Updating NHD Infrastructure with Elevation Derived Hydrography—Alaska

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Topic: Building the infrastructure for updating the National Hydrography Datasets with Elevation-Derived Hydrography – Alaska leads the way

Presenters: Steve Aichele, Geographer, USGS User Engagement Hydrography Focus Area Lead, and Amanda Lowe, Supervisory Geographer, USGS Topographic Applied Research Section Chief

Abstract: The completion of Alaska statewide high-resolution IfSAR elevation data in 2019 created the opportunity to derive products, like hydrography. Since 2019, the USGS has been working to build the supporting infrastructure, including specifications, contracting language, and contractor understanding of requirements. Also, under development are processes for data inspection and data management, and tools for data validation, improved conflation, and updating the National Hydrography Dataset (NHD) and the Watershed Boundary Dataset (WBD). This presentation will describe some of the underlying documents, processes, and tools employed to facilitate elevation-derived hydrography development to update the NHD and WBD.



Date Taken:

Length: 00:46:40

Location Taken: AK, US


I'm Steve Aichele. I'm the user engagement focus area, lead for hydrography and I'll be talking about some of the infrastructure. Will be we've been building for updating the NHD with elevation data, ably assisted by Amanda Lowe from NGTOC. So for those of you that have been tuning into this community, call for the last eight or ten years. You know we've been talking about elevation, derived hydrography, previously, elehydro for quite a long time. This goes back to probably about 2010 or so, maybe even a little before that. Jeff Simley was the initial advocate for it on the last few years we've been really trying to build the structures and find some of the pitfalls associated with trying to standardize those acquisitions to leverage our 3DEP data. And we've been fortunate in that we have had a steady funding stream associated with mapping Alaska that we've been able to leverage to do some of that developmental work. It's also real benefit for Alaska, you know, for many years, mapping Alaska was kind of a second thought, an afterthought. And they had by some of the worst elevation and hydrography data anywhere in the country up until we start remapping them about 10 years ago. But with the completion of IfSAR are up there and you know some of the governance structures we've been able to build through the Alaska Mapping Executive Committee and the Alaskan Mapping program. We've been able to launch this elevation derived hydrography update process in Alaska, and I think the experiment has been a very educational and building the basis to launch this program in CONUS going forward. Oh I hopefully I don't have to elaborate too much on to the national hydrography data sets, but they they need these datasets even in their current form provide a lot of benefits estimated about $538 million in annual benefits, largely through cost savings to state and local governments in. And this is back in 2016 when we did the HRBS. An updated modernized 3D hydrography program that actually it addressed, actually aligned with the  3DEP data could actually provide up to over a billion dollars a year in annual benefits to users. Depending on exactly how that program is configured, and that's some of what's being what Becci's been working on in the program plan and call to action that she's talked about a couple times. So many of you are engaged in our current data management approach and it's been very much a collaborative effort. Working with Joel Skalet, and the Partnership support section. at NGTOC. We've had stewards and data editors across the country updating what has been based on the 1:24K scale line work in a lot of places that's been improved, a lot of places. He hasn't errors in that date have been fixed, and currently includes almost eight and a half million miles of stream network and 130,000 you know nested hydrologic units the the HUCs and WBD. And I think maybe the most important thing that that local stewardship brings to the brings to the table is knowledge about how some of these local systems work. You know they're particularly in some of the lowland areas. You can look at that in an airphoto or elevation model, Lidar Point Cloud. And it's just not at all clear what's going on in that environment, and you really need to have some idea how that local hydrology works and what's going on on the ground. to be able to make meaningful edits or updates to that data. Unfortunately, one of the drawbacks of this stewardship program is that really, the updates aren't very uniform. In some places this data has been updated regularly and some place have been done very well in some places that 24K data hasn't really been touched, which means that 24K data is largely the same blue line data that was collected when we surveyed those maps may be back in the 60s and 70s, and so there's some real questions about that the quality of the data. You know the variable data quality across the database, and much of that older data doesn't align at all well with this shiny new 3DEP elevation data. I'm really at this point in time. People are people expect those datasets to align and interact and cooperate so that you can do with watershed models. Really use the leverage those datasets against each other for benefit. And so where we're going with this is to use that 3DEP data as a source to create the