Episode 15: Dam Breach Analysis & Johnstown Dam Failure

[Music] do welcome everybody to full momentum in hec raz vodcast i am your host ben carey and here joining me as always is chris goodell chris welcome to episode 15 of full momentum it has been a minute since we got together and talked about hcc rads on this forum how you been i've been good yeah it's been a long minute um we've been really busy huh we've been trying to do this vodcast for several weeks now and it seems like something always jumps in the way you know project work or meetings or whatever and so finally we got some time to talk a little hec-ras today so uh no things have been good it's um the weather's starting to get better here seeing more sunny days that's always a good thing um kind of a in a lull sports wise we got some college baseball going on which i've been following it's been a little frustrating at times with my beavers but i want to ask you about the ncaa tournament because man was that a roller coaster ride and not surprising gonzaga was there at the very end what was surprising though was my beavers got to the elite eight and i was thinking man wouldn't this be an awesome broadcast for ben and i to talk about how oregon state beat gonzaga in the finals i don't know if it would have worked out that way but you know what i mean it would have quickly transitioned into a quality basketball podcast we would have ditched htc razz for the day but alas the beavers bowed out in the elite eight after a amazing beyond improbable run um yeah it was very surprising each each game i thought there's no way we're gonna win this and then it's like oh my gosh we won this game now we're into the next level and we got to houston and houston just just had our number i mean there was there was nothing to do against hughes they were really good um but i wanted i want to ask you about gonzaga i mean i think one of the best games i've ever seen in my entire life was that ucla gonzaga game semifinals that was incredible and that must have just been for me as a fan i was just wired to i can only imagine what it was like for a gonzaga fan watching that game yeah for that matter it was a special night for sure um obviously with what happened on monday uh as a gonzaga fan a lot of that you lose a lot of the perspective on how cool that game was but i'm sure over time we'll regain that but a lot of us are still in warning from what happened against against baylor in the national championship but like you said that that game was incredible it was a great ncaa tournament overall um i know for everybody who likes college basketball in the us and you know abroad it was it was just really awesome having the ncaa tournament back after missing it last year um hopefully man alive hopefully we never ever ever have to miss another ncaa tournament again for for health reasons so yeah it was it was very cool exactly so um how are the bulldogs going to look for next year yeah they're going to run you think yeah they're going to be really good again uh you know i think they're pretty consensusly looked at as another you know pre-season top five team and anytime that you're rated that high you're going to have a chance so but you know as we learned with the beavers and gonzaga in a single limit in a single elimination tournament anything can happen that's right that's right well cool well hey uh this vodcast uh let's get back to heck razz talk because that's what this is all about but uh ben and i thought hey why don't we uh we do a little danbridge talk today um it's one of the things i really enjoy doing i've been doing danbridge modeling for i mean almost 20 years now in heck razz and things have evolved quite a bit not just in heck rise but in general the the dam breach process that people do and um there have been dam breaches all throughout history um dating to the time when dams were first made first built right but even in the u.s we've had some uh some damn failures of note and uh ben you did a little research on one of those and i'd like to hear about it let's let's see what you got yeah that's a good transition there chris like chris said danbridge modeling is is really interesting it's challenging um in chris and i's 1d and 2d agc raz class we talk a lot about how even if you don't do dam breach analysis in your consulting career knowing how to do damage analysis is a real valuable tool because if you can if you can set up and execute a damn breach model you can do just about any type of modeling because of how dynamic quick changing uh dam breach model is and one of the things that chris always likes to to emphasize is razz doesn't like sudden changes right so as a modeler you want to avoid those sudden quick changes uh if you can those are likely to lead to instabilities and you cannot have anything that changes quicker than when you have a dam breach analysis so that's true i mean we we know by now that a lot or most of the instabilities in unsteady flow modeling come out of those acceleration terms right and if you think about a dam break what accelerates more than a dam brake flood wave right i mean you've got both local acceleration you've got convective acceleration with change in geometry and a lot of times these dams are built on steep slopes you know in canonized areas those are good places to put dams and you throw all that into a hec-ras model and it's tough it can be really tough to stabilize but fortunately there's lots of tricks and um once ben's done with his uh demonstration here i'm gonna provide a little bit of information on how do you go about stabilizing your model what are some tricks you can use how do you set it up for you know your best chance of success and then i'll go through and talk a little bit about the actual window the dam breach editor in heck raz and what everything means and you know what are the numbers for that great yeah so along with some of the technical conversations around danbridge analysis that we're going to have today um as many of you who follow the vodcast know we traditionally like to at least try to touch on a historic hydraulic event and kind of frame that in terms of hec ras and hydraulic modeling and so as we were kind of going to get into some dam breach analysis discussion today i wanted to look back at a historic event that had happened in the u.s regarding dam breach analysis and as chris mentioned there's been a lot of breach damn events uh in the u.s history obviously there were a lot more in its early days as a country because there weren't the regulations and the quality engineering that we have today and the event that i stumbled upon that i thought would be interesting to explore today is the johnstown dam failure which is in eastern or western pennsylvania just a little ways outside of pittsburgh and so i'm going to share my screen here so you guys can see kind of the area where the johnstown dam failure occurred so if i zoom out a little bit you can see that we're just east of pittsburgh here right up upstream of the town of johnstown and the johnstown dam was actually constructed on the kunama river i'm kind of i'm guessing on that a little bit and the kuma river flows from an east to west direction down into the town of johnstown here and the dam was constructed upstream at this location here where there's an existing flood national memorial because of the dam breach that occurred in 1889 i believe it was in may uh let me verify that really quick um yeah may of 1889 there was a large rainfall event that occurred over really the entire state of pennsylvania caused flooding in many many rivers including the the kunama and the flood from that rain event caused water to back up behind the johnstown dam eventually over top the dam and cause a failure the john sound dam was an earthen embankment dam with a concrete emergency spillway and uh basically the entire dam failed causing a massive flood wave to move