Sediment Transport Features in HEC-RAS 5.0

Written by Stanford Gibson, Ph.D. |  Hydrologic Engineering Center
Copyright © Stanford Gibson 2015.  All rights reserved.

The new 2D features and mapping tools are the most anticipated new features in HEC-RAS 5.0. However, HEC also added a couple major new sediment features, as well as many minor features and a few substantial bug fixes (e.g. SI Units). The two major features are the ARS-USDA Bank Stability and Toe Erosion Model (BSTEM) and Unsteady Sediment transport.

USDA-ARS Bank Stability and Toe Erosion Model (BSTEM)
HEC collaborated with Andrew Simon (Cardno) and Eddy Langendoen (USDA-ARS) to couple the HEC-RAS mobile bed model with the USDA-ARS Bank Stability and Toe Erosion model (BSTEM).  This model coupling adds BSTEM’s lateral processes (geotechnical bank failure, groundwater lag and toe scour) to HEC-RAS’ vertical, deposition and erosion processes.  This tool has a separate User/Technical Reference manual available from HEC.


Goodwin Creek, MS, repeated right bank surveys compared with computed HEC-RAS/BSTEM cross section migration from Gibson et al. (2015).
 
Unsteady Sediment Transport:
Previous versions of sediment transport in HEC-RAS used the quasi-unsteady hydraulic model exclusively, simulating hydrodynamics with a series of steady flows. HEC-RAS 5.0 couples the sediment computations with unsteady flow. Hydrologic mass conservation is the biggest advantage of unsteady sediment transport, making reservoir models and even multi-reservoir cascade models much more practical in HEC-RAS. However, coupling sediment transport to the unsteady flow capabilities also brings several powerful features, native to the unsteady hydraulic analysis environment, into sediment transport analyses including: lateral structures, flow networks, mixed flow (figure), and especially operational rules (Gibson and Boyd, 2014). Version 5.0 even includes sediment based operational parameters, operating structures based on bed change and concentration (e.g. TMDL).


Initial and bed profile and water surface elevation for a mixed flow sediment transport simulation with equilibrium sediment load and hard bottom. Sediment deposited in the sub-critical reach.
 
Other Features:
HEC-RAS 5.0 also includes a range of other new sediment features including:
· HDF5 Sediment Output and a New Sediment Output Viewer
· Copeland (1993) Sorting and Armoring Method (Exner 7 in HEC 6T)
· Gradational Hotstart
· Sediment Flow Splits
· New Dredging Tools
· Bed Roughness Predictors
· New User Manual
· DSS Sediment Time Series Boundary Condition
· Specific Gage Capabilities




HEC-RAS 5.0 will be released shortly. To test a final beta version contact Stanford Gibson at HEC.


References:
Copeland, R (1993) Numerical Modeling of Hydraulic Sorting and Armoring in Alluvial Rivers, PhD Thesis, The University of Iowa, 284 p.

Gibson, S. and Boyd, P. (2014) “Modeling Long Term Alternatives for Sustainable Sediment Management Using Operational Sediment Transport Rules,” Reservoir Sedimentation –Scheiss et al. (eds), 229-236.

Gibson, S., Simon, A., Langendoen, E., Bankhead, N., Shelley, J. (2015) A Physically-Based Channel-Modeling Framework Integrating HEC-RAS Sediment Transport Capabilities and the USDA-ARS Bank-Stability and Toe-Erosion Model (BSTEM), SEDHYD Interagency Sediment Conference, April 2015, In Press.