hydrography data. And in some ways goes back to the old world. Over 100 years ago, right using you were compiling the maps together into a 24K source ah 24K product. But the goal is to standardize these so they align vertically, horizontally, and temporarily. So same source day as the 3DEP and really leverage them for applications. HBRS documented some more widespread need for this. Integration is certainly one of the most persistent complaints, particularly for modeling community that try to use elevation data to inform some 2D hydrography at this moment and then. Really, where I think we're going with this is towards a stewardship model that relies less on stewards for sort of bulk editing and wiggling the lines rather than, but rather looks for that local knowledge and information about how those changes to the geometry through a lighter weight client like the markup tool. So we've been, we've been grateful for the labor that made the stewards have provided over the years to update the data set, but really, you know that's not necessarily are the best use of your expertise. We're going to try to move towards a system where we're really looking for that local knowledge rather than sort of local labor. Again, those of you they've been tuning into this program for awhile. No, we've been at this off and on for quite awhile, and some of these names are blast from the past for you. GeoNet and BotHat, Arc Hydro is out there. There are a lot of different techniques out there to derive hydrography from elevation, but despite each of them having strengths and weaknesses, none of them was really, you know, the magic bullet they were looking for. They got this thing done right. Each of them required some significant manual editing. When you know, when they were done and so. Rather than rather than try to prescribe an approach or a toolkit for creating this data, we took a step back and decided it really what we want to define is the product and then verify that we're getting that product into the data set such that we have a standard quality in the hydrography data that we're providing. But that way people are flexible to use methods that you know methods that suit their terrain more appropriately. To try to figure out you know what this world was, we're getting into, ah, in 2016, we launched a few few very small pilot projects. So five separate HUC10s scattered across the country. There was two in Colorado, one in the mountains, one in the flats, two in on the Delmarva Peninsula, so both pretty flat, but one coastal, one inland, and then one on the edge of the Appalachian Mountains. So a little bit of you know, Eastern, Humid topography there. And we wanted what we were tending to find out primarily was how much it might cost to launch a nationwide program. And so we ran these 5 HUCs through two different contractors and compared results on them both the data and the labor involved. But also we wanted to get a sense of the technical issues that would need to be resolved before launching something like this. Oddly enough, the costing side of the thing came out relatively smoothly. But we had a long list of technical issues that we needed to get under control before we could move Move further on. This exercise may be one of the 1st and biggest issues was just an understanding of the NHD and the NHD data model. Those of you have been around it for awhile. No, it is fairly complex, but you know many of you also probably regarded as a friend. The. Expanding the circle of people that really understand that data set data model to include you know contractors and technicians and contractors Shops has been a learning curve and it's something that we need to. We've needed to sort of ramp up gradually to get that moving in a similar sort of way we hadn't contracted for hydrography data before, and so we needed a whole new set of documents to support that you know, so that we were communicating effectively with the contractors. They were understanding what we're saying. It's not something that, uh, and it's just necessarily think a lot about from a, you know, from the geographer side of the picture. But if you're looking at launching a nationwide program similar to 3DEP, you need to get that kind of thing under control. Ah? And then looking at this idea of defining a product rather than defining a process, we needed to have some pretty good standards and methods in place to test those standards and confirm that the data we were receiving you know met our specs. And again, that's not something we had done a lot of in the past. We have largely relied on Expert editors on your local knowledge to confirm that the data  the data we're getting was good. So we didn't have We didn't have nearly the same kind of rigor to our data checks in hydrography that we have in elevation or formerly in orthoimagery. So putting that all together and building that sort of that process to move from kind of a boutique environment to a production environment actually was a fair amount of work. Ah, we made a lot of progress on that, and we're going to show you some of that progress. But we're also going to talk a little bit about sort of our next wave of testing. You know how we were doing on those things? So that was 2016 when those first 5 pilots where we said, well, we need to do some work on this, so we did go back. We did some work. We tried to pull together some standardized. You know, some specifications and standards, task order language, various other sort of supporting documents. And managed to put that together and