Hi everyone,

I'm calculating a HAND raster using WhiteboxTools in QGIS.

Workflow

• ALOS PALSAR DEM
• Breach Single Cell Pits
• Breach Depressions (Least Cost)
• D8 Pointer
• D8 Flow Accumulation
• Extract Streams (threshold = 3000)
• Elevation Above Stream

Problem

The HAND output contains several relatively large NoData holes, mostly located in valley bottoms. Stream cells themselves are NoData (which I assume is expected), but these larger holes are not.

I've checked the inputs:

• the breached DEM has valid elevation values everywhere
• the D8 Pointer has valid flow directions in these areas
• the Flow Accumulation raster has valid values (including high accumulation values in some of the holes)
• the stream raster is valid (streams = 1, background = 0)
• WhiteboxTools finishes without warnings or errors

Interestingly, I observed what seems to be the same issue during watershed delineation. In those locations, the watershed boundary unexpectedly stops even though the extracted stream continues downstream.

Because both tools fail in nearly the same locations, I suspect there may be a missing hydrological connection somewhere in the processing chain, possibly introduced or exposed during the DEM preprocessing.

I also tried using the original (unbreached) PULSAR DEM, but then the HAND result becomes much worse and is largely unusable due to uncorrected depressions.

The Elevation Above Stream Euclidean tool works much better and does not produce these large holes, only a few isolated NoData pixels near streams.

Question

Has anyone encountered this behaviour before?

Could this indicate a problem with the Breach Depressions workflow, D8 flow routing, or is it a known limitation or bug in WhiteboxTools' HAND implementation?

Any suggestions on how to diagnose or fix this would be greatly appreciated.

Zoomed view of the location where the watershed delineation terminates. The extracted stream network (yellow) is interrupted, whereas the HydroRIVERS network (blue) indicates a continuous river channel. This suggests a missing hydrological connection in the DEM-derived flow network, resulting in the premature termination of the watershed.

Watershed delineation result. The watershed should extend considerably farther upstream, but the delineation terminates prematurely due to an apparent missing hydrological connection. The yellow lines show the extracted stream network.

Elevation Above Stream Euclidean result (gray). Compared to the standard Elevation Above Stream output, the large NoData gaps are largely absent. However, the affected areas are replaced by irregular, stream-like patterns that do not appear to represent the actual drainage network, indicating that the underlying problem persists.

Elevation Above Stream result. Stream cells are represented as NoData (visible as the underlying DEM). In addition, several larger NoData areas occur predominantly within flat valley bottoms and floodplains, where valid elevation values are present in the input DEM. These unexpected gaps appear to coincide with areas of missing hydrological connectivity identified during the watershed delineation.