tag:blogger.com,1999:blog-1675184707067447729.post7390653219943237587..comments2023-07-12T07:12:04.697-07:00Comments on The RAS Solution: Permanent and Non-Permanent Ineffective Flow AreasChris G.http://www.blogger.com/profile/00354834185663924786noreply@blogger.comBlogger9125tag:blogger.com,1999:blog-1675184707067447729.post-71101238750520757052018-02-26T05:15:14.085-08:002018-02-26T05:15:14.085-08:00Thanks Chris,
PawelThanks Chris,<br />PawelPawelnoreply@blogger.comtag:blogger.com,1999:blog-1675184707067447729.post-75553708096411646832018-02-21T09:13:35.279-08:002018-02-21T09:13:35.279-08:00You are correct. The higher coefficients should be...You are correct. The higher coefficients should be applied at all Criss sections within the contraction and expansion zones. Chris G.https://www.blogger.com/profile/03272464763887890080noreply@blogger.comtag:blogger.com,1999:blog-1675184707067447729.post-5488273219652219832018-02-21T07:00:59.038-08:002018-02-21T07:00:59.038-08:00There is another issue: expansion and contraction ...There is another issue: expansion and contraction coefficients. FEMA models I saw use higher expansion coefficients (say 0.5 vs. 0.3) for 2 (yes just 2)cross sections D/S of bridge. I am using higher expansion coefficients for all cross sections within expansion zone. Some people increase the coefficient just at one cross section. Any thoughts on it? Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-1675184707067447729.post-16116557760279869402017-10-12T14:39:45.678-07:002017-10-12T14:39:45.678-07:00Hi Alex. Thanks for the kind words. First off, if...Hi Alex. Thanks for the kind words. First off, if your two bridges are too close that flow doesn't fully expand in between them, just make sure that your cross sections in between have ineffective flow areas defined to limit the full expansion. Second point-Yes! You can definitely have intermediate cross sections with ineffective flow areas set to properly define the contraction and expansion of flow. The 4 cross section layout is just a conceptual concept. You can have many more cross sections in between if you need to. Chris G.https://www.blogger.com/profile/03272464763887890080noreply@blogger.comtag:blogger.com,1999:blog-1675184707067447729.post-38029995013614580472017-10-11T07:12:29.082-07:002017-10-11T07:12:29.082-07:00Hey Chris, thanks for all the help!
This may not ...Hey Chris, thanks for all the help!<br /><br />This may not be the appropriate blog post to ask but I am hoping to confirm something about ineffective flow areas upstream and downstream at culverts and bridges.<br /><br />I understand that ineffective flows are to be placed upstream and downstream of the structure with their respective ratios as well as the idea of the 4 cross-section set-up to a bridge or culvert as described in the HEC-RAS Reference Manual 4.1 in beginning of Chapters 5 and 6.<br /><br />From the Manual, it appears as though Cross Section 1 and 4 are to be located sufficient distance from the structure where a fully active flow is considered to exist.<br /><br />What if a situation exists where two bridges are located along the same channel that has wide overbanks and a point does not exist between either bridge that allows for flow to become fully effective before being under the influence of the other structure(high flood flows throughout)?<br /><br />More generally, what if the point at which the criteria for placing cross-sections 1 and 4 are incredibly far upstream and downstream and miss a lot of channel features in the area between? Are intermediate cross-sections with ineffective flow areas (as defined by the contraction and expansion ratios) advised? Or, does this interfere with how the effects of the bridge are determine by the model?<br /><br />We are all lucky to have this blog,<br />AlexAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-1675184707067447729.post-39815434476028959032017-02-10T06:19:50.060-08:002017-02-10T06:19:50.060-08:00I like to add some elevation above the crest for m...I like to add some elevation above the crest for my ineffective triggers. Typically I'll add 0.5 ft on the upstream side, and subtract 0.5 ft on the downstream side. Then adjust to maintain consistency on both sides (i.e. either both overtopped, or both not overtopped for a given timestep).Chris G.https://www.blogger.com/profile/03272464763887890080noreply@blogger.comtag:blogger.com,1999:blog-1675184707067447729.post-75676694379938816742017-02-06T13:55:50.773-08:002017-02-06T13:55:50.773-08:00Is there any guidance for setting ineffective area...Is there any guidance for setting ineffective area elevations? I tend to set the ineffective area top elevation as 0.5 ft above a roadway crest. However, I know that a lot of people and regulations require they be set at the same elevation as the road crest. What guidance do you follow? Thanks.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-1675184707067447729.post-70393458545351090952013-01-02T08:30:54.630-08:002013-01-02T08:30:54.630-08:00If you have measurements, then you can use that as...If you have measurements, then you can use that as a way to calibrate your ineffective flow areas. I would start with a 1:1 contraction ratio and a 2:1 expansion ratio and adjust from there. For more information on setting ineffective flow areas at bridges (flumes or natural rivers), check the HEC-RAS manuals-especially Appendix B of the HEC-RAS Hydraulic Reference Manual. Chris G.https://www.blogger.com/profile/00354834185663924786noreply@blogger.comtag:blogger.com,1999:blog-1675184707067447729.post-42322705825055303352012-12-13T12:39:16.238-08:002012-12-13T12:39:16.238-08:00How can i appropriately define the ineffective flo...How can i appropriately define the ineffective flow area for my model which is based on the labratory flume of length 10m wher at every x-section of 0.1m (10cm) i record the water level measurment in which i put the bridge model at 5.4m (midway) of the flume.....any help and comment would appriciateAnonymousnoreply@blogger.com