again we had an opportunity in Alaska because of a funding stream to test these. So we took the Kobuk River basin which that tiny little blue spot in Alaska up in the up in the northeast. But the upper right of your frame. That little blue spot, by the way, about the size of Connecticut. But we took that space and divided it up into three different among three different contractors to figure out. You know how again how these sort of second generation documents and specifications and task order language and so forth were working in those projects have actually mostly been completed. Now all the elevation derived hydrography has been accepted. We are still sort of working back and forth a little bit on some of the WBD up there. And then similarly in 2020 we had an opportunity because of a special initiative to have some have a project in Southeast Texas. Where we tested some of these things in a CONUS environment. And I would say that one of the challenges we maybe couldn't have picked a more challenging environment to work in in CONUS because it is down there. It is awfully flat, awfully wet, and in many parts of it are very urbanized. There's a lot of interesting stuff going on with the water system down there. Curious to see, well We're still working out a little bit how that's all going to play out. Ah so again we mentioned that Alaska is really an ideal place to start, and that was because of the completion IfSAR. We wanted to you know the next thing on the agenda. Once we had good elevation across Alaska was to move to deriving things from elevation, interpreting that elevation and pulling that hydrography data was the place to go. Ah, obviously it's the difference between working in even 5 meter IfSAR environment as compared to you know the 10 or 30 meter DEM contour- derived DEM environment that we had been in is dramatic and you see the different features on the glacier here. That's a level of detail that was almost, you know, pretty much unimaginable. Working from a contour map source. Ah, I guess I'll also mention that the. This is where we are going to talk about a little piece of this whole sort of workflow here to get from initial contracting up in the upper left over to this distributed products in the cloud. This is really just about fixing the about tidying up the line work, and you know bringing that into the NHD and WBD there's still a whole another set of processes in place to make the NHD into the NHDPlus high res and do some various other tasks in here. Actually a lot of what we're going to talk about today is that even just in those three purple boxes looking at EDH production, EDH inspection. And then I'll come. So the the other item that I'm that will sort of laying out some of the things we talk about here. Or some internal processes to talk about how the to talk about, you know the the back end for maintaining this data, right? It's one thing to get it's one thing to. Talk about getting hydrography data from elevation there is a whole  set of technical issues there, obviously, but there's also just a whole bunch of data management and contracting issues that we've fortunately been able to work through with the Alaska projects to the point where maybe not quite fully operational. But we're getting pretty close on having a standard template for the task orders having the contracting office and the contractor speaking the same language. Understand having contractors understand our expectations and inspection and having our inspection processes standardized and and routine rather than kind of developmental where they were a couple years ago. and then really were sort of the last stage of this process is coming up with some funding mechanisms. And this is again fortunate place where where the Alaska projects are able to provide that infrastructure to build the Alaska work. So the the first stop here. First the initiation of the project is really building the task order language. Back when we did those 2016 projects and Ellen Finelli and I sort of sat down for an afternoon and went from the old cartographic standards for 24K data and tried to come up with what you know what that task order should look like and we didn't do a very good job of it. Actually that it was there a lot of. Uncertainty a lot of vague stuff in the in the task order. A lot of things that we knew what we were talking about, but the people were passing the task to didn't understand the words we were using because you know, the NHD had been kind of a closed environment for so long. So we had to go back and rearrange that and get work back and forth in several different levels to try to figure out, you know, on appropriate way of communicating these expectations to contractors. And that involved a whole set of supporting documentation as well. You know. So data templates and schema so that that ever is communicating with a standard set of, you know data fields and so forth. Extensive contractor questions and responses to the first batch of task orders. One of the things that we hadn't really considered, but you know retrospectively looks obvious is that we really do need drainage density targets, particularly in Alaska where there isn't a lot of control. You can map every low spot in the ground, but many of those don't have water in them. Coming up with some kind of prediction about what, how much, how many of those features should be drawn as part of the NHD. To make it useful and functional was an important piece of this, and then we've had an iterative set of updates to the specifications. Have