, Sediment Transport, and Contaminant Transport and Fate

Home

Overview

Applications

   Extreme Storms (pdf)

   Metals Transport (pdf)

User Manual (pdf)

Examples

   Hydrology (zip)

   Sediment Transport (zip)

   Chemical Transport (zip)

   Radar Rainfall (zip)

Source Code

Contacts

 

 

Model Development
The starting point for TREX development was CASC2D (Julien and Saghafian, 1991; Julien et al. 1995; Johnson et al. 2000; Ogden and Julien, 2002; Julien and Rojas, 2002). The basic framework is an event-based model that simulates overland flow, surface soil erosion and deposition, channel flow and sediment transport through stream channels. As part of TREX development, the hydrologic and sediment transport components of CASC2D were significantly expanded and enhanced to support flood modeling and chemical transport features (Velleux, 2005; England, 2005; Velleux et al. 2006; England et al. 2007; Velleux et al. 2008). Chemical transport and fate components were formulated based on those in the USEPA WASP/IPX series of stream water quality models (Ambrose et al. 1993; Velleux et al. 2001) to create a fully distributed model to simulate chemical transport and fate at the watershed scale. A conceptual diagram of chemical model processes is presented below.



TREX Model Framework (Velleux et al. 2008)



Chemical transport and fate processes in TREX (after Velleux et al. 2001)


Modeled Processes
The hydrologic processes in the model are:

  1. rainfall, interception, and surface storage;
  2. infiltration and transmission loss; and
  3. overland and channel flow.
The model state variables are water depth in the overland plane and stream channels.  Rainfall can be uniform or distributed in both time and space. When spatially distributed rainfall is simulated, areal rainfall estimates are interpolated from point rain gage data using an inverse distance weighting approach. Interception and surface storage are simulated as equivalent depths. 

The sediment transport processes in the model are:

  1. advection and dispersion;
  2. erosion and deposition; and
  3. bed elevation adjustment.
All processes occur in both the overland plane and stream channels. Any number of particle sizes can be simulated. Advection is computed from flow and concentration.  Erosion and deposition rates are calculated as a function of the hydraulic properties of the flow, the physical properties of the soils and sediments such as particle grain size and surface characteristics such as slope.

The chemical transport and fate processes in the model include:

  1. chemical partitioning and phase distribution;
  2. advection-diffusion;
  3. erosion and deposition;
  4. infiltration and transmission loss; and
  5. mass transfer and transformation processes.
All processes can occur in both the overland plane and stream channels. Any number of chemicals can be simulated. Advection is computed from flow and concentration.  Partitioning can be simulated on a concentration or organic carbon normalized basis.

References
Ambrose, R.B., Martin, J.L. and Wool, T.A. 1993. WASP5, A hydrodynamic and water quality model - Model theory, userís manual, and programmerís guide. U.S. Environmental Protection Agency, Office of Research and Development, Environmental Research Laboratory, Athens, Georgia.

England, J.F. Jr., 2005. Frequency analysis and two-dimensional simulations of extreme floods on a large watershed. Ph.D. dissertation, Department of Civil Engineering, Colorado State Univ., Fort Collins, Colorado.

England, J., Velleux, M., and Julien, P. 2007. Two-dimensional simulations of extreme floods on a large watershed. Journal of Hydrology, 347(1):229-241.

Johnson, B.E., Julien, P.Y., Molnar, D.K., and Watson, C.C. 2000. The two-dimensional upland erosion model CASC2D-SED. Journal of the American Water Resources Association, 36(1):31-42.

Julien, P.Y. and Saghafian, B. 1991. CASC2D Userís Manual - A Two Dimensional Watershed Rainfall-Runoff Model. Department of Civil Engineering, Colorado State University, Fort Collins, Colorado. Report CER90-91PYJ-BS-12. 66 p.

Julien, P.Y., Saghafian, B., and Ogden, F.L. 1995. Raster-Based hydrologic modeling of spatially-varied surface runoff. Water Resources Bulletin, AWRA, 31(3):523-536.

Julien, P.Y. and Rojas, R. 2002. Upland erosion modeling with CASC2D-SED. International Journal of Sediment Research, 17(4):265-274.

Ogden, F.L. and Julien, P.Y. 2002. CASC2D: A Two-Dimensional, Physically-Based, Hortonian Hydrologic Model. In: Mathematical Models of Small Watershed Hydrology and Applications, Singh, V.P. and Frevert, D., eds., Water Resources Publications, Littleton, Colorado. pp. 69-112.

Velleux, M.L. 2005. Spatially distributed model to assess watershed contaminant transport and fate. Ph.D. dissertation, Department of Civil Engineering, Colorado State University, Fort Collins, Colorado.

Velleux, M., Westenbroek, S., Ruppel, J., Settles, M., and Endicott, D. 2001. A Userís Guide to IPX, the In-Place Pollutant Export Water Quality Modeling Framework, Version 2.7.4. U.S. Environmental Protection Agency, Office of Research and Development, National Health and Environmental Effects Research Laboratory, Mid-Continent Ecology Division, Large Lakes Research Station, Grosse Ile, Michigan. 179 pp. EPA/600/R-01/079.

Velleux, M., Julien, P., Rojas-Sanchez, R., Clements, W., and England, J. 2006. Simulation of metals transport and toxicity at a mine-impacted watershed: California Gulch, Colorado. Environmental Science and Technology, 40(22):6996-7004.

Velleux, M., England, J., and Julien P. 2008. TREX: Spatially Distributed Model to Assess Watershed Contaminant Transport and Fate. Science of the Total Environment, 404(1):113-128.

 

Home | Overview | Applications | User Manual | Examples | Source Code | Contacts

Department of Civil and Environmental Engineering - Colorado State University
Fort Collins, Colorado 80523-2028  USA   (970) 491-5048

Last update: 10 February 2011