downstream just in a few minutes this is a pretty short river reach here into the town of johnstown which was a pretty happening town at the time and there were over 200 people that were killed from this so it's one of the deadliest damn breaches in american history so it's a pretty significant event and as i started reading more into it and looking at the surrounding area i realized that this would be a really good one to analyze in hcc raz and maybe explore some of the new 6-0 features that are available to us so this is kind of setting the stage what i did is i set up a new htc raz project in raz mapper in the new 60 razz mapper so i'm going to pull that up here and show you guys what it looks like so again i'm zoomed in here to the area where the dam uh existed at the time of the failure and if we zoom in you can actually see as this takes a a little bit to to refresh here you can actually see the old wing walls from the dam so you can see the dam extend out to about here on on the right over bank and then here you can see the elevated wing wall on the left here now this is even more obvious if we turn off google satellite and look at the terrain you can see how lidar of this area actually picks up what's left of that damp structure here this this hi this is a highway downstream of it that obviously wasn't constructed at the time of the damn failure in 1889 and so uh what i wanted to do is i wanted to explore a couple different things i wanted to look at terrain modifications because that's a new really exciting feature in 6.0 i wanted to look at rain on grid because that's something that more and more people are going to start using now that there's infiltration and some other capabilities that really enhance uh the rain on grid functionality of hcc raz and then i wanted to use the 3d viewer to analyze what a dam breach analysis looks like if we're using that 3d viewer so i i went through each one of those items so the first thing i did is i wanted to add back in the historic johnstown dam via terrain modifications and so for those of you who are not aware one of the updates with 6.0 is you now have the ability to manipulate your underlying terrain with polygons and you can change individual elevations within the terrain you can add levees or river channels you can add high ground points you can add piers all of this by adding polygons or polylines to your terrain and then adding some information to those modifications in order to to actually modify your terrain so what you do is you if you're wanting to make some modifications you simply right click on the terrain file that you're using so in this case it's called terrain and you're going to clone this terrain and that's important because the modifications that you make are going to be to your clone terrain not the underlying terrain and of itself so your original terrain stays unmodified so if we right click here and we're going to add a name so i'm going to call this f5 and then as that should just take a few minutes to generate here when that comes up we'll have the ability to add what are called modification layers so if we right click on that cloned terrain under modification layers you can see we have a number of different options here so we can add shapes so this would be a polygon circle rectangular triangle each shape is going to have a specified elevation associated with it so this is a great application for a pier for instance if you want to add a pier to your drain now a natural question that comes out of this is well why would you want to add a pier to the train you can just add that into an inline structure like a bridge or whatnot but if you're doing 2d modeling the current way that the bridge routines are set up in hcc raz although they take into account the losses that are added to that bridge opening because of the pier um it's not going to actually show you what the near field flow patterns are around that pier because it's only going to take into account what's in the actual underlying terrain when it comes to how those flow patterns are going to be propagated in your model and so by adding a pier using terrain modifications you'll have the ability to actually see how flow is moving around piers through a bridge opening for instance okay in this case what i wanted to do is i wanted to add a line though and i wanted to add a line that represents high ground so i'm going to go ahead and click that go ahead and just call it high ground you can see you add this as a new feature just like you would a cross section or anything else in raz mapper my high ground is selected i click add new feature and what i want to do is i want to draw this line as close to the crest of the old dam as i can so i'm going to start here on the left wing wall over to the right wing wall and double click that will finish up and then you're going to get something pops up here and you can have you have a bunch of different options to modify this terrain and if you haven't um worked with the train modification layer go back and watch some of our previous previous vodcast we do a great job of covering this in depth um but what i'm going to what i'm going to do here is you can see that as a default what raz wants to do is it wants to take the elevation on the left and interpolate it over to the elevation on the right and create a new polygon that represents that in this case that's exactly what we want to do because we're basically just replacing that original crest elevation which should be the same and it is on the left and right over banks and so i'm just going to go ahead and press ok and what we're going to see what about the what about the side slopes man are you getting to that yeah i mean so again sideslips are one of those modification tools that you can you can modify in this case i believe when i created this modification layer um it did a pretty good job of representing it just as the default side slope so i didn't have to modify it but that's kind of again one of those one of those many options in that modification tool that you have the ability to touch on right right and what i'm gonna do so let me go ahead and re-display this so it's a little bit easier to view and so you can see now that i've added that uh high ground line in it does a really good job of replacing that in fact like chris said the side slopes seem to match really the damn shape overall very very well so i'm happy with that modification there so if we were for instance to set up a 2d model of this area and we would have make sure our cell faces were aligned to the crest of this dam we would get water impounded behind this this dam here um until it would over top and that was kind of the goal of the exercise yeah so ben it almost looks in this view like you've created a bridge deck versus a dam that feels all the way to the bottom and and i assume that's just kind of a graphical thing it actually does extend all the way to the bottom right yeah so if we again anytime that you want to explore what the elevations in your terrain are you can always select the terrain that you want to explore and then just hover over it and get an idea for what the elevations are here so you can see that if we go to the edge here where chris has talked about it looks like there's a bridge deck we do have a pretty serious drop-off so we go from about 1596 down to 1543 so we do have a 50 foot drop off here on the edge um and so again that's not a perfect representation of what this dam looked like there was likely some a more gradual dissension here but for the exercise that we're looking at today where we just simply want to replicate that damn breach analysis uh this is this is going to be fine so you got it you have slopes coming down from the crest down to a point and then it goes straight down vertical correct yep gotcha okay yeah and i believe you wanted to if you wanted to extend those slopes you just go back to the editor