a lot of challenges with scheduling because we don't have. We have a fully built production operation at NGTOC to inspect these things, so we're we're sort of building that as we provide new as we contract new data and then building a system to manage the communications and records back and forth between The USGS and the contractors. Uh, so I think with that I'm going to pass it over Amanda to talk details rather than sort of glittering generalities. (Amanda) OK thanks Steve. (Steve) Sure (Amanda) yeah yeah. A little bit more specifically, I'm going to and talk a little bit about specifications and then I'll talk a little bit about data management. So what do we do with the data once we receive it from the contractor? And I'll talk a little bit again about our inspection process and just some of the communication that we've had back and forth with their contractors trying to ensure that the dataset meet their requirements of the program. So first I'll talk about specifications and for our initial set of task orders, so the pilot project Steve referenced for the Kobuk area in Alaska. And these were task orders that were developed in FY19 for these pilot projects and they were prior to the publication of any USGS specifications. So as a result, these task orders referenced alternative documents containing requirements for the collection of hydrographic features derived from IfSAR elevation data. So these two documents were the Alaska Hydro data editing standards and then also a draft version of the Alaska NHD specifications. So this included many of their requirements from the upcoming EDH specifications to be published. OK, so in July of 2020 to support the objective of obtaining EDH that will be used to update and enhance the NHD, USGS has published the EDH acquisition specifications and the representation, extraction, attribution and delineation rules, also known as the read rules. And hopefully you were able to attend the session of this Community communications call where Christy-Ann Archuleta and Sylvia Terziotti presented on these two documents. And basically they provide requirements and guidelines for developing elevation-derived hydrography. So I'll EDH task orders developed in 2020 and later referenced these two publications. And this is true for both Alaska as well as CONUS. so as we work through delivery of these initial data sets, and as we did, the inspections on those and gave feedback to the contractors, especially for the 2019 pilot projects, Uh, we've responded to inquiries regarding specification interpretation from contractors in the form of Guidance papers, so these are intended as aids to clarify existing requirements in the EDH specifications and read rules and there are two basic categories of these guidance papers that we've issued so far. So they include those that describe our inspection process and also those that clarified data collection scenarios. These documents have been issued directly to contractors with existing task orders only to this point. We're also in the process of preparing them for access through our standards website for public access. OK, so as far as data management goes. And once we receive data at NGTOC talk for inspection, we first receive received the data from the contractors. This is usually done via FTP and the datasets are small enough at this point that we can do that and. So were notified through our commercial partnerships team that the data are ready to download and the commercial  partners is the group responsible for managing all task orders under under the Geospatial Products and services contract or GPSC. Next, we distribute the data to our research in data validation teams on our internal network. And these teams work together to inspect the data and compile feedback for the contractors using an inspection process, process developed to ensure adherence to the specifications. OK, so for Alaska, EDH data are delivered to the USGS by HUC8s and part of this inspection processes performed at that level and I'll talk more about what that involves. And then, uh, the data are further divided into HUC10 groupings for further review. So Alaska EDH deliveries consist of three components and EDH deliveries for CONUS for that matter, and so part A is delivery of elevation derived. Hydrography and the schema defined in this specification. And the validation of this data set is performed by a dedicated EDH team, many of whom I see here on the call today, and this is a team that was newly formed at NGTOC and we're still building it by hiring and training new members. Part B is conflation to the NHD, and it's managed by our NHD conflation specialists in our partner support section. And then finally part C is making updates to the watershed boundary data set and the validation of this data set is performed by the WBD team. So the remainder of this presentation focuses mainly on the part, A part of that inspection process. OK, so initial deliveries of the Alaska EDH from the 2019 pilot projects were used to further develop and refine inspection methods intended for contract deliverables. So this image depicts the NHD in a small area of the Kobuk River region prior to EDH updates. And then the next slide. It comes up here. There it is. OK, so this image depicts the LDH data delivered for the same area and as expected. The density of features has increased significantly. Sorry, new visual inspections of data delivered for the pilot areas aimed to perform a manual visual review of 100% of the delivered features. And as you can