Hi,
I have created a very simple breach model of a watercourse – modelled in 2d entirely with a stage-time boundary and downstream normal depth boundary. I have created a 2d domain over the watercourse area only and run this element of the 2d model without any issues. I have then created another 2d grid of the wider floodplain area. A SA/2d connection was then created along a 60m stretch of the river bank set to breach after 6 hours of run time across a bank length of 40m.
The model runs fine (no level tolerance or instability issues at all) and the output is reasonable. The issue is the volume accounting balance reported at the end of the simulation – I am getting overall errors of 84.03% reported in the log as follows:-
2D Area Starting Vol Ending Vol Cum Inflow Cum Outflow Error Percent Error
******* ************ ********** ********** *********** ***** *************
Watercourse 455.5 339.9 243.9 947.2 587.7 163.5
WiderSite 947.3 947.2 0.001547 0.09370 0.009893
I am using HecRAS 6.5.
I am wondering if this is actually a real issue or a function of how the stage time upstream boundary works and how the two regions balance between each other. Or is it in fact a real issue caused by some stability or grid spacing issues associated with the breach.
I have also tried modelling the scenario as single 2d area with a SA/2D connection inserted into the grid. There are two problems with this approach. I have to tighten or reinforce the grid along the river bank in order to prevent any leaking along the raised riverbank. I then insert the sa/2d connection and it covers multiple grid squares yet the TW/HW connections are along the line of the feature. Even if I make the feature 20m wide as a weir HEC-Ras still seems to assume that the breach occurs either side of the line. I would’ve thought that the width of the weir would be used and HEC would connect faces on the HW side to the edge of the weir/embankment through the connection to faces on the other side of the weir but it appears to do it along the central line. This leaves the breach discharging to the top of the weir – it seems a strange way to do things. Am i missing something with this ?
Any advice on whether the volume accounting error is real or not would be appreciated. Any advice on how to create the 2d breach within 1 2d area – potentially to avoid the accounting area would be appreciated.
-
This topic was modified 1 month, 3 weeks ago by Dazzler.