10 votes
Accepted

Extracting flat areas and saving them as lakes using QGIS?

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 ...
ahmadhanb's user avatar
  • 40.7k
9 votes

Get drainage basin of a polygon (with QGIS, GRASS or other FOSS)

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 ...
Micha's user avatar
  • 15.6k
8 votes
Accepted

Basin creation GRASS vs. flow direction

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!
Riccardo's user avatar
  • 2,648
6 votes
Accepted

Getting 8 digit watersheds for USA

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 - ...
whyzar's user avatar
  • 12k
6 votes
Accepted

DEM File "not found" Error when running r.watershed with Processing Toolbox in QGIS 3.4.2 with GRASS

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 ...
Micha's user avatar
  • 15.6k
5 votes
Accepted

Is D8 flow accumulation algorithm still suitable for watershed computation if terrain contains lots of flat area?

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 ...
WhiteboxDev's user avatar
5 votes
Accepted

Exporting same attribute values to separate layers and merging them in QGIS

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.
wingnut's user avatar
  • 2,090
5 votes
Accepted

Selecting the transect lines which touches the divide of a polygon from the river line

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 ...
wingnut's user avatar
  • 2,090
4 votes
Accepted

Can't get GRASS r.water.outlet to work

As mentionned by Micha, my problem was that I was using my original stream vector layer instead of the one generated by r.watershed. So to be clear: - With r.watershed, create both Drainage direction ...
Horizen's user avatar
  • 567
4 votes

Getting 8 digit watersheds for USA

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-...
Dan C's user avatar
  • 12.2k
4 votes
Accepted

Drainage basins ignoring lake

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 ...
Louis's user avatar
  • 674
4 votes
Accepted

Selecting point to obtain water basin leading to it

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 ...
Louis's user avatar
  • 674
4 votes
Accepted

Does r.stream.basin still exist? GRASS-QGIS2.18.7

The module r.stream.basins is an addon: https://grass.osgeo.org/grass72/manuals/addons/r.stream.basins.html In order to use it from QGIS, you need to have the module being installed in the ...
markusN's user avatar
  • 13k
4 votes

How to delineate watersheds in QGIS?

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 | ...
Kazuhito's user avatar
  • 30.7k
4 votes
Accepted

r.water.outlet is returning blank raster in QGIS

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 ...
Marco's user avatar
  • 3,230
4 votes

Watersheds in SAGA Fill Sinks Wang & Liu tool

If you look closely at the tool documentation, there's some references info . The problem is that the text needs to be bought or to have some student account access. Wang, L. & H. Liu (2006): ...
gisnside's user avatar
  • 7,818
4 votes
Accepted

Rockfall analysis (Nearest neighbor downhill) in QGIS

Here you have a simple script that iterates over points and apply r.water.outlet to each one. You just need to add this code as a new script. It will ask for three things: Points layer. Flowdir ...
César Arquero Cabral's user avatar
3 votes

How to design a flood with water elevation on a specific point?

Did you check GRASS r.lake function: https://grass.osgeo.org/grass70/manuals/r.lake.html
WKT's user avatar
  • 2,183
3 votes

Finding watershed area for each point in river network using DEM using QGIS

There is a new tool available made by Hans van der Kwast. This plugin creates a vector watershed for every pour point. Here it looks like. This tool creates a separate shapefile for every pour point. ...
Anatolii's user avatar
  • 201
3 votes

Finding watershed area for each point in river network using DEM using QGIS

r.stream.basins would do what you are after. https://grass.osgeo.org/grass70/manuals/addons/r.stream.basins.html But since it is (currently) a GRASS addon, it is not available in QGIS. It might be ...
Stefan B.'s user avatar
  • 286
3 votes
Accepted

Calculating watershed using snap pour points?

Depends on the machine specs and dataset size and number of points. One way to speed things up is to set the environment processing extent of the snap pour point tool. So if you are snapping a few ...
Hornbydd's user avatar
  • 43.2k
3 votes
Accepted

Doing watershed delineation properly using ArcGIS Desktop?

Watershed delineation is tricky, I usually include a larger area then my study area so I don't have anything weird at the edges. i.e. like the edges are cliffs or walls. With that being said, I also ...
Bill Chappell's user avatar
3 votes

Doing watershed delineation properly using ArcGIS Desktop?

It looks like your issues may in large part be caused by the large flat in the NE portion of your basin. Different pit filling and flow direction algorithms will handle this area differently, and it ...
Lovette's user avatar
  • 979
3 votes
Accepted

Distance to a polygon along the stream flow path

The Flow Distance tool will calculate the distance from each cell to the closest flow path. I believe you could change the polygons to polylines in the shape of the polygon and then use those lines as ...
jcholly's user avatar
  • 166
2 votes
Accepted

Could bridges prevent ArcMap from creating correct watersheds?

Yes it will mess things up completely but this is not an ArcGIS issue. How is ArcGIS supposed to know from a DEM that pipes run underground? Whitebox has developed a tool that will fix this issue and ...
If you do not know- just GIS's user avatar
2 votes
Accepted

What are the meaning of Grass drainage direction values from r.watershed

GRASS numbers the directions in a drainage (flow direction) raster from 1-8 starting eastward and going counter clock-wise. What about the negative numbers? GRASS uses negative direction to indicate ...
Richard's user avatar
  • 1,831
2 votes
Accepted

How to calculate stream order in GRASS 7.0.2?

Not sure how you are accessing GRASS, but the documentation reads to me like this is an Addon. I just went to the command line typed "g.extension" and a window popped up that I linked to the source ...
Mike's user avatar
  • 718
2 votes
Accepted

Expression into the raster calculator to invert DEM

I would subtact the last pass and the first pass elevation if you want the height. You could also possibly add a constant (e.g. 100) in order to have positive values but this is more an esthetic ...
radouxju's user avatar
  • 49.6k
2 votes

Calculating mean altitude of watershed for each cell of DEM?

You can use In_weight_raster in Flow accumulation Use your DEM as one, this will produce total of elevations inside cell's catchment. Compute flow accumulation without weight, this will produce ...
FelixIP's user avatar
  • 22.8k
2 votes
Accepted

r.watershed basins at coast / ocean lines

Resolved. In addition to my previous comment. To ensure that the r.watershed program creates basins with total coverage at coastal or around inland water bodies, you will need to have elevation ...
BenP's user avatar
  • 259

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