imagine, we quickly realized this was not feasible given the resources available and contractual deadlines for inspections. So we instead turned our focus to ensuring our automated tools or giving us the most accurate results possible and to developing sampling methods for manual review. So the pre-screening of EDH data as I mentioned earlier, this is automated checks and these are checks done at the HUC8 level and this is performed using a suite of automated tools and processes. So these include looking at drainage density by HUC12 based on guidance issued with the task order. Uhm, artificial paths. Are they inside or artificial path outside or streams inside polygons? And we're also looking at monotonicity looking at vertex spacing. So vertices must be no closer than 1 1/2 meters from another vertex, vertical placement above and below ground, so no vertex Z-values should be above the DTM surface and no vertex z-values should be more than two meters below the DTM surface. And this is that specific to Alaska. Horizontal placement. XYZ coordinates of intersections in water body vertices relative to hydroflattened surfaces. Topology and the geometric network. So. The results of all these pre- screening processes are used to determine whether the dataset should proceed to manual inspection. So once the data are approved for manual inspection, the HUC8 deliverable is subdivided into groups of HUC10 areas. And these groups are assigned to inspectors for review and within each area some features will have a 100% inspection and some will have a sample inspected. So those features that will have 100% inspection done are subsurface connection features so underground conduits, connectors and culverts. And also glaciers and features with new capture, conditions, so areas of complex channels and coastlines. And then the features that we're taking a sample of include streams, drainage ways, artificial paths, lake, ponds, reservoirs and double line streams. So the way we're sampling these is by, a stratified random sample and the weighted error. Is based on LCD classes slope, geomorphic index D, Infinity flow path, geomorphons, plan curvature, and we're reassessing how these samples need to be done based on terrain and based on, you know, all these different things and how the how the area we're looking at. Is different from those that we've inspected in the past. So during the manual inspection, the review team is looking for potential errors in three different categories. So they're looking for completeness, so errors of omission or Commission. And they're looking at integrity, so they're looking at the schema and codes used. They're also looking at hydrography types. And then they're looking at placement. So horizontal... both horizontal and vertical placement. So this image gives an example of some horizontal placement errors that a  reviewer might encounter during their inspection. So once the full inspection is complete, the errors are compiled from both pre- screening in manual inspections and manual inspection errors are flagged specially and categorized by error type and then we write a summary report. And so if if the number of errors exceeds the thresholds set for a given category, then we request corrections. We provide this feedback to the contractor and ask, ask them to provide back a set of corrections. So also, UM. This has become a, UM, you know, central part to developing processes and developing, Developing these datasets in coordination with our commercial commercial partnership team and so like I already mentioned, we're issuing formal inspection feed back to contractors. And we're also having monthly meetings as per the task order if those are required. We also have ad hoc technical discussions, or, you know, via emails and sometimes they'll send in questions for us. And then one other thing that we've added recently is Bi-monthly technical technical exchange meetings with all GPSC contractors who have current. EDH task orders so these are alternating months with EDH and 3DEP and so this gives us a forum to discuss any guidance that we would need to issue, any kind of clarification or description of our inspection process that we would need to have with their contractors so this has been a good good addition. We've only had one of those so far, but we think that this will really help us to Uh, improve that communication with our our contractor groups so. I think with that I think there's one more slide for Steve. (Steve) Alright, so the idea here is to really where do we go next? That's a question that's what we've been trying to lay out in the 3D national terrain model call to action part one 3D hydrography program. So again this as a sort of implies there might be other 3DEP derivatives in the pipeline. But first round focus on building a hydrography network to leverage that 3DEP elevation data. That plan was sort of the first draft was completed. I think the end of April, ah, and is out for review in a variety of places at the moment. We're looking for feedback by the end of August, and should have that out fully, fully published by the end of the calendar year. Uhm, and at that point you know really the the question is to go from there to building a building a full program. We think we have the the back end, the plan, the processes in place really what we would need, you know, is is the funding. Much like with 3DEP in the early years. Uhm, so this is this is really, you know it's an evolution, but it's also in many ways a clean break. Yeah, we've learned a lot mapping