LiDAR Hydrology: Flow, Drainage, Depressions, Shorelines

The challenge

Hydrology is where a survey turns into a second project

The terrain model is the easy half. Turning it into a drainage network usually means a desktop GIS, a chain of tools run by hand, and a threshold nobody can defend.

The manual chain

Export the terrain, open a desktop GIS, run a dozen tools in order
Pick a flow threshold by trial and error, then argue about it
Fill every hollow so the water runs — and lose the ponds you were asked to measure
Run the whole chain again from scratch when the site is re-flown

Lidarvisor

Tick the layers you want before processing; the chain runs with the survey
Thresholds derived from your site — surveyed area, median slope and measured surface noise
Depressions measured before the terrain is conditioned, so the hollows survive into the deliverable
Every run rebuilds the layers from the current point cloud

The layers

Four hydrology deliverables from one processing run

Flow accumulation

Where Water Concentrates, Cell by Cell

A catchment-area raster over hillshaded terrain.

Every cell carries the area that drains through it, computed on a hydrologically conditioned surface built from your ground points. The display raster shades the whole field on a logarithmic ramp over a hillshade of that surface, so the network reads against the relief that produces it instead of floating on a flat background.

Catchment area in square metres per cell
Colour ramp anchored on the channel-start threshold, so two sites can be compared
The conditioned terrain surface delivered alongside it as GeoTIFF
Legend image carrying the drained-area values for your own project

Map the flow paths

Drainage axes

The Stream Network, Ordered and Attributed

One 3D line per stream link, carrying what it drains.

The network above the channel-start threshold is split into links, Strahler-ordered, smoothed and traced along the conditioned surface. Every vertex carries an elevation, so the axes sit on the terrain in the 3D viewer and come into CAD as 3D polylines rather than flat lines you have to drape yourself.

Strahler order and upstream drained area on every link
Length and average slope per link
Links flagged where the water enters the survey from outside it
3D vertices, sampled from the conditioned surface

See the vector outputs

Drainage axis centrelines traced across a survey area

Depressions

Closed Hollows, Measured Before Anything Is Filled

Depth, volume and spill level for every basin that holds water.

Depressions are computed on the raw ground surface, before conditioning, so what you receive is the hollow as it was surveyed rather than the remainder left after an algorithm smoothed the terrain. Each polygon records how deep it is, how much it holds, and how the conditioning treated it.

Maximum depth, mean depth, area and volume
Spill level — the elevation at which the hollow overflows
Breached or filled, recorded per depression
Delivered as rings at the spill level, in 3D

Measure the hollows

Closed depressions detected across a survey area, shown as filled polygons

Sub-basins

The Catchment Behind Every Outlet

The survey divided into the area feeding each stream outlet.

The site is split into the drainage area that feeds each outlet of the network and clipped to the surveyed footprint. Basins below a usable size are dissolved into the one downstream, so you get catchments you can work with rather than one polygon per pixel.

Area in hectares, and the stream order at the outlet
Outlet coordinates and elevation on every basin
Basins touching the edge of the survey are flagged
Draped on the conditioned surface for 3D display

Delineate the catchments

Catchment sub-basins delineated over a survey area, each drainage area in its own colour

Detail

One control, not a parameter sheet

The channel-start threshold is derived from the surveyed area, the median slope and the surface noise measured on your own cloud. A single setting shifts the whole ladder when you want a denser or a sparser network.

Finer

Halves the channel-start area: more headwater branches, smaller sub-basins.

Balanced

The default. The threshold follows the site, and steeper ground lowers it on its own.

Coarser

Doubles it: the main network only, and larger catchments behind it.

Water surfaces

Lakes, rivers and coastlines

Water bodies & shorelines

Detected on the Imagery, Grown Against the Cloud

Enclosed water closes