DanielCopelin 0 Report post Posted March 26, 2013 Hi, I have a weir (W) channel with a crest level of 19m as part of a 1D network. The weir geometry is being read from a mid cross-section file, and the check files seem to indicate that the geometry is being read correctly and the hydraulic properties seem correct. However, I am seeing very large afflux (approx 1.5m) across the structure even under very high flows where the weir is drowned by ~20m+ of water over the crest. By comparison, a steady state HECRAS model only predicts about 0.15m difference in upstream and downstream water level, which is more reasonable. If I model the W channels as normal S channels, I get results that are similar to HECRAS. I have a suspicion that the W channels are not using the submerged flow regime, but I don't know how to go about diagnosing this. I can't seem to find anything of relevance in the check files and .eof file. I am using the latest version of TUFLOW. Does anyone have any experience with this? Quote Share this post Link to post Share on other sites
katebradbrook 0 Report post Posted March 26, 2013 Daniel, Yes, I had noticed this problem and did a considerable amount of benchmarking of weirs modelling between ESTRY, ISIS, HEC-RAS and hand-calculations and contacted Bill Syme. He investigated and recommended using Weir Flow == Method A in these situations where weirs are drowned and we are not expecting much headloss....see if this helps your weir.... all the best, Kate Quote Share this post Link to post Share on other sites
DanielCopelin 0 Report post Posted March 26, 2013 Daniel, Yes, I had noticed this problem and did a considerable amount of benchmarking of weirs modelling between ESTRY, ISIS, HEC-RAS and hand-calculations and contacted Bill Syme. He investigated and recommended using Weir Flow == Method A in these situations where weirs are drowned and we are not expecting much headloss....see if this helps your weir.... all the best, Kate Thanks, Kate! This seems to have worked. I have upstream levels within 0.1m of HECRAS now. Quote Share this post Link to post Share on other sites
Bill Syme 0 Report post Posted April 2, 2013 Hi Daniel and thanks Kate. For further explanation, Method B (the default in recent releases), was introduced to provide better stability for weirs embedded within 2D domains (eg. over culverts or a bridge that are modelled in 2D using 2D FCs). We're still investigating, however, it seems that in some situations it does not converge well and can cause a large head drop. For the 2013 release, you'll be able to select which method to apply on a weir by weir basis, and Method A is likely to be set back as the default (unless using a Defaults == Pre... command). In the meantime, should there be a concern over the head drop of a drowned weir, try setting Weir Flow == Method A in the .ecf file. If anyone has any feedback, please add to this topic or email support@tuflow.com. Cheers Bill Quote Share this post Link to post Share on other sites