and um change the how would you change that yeah so you come down here um again the if we want to go into each one of these so you can change the top width which is going to change the the width here that you see in this x in this cross section view you can change the left side slope and the right slide slope which is going to adjust the slope here and then the maximum extent width which is going to be the maximum width that you want to to modify um on either side of your top width so that's the limiting thing right there correct yeah so if i handed this out i made this 200 feet we looked at what this looked like you can see there we go yeah slope down okay um again we could also if we wanted to see how far this actually needs to go to tie into the channel it's probably going to be pretty far but let's go ahead and make this 500 feet and see what that looks like you can see that at that there you go yeah a little bit a little bit better so and you might play with the slope a little bit to line up the um the elevations because there's a little disjointedness going across there but um yeah that's cool yeah so again you if you were um really focused on replicating the existing or at the time existing structure um you could spend you know a good amount of time uh adjusting this let's see so in this case i want to make steeper so no that i think that's shallower yeah try one and a half yeah thank you see this does if we adjust this down it's actually fixing it in real time that actually looks really good on the downstream anyway maybe the upstream might might need a shallower slope sure so yeah this that chris i think that's a good little exercise there and you know not only just adding that terrain but tying it into the existing terrain yeah so that was a good idea to do that again for a damn breach analysis and i'll show you guys the extent of this 2d model for a dam breach analysis the size of what we're doing you know the the the side slopes on either side of this dam aren't going to make too much of a difference at all to the to the final solution especially given the fact that you know this is going to be represented by an essay 2d area connection in which water is going to be passed through this high ground feature based on our dam breach opening not necessarily the side the existing side slopes of the dam here so yeah i know that that you did this just you know as a way to demonstrate the terrain modification but in reality you could set this up even without modifying the terrain just putting an sa 2d area connection across there but it wouldn't look as fun it wouldn't look as cool no doubt yeah exactly and if you wanted to just simply analyze how this damn impounded water over time you know this is like this is a good way to do that as well so that that's a that's a good highlight of what the terrain modification tool um you know can can add to a to a model into an exercise next what i wanted to do is i wanted to set up um the dam breach analysis using a large 2d model so let me go ahead and open up the geometry of what that looks like while you're opening that up the another thing you could do is take out the highway embankments too kind of using a instead of filling in you can actually remove material with this modification my guess is back in 1897 or whatever it was that highway probably didn't exist there uh or certainly not to that size so you could even take that out to get even more accurate yep yeah definitely yeah a lot of the lighter that's taken in obviously the last 10 years isn't going to reflect what the existing conditions were in 1889 so there's there's uh almost unlimited number of modifications you could do if you wanted to right yeah um all right so this is the 2d model that i added for this exercise you can see what i've done is i've created two separate 2d areas i have this downstream johnstown here and then the upstream johnstown here the reason i separated them is one i wanted to have that sa2d area connection um that represented the dam uh that connected both of the the 2d areas in order to in order to have an existing water surface elevation upstream of the dam because at the time of the large precipitation event in 1889 there was standing water behind the dam there was a reservoir that was what that was present and if we had made this a single 2d area we wouldn't be able to start with an existing water surface elevation in this upstream 2d area we would have to fill that up over time and so in order to start with the water surface elevation that represented what the reservoir may have been i split this up into two 2d areas the other reason i did that is i wanted to add precipitation to this 2d area and not necessarily this 2d area now in reality as we know and for this event there was undoubtedly rainfall that occurred on this downstream 2d area preceding the the dam breach itself but anytime that you have a rain on grid 2d model that's going to be a significantly computationally intensive model because every single 2d cell here is going to be receiving water and therefore it is going to be requiring computation time and computation power from your computer and so in the spirit of expediting this model as efficiently as i could i just simply had one 2d area receiving uh 2d rain on grid and then the downstream 2d area i simply had downstream or upstream boundary conditions that had uh water coming into the various tributaries here uh going into the town of johnstown so that was the general model setup that i had i did spend some time adding some refinement regions to represent the channels you can see and then we had that essay 2d area connection that represented the dam itself so if we look at a few videos of what the results of this was let me go ahead and pull up a few videos that kind of capture what this uh danbridge event looked like and if we had more time i'd love to get into what we used for danbridge parameters and all that stuff but we have some other really good content that we want to share with you guys today so we're just going to show some of the results from this damn breach analysis you can see the rain on grid artifacts over there on the bottom right all the the fragmentation that's classic for a rain on grid model yep yep exactly and so every single cell again in that 2d area is going to be receiving flow via boundary condition of precipitation and therefore it's going to take some some computational power to to run that model so what i'm going to do is i'm going to show results from a traditional razz mapper output sense so we're going to look at you know if we were using raz 5.07 these are results that we could view um and then they'd be helpful to understand kind of what happens when the dam is breached how that impacts the downstream areas and then i'm going to go into the 3d viewer and show how that can really enhance the presentation of results from an htc ras model particularly a dam reach model of this size so first let's go ahead and watch this video which again represents uh the radon grid occurring in the upstream basin we have inflow boundary conditions representing these two tributaries and then the town of johnstown is right here you can see the town of johnstown obviously is much larger than it was in 1889 but nevertheless as we see that breach wave moving downstream i keep in mind that when that arrived at johnstown just the devastation that occurred when that happened so you can see that with that dam breach begins i'm starting to move downstream and this is it really i think it took seven seven to nine minutes to reach johnstown from when the dam was breached so not a lot of time uh for any type of emergency action plans not that there were any at that at that time do you have a do you have a sense of the distance that is from the dam to the town yeah i'd have to hop into erasmus mean yeah it can't be that far for seven to nine minutes that is that's a quick