Latest Contributions by FernandoVasconcellos

Hi all! (I hope there is some Ghost busters reading me) Well, after months of work, I finally have my culverts and bridges watersheds well defined by ArcGIS(MAP) with ArcHydro! I'm working in a mask with 'only' 172 of them. Now I need to perform complex hydrologic and hydraulic calculations, but strange things have happened... Believe me, there are GHOSTS in the ArcHydro outputs! I have 2 examples: 1) I used the 'Join Field' function (ArcMap/Data Management) to bring 'L' and 'S' from the layer 'Long Flow Path' to the layer 'Watershed' (where I was planning to concentrate my automatic calculations, the model I want to build). The fields are copied, but... with 172 "NULL" values!? Well, let us right-click and delete them, right? Wrong: the 'delete field' button is not iluminated, not available for use. Of course I tried to use the 'delete field' function (ArcMap/Data Management), but guess what? The fields brought by 'Join Field' with no values are not listed! I'm quite convinced they are ghost fields. But they are not the only ones... 2) I created a raster of slopes (actually two, one with ArcMap and another one with ArcHydro, both perfect!) and was finally going to obtain the average slope of each one of the 172 watersheds! How excited I was about that! The best way I've found to do it, as a newcomer self-learner of ArcGIS, was the 'zonal statistics', maybe 'zonal statistics as table'. The zone data was, of course, my brand new watershed layer, a polygon feature (a perfectly valid one, according to the ArcGIS Desktop Help).  The input value raster was the slope layer (I tried both of them). Could I have the mean values, please? NO, ArcGIS answered me. WHY, did I ask? Error 010160, unable to open raster watershed. But this is not a raster and you are not supposed to assume that it's a a raster! OK, I changed the zone field, the one which is supposed to indentify each one of the waterhseads; maybe it could help. YES, now ArcGIS could read the feature zone data! YET it told me: error 010067 now, 'error in executing grid expression'. You must check your Map Algebra expression: it's probably wrong, because I can't understand it, 'he' told me. But that Map Algebra is actually a function created by ESRI!!! How could I revise it? Well, a whole lost day with dozens of unsuccessful tries... I can't perform any statistics or operation within my 172 watersheds... THEY ARE LIKE GHOSTS. Well, if someone doubt that softwares (even a sofisticated one, like ArcGIS), have the power to produce GHOSTS, please answer this post with at least one good explanation for the useless of layers and fields constructed in months of hard work with this sofisticated software (which is driving me crazy). THANK YOU, GHOST BUSTERS ON CALL!!! ... View more

Hi all! After a long pathway, I obtained the synthetic drainage lines of my study area, quite well defined (ArcMap tools were not enough for this, I had do install and use ArcHydro). I intersected them with a roads layer and found about 3,000 consistently defined drainage points. I also have the catchments and the adjoint catchment well defined at the drainage lines joints. But I need to delineate the watersheds for each culvert or bridge. When I try to use "Delineate from multiple I and O" (ArcHydro 2.1) the ArcMap (10.0) simply stops responding. I think the "Batch watershed delineation" (ArcHydro function) would be a better way to do what I need, but I can't find a way to automatically generate the 3,000 batch points I have (actually I'm working in a small mask, with 150 pilot points). Even when I use the tool/button "Batch point generation" (ArcHydro) to manually define just 1 of the 150 points I have, the "batchdone" field gets a "-1", what means that the delineation has failed (with no explanation why that or any clue in the ArcHydro help to solve the problem). I also went back to the Sapatial Analyst tools and tryed "watershed", after using "snap pour point" in order to get better results. It didn't work, the output layers are empty or delineate one single waterhsed (adjoint catchment). DOES ANYONE KNOW HOW TO DELINEATE THE WATERSHEDS TO PREDETERMINED POINTS (THOUSANDS OF THEM)? I'd appreciate any help at all!!! ... View more

Hi everybody, I'm trying to build synthetic drainage lines as coincident as possible with the "real world" shown in the cartography. I think that is a basic purpose of everyone performing hydrological analysis of natural areas, right? 1st I used ArcGIS without the help of ArcHydro and the results were simply unacceptable! (My area has a complicated topography, with many lakes, large and flat valleys, etc.) Then I used ArcHydro to recondition the DEM and also to adjust flow direction in lakes. The results were much better! But I still have problems. For example, it gives me 3 parallel drainage lines where I had burnt the only existing one with the reconditioning function. I wish I could erase the two obvious wrong lines, but even if that was possible, it would take me weeks or months to "clean" all the study area (of about 10,000 km2). So, now I'm trying to use "Flow Direction with Streams" instead of "Stream Definition", as the help file stays it's possible; but it seems impossible! The "Flow Dir with Streams" simply doesn't work and many people in the forum, from 2009 to 2012, have mentioned the same hermetic error messages (only software engineers and other experts would understand such messages; I'm just a water resources engineer). None of those people got answers. The forum is a good idea, but not powerful enough to help in many cases. I wish the ESRI technical staff who designed so many specialised functions had written more comprehensive description of their use in the help files. What could I do to have a synthetic drainage network closer to the real world, so that I can work with it to perform the sound hydrological analysis I need? I'D APPRECIATE ANY SUGGESTION (EVEN FROM THOSE IN SAME HOPELESS SITUATION, MAYBE ONLY A FEW STEPS AHEAD OF ME). THANKS! ... View more

