tag:blogger.com,1999:blog-1675184707067447729.post1454243263174850062..comments2023-07-12T07:12:04.697-07:00Comments on The RAS Solution: Weir Equations in HEC-RASChris G.http://www.blogger.com/profile/00354834185663924786noreply@blogger.comBlogger48125tag:blogger.com,1999:blog-1675184707067447729.post-17448526459786147772019-03-18T10:34:15.463-07:002019-03-18T10:34:15.463-07:00RAS uses a flow reduction factor based on percenta...RAS uses a flow reduction factor based on percentage of submergence. You can check the hydraulic reference manual for more detail.Chris G.https://www.blogger.com/profile/03272464763887890080noreply@blogger.comtag:blogger.com,1999:blog-1675184707067447729.post-33925172245220726212019-03-15T07:46:32.512-07:002019-03-15T07:46:32.512-07:00For a spillway, how downstream conditions taken in...For a spillway, how downstream conditions taken into account? For example for a semi submerged crest...Anonymoushttps://www.blogger.com/profile/00465531240796685858noreply@blogger.comtag:blogger.com,1999:blog-1675184707067447729.post-70557123752317142052018-11-20T06:31:14.788-08:002018-11-20T06:31:14.788-08:00Hi,
I found two ways to model inline structures (E...Hi,<br />I found two ways to model inline structures (Eg. Broad crested and Ogee weir). One approach would be by creating the broad crested profile with the input of series of cross section while as another approach is to add inline structure on the channel section and define broad crested weir. Would you please inform me which method is more accurate ?Bikashhttps://www.blogger.com/profile/05500342919446184311noreply@blogger.comtag:blogger.com,1999:blog-1675184707067447729.post-85923522328605882652018-11-01T04:09:43.861-07:002018-11-01T04:09:43.861-07:00The HECRAS 5.05 version has an option to compute w...The HECRAS 5.05 version has an option to compute weir coefficient of Ogee weir by supplying Spillway Approach Height and Design Energy head. for example. I supplied 15.98 and 10 respectively and weir coefficient was 2.17. which equation is invoked for calculation?AdhikariKirtanhttps://www.blogger.com/profile/10956681575482526896noreply@blogger.comtag:blogger.com,1999:blog-1675184707067447729.post-26628303271188617652018-05-29T17:53:58.293-07:002018-05-29T17:53:58.293-07:00Greetings,
I am having stability issues while try...Greetings,<br /><br />I am having stability issues while trying to run a steady flow model with a lateral weir. The downstream end of my model is a constrictive rating curve. Then 200 feet upstream of the end of the model is a 100 foot lateral weir overflow with the TW connection set to “out of system”. I am trying to determine the elevation of the channel at various high flows. The weir has a sloped height of 2 to 5 feet. When running the model I get “Flow Optimization Failed to Converge.” I have tried inputting the resulting flows into the “initial split flow optimization” of the steady flow data but that just makes the next results worse. I am getting flows leaving the weir much greater than my steady flow input.<br /><br />I have tried various weir coefficients ranging from 1.5 - 3.0, with similar optimization failures. Should I go to an even lower coefficient based on the weir geometry? I have tried both the standard weir equation and the Hager’s eqn. Based on my model set up is one method preferable? If I used the standard equation should I have separate geometries with different coefficients for different flows? <br /><br />I have 50 foot cross section spacing. Is there a place along the channel (above weir, through weir, below weir) where I should have greater or smaller cross section spacing?<br /><br />Any advice or thoughts would be greatly appreciated!! <br /><br />Thanks, <br />Clark<br />Clarknoreply@blogger.comtag:blogger.com,1999:blog-1675184707067447729.post-69368607079470426232018-05-28T07:45:47.585-07:002018-05-28T07:45:47.585-07:00Hi Chris! I'd like to ask you about conservati...Hi Chris! I'd like to ask you about conservation of flow in a 2D model.