arrival time yeah oh you can see did this yeah sorry go ahead oh no go ahead chris i was going to ask did this happen what time of day was this middle of the night during during the day i believe it was in the afternoon like one or two in the afternoon okay yeah so there were there were people on site kind of trying to mitigate against the impending disaster at the dam but it got to the point where they realized there was nothing they could do and at that point it was too late so here's uh here's another video of again just kind of a traditional rasmapper output really of the town of johnstown itself and you'll see that breach weight moving through and just how devastating that would be uh if you were related so yeah a serious serious serious event so that's the traditional rasmapper output from this i also wanted to look at what some of the 3d output for this would look like and so this first video is going to be just a a stagnant video of downstream of the dam so you can see that in the new 3d viewer you have the ability to pan around and and pan around the terrain and look at the results from a 3d standpoint we actually wanted to do this live with you guys but because of the fact that when you share a 3d video or i should say a 3d output over a recording it really slows down the processing um it would make it unwatchable so we we decided the best way to do this would be to show videos of kind of what that 3d rendering looks like if you want some more information on how to move around in the 3d viewer what that looks like please look at our last uh vodcast episode episode 14. we had a couple people from uh hec actually come on and talk us through what that 3d viewer looks like and how to utilize it so that i highly encourage you to use that video if you want more information on the 3d viewer so this video again is shows basically just downstream of the dam so we're going to kind of zoom down here this is the looking at the uh face of johnstown dam from the downstream direction you're going to see as that breach occurs the downstream water surface elevation increasing pretty drastically we see a dropping of the downstream water surface elevation and those really high velocities that are that come with the dam bridge analysis and it's you can see clearly that the model does not actually show a breach in the dam so in case anybody's wondering about that it won't modify the terrain during the simulation but um it definitely did breach you can tell so that that's a an example of a somewhat static point of view in which you can view 3d output you can also create what are called flight paths in 3d where you set a specific path that you'd like the camera to take over a period of time and that can either be if the result you can have the results being held constant so at a single time step and you can kind of fly around to view the results or what i've done here is i've created a flight path so our camera is going to kind of follow a specified path at the same time that the dam breach wave is actually moving downstream so we're going to be kind of chasing uh the dam breach moving downstream it's a little uh little indiana jones-ish for those of you guys of the generation that watched indiana jones so so again you can see the 3d viewer here we're starting up a very high elevation you can see our downstream reach here the town of johnstown is down here in this location and what we're going to do is we're going to zoom down so we're a little bit closer to the water surface elevation and then we're going to kind of just follow the dam breach as it moves downstream so looks like the elevation is exaggerated a certain amount to kind of make it show better right yeah for sure so again you can see it moving downstream and you're going to notice the dam breach pop here right as we cross over that dam and then we're going to kind of chase that breech way moving downstream and again this is this probably took me 30 minutes to set up um but it's an extremely powerful way to display results um of any hydraulic model that you have but particularly a dam breach model if you have a client or if you have you know if this is part of an emergency action plan that you want to develop some some material for those that could be affected to understand the significance of a dam breach this is a great way to to do that then we're right over the town of johnstown you can see how inundated the area is and then moving downstream into the the canyon area downstream of johnstown where there isn't quite as much flooding this is really awesome ben really cool looking i i would uh i just want to point out too because i've done a little tinkering around with the 3d viewer and just be aware it's it takes a lot of resources to run this 3d viewer on your computer so a few things to think about one uh you might want to before you get into it just do a reboot of your computer just to clean out everything get all the junk out and then just start up open razz run it from your local drive don't try to do this over a network drive or on a shared drive that's just asking for trouble so do it on your local drive and make sure you've got enough hard drive space too because it does crank out a lot of gigabytes when you're doing this so just be aware of that um it's new so it has some quirkiness to it but it's super cool as you could just see from what ben showed yep and i'm sure you know like anything hcc releases in future versions that'll continue to be improved and and refined so yeah just be patient with it but if you take some time you can really create some cool output from it yeah yeah that's really cool i can see us using that more and more with even just regular project work just like you said it's it's great for demonstrating to the client because people who aren't hydraulic modelers don't necessarily understand how to interpret even just a regular velocity map certainly profile lines and cross-section plots are a little bit hard for them to understand exactly what's going on sometimes but when you can show the view as if you were a drone flying over um a dam failure like that um that's that's really powerful powerful way to to communicate what's potentially could happen in a damn failure so i just want to provide some clarification information here because i've looked up um some of the details about the breach wave so it was seven to nine minutes before the breach wave hit the first town but that wasn't johnstown that was south fork it took 57 minutes for the breach wave to reach johnstown so that distance probably is a little bit longer i think the flood wave was traveling roughly 40 miles per hour yeah and this is all estimated based on modern dam breach analysis so somebody else has probably developed a damage model similar to this one um and they estimate that the flood wave reached 60 feet in some places significant significant event so they did have an hour to potentially alert the town but again in that day and age it was tough to travel that far in an hour so yeah there's a lot of really interesting history too about that that dam and the actual event that um if this interests you at all i would highly encourage you to get on and do some research and reading about it probably just start with wikipedia and go from there but um yes it was very interesting how that happened and what happened afterwards yeah and there was like like many instances where you have damn breach removal or or failure there was so much sediment released um that you know most of the town was covered in sediment there were a number of bridges that had to be basically extracted with dynamite in order to remove all the sediment and carnage around them so it was yeah a big pain from a cleanup standpoint but obviously even more significant from a loss of lifestyle yeah yeah i still have not gotten out there but it's on my bucket list next time i'm in the area i'm gonna make a trip out to