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QGIS 3.4 Stream delineation problem, lines running too far into ocean

Problem with hub lines (in Qgis)Watershed delineation with meandering river?Lines to Polygons problem qgis 2.14.9Multiple flow distance rasters produce low distance values along catchment boundaryDelineating coastal subbasins using SAGA GIS or GRASS in QGIS?Save ocean shape layer using another CRS problem using QGISMerging overlapping lines into one line. QGISDEM reconditioning?UBUNTU 16.04, QGIS 3.4 above Installation problemProblem editing, clipping, and saving large shapefile QGIS 3.4

0

I am using QGIS 3.4.4 Madeira version trying to delineate the stream and catchment areas of a small Bay in Honduras based on the technique of Hanz van der kwast tutorial "Stream and Catchment delineation in QGIS 3".
I imported DEM > reprojected > Used SAGAs Fill Sinks (Wang and Liu) > USED SAGAs Strahler Order to delineate streams.

What happens is that the tool cannot decipher what is land at sea level and what is the actual sea and creates channels running straight off into the ocean. HOW CAN I CORRECT THE DEM BEFORE USING STREAM DELINEATION TOOL SO I DON'T HAVE MY STREAMS RUNNING FAR OFF INTO THE OCEAN? I WANT THEM TO STOP WHEN THEY HIT THEIR DRAINAGE POINT (i.e. Bay/Ocean).

I've already tried clipping the raster to a polygon of the land area to simply cut out the ocean from the raster, but then the results don't work as I am guessing I cut out important information that the tool needs to process (streams and basins are completely missing).

Let me know if I haven't voiced the problem clearly. I'm rusty with GIS in general and am totally new to QGIS. Please use layman's terms if possible. Thanks

qgis dem ocean strahler stream

share|improve this question

asked 33 mins ago

Olivia DatOlivia Dat

1

New contributor

Olivia Dat is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  are you open to a python-based solution?
  
  – Paul H
  22 mins ago
  

  
  
  
  

add a comment | 

0

I am using QGIS 3.4.4 Madeira version trying to delineate the stream and catchment areas of a small Bay in Honduras based on the technique of Hanz van der kwast tutorial "Stream and Catchment delineation in QGIS 3".
I imported DEM > reprojected > Used SAGAs Fill Sinks (Wang and Liu) > USED SAGAs Strahler Order to delineate streams.

What happens is that the tool cannot decipher what is land at sea level and what is the actual sea and creates channels running straight off into the ocean. HOW CAN I CORRECT THE DEM BEFORE USING STREAM DELINEATION TOOL SO I DON'T HAVE MY STREAMS RUNNING FAR OFF INTO THE OCEAN? I WANT THEM TO STOP WHEN THEY HIT THEIR DRAINAGE POINT (i.e. Bay/Ocean).

I've already tried clipping the raster to a polygon of the land area to simply cut out the ocean from the raster, but then the results don't work as I am guessing I cut out important information that the tool needs to process (streams and basins are completely missing).

Let me know if I haven't voiced the problem clearly. I'm rusty with GIS in general and am totally new to QGIS. Please use layman's terms if possible. Thanks

qgis dem ocean strahler stream

share|improve this question

asked 33 mins ago

Olivia DatOlivia Dat

1

New contributor

Olivia Dat is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  are you open to a python-based solution?
  
  – Paul H
  22 mins ago
  

  
  
  
  

add a comment | 

I am using QGIS 3.4.4 Madeira version trying to delineate the stream and catchment areas of a small Bay in Honduras based on the technique of Hanz van der kwast tutorial "Stream and Catchment delineation in QGIS 3".
I imported DEM > reprojected > Used SAGAs Fill Sinks (Wang and Liu) > USED SAGAs Strahler Order to delineate streams.

What happens is that the tool cannot decipher what is land at sea level and what is the actual sea and creates channels running straight off into the ocean. HOW CAN I CORRECT THE DEM BEFORE USING STREAM DELINEATION TOOL SO I DON'T HAVE MY STREAMS RUNNING FAR OFF INTO THE OCEAN? I WANT THEM TO STOP WHEN THEY HIT THEIR DRAINAGE POINT (i.e. Bay/Ocean).