<br />I have a model with 2 boudaries upstream with an constant flow going into the model, a dam with 10 radial gates in the middle and 1 boundary condition downstream. The proble I have is I'm losing 7% of flow: <br />Upstream flow: 6500 mcs, fow through the dam 6000 mcs, Downstream flow 6500 mcs. Did you hear about this before? Thanks!Ramirohttps://www.blogger.com/profile/01896710477190766829noreply@blogger.comtag:blogger.com,1999:blog-1675184707067447729.post-23605209621760182122018-05-27T04:29:19.919-07:002018-05-27T04:29:19.919-07:00Hello chris! great work on this blog, it helped me...Hello chris! great work on this blog, it helped me a lot during my study. I'm doing a dam break analysis study and I'm having a problem with lateral structures, the model is a combined 1D-2D model where the channel is 1d and both the right and left floodplain are 2d, they're connected with lateral structures. the problem is that the WSE and EG are acting weird and doing these little steps in various locations in my reach https://imgur.com/4QXcugl and these are the only places where the water overflows from the river to the floodplain. I've tried: using very small timesteps (from 0.5s to 10s ), increasing HTAB points, small cross section spacing(15m). if you have any tips or hints that can help it would be greatly appreciated.<br />thank you <br />Alialihttps://www.blogger.com/profile/01143436267088052764noreply@blogger.comtag:blogger.com,1999:blog-1675184707067447729.post-44687647254776151002018-05-25T12:51:25.775-07:002018-05-25T12:51:25.775-07:00Hi Chris!
I'm Ramiro from Montreal. I work for...Hi Chris!<br />I'm Ramiro from Montreal. I work for Hydro Québec.<br />I have a 2D model and I'm having a problem with conservation of flow. <br />I have 2 boundaries condition upstream (total flow of 6500 mcs), an inline structure located 5 km downstream and a downstream boundary condition 10 km downstream from there.<br />The problem I have is I'm losing flow from upstream boundaries conditions to my in line structure, about 7%-10% less flow pass through the in line structure (6000 mcs) . I have the good flow 6500 mcs at the downstream boundary condition. I made 2 geometry files : One with the in line structure with rating curves and another one with 10 radial gates. Both give the same result.<br />The levels are steady and I have no loses anywhere else.<br />Do you have any idea how I can improve my simulation?<br />thanks a lot!Ramirohttps://www.blogger.com/profile/01896710477190766829noreply@blogger.comtag:blogger.com,1999:blog-1675184707067447729.post-32641245445274582152018-04-21T17:07:12.014-07:002018-04-21T17:07:12.014-07:00That would be a nice option!That would be a nice option!Chris G.https://www.blogger.com/profile/03272464763887890080noreply@blogger.comtag:blogger.com,1999:blog-1675184707067447729.post-27958807053610881662018-04-19T16:32:24.382-07:002018-04-19T16:32:24.382-07:00Chris, what about user-defined rating curves, such...Chris, what about user-defined rating curves, such as for a gate in an inline spillway? Does RAS assume you are using Energy Head to define the rating, or Water Surface (hydraulic head)? Examination of results seems to indicate it's using Energy, but what if the gate rating provided (say from a dam operator) is based on WS? I think we'd prefer it use WS rather than Energy, or at least provide an option to switch. Thanks! Bob Elliothttp://www.watershedse.comnoreply@blogger.comtag:blogger.com,1999:blog-1675184707067447729.post-8998602715594740352018-03-14T17:02:02.228-07:002018-03-14T17:02:02.228-07:00Even though the gates are fully opened RAS still c...Even though the gates are fully opened RAS still considers that gate flow. Weir flow would be what’s going over the inline structure. Chris G.https://www.blogger.com/profile/03272464763887890080noreply@blogger.comtag:blogger.com,1999:blog-1675184707067447729.post-81573208457290255362018-03-14T04:45:17.015-07:002018-03-14T04:45:17.015-07:00Hi Chris, i'd like to ask you something about ...Hi Chris, i'd like to ask you something about radial gates in the inline structure. I have to simulate a weir with three radial gates 10 m x 10 m in steady flow conditions in the case of all the gates opened. <br />When i finish the simulation and i look at the inline structure output table i see that the whole discharge is splitted in Qweir and Qgates. I don't understand this thing because i'm simulating a weir with three gates totally opened: