Advanced Modeling 2.5 - Land Cover Layer and Manning's N Values

what's the first thing that we all need once we have a hydraulic model is the end value you know i like to say that the hydraulic um the the hydrology folks the sediment folks the groundwater folks they have uncertainty all over the place you know our our equations are beautiful we're just strictly physics based except we put all of our uncertainty in one parameter the the n value right so we we need n values um in one dimension you just define them in your cross section um but you know this is two dimension is spatially distributed and so you're gonna want spatially distributed n values so this is what we're gonna do we're gonna kind of use we're gonna map our n values so that raz can adopt them in each of the cells the problem is is if you go into um raz mapper and look around for a place that says import n-value shapes or something like that you're not going to find it because the manning's n values are are part of a more general feature which is called land cover and so we're going to teach you how to create a land cover and then associate mannings and values with the land cover so this is what we're going to do in 15 minutes um i'm going to briefly tell you about the sources and then how to import a land cover how to associate the many against values and then how to modify it um all right so let's start with where do you get these data um because data are plural uh the uh there are two main places one is the uh the multi-resolution land characteristics consortium because it uh it's a consortium it must be cool um and uh here we've got 30 meter rasters um with complete coverage um and then the usgs also has some uh land use land classification data you can go in um and uh and look at the maps of your particular um area um and this is gonna be important because you're probably not gonna wanna draw there are going to be times you'll want to draw which we'll talk about later but you're going to want to have a base classification to work off of and so these are the data sources that you're going to go to the and really that's all i'm going to say about this because really you're just going to want to keep this slide around and have it ready for when you do that um so once you have these data well then we're going to import the land cover data into raz and you know i i am a mapper user and fan and i just think the i think that uh my team has done an unbelievable job essentially recreating a gis exactly for the like subset of things that you need it to do um but the language here i have found a little confusing so i want to make sure that you understand what's going on if you try to import a land cover data again you're not going to find that language anywhere what you're actually going to do is create a land cover layer and add data in one step and so we have the two things that you might want to do or the way i think about it the two things i might want to do with you know land cover data is i either want to import it from a gis file or i want to draw it the way that that gets translated into the language of layers is if you want to import land cover you're going to create a new raz layer because you're going to create a layer and then in the same step you're going to import the shapefile if you want to draw it you're going to create an empty razz layer because then it's just going to show up empty and you're going to get to drawing um and so we're going to in general you're going to just import these data so you're going to create a new raz layer okay and so this is this is the workflow um and the reason that i i want to kind of be explicit about the workflow is that generally in raz when you want to this is part of gary's design philosophy when you want to do something it generally you do it in order from top down or from left to right almost everywhere you are in raz that happens but because of the way that this works into the design it's non-linear you actually have to jump around the tree from like low to high to low in order to do what you need to do and so these are the steps you have to create a land cover layer and import the land cover data in the same step then you have to define the base n values then you have to associate the land cover with the geometry which is a step i almost always forget until raz very helpfully tells me hey you didn't do that and i go back and do it but in general um you're not going to be very happy with the the 30 meter land cover data that you get you're not going to want to build a hydraulic model on that you're going to want to add some resolution with some drawn polygons so we have this optional step of land classification polygons and then how often are our n values um good enough right out of the box i would estimate zero percent of the time you know the because all of our uncertainties in the n values particularly these spatially distributed n values of even ones that we put in ourselves are almost always wrong um and so you're going to have to calibrate and calibration is really intuitive in 1d actually calibration is never intuitive but it's more intuitive than 1d in 2d you're going to have to calibrate spatially and so um the mapper team has developed these really slick tools to help you think about that and uh and try multiple calibration reps um without going in and you know you know re remaking your entire um geometry okay so i think that the best way to do this right now um instead of a slide because the problem is with the slide is that because it they're distributed high and low it's actually hard to uh to show you spatially where this is in mapper in a slide so let me just walk you through the steps in mapper very quickly and then we'll talk about each one so here is the mapper tree um this is the chippewa this is the model sediment 2d sediment model i'm working on right now um and the first thing you're going to do is you're going to create a new layer which means that you're going to come into this process kind of two-thirds to three-quarters of the way down the tree um you could go to project and say create create a new layer land cover layer um but generally when you kind of get into razzmapper you're going to want to right click on the tree that's the way you generally interact with mapper and so you'll go to the layers you'll right click on it and you'll say create a new raz layer and you'll see we have lots of very cool types of layers that you can add some of this is for infiltration a lot of this is for sediment transport but you're going to start with the most simple type of layer a land cover layer and so i'll say hey i want to let i want to create a land cover layer and we say well you're not going to want to create a land cover layer without importing data so we automatically give you the data import window um and this looks a lot like the terrain import window because it's the same idea you can bring in multiple shape files now and we're going to concatenate all those shape files into one layer but generally if you've gone and gotten one of those 30 meter shape those 30 meter coverages um you'll go and uh and and get that and so i'm gonna go get my land cover data and that'll come in and then um what you'll see is that you actually have a lot of flexibility at this point you can change all this stuff later but at this point you know you get the the field names