johnstown and check out the memorial and and just see what's what's going on out there uh i have been out to teton though teton dam and what's left of that and that's that's pretty cool one um if you're out in the area to go swing by and take a look uh you get a really nice overlooked view of what's left of the dam and a little bit of history there too so but um anyway that was really good ben thanks for sharing that um i always like doing stuff like that you know finding an interesting historical breach and even though it's not necessarily a project but um you're able to put razz to the test see what it can do um and get some pretty cool graphics out of it too yep yeah obviously nothing nothing was cooler than the missoula flood one that you did chris so we're all we're all playing for a second oh man i got some more work to do on that one too so um stay tuned but um anyway cool well hey since we're talking about danbridge modeling why don't i do a little quick overview about how you go about setting up a hec-ras dambreach model uh for those of you who might be new to it or thinking about doing it um let me get this this powerpoint started real quick quick and then i'll demo in the software itself but um i tell you even even with three screens ben i still have trouble managing all this when i'm doing um presentations yeah it can be i think i need four screens although you know to give to give you a little bit of credit i'm sure having done this over the last year you're you're much better at it now than you would have been a year ago so much more comfortable with it yes that's for sure but still run into trouble here and there so what we're looking at here is what i would call the scope of a hec-ras dambreach model you start with the hydrology if you have any if you're doing a flood-loaded breach for example say a pmf coming in you need to know what the hydrology is you need to do a little bit of work up front that's not done in the raz model now ben showed an example of rain on grid and so that in a sense is a way to add some hydrology to your razz model directly without computing it external but if you're talking about a pmf flood and you want to route it through your watershed and have a really good hydrograph coming into your reservoir you would do that external to raz maybe with hms or something else and so that's the first part that's the upstream and then you've got your reservoir and this is um a large volume of water that we're going to effectively drain during the simulation in the hec-ras in raz you can model your reservoir either as a storage area as a one-dimensional reach or as a two-dimensional area all three of those are available to model a reservoir and they all have pluses and minuses to them i'll talk about that in just a second then we have the dam itself and this could be an inline structure if this is an entirely one-dimensional model it could be um a sa 2d area connection if it's a 2d model either way you could put a breach in it and with that breach you would prescribe some breach parameters okay and these are up to you to determine although the software is now evolving to a point where it can actually compute these breach parameters for you on the fly based on the loading the hydraulic loading on the dam as well as some of the makeup of the dam itself and i'll show you some examples of that in just a second and then finally we have the downstream routing reach and so this is where all the most of the action occurs where you have inundation you have damage you have consequence and life loss and so this is a very important piece of it but this is also the hardest part of your model to stabilize because this is where you have all of the sudden change in velocity all the extreme acceleration as flow is moving through the reach as well as a lot of times this downstream reach is either very shallow water or could be completely dry if you've got an ephemeral stream and this is a storage reservoir it may be completely dry if you're trying to do that in 1d it can be really tricky 2d is a lot easier for shallow or dry conditions to model because it uses that finite volume solution scheme so this is kind of a generic scope or setup of your model now the next question you want to ask yourself before you actually build your model is do do i want to make the reservoir a storage area do i want to make it out of a 1d reach with cross sections or do i want to make it a big 2d area all three of those are available in heck razz but as i mentioned they have their pluses and minuses the storage area is simply just a level pool that goes up and down there's no hydraulic gradient established in that storage area there's no communication of velocity there's no travel time communication through that storage area because it is just a level pool but the advantage is it's very simple to use it's simple to add into your model all it requires is a stage storage curve and off you go you connect it up with your your 1d reach going downstream from that and you've got yourself a dam reach model so the way it works is you've got a q coming in a discharge coming in at a given time step raz will look at that stage storage curve that goes with the storage area and using that q it picks up it um it picks up a new or sorry measuring the amount of q comes in coming in gives you a new volume so it goes to the volume curve figures out what that new volume is gets the stage that goes with that volume then it looks at the downstream control whatever that is in this case it's going to be your dam it could be gates at the dam it could be the weir or the spillway with the weir equation or it could be a combination but it looks at that and figures out what the stage discharge relationship or the rating curve is there and so knowing the new stage it can now pick off the outflow cue so you've got an inflow that translates to a new volume that translates to a new stage which translates to a new cue out and this is all done in one time step there's no in a storage area no travel time through here yeah that's a good explanation there chris yeah thanks and then let's say you want to do uh your reservoir with cross sections you want to build it with cross sections why would you want to do that well what cross sections can do for you is it can set up a hydraulic gradient and this could be very pronounced especially in a dam breach model in a typical reservoir routing model where we're not breaching the dam but we're just routing flows through a reservoir level pool will work in more cases than it would in a dam breach model because with the dam breach you have a sudden opening in the dam and a quick release of water and that sets up a significant hydraulic gradient and a negative wave that moves upstream which would not be captured with a storage area so you'd want to model it with one-dimensional cross-sections or a 2d area now a 1d reach like you see here is going to show that gradient in the direction of flow along the axis of the reservoir so you get a gradient in this direction but because cross sections only get one water surface per cross section per time step you don't have any gradient laterally okay so that's the limitation of 1d is you only have the gradient in the direction of flow through the reservoir but in this case what it does is it actually runs your conservation mass and conservation of momentum equations and it determines q your q and your h your discharge and your stage at each one of these as it progresses through the reservoirs it's routing through the reservoir okay now for a 2d area the reason you might switch to a 2d area is because you've got considerable lateral velocity components okay it's not just a gradient in the downstream direction but you have gradients going laterally as well and those can be picked up with a 2d area now the 1d reach and the 2d area um are pretty both fairly easy to set up provided you have terrain or