16

Here are the general steps involved in creating a watershed boundary. You need to work with a raster DEM, not vector contours. This means that you have two options; you can either try to interpolate your contours or you can look for an existing raster DEM of the study area. Most of the interpolation methods contained within ArcGIS's interpolation toolbox ...


12

Assuming your stream polylines do not already have an attribute that states which watershed they belong to, you can run Identity (Advanced license only) or Intersect to get that attribute assigned in a new feature class. This also makes sure your streams actually break at the boundary rather than continuing through multiple areas. Then you can open the ...


8

It may seem like laziness on the part of Watershed tool developers to stick with the simplest and oldest flow algorithm, D8, but there is a very sound reason for doing so. The difference between the D8/Rho8 flow algorithm and the more advanced algorithms that you mention (e.g. D-infinity) is mainly in their inability to represent the dispersion of overland ...


8

The problem was the parameter "allow only horizontal and vertical flow of water". I really don't know why this is set by default in QGIS/Processing!!! damn noob error!


8

If you need only the total drainage area (not the actual geography of the area) then you can do this with flow accumulation. Run r.watershed with your DEM as input, and define a name for the flow accumulation output raster. Each pixel contains the upstream area (actually number of cells) that flows into that pixel. Next you need to extract the boundary of ...


7

It is an error. Your link and presumably image source is the 10.0 help. The error is still present in the 10.1 help. However in the 10.2 help, it has been corrected to show only a 1. It's also worth noting that if you work through the math matrix as whuber has done at Arcmap 10 restrict Flow Accumulation, that error is apparent as well as the adjacent 35 ...


7

You need to extract the slope first from the DEM using the Raster -> Terrain Analysis -> Slope OR Raster -> Analysis -> DEM (Terrain Models). Then use the slope raster to extract the lakes or sea where the slope = 0 Using Raster Calculator, it will be like this: "Slope@1" = 0 Where "Slope@1" is the raster name. So The general form is "...


6

The method that I've implemented in a couple of languages and believe that ESRI uses (sorry, no references other than Jenson and Domingue cited elsewhere in this page) is to start at a user-supplied "pour-point" cell or a cell at the edge of the flow direction grid (fdr), examine its eight neighbors to find which of those direct flow into the current cell, ...


6

I think that the problem is the missing threshold parameter. In the GUI window it appears as "optional" since there are some simple uses for r.watershed that do not require a threshold. But for any normal use of this module you must provide the threshold. It is worth to notice that in the QGIS GUI, the parameter is not mentioned at all by its original name ...


5

I can think of a few ways to do this: Symbolize the lines so they have direction indicated, and manually Flip those in the wrong direction. Use an attribute if available or a calculation (such as end z > start z) to select segments going the wrong direction and Flip (GP) them. Create a geometric network of the lines and use the Flow Direction tools, setting ...


5

In the context of airborne LiDAR and forestry, local maxima algorithms such as the one described in Popescu et al. (2002) were designed to identify and extract individual trees in the forest. Given some digital surface model (usually, a canopy height model), the local maxima algorithm will search for the highest point inside a window of search, and it will ...


5

You need to nest your search cursor loops to iterate through both at the same time, while relating the rows in some way (so arcpy knows when it is at the right one, and will stop looping to compare the value). Luckily you've got those matching ID fields already. This should get you started comparing the area values. Let me know if it doesn't run or I've put ...


5

it looks like there's a wee bit of confusion on what's greater/smaller than what but I'll leave that for you to manipulate. This solution will iterate ONLY ONCE through each table which will not confuse the cursors and will save you 10 million iterations(from loop in a loop iteration). Using a dictionary lookup is so fast it's considered 'free'. So populate ...


5

I have a tremendous respect for GRASS and the r.tarraflow algorithm and I'm sure that given enough effort, you would be able to make it work for this application. But as an alternative, I develop a cross-platform free and open-source GIS called Whitebox Geospatial Analysis Tools (download here). Here is an example for how to use it for hydrological ...


5

I was looking at this dataset myself today, I opted to send an e-mail and the data layers that I needed. I'll see if they hold true to the 1-2 business days. However, I also came across this site - http://130.179.67.140/dataset/usgs-huc-10-watershed-layer Which contains the 8-digit HUCs you are looking for both in shapefile and KML format.