hydrography over the last 20 odd years with you know everything from (inaudible) and 100K and NHD and NHDPlus and NHDHigh res and High res NHDPlus. And somewhere only we are learning from that. But really, I think this outlines in some ways a new beginning for really again, a really 3D Hydrography activity that is is conscious of and works in coordination and and compliment to the elevation data. So really, the the keys there are again to move to an operational posture in terms of deriving hydrography from the elevation data. And shifting in a lot of ways from kind of a cartographic data set that did some GIS and modeling things which largely with the NHD has been into a better accounting of the entire hydrologic cycle trying to provide connections to engineered hydrologic systems like we've seen in DC pilot projects, trying to provide some better understanding of groundwater surface water interactions. Up and provide you know something other than just overlap with the NWI ah, really provide certain high high tempo communications with NWI. Trying to understand how to build linkages between both datasets so that they don't have to. There's nothing redundant, but they those those two datasets would work in in compliment as well, and then again we've heard about the national hydrography Infrastructure number of times on this call, but really fully implement that vision of the 3DHP as as something akin to the road network as a set of addressing and routing and indexing tools that position hydrologic features or hydrologic events hydrologic activities in space and relative to each other. Ah, that's yeah we, We played with that from time to time, but really building that out as a functional operation, it's kind of the the final the end goal of the the 3DHP and I think you know as we roll out this plan you'll you'll hear a lot more about it in the next several months, and I think with that that's the program. And so with that, do you have any questions out there in the crowd? Yeah, hi Steve, this is Ivonne Allen. UM so there are. There are a whole lot of obviously I I. I think that Alaska is a great place to start with working out some of these task order related issues because the collection of the lidars, perhaps a little more standardized, but as we get into CONUS it seems like you know we have we run into problems with acquisition or environmental conditions at the time of acquisition, and I was wondering how those problems that are inherent in the LIDAR, How are those uncertainties and problems propagated into the EDH? Well, their probably, They're probably two different directions on that one is if in the areas of very low relief that you probably you're probably thinking of. You know if something is flooded, it's at the time of collection. It's flooding there isn't. I mean it, frankly isn't a whole lot we can do with lidar. To sort that out. We do, when we do have ambiguities in the elevation surface, we do allow, uhm, we do allow imagery or other complementary data sources to be used, but we were all our inspection processes are based on matching the hydrography to the elevation. So this is also something actually. This is something where we run into a fair amount in Alaska where you know a stream will come across, come out of an upland out into a an alluvial plain next to a river, and just kind of disappear at least from elevation standpoint. In those instances, we can, you know, we do use elevation, or we do use imagery rather sort of inform that elevation informed that Channel shape. But then we compare that Channel Shape to the elevation data to make sure we're staying below of the land surface and maintaining monotonicity. Uhm, I mean the other thing that does come through this that working in a network and knowing that there's something upstream and something downstream rather than sort of a more pure remote sensing context, is that you do have that kind of Hint that there should be a feature there. There's some some amount of information that comes about just by knowing what's you know what's upstream and downstream, and there should probably be some way to connect those things. (Amanda) There's a couple other so I think. In order to fully understand the uncertainty of the elevation derived hydrography. First have to fully understand the uncertainty of the elevation data. So one of the research tasks that we've been working on the past year and will continue on into next year is developing uncertainty rosters for the 3D Elevation program and basically what those are meant to do, or to describe different sources of uncertainty and how you can be more or less sure about the elevation data values and. You know, based on a number of different criteria like interpolation. I guess environmental conditions could be incorporated into that, slope All these different things. But you know, understanding the uncertainty of the elevation data is the first first thing I think. for my personal stuff. (Yvonne) That makes me really excited to hear, I'm really glad you said that. Thank you, Amanda. (Steve) that's great. We were very fortunate to have, you know, been able to bring Amanda over to the hydro side. She spent a long time in elevation inspection and we've really, really capitalized on some of her experience there to help build these processes for hydrography. Uhm? I see I see I see a question about the vertical accuracy, needs differences and those do vary. uhm. I think Amanda mentioned so 2 meters in Alaska is sort of has been our starting point. Although we are doing some work