in my mind it is like a weir without gates. <br />Thanks for any advice assistance<br /><br /><br />MirkoAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-1675184707067447729.post-37329405265891600872018-02-27T17:36:15.525-08:002018-02-27T17:36:15.525-08:00Brian- too much for me to type a response. Why do...Brian- too much for me to type a response. Why don’t you give me a call at 503-793-2700. Chris G.https://www.blogger.com/profile/03272464763887890080noreply@blogger.comtag:blogger.com,1999:blog-1675184707067447729.post-55458845066339206592018-02-27T12:58:09.112-08:002018-02-27T12:58:09.112-08:00I have a small dam that has 2 secondary discharge ...I have a small dam that has 2 secondary discharge channel in addition to the primary discharge pipe. The two secondary discharge channels go in two different directions. I am modeling a dam breach and have to had a 1D model through the dam breach, then can switch to 2D for the overland flow through a subdivision that is needed to be mapped. I model the one secondary discharge as a lateral weir leaving the system (and into a 2D flow area) and leave the remaining primary and other secondary discharge as part of the main dam. If the dam were breached the initial secondary discharge would not be part of the breach flows, therefore I need to remove it from the system for the breach. nothing is gated or controlled, it is all gravity. I can get the entire model to work including the 1D unsteady, breach and 2D connections. I have modelled all the weirs as rating curves. Where I am having a problem is that my lateral weir requires that I have a physical weir shown in the model or it will not transfer the flows. However, when I do this, it sets a tailwater elevation that is more than 0.8' higher than the incoming flow elevation. Where this become a problem is that my 2D flow now routes around the dam in a manner that it cannot at the elevations it should be at. This causes additional flow in areas where it should not be. How can I control the tailwater elevation for lateral weirs?<br /><br />I am using 5.0.3. Would also like to see how you can breach a dam in 2D without having to go back to the 1D cross-sections. Guess i'll need to wait for future version...<br /><br />Thanks for any advice assistance.<br /><br />BrianAnonymoushttps://www.blogger.com/profile/00030374084574946821noreply@blogger.comtag:blogger.com,1999:blog-1675184707067447729.post-18876612700346180332018-02-12T14:39:14.924-08:002018-02-12T14:39:14.924-08:00Just heard back and the answer is RAS uses the wat...Just heard back and the answer is RAS uses the water surface elevation as the headwater reference for SA/2D area connection weirs. Chris G.https://www.blogger.com/profile/03272464763887890080noreply@blogger.comtag:blogger.com,1999:blog-1675184707067447729.post-42312792431104682442018-02-12T14:25:10.938-08:002018-02-12T14:25:10.938-08:00That's a good question. I don't think it ...That's a good question. I don't think it is explicitly stated in the manual. I would assume that to be consistent, it uses the energy level. But honestly I don't know for sure. Let us all know if you find out. I'll do the same...Chris G.https://www.blogger.com/profile/03272464763887890080noreply@blogger.comtag:blogger.com,1999:blog-1675184707067447729.post-78458869539866315662018-02-12T13:48:06.298-08:002018-02-12T13:48:06.298-08:00Hi Chris
When using the 2D connection as a weir e...Hi Chris<br /><br />When using the 2D connection as a weir embedded in 2D grid, is flow over the weir based on energy level or water level? I'm just cross-checking some HEC 2D results and am trying to resolve some inconsistencies.<br /><br />Thanks<br />Craig<br />EnturaAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-1675184707067447729.post-71133785113140632202018-02-06T23:20:01.222-08:002018-02-06T23:20:01.222-08:00Hi Chris,