I've already tried clipping the raster to a polygon of the land area to simply cut out the ocean from the raster, but then the results don't work as I am guessing I cut out important information that the tool needs to process (streams and basins are completely missing).

Let me know if I haven't voiced the problem clearly. I'm rusty with GIS in general and am totally new to QGIS. Please use layman's terms if possible. Thanks

qgis dem ocean strahler stream

share|improve this question

asked 33 mins ago

Olivia DatOlivia Dat

1

New contributor

Olivia Dat is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

share|improve this question

asked 33 mins ago

Olivia DatOlivia Dat

1

New contributor

Olivia Dat is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

share|improve this question

asked 33 mins ago

Olivia DatOlivia Dat

1

New contributor

Olivia Dat is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

asked 33 mins ago

Olivia DatOlivia Dat

1

New contributor

Olivia Dat is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

asked 33 mins ago

Olivia DatOlivia Dat

1

1 Answer
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I would create a new raster dataset with the ocean's masked out. Assuming any cell with an elevation less than or equal to zero, I would do:

import numpy

import rasterio

with rasterio.open('path/to/orig.tif', 'r') as orig:

    land_and_sea = orig.read(1)

    meta_data = orig.meta.copy()



nodata_value = -9999

meta_data['nodata'] = nodata_value

with rasterio.open('/path/to/masked.tif', 'w', **meta_data) as masked:

    land_only = numpy.where(land_and_sea >= 0, land_and_sea, nodata_value)

    masked.write(land_only, 1)

share|improve this answer

answered 11 mins ago

Paul HPaul H

374211

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0

I would create a new raster dataset with the ocean's masked out. Assuming any cell with an elevation less than or equal to zero, I would do:

import numpy

import rasterio

with rasterio.open('path/to/orig.tif', 'r') as orig:

    land_and_sea = orig.read(1)

    meta_data = orig.meta.copy()



nodata_value = -9999

meta_data['nodata'] = nodata_value

with rasterio.open('/path/to/masked.tif', 'w', **meta_data) as masked:

    land_only = numpy.where(land_and_sea >= 0, land_and_sea, nodata_value)

    masked.write(land_only, 1)

share|improve this answer

answered 11 mins ago

Paul HPaul H

374211

add a comment | 

0

I would create a new raster dataset with the ocean's masked out. Assuming any cell with an elevation less than or equal to zero, I would do:

import numpy

import rasterio

with rasterio.open('path/to/orig.tif', 'r') as orig:

    land_and_sea = orig.read(1)

    meta_data = orig.meta.copy()



nodata_value = -9999

meta_data['nodata'] = nodata_value

with rasterio.open('/path/to/masked.tif', 'w', **meta_data) as masked:

    land_only = numpy.where(land_and_sea >= 0, land_and_sea, nodata_value)

    masked.write(land_only, 1)

share|improve this answer

answered 11 mins ago

Paul HPaul H

374211

add a comment | 

I would create a new raster dataset with the ocean's masked out. Assuming any cell with an elevation less than or equal to zero, I would do:

import numpy

import rasterio

with rasterio.open('path/to/orig.tif', 'r') as orig:

    land_and_sea = orig.read(1)

    meta_data = orig.meta.copy()



nodata_value = -9999

meta_data['nodata'] = nodata_value

with rasterio.open('/path/to/masked.tif', 'w', **meta_data) as masked:

    land_only = numpy.where(land_and_sea >= 0, land_and_sea, nodata_value)

    masked.write(land_only, 1)

share|improve this answer

answered 11 mins ago

Paul HPaul H

374211

import numpy

import rasterio

with rasterio.open('path/to/orig.tif', 'r') as orig:

    land_and_sea = orig.read(1)

    meta_data = orig.meta.copy()



nodata_value = -9999

meta_data['nodata'] = nodata_value

with rasterio.open('/path/to/masked.tif', 'w', **meta_data) as masked:

    land_only = numpy.where(land_and_sea >= 0, land_and_sea, nodata_value)

    masked.write(land_only, 1)

share|improve this answer

answered 11 mins ago

Paul HPaul H

374211

answered 11 mins ago

Paul HPaul H

374211

answered 11 mins ago

Paul HPaul H

374211