I need to define the stream network for a huge area and I???ve finally managed to do so with the ArcGIS 10 hydrologic functions. But the results in a very small area are not accurate enough for me to reproduce the process to the whole project area (ArcGIS would lead me to deal with 1 culvert as if it was a set of many wrongly placed culverts; and I have more than 13,000 culverts in the project area!)   I???m attaching a Word file with 3 images of a stream network (and the road network, once I???m studying roads drainage).  The ArcGIS results are very close of what we could deduce (image 1) and confirm with satellite photos (image 2). Actually, what we can deduce is confirmed by a hydrography layer (image 3, planimetric information).  But I need to work with the ArcGIS results. Because of that, I???m trying to realise how we could ???force??? the mathematical ArcGIS results so that they would better reproduce the real world. I???ve read in the ArcGIS help about the Flow Accumulation function that ???If no weight raster is specified, a default weight of 1 will be applied to each cell???. I couldn???t find much more about the use of a weight raster and I???d like to ask anyone who has faced similar hydrologic problems: COULD WE CONVERT A HYDROGRAPH LAYER (WITH DRAINAGE LINES) IN A WEIGHT RASTER TO USE WITH FLOW ACCUMULATION, SO THAT ITS RESULTS WOULD COINCIDE WITH THE PLANIMETRIC ONES? Any tips on how to do that? Any other ideas on how to teach ???common sense??? to the flow accumulation function? (Any hydrologist wouldn't draw 3 parallel drainage lines, like ArcGIS did in that small area, where there???s obvious only one preferential way to the water.) Thank you to anyone who would take some time to think on this problem and share his/her ideas with me! *** Sorry, the file is 4MB and the maximum allowed is 1MB. But its not essential to discuss the problem, I think. ... View more

The ArcGIS Desktop Help leads to a wrong understanding about the order some basic hydrologic functions are supposed to be performed. It should be urgently revised. I???m new to GIS and tried to follow the help flowchart (???An overview of the Hydrology toolset / Deriving runoff characteristics???) to define a stream network. 1st problem: starting with a DEM, it shows [flow direction] as the first function. That???s right, but if the DEM has sinks we need to make it a depressionless DEM and, after that, perform [flow direction] AGAIN (what is not clear!) 2nd problem: if the [flow direction] output has sinks, we can use it as an input to the [sink] function in order to identify them. But this is only an optional step, especially if we want to fill the sinks without specifying a ???z??? limit.  The [sink] is not a pre-requisite to run [fill], as the flowchart show us. 3rd problem: the input to run [fill] is not the output of sink, as the flowchart lead us to think. Neither is it the output of [flow direction], used in the previous action (performing [sink]). The input to [fill] is simply the original DEM. All other functions needed in hydrologic analysis, shown in the flowchart (and some which are not shown), need, as inputs, the outputs of either or both: [flow direction] and [flow accumulation]. Then, a better understanding of the hydrologic analysis process using ArcGIS could be reached substituting this flowchart by two very simple ones: a) Without sinks: DEM => [flow direction] => [flow accumulation] => Stream network defined; and b) With sinks: DEM => [fill] => Depressionless DEM => [flow direction] => [flow accumulation] => Stream network defined. The only thing that needs to be added is a clear explanation: ???We start with the flowchart (a) and run the [flow direction].  If the output  raster has any cells with a value which is not 1, 2, 4, 8, 16, 32, 64 or 128, this is a sink (a numerical error or a natural sink, like a pond or a lake). Then we need to go back and use the flowchart (b). Just that simple! But it took me a long trial and error process to arrive at such conclusions, not to mention the extensive discussions in the hydro forum, which almost led me to install a complementary software (ArcHydro) which, actually, it???s not essential to the initial analysis I???m performing. I hope this thread can help the ESRI developers to improve the ArcGIS Help; or can help other beginners to save time when performing hydrological analysis. ... View more