Extract a stream network with Strahler order from a DEM, or delineate the watershed for any point. Mask to an area of interest first to skip processing the rest of a large DEM.
8 Hydrology Operations, Explained
Depression Filling
Raises small artificial pits in the DEM just enough that water always has a path downhill — the standard Priority-Flood algorithm, required before any other step gives correct results.
Flow Direction
The D8 steepest-descent direction for every cell, toward one of its 8 neighbors.
Flow Accumulation
How many upstream cells drain through each cell — the basis for deciding where a real stream channel actually forms.
Stream Extraction
Cells whose flow accumulation exceeds your chosen threshold, classified as a stream.
Stream Link
A unique ID for every stream reach between a headwater, a confluence, or the outlet.
Stream Order
Strahler order for every stream cell — headwaters start at 1, and order increases only where two equal-order streams merge.
Stream to Feature
The full stream network vectorized into real, exportable line geometry with stream ID and Strahler order as attributes.
Watershed Delineation
The complete upstream contributing area for any pour point you click, as a real polygon with computed area.
Frequently Asked Questions
Why mask my DEM to an area of interest first?
Real-world DEM downloads (SRTM, etc.) often cover a much larger area than you actually need. Masking to your area of interest before analysis genuinely reduces the amount of data processed, not just what's displayed — saving real time on large DEMs.
How is the stream threshold chosen?
A sensible starting value is suggested automatically (the 95th percentile of flow accumulation) after your first run. Raise it for a sparser network of only major channels, or lower it for a denser network including smaller tributaries.
Do I need to run each of the 8 steps myself, in order?
No — selecting any single operation automatically runs whatever earlier steps it depends on. Asking for Flow Accumulation runs Depression Filling and Flow Direction first without you triggering those separately.
What file format do I need to upload?
A single-band DEM in GeoTIFF, ERDAS IMAGINE, ASCII Grid, JPEG2000, or SRTM format (.tif/.tiff/.img/.asc/.jp2/.hgt). The optional area-of-interest layer accepts GeoJSON, Shapefile, GeoPackage, KML, or KMZ.
Is my uploaded data stored on your servers?
No. Files are processed in memory for your request and discarded immediately afterward.
Is this free to use for commercial or research work?
Yes, free for any use. For larger watershed studies or hydrological modeling projects, Sagarmekhla GIS Consultancy offers professional GIS and hydrology services.
Need a full watershed study or hydrological model? Our team provides professional GIS and hydrology analysis services for government, research, and industry.
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