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 ...
- 40.2k
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 ...
- 15.4k
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!
- 2,608
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 - ...
- 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 ...
- 15.4k
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 ...
- 10.9k
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.
- 2,060
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 ...
- 2,060
4
votes
Watershed Tool Straight Edge Problem
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/...
- 22.5k
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 ...
- 547
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-...
- 12.1k
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 ...
- 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 ...
- 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 ...
- 12.9k
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 | ...
- 30.4k
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 ...
- 3,180
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): ...
- 7,768
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 ...
- 3,371
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
- 2,183
3
votes
Accepted
How to create a reservoir for a dam site?
I'm not an expert in defining reservoir limits and capacities so my suggestion may be too crude or even flawed?
To pond up behind the dam, you have to know the height of the dam, that seems ...
- 42.6k
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 ...
- 42.6k
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.
...
- 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 ...
- 286
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 ...
- 4,710
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 ...
- 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 ...
- 156
2
votes
Is there a way to automatically find errors made by the Watershed tool?
In my old job I had developed a tool that would identify this scenario so you could go back and replace the pour point. It required the vector network (do you have that ?) and tracing upstream to the ...
- 42.6k
2
votes
Is there a method to create watershed on google earth?
Well watershed is quite advanced spatial analysis and I really doubt that Google Earth is focused on this kind of things. I have to say I am not using GE often, but after quick look at capabilities of ...
- 291
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 ...
2
votes
Python code to select streamlines within selected watershed
Scripting this task is wrong way to go as I mentioned in my comment, but if OP insists, the code below should work on FGDB inputs and it doesn't matter if streams are not split at polygons boundaries ...
- 22.5k
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