5

All flow algorithms are based on the assumption that surface and near-surface flow paths are determined by local topographic gradients. Flow algorithms calculate flow paths by comparing the elevation drops between grid cells in a DEM and their eight neighbouring cells. The difference between non-dispersive (D8, Rho8, D8-LTD) and dispersive (D-infinity, FD8) ...


5

Look into Split Vector Layer in QGIS's Processing Toolbox. You can use a field to split an existing layer into layers containing unique values of that field.


5

If you want to create this sort of thing, then there is a way. I am assuming you have already broken the transects at the river. Looks like you have. Convert the watershed polygon to a line. This creates a polyline boundary. You can use Vector - Geometry - Polygons to Lines Vector - Geoprocessing Tools - Buffer the boundary by a small amount so that the ...


4

The ArcGIS help says: Watersheds can be delineated from a DEM by computing the flow direction and using it in the Watershed tool. To determine the contributing area, a raster representing the direction of flow must first be created with the Flow Direction tool. The Flow Direction is calculated from the DEM using the D8 method, Where the flow is ...


4

This has been asked before, though perhaps in a slightly different context. All of the geoprocessing tools in the Hydrological toolset of Spatial Analyst use the D8 flow direction model, as stated in the How Flow Direction Works page: There are eight valid output directions relating to the eight adjacent cells into which flow could travel. This approach ...


4

Please do not use sink-filling for r.watershed, it is nor needed nor desired. r.watershed takes care by itself due to its internal least cost routing algorithm. A minimalistic example: r.watershed elev=dem basin=catchments thresh=10000 For a tutorial, see http://grasswiki.osgeo.org/wiki/Creating_watersheds


4

I think you are going to have to break (as a node) the road at the polygon edges to do this in vector space. Use Identity Tool in ArcGIS and this should do the trick. Just option that is something like Just ID Remember to recalculate lengths in the attribute table after the identity (just to be sure) It will add the polygon details (in this case thee ID) ...


4

The flow accumulation is the right tool for you, after as mentioned filling sinks (fill tool) and create a flow direction raster. "The Flow Accumulation tool calculates accumulated flow as the accumulated weight of all cells flowing into each downslope cell in the output raster. If no weight raster is provided, a weight of 1 is applied to each cell, and the ...


4

Watershed straight edge is usually clear indication of processing extent being not large enough. I guess that dams extent affected result shown. Output of watershed tool http://resources.arcgis.com/EN/HELP/MAIN/10.2/index.html#/Watershed/009z00000059000000/ depends on correct value of extent. It is a good idea to set your extent to DEM extent, set cellsize ...


4

The National Hydrography Dataset contains the Watershed Boundary Dataset, which contains 8-digit watersheds (also 2,4,6,10,12,14, and 16-digit where available) for every state in the USA. The high-resolution version is available for download by state here: ftp://nhdftp.usgs.gov/DataSets/Staged/States/FileGDB/HighResolution/.


4

Through discussions and research, I have figure out that the processes I have used simply do not identify the lake as being a lake and "simulate" a stream flowing through what the DEM identifies as being a flow direction. My main issue with this lake was that I know for a fact that water does not flow out from the south, it's actually a reservoir and ...


4

Having fiddled some more with the subject, I've come to find an answer to this question and will follow up on it in case someone finds themselves in the same situation. First off, I have run the GRASS geoalgorithm r.stream.extract, which produces three results: Flow direction (raster), Unique stream ids (point vector) and Unique stream ids (raster). Details ...


4

Assuming your QGIS 2.14.17 is equipped with SAGA 2.3.1 or 2.3.2, let me answer only the first question "where to find Catchment area (Parallel) in the QGIS Processing Toolbox?" Try and find SAGA | Terrain Analysis - Hydrology | Catchment area This tool uses parallel processing, so you would find it was called Catchment area (Parallel) in some older ...


4

The r.water.outlet needs the outlet coordinates in the same CRS as the input file. Since your "computational region is North:1570225.7, East:739499.1, South:1319713.3, west:474246" and in your screen shot says "EPSG: 32643 (OTF)" means your are mixing units. The outlet point should be meters as CRS and not in lon/lat. My screen is a bit different from your ...


3

I am not sure that following the boundary will be more efficient than expanding the area. With raster data, you need to account for the number of times that you "go through" the entire image. With a region growing method, each pass will process an increasing number of pixels until you reach the boundary. If you look at the contour only, you might end up with ...


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