This sample data set is available from The RAS Solution Google Drive site at: Over 2 days of simulation time with a 10 second computation interval and 40 m x 40 m initial cell size ran rather quickly at around 2.5 minutes on my computer. A lot more of this could be done with this data set to completely eliminate fragmentation. Īs shown in this figure, I added some resolution and strategic cell center orientation to minimize inundation fragmentation. This helps to prevent “leaking” through the high ground, which occurs when a cell is large enough to straddle the high ground feature. Notice in this figure I’ve oriented some additional cell centers to try to align the cell faces with the high ground just to the southwest of the main channel. In the 2D mesh, you’ll also notice I’ve added some refinement to the initial 40m x 40m cell center spacing to better capture the geometry along the levee and to minimize inundation fragmentation. I used a ramp-up time of 4 hours to set the model up with a more appropriate initial conditions solution. But in this case it worked, with a little help from the Initial Conditions Ramp-Up option in the Unsteady Computation Options and Tolerances window. This will not always work, especially if there is significant changes in water surface elevation throughout the 2D area. The easiest way to set initial conditions is to just apply a single starting water surface elevation for the entire domain. These were placed at the same location as the upstream and downstream cross sections from the original model. Once you’ve drawn your 2D area boundary and have assigned a mesh cell center spacing (DX and DY) and Manning’s roughness value(s), really all that is left is toĪssign boundary conditions at the upstream and downstream ends using 2D Area BC Lines. The following figure presents the geometry file for Muncie when modeled with a single 2D area. To keep things simple, the levee breach was removed and flow moving into the overbank areas is purely due to overtopping of the levee. In this example, the standard Muncie project offered by the Hydrologic Engineering Center has been converted first to SI units, then to a single 2D mesh. There have been many questions lately about whether HEC-RAS 5.0 can perform a simulation with ONLY a 2D mesh (i.e. Written by Chris Goodell | January 12, 2015