bathymetry more specifically so you need to have bathymetry in the reservoir or what's the the topography below the water surface in order to cut these cross sections or to extract onto this two-dimensional area without that you are either stuck with the storage area method because all it requires is the elevation volume curve or you're going to have to synthesize your own bathymetric surface and there's ways to do that but you're never going to be perfect with it so that's one reason why you might switch to a storage area if it's appropriate to use a storage area it's not always appropriate but as far as setting up it's pretty easy you just draw your cross sections covering the reservoir like you see right here now if you have a pretty complicated looking reservoir a lot of fingers coming into it then you have to get a little bit tricky with how you set up junctions and that might actually bump you into doing a 2d area because with the 2d area all you do is you simply draw your 2d area around the reservoir you add a dx and a dy for your cell spacing and you've got it right there so it's this is a lot easier to set up than cross sections in my opinion but it's also more computationally intensive as well so they all have pluses and minuses now when you're talking about developing your breach um i usually start with rules of thumb to kind of get me in the ballpark uh as far as what's the breach with what's the side slopes of the breach how long does it take to form things like that that can all be determined at an initial level with these rules of thumb here you see three different agencies and actually the core of engineers which is this usage one has two different methods from two different years but you've got the core you've got the federal energy regulatory commission and the national weather service and they all sort of are relatively similar slightly different but you can see you've got your breech width you've got your side slopes and you've got your time to failure or your failure time actually this could probably better be described as your breach development time is it fair to say to chris that given the fact that the corps of engineers came out with new guidance in 2007 that they wouldn't advise using the old guidance from 1980 honestly i don't know i don't know the difference and i don't know what prompted this update and whether this is thought of as better um i would make the same assumption ben it looks more conservative i mean the average breach width is larger the failure time is lower so that's right more conservative yeah my guess is maybe there's been some more research done since 1980 and they figured out oh you know what earth dams can actually fail faster than a half an hour now a lot of that depends on the size of the earth dam how high it is and what kind of material it's made up of but yeah i bet you're right there but you can look at earth dams concrete gravity dams concrete arch dams these are all going to fail differently because they're constructed differently and they have different strength properties the archdam is interesting because once you lose the integrity of that arch you develop a little bit of a crack in it it loses all of its strength because the con concrete archdam is held in place not by its weight but by the arch itself so the arch translates all the force of the water behind it out to the abutment walls and once you lose that arch the whole thing comes down and that's why you see the average breach with is the entire dam or almost the entire dam and the side slopes match the valley wall slopes and look at this the failure time is extremely fast less than six minutes um because hey once you once you lose the strength integrity that thing is coming down and yeah maybe maybe you've seen that uh that um old superman movie right with uh christopher reeves you ever see that ben yeah that's that's your a you're aging yourself oh my gosh i can't believe you haven't you got to watch that movie because they have one of the the best dam breaches ever and it was of hoover dam which is an archdam um and you can you can see the whole thing crumble really quickly now i'll just warn you ben when you watch the flood wave move downstream in that movie it is pretty hokey and certainly doesn't have the uh um the cgi effects we have of today's movies but it's still kind of fun to watch anyway as again each modeler it wasn't as accurate as what we can produce with brass bueno raz mapper the 3d viewer now you would do better yeah we would do better with the 3d viewer with an aerial image behind it than what you see in that movie it it was basically it was a miniature model that they built and then they slowed it down to try and make it look like a full-scale event and you can actually see you can see these little miniature cars [Laughter] anyway it's yeah it's pretty hokey but um it does give you a pretty decent idea of what would happen if you know an archdam were to fail but anyway i highly recommend you take a look at that movie then i can't believe that that's one of the great movies of all time too by the way i think this is i think this is turning into maybe a free movie discussion before our next modcast we'll have to do that yeah the next one we'll have to come with some movies you know maybe some water related movies yeah you know we could do we could do like a top five movies that have damn failures in them or flooding events or something so yeah yeah absolutely all right so this is where i start start with the the the rules of thumb and this like i said get you kind of in the zone in the ballpark and and let you know where about where you should be you can notice that that a lot of these are just ranges right but beyond that then oops i'm having trouble with my slides here let me just advance one beyond that you're going to have to figure out breach parameters using regression equations and those apply to earth embankment dams concrete dams unfortunately you're stuck with these kinds of tables the rules of thumb and common sense but if you're talking about an earth pill or rock filled dam you can use regression equations and i want to introduce this td 39 document right here so if you're going to do damn breach modeling especially in heckras get this document it's td 39 using hec-ras for dan break studies you can get it right off of the hec website just search for that or you can go just google td-39 it's going to come up um but in here you've got not only that table i showed you with the rules of thumb uh see how quickly i could scan down to it uh it tells you everything about the process there's the table i was just showing you but it also has regression equations in here like you see right here okay and so these regression equations in this case we've got breach with here we've got failure time as well and you can see several different methods are in here and they all have different ways of computing it now there's some that are used more than others the frolic is very popular he's got two methods 1987 and 95. uh similar to that discussion we just had been i would probably gravitate to 95 stuff more but you've got uh mcdonald and language monopolist that's another common one that i see people von tuntun gillette is another one so these are all um equations that you can use to narrow down on your breach widths and formation times in side slopes so definitely recommend you look into that and they have descriptions of each of those down below so here you can see frolic and so forth so what that's going to do for you is it's going to allow you to fill out this table right here under the unsteady flow analysis window options dam and levy breach and here you can see we've got our breach parameters on the side breech width side slopes and formation time you can get from those regression equations the others you have to use some common sense maybe an understanding of what what's out there on the