Thanks for your feedback. Actually I hav...Hi Chris,<br />Thanks for your feedback. Actually I have used HEC-RAS before but in a class work. Its not really damming the river maybe I used the wrong words, but rather constructing a short weir across the river(2-2.5m high). I was just interested to know what other data I might need for this specific task besides the channel geometry,. Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-1675184707067447729.post-28243349935258767022018-01-30T09:22:59.660-08:002018-01-30T09:22:59.660-08:00HEC-RAS is a great tool for this type of analysis....HEC-RAS is a great tool for this type of analysis. Based on your question, I assume you are new to HEC-RAS. My advice would be to hire a qualified and experienced HEC-RAS modeler to do this for you. Trust me, it will save you money in the long run and make your client happy. That person would know all of the requirements for setting up and running this analysis. Plus, every site is different, so before recommending what survey data is needed, one needs to know what survey data is already available, it's quality, as well as site-specific conditions that will have an influence on the hydraulics of the system, among many other things. And finally, damming a river with a weir is not a trivial thing. You want to make sure to get it right. Chris G.https://www.blogger.com/profile/03272464763887890080noreply@blogger.comtag:blogger.com,1999:blog-1675184707067447729.post-80281474766025462802018-01-30T08:50:18.468-08:002018-01-30T08:50:18.468-08:00Hi Chris, Am considering damming a section of a ri...Hi Chris, Am considering damming a section of a river using a weir to abstract water for domestic supply. Our client is interested to know the effect of building this weir on the upstream side of the river and if there will be any flooding during the max design flood which is 1:100. I was wondering how I can simulate this using HEC-RAS. Our surveyor is going to site soon to do a topo survey of the area. what would be the most important data I could advice he collects for this exercise? Please advice. ThanksAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-1675184707067447729.post-62250629879601509852018-01-17T12:50:34.392-08:002018-01-17T12:50:34.392-08:00Theoretically a weir with any height to it will af...Theoretically a weir with any height to it will affect water levels upstream. But why not give it a try. Use progressively shorter weirs until you don't see a significant change.Chris G.https://www.blogger.com/profile/03272464763887890080noreply@blogger.comtag:blogger.com,1999:blog-1675184707067447729.post-90818591991486437562018-01-17T10:52:07.176-08:002018-01-17T10:52:07.176-08:00I want to place a weir (an inline structure) in my...I want to place a weir (an inline structure) in my channel (irregular x-section) and I want to make sure that it acts as weir i.e flow passes through critical depth over the weir. I think you can easily put in a weir with crest height so low that it does not effect the flow and the flow does not pass through critical depth. Basically, I am looking for minimum height of the weir that I can use without effecting the water levels upstream. Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-1675184707067447729.post-78245718579290052532018-01-15T10:07:54.825-08:002018-01-15T10:07:54.825-08:00I'm curious why you want to set your crest to ...I'm curious why you want to set your crest to critical depth? Not a critique...just wondering. Why don't you run the model first without the weir, but instead with a cross section in the same location. Get the critical depth elevation from that run, then remove the cross section and replace it with a weir with the elevation of critical depth. Chris G.https://www.blogger.com/profile/03272464763887890080noreply@blogger.comtag:blogger.com,1999:blog-1675184707067447729.post-44517057068041219282018-01-10T15:24:04.569-08:002018-01-10T15:24:04.569-08:00Just a clarification on seeing critical depth for ...Just a clarification on seeing critical depth for weirs - this is with relevance to inline structures.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-1675184707067447729.post-25522556382906971692018-01-10T15:21:56.451-08:002018-01-10T15:21:56.451-08:00Hi Chris,
When putting a weir in my model, I want...Hi Chris,<br /><br />When putting a weir in my model, I want to set its crest at critical depth. Is their any way I can see critical depth in the result files? In the result files, I can turn on the critical depths for the x-sections but not for the weir. Is it possible? Thanks.<br />Anonymousnoreply@blogger.com