and the classification which you can go in and change we can say maybe deciduous is uh is not sufficiently um it's not actually decision deciduous it's actually conifer um and uh then you put in your cell size and then of course um when if i just want this to be called land cover i can do that but if i want to change the name i'll push this button as well um and so then i'm going to create it um no i don't want to overwrite i want to give its own name uh i'm going to call this class so then just like your tit we're going to create that and then it will exist and you'll see it came in we have a land cover and now i can go in and right click on it um right now we have no manning zen so now i can go right click on it and edit land cover data table and now we get the possibility to enter manning's n values and this is actually why we call it a land cover a land covered layer instead of just a mattings n layer is because you can also go in and put in percent impervious this has multiple data fields associated with it okay so back to the story you're going to create a land cover layer and import the data at the same time then you'll right click on it and edit the land cover data table and then um you'll associate it with a geometry but let's just go through those so you'll right-click and bring it in and the idea here is that land cover is just one type of a map or layer and it's not an n value table because it has multiple things under it um and so that that's one of the first confusions is how do i define an n value well it's going to be a land cover layer that also has other information in it um you get to make a bunch of modifications as you bring it in then there it is you've got a land cover layer you can change the the color scheme just like you would change anything else um then associating meanings and values you go in and you right click on your land cover layer and you can go in and you know define the the mannings then associated with each one okay so that's kind of the most basic functionality but the truth is is that generally that's generally fine for the floodplains that's basically what you want for the floodplains but for the channel itself it's terrible right like a 30 a a 30 by 30 grid you can see here's our favorite muncie um and uh is this likely to be the end value for muncie no certainly not um enough for the channel certainly not so the next thing you can do is you can go and add a lan classification polygon and this will allow you to do detailed channel work or any other kind of detailed work and so you um you right click so the the under the land cover there's this sub node called classification polygon you start editing that you can draw a polygon and select one of the classification types to override that polygon okay and so now here what we have is we've drawn the channel in muncie and then we've gone in and chosen the channel classification for muncie okay now the the channel portion of our 2d model has the kind of like polit vector resolution um that we that we would want for the the n values through the channel whereas we have this kind of course land use resolution for the overbank um this is imperative doing something like this is it you absolutely have to do for um for most hydraulic models all right and so then our actual n value classification has um has that and so then the next thing you're going to do is you're going to associate it with a geometry okay it's great that you have a land classification but the geometry is geometry is completely agnostic the geometry has no idea actually sometimes it does sometimes it guesses but generally the geometry has no idea that it's been associated with an that there's an n value map out there ready for it and so what you need to do this is where it becomes non-linear is you have to jump up the tree back to where your geometries are and you're going to right click on your geometries and say manage geometry associations now this is exactly the same thing you do with the train you know the geometry doesn't know which terrain is associated with it unless there's only one then sometimes guesses but that's the same thing that's true with all of these other layers um you can see we have a very special bed material layer here because the sediment transport model um content you get only because cam had to give me a lecture um but the uh the manning's n also it is the most common layer other than train that you have to select so you select here we've actually switched it i want to switch to class and now i've associated it with my with my geometry right so then back to the story at that point we've asso we associate our geometry with a land cover and now we can go into our geometry i think one of the things that i found i was working with an engineer just last week and when they wanted and find n values they go into their geometry they see manning's n and they want to kind of load it here but you can't actually do anything in this node that says manning's n until you do these other steps you create your land cover you tell your geometry to go look at it now it knows where it is and so now you can map your manning zen um you can uh you can actually like right click on the grids on the grid edges and look at what manning what manning's n does what composite meanings then does this cell face see um and you just have all sorts of access to the numerics um you can build your property tables um so that you can look at your uh your stage end value and those sorts of relationships all right and then you also have the opportunity for overrides um and that's where there there are a couple of ways that once you have your end values established you know at this point you're going to run you're going to go yeah i think i've done a great job with bringing in my end values and defining my channel um now i'm just going to simulate my model and it's hot it's hot garbage right like i'm i'm three feet away from any sort of high water mark um and so now it's time to calibrate um and so the uh that's where now we can introduce calibration regions if you look under that mannings and node now you can start with your calibration regions if i go back to my chippewa model um you'll see that uh if i expand my geometry and now i go look at my manning's n um i've got these calibration regions and for me the calibration regions are associated with you know some of my channel members but there you can um you can define n values associated with different geometries and different runs and adjust them on the production scale so you can go in and you can draw your calibration region and then it will give you um an additional an additional uh column that will help you they'll allow you to to override the initial manning zen values so you can do production level reps to uh to look at how how your results change with your calibration data all right what if i don't have any well if you don't have any you need to draw some you know at the very least you should probably draw a rectangle um but uh you if you don't have any um you're not going to you're you can um draw it based on the web imagery and if you're going to draw it you'll create an empty um and then go and use the razzmapper tools to draw all right

Channel: HEC RAS

Views: 11,088

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Id: k_3fpF-OWHo

Length: 16min 21sec (981 seconds)

Published: Tue Nov 02 2021