site like the final bottom elevation usually you set that to the foundation of your dam okay so that's a good way to fill out this table but again some of the stuff you're going to have to use some common sense on so let's go through these breach parameters this center station just defines where the center of the breach is you can see the breach outline in red the dam the normal dam is in gray once you run this model you'll actually see in the cross section viewer you can see this breech grow to its final shape which is the red line then you got the bottom width down here be careful because a lot of these regression equations they'll compute the average breach width so when you get that you have to convert that to the bottom width using the side slopes and the height of the dam little geometry and then um you got your bottom elevation down here you got your side slopes left and right and the breech weir coefficient that obviously doesn't show on the graphic but this is the c value that's used in the weir equation just for the breach itself not for the rest of the dam but for the breach opening itself that's the weird coefficient 2.6 i think might be the default value uh you can make a case it's probably not going to be a very smooth and efficient shape going through there so your breach where coefficient is probably going to be a little bit lower than a standard coefficient you'd use for a constructed weir that would be an important one to do sensitivity yes well in all of these as a matter of fact you would want to do sensitivity on yeah but yeah breach coefficient especially because there's there's so much uncertainty there um and a breach formation time how long does it take for it to go from no breach to grow into this final shape that's the 3.2 hours there okay now you have us you have an option here you can either do a piping failure or an over topping failure a piping failure is this as if you get some internal erosion somewhere down below the crest usually it starts down lower and that erosion starts to bring material out from the dam and opens this this hole this orifice through the dam that's called a a pipe which is why it's called a piping failure and that pipe will grow and grow and grow until eventually you get big enough that the top collapses down and you've got a fully opened breach so that's the piping failure mode over topping starts at the top it's like if you get a hydraulic or hydrologic flood event coming in say a pmf and that raises the reservoir faster than you can drain it through your spill your emergency spillway or other outlet means and it starts to over top and then erodes from the top down now if you select piping you have to provide a piping coefficient because raz uses the orifice equation to simulate flows through the pipe until it fully forms the breach and at which point it will switch to the weir equation then you have to tell it where to start the the pipe at the very bottom do you start near the top somewhere in the middle nobody really knows there's a lot of uncertainty with that so definitely do sensitivity on where this pipe occurs and then um finally you have to tell raz when to start breaching it what's the trigger what initiates the breach here we see we have initiated it based on a water surface meaning as the water rises once it gets to 676.8 that's when the breach starts to form so it starts this 3.2 hour clock and it will form the breach over 3.2 hours another way to do it is by water surface elevation plus duration so once you get up to this elevation it's going to run its own clock and once you exceed the duration which would be another input for that then it starts to fail so this kind of communicates that hey i think my dam can take a certain amount of over topping before it finally starts to erode and that's that's usually the case so i like using that water surface plus duration and then the third method is just by time basically you say hey at this time in the simulation this is when i want you to start the breach and that's going to be more used for sunny day failures where you've got no hydrologic loading the water is just at normal reservoir pool elevation and you're just going to breach it and so you just provide a time somewhere in your simulation to have a go all right so now you've got your breach parameters in take a look at this breach progression you have two automatic entries linear and sine wave right here you see the sine wave and this this actually tells raz at what rate to grow so we have the time it forms but this tells the rate and so here you can see it starts off growing slowly and then it speeds up its growth here and then it slows down again and that's the sine wave curve linear is just a simple linear line across here uh nobody knows what your dam will will follow when it fails so i always suggest people try both of these although the sine wave does kind of make sense to me it seems like the sine wave would maybe be more tied to like an urban embankment failure where you're going to have piping or over-topping failure as opposed to a concrete damp failure where it's just gonna go you know yeah yeah maybe that's not maybe that's not reasonable i don't know no that's so that's a really good point that makes a lot of sense too um those faster breaches probably are more linear but yeah nobody knows so try them both and and see which one gives you the the highest discharge for conservativeness or this is a plug for probabilistic dam breach modeling which is another discussion we can have but you can work this into a probabilistic dam breach approach and i give tons of presentations on that so if you're interested in that just google it and you'll see stuff all right so i'm going to quickly go through these other tabs i don't want to get into too much detail but if you'd like to have raz compute the breach for you rather than using these breach parameters you can go over here and you can select from two options the simplified physical which is right here and you're just providing a velocity and down cutting rate relationship this is another thing you don't know what this will be i mean there is some guidance on it but nobody really knows what your dam's velocity down cutting rate relationship will be um until it actually fails so you just kind of have to take your best guess there this is why i don't like using this too much but it is there people use it for levees more than dams in my experience the next one is this physical breaching dl breach this is brand new to version six and this actually will compute your breach based on the makeup of your dam and so you put in things like your embankment width and slopes and then even some soil parameters and what erosion model you want to use you can even put a cover layer on top of your dam and have a different description of that so this is pretty slick i've not had a chance to use it yet so i can't demonstrate it but you can google dl breach and read more about it dl breach is actually developed by um weiming wu from the from clarkson university and so just google it you'll find this information here if you want to learn more about it does it just take your input parameters and select which equation to use to calculate based on your input parameters or is it a single equation that can take all this information and to estimate a damn breach size yeah he's he's got his own equations that he's developed okay and i have not so this is all theoretically based yeah i don't know what went into developing this because i've not read up on his stuff yet but i want to do that but if i know if it's like the stuff that the agricultural research service has done ars and their um wind dam model or or national weather service breach hr breach um h.r wallingford is the company that put that out um they all kind of have a mix of theory and some um some actual real world prototype measurements that they've kind of worked into