on the North Slope at the moment where 2 meters probably is a little bit too too loose, I think we started with 1 meter for the Southeast Texas project and you know found that was probably a little bit loose as well, so this is something I think would probably refine as we get a better sense of different terrains and the expectations in those different environments. Uh, who else do we have here, (Vanessa) Steve We've got a hand raised up by Jane. Jane do you wanna meet yourself? (Jane) Hi yeah this is Jane from California. Wondering how much of this Uhm, I mean I'm all for public private partnerships but but how much of the of the workflow information is going to remain proprietary is how are you dealing with that? (Steve) Several several of the contracts we work with have been doing presentations I think a couple of them actually presented on this this venue, but in in other contexts and you know, publishing papers describing the process, perhaps not in perfect detail, but in sufficient detail to understand the workflow. Uhm, we also do have the opportunity to ah much like we work with our LIDAR vendors, we do have the opportunity to go, you know, really get a better. Yeah, much more detailed understanding of their process. UM, but those are typically, you know, those are typically they have some disclosure restrictions on that. Uhm. I don't know, I guess. Does that sort of get where you're going with that, Jane? (Jane) Yeah, uhm. You know, as a steward you know we may or may not choose to work with you know, one of the contractors that are already in the process and so. Just figuring out how to how to figure out our own best practices along the way. (Steve) Sure, I think I suspect this is gonna be a learning process for all of us really, as we try to stand up a program. (Jane)Yeah, thank you. (Steve) Sure, and so Ellen Fehers had her hand up as well. (Ellen) Hey Steve, this is Ellen from Pennsylvania. Hey, I kind of perked up when I saw one of your slides that mentioned the Geo conflation team, because a theme I've kind of seen repeated in some of the USGS papers, particularly the ones by Sylvia and Christy, was the idea of conflation. And there's kind of a through- line of treating EDH as features that will have equivalencies. But I haven't been able to find information online about how these equivalencies are determined, and I took the the NHD training and they said that conflation was beyond the scope of the training. So I was wondering if you either knew a place online that would have resources for proposed NHD conflation, or if you could share the contact info for somebody from the Geo conflation team? (Steve) You bet cha. Uhm, there's a fellow. He was on the call earlier today a David Anderson. I don't know if he's still on or not. I can't see the list here, but he knows more about Geo conflation there he is...he knows more about Geo conflation than any other living human being, so he could he. He will gladly gladly talk to you at length about Geo conflation. (Ellen) OK, thank you so much. (Steve) There might have been a little bit of a misunderstanding. NHD class. There's a separate Geo conflation training. That's like, OK, that was beyond the scope of that class you took. (Ellen) OK, OK, well, thank you for clarifying. (Steve) Sure enough, and David will gladly help you with conflation. Other questions. There is a question from Francis,  It says where can we obtain the draft Alaska EDH specifications document? Uhm? The draft doc? So this is from the 2019 projects. Uhm, I suppose you just send me an email and I can,  I can provide that to you that because that was kind of a just an artifact of those particular task orders. That was I wasn't really a published document, but other questions. Now there's a question from George in DC. Yep, and he's absolutely right is a fair amount of. A fair, he knows quite a lot about the complexities of urban systems. George is our partner in the DC Metro Hydro project. And that is definitely an area that we're still still working on as many complexities as there are in in LIDAR and IfSAR, and deriving those things from elevation data. There are quite possibly more variables in the engineered systems, not the least of which is record keeping on those engineered systems. DC had pretty good records of their their plumbing. You know many other cities don't have such such great records of their plumbing. And it's some level we also need to figure out programmatically what are our mission is in terms of, you know, representing those connections and DC is a great example because it does include both highly detailed connections of how individual catch basins and grates in the road connect to individual outfalls. But we've generalized that somewhat to include in the in the NHD. You know, as I mean, that was the first shot at it with something we need to work on going forward. But you're absolutely right, George. There are a lot of complexities in urban systems. And then how are you getting culvert data? A culvert data is coming from from the elevation data, and they're different processes that the different contractors used to identify those culverts. But you know, at some level it's a matter of looking for where looking where the water ponds and seeing if there's a road holding it back. Other questions. OK well it seems like the chats and the questions have tapered off so well. We'll call it a day, thanks. You've been a great audience and tune in next month for another installment of the hydrography community call. Ah hmm alright, thanks a lot.