their into their equations and their methods but i don't know what's inside this black box so give it a read if you want to know more about it and see how it goes then we've got if we go back to the user enter data you've got the ability to calculate those regression equations right here in raz it'll save you a little bit of time of setting up a spreadsheet and doing it yourself and so you can see the ones we have here mcdonald frolich fontune xinjiang uh it just requires some input data here and then finally we've got breach repair that nobody uses um actually it's there i think it was put in when they were trying to do some model simulations of hurricane katrina down in new orleans when all those levees were breaching and they were trying to actually repair them in the middle of the breach event by dropping these giant sandbags in so i think that's why that got put in there so they could simulate that event but in reality nobody's going out trying to repair a dam in the middle of it failing um so well i have an example chris so uh on the spokane river um i don't remember when this was uh it had to be at least 30 years ago there was a breach of one of the dams uh on the upper spokane river and the failu it started to fail and they were worried about the whole damn cascading and so the story goes at least this was from a damn operator who we talked to when i was in school in spokane and he said they basically called up every contractor in the greater spokane area who had a dump truck and had every one of them loaded up come come out and they drove out on the on the dam crest dumped their jump truck load and they apparently filled the gap and it didn't it didn't fail so uh again that may be a little bit of a forklord legend but the guy he was a damn breach or a damn operator for a number of years so um there's probably some truth to that so this would be a good example of when to use that wow yeah i've not heard that story i hope i hope those dump truck drivers got um danger pay for that can you imagine yeah how much coaxing it would take to have them drive across that dam crest as it's failing um wow yeah that's crazy uh but yeah so i suppose if you do have a situation like that you can make use of this but you know i i've never used it for an actual project before but i've played around with it for fun we used to do it in a workshop that i would give for danbridge modeling um but anyway that's that um just really quick um a couple things to think about when you're doing a damn breach modeling all of the action is going to be downstream of the dam it's going to be very unstable potentially so think about adding more base flow in there to help stabilizing your to help stabilize your model add higher end values you're going to have a lot more turbulence so you can justify and higher end values give you higher stage which gives you more stability and then the other thing i want to mention too is definitely turn on mixed flow especially if it's a small stream downstream of the dam because mixed flow is going to help smooth out instabilities at the front of the flood wave where you've got this uh near critical or even supercritical flow that tends to happen there so so definitely look into those features and and like like anything if you're increasing maintenance values adding base flow turning on mixed flow those are all good things to do to get the model stable but then try to back off some of those and bring them back into uh i guess a more accepted or normal range for mannings uh the known base flow for flow yadda yadda um you know you always want to stabilize your model and then slowly kind of try to bring those parameters back to a defensible position and then if you're having issues with instability you can there might be something underlying that's causing that yeah that's that's the key word there ben defensible i'm glad you brought that up because anytime you are putting in a parameter into raz you have to be be ready to defend that to whoever's reviewing it and if you're using n values in your routing reach of you know 0.5 you're going to have a hard time defending that value even if it is a dam breach model 0.05 now okay that's more dependable um probably you could use something higher even than that up in the 0.1 range maybe right below the dam itself during the breach but yeah you have to defend everything and then finally i want to leave everybody with this uh finite volume solution scheme for 1d if you're doing your damn reach model in 1d and you're having lots of stability issues because you've got really shallow depths and then a big flood wave dumping onto that this finite volume solution scheme has some potential to take care of that problem so take a look at that read up about it um basically one of the big benefits of finite volume is you can go completely dry in your 1d reach now with that solution scheme if you opt to use it but even if you're not going dry it gives you much more stability at low stages especially when you've got a big hydrograph coming in on top of that so awesome yeah well thanks chris that was a that was a great little summary of kind of how to start dam breach analysis um again there's a lot more information um that we could could talk about when it comes to damage analysis a lot of nuance again if you can model a dam breach now a dam bridge event you can model just about anything because of how dynamic the event is so that's right it's a great thing to learn how to do and if you're interested in learning how to do it chris and i have our next online 1d2d modeling htc raz class using the new 6.0 version coming up next week we're starting on may 12th wednesday may 12th the class is going to run for six weeks so i believe that brings us to june 20 june 30th i think is the last session um and it's basically the format of the class is one four hour lecture every wednesday from eight to noon pacific time it's eight a.m to noon pacific time um and then in between the lecture sessions we have workshops that all uh you guys can can do take basically what you've learned in the lectures apply them to actually using the model in software and then we get back together we review that workshop we answer questions about it it's a really really great way to learn we've had some great reviews typically chris and i had always taught this class in person over just a three day period so it was more concentrated but people seem to really really enjoy the spaced out class because not only does it allow them to really have time to really dive into the workshops and explore some of the new 6-0 features but um they seem to just pick up things better and remember things better after the class is finished so if you are interested in learning more about 1d2d modeling in hcc raz i would really encourage you guys to sign up for this class if you need more information you can email atcraz at clientsmakgroup.com we'd love to get many many people signed up for the class anything else on that chris no that was that was good ben good uh summary of that and there's there's still time to sign up but it is filling up so don't wait too long and we hope to see you there it's we have a lot of fun i mean it's almost kind of like this vodcast in a way it's very casual we talk about food we talk about uh sports and but more importantly we talk about heck rise too and we get you guys up and running for uh 1d 2d hec-ras modeling so come join us it'll be fun awesome all right well thanks everybody again uh for joining us on this episode of full momentum we really focused in on danbreach analysis both the historic event associated with the dam breach as well as kind of how to get started hope you enjoyed it this has been full momentum in hcc raz podcast thanks everybody [Music]

Channel: The RAS Solution

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Id: DUCZlCvMnaY

Length: 67min 52sec (4072 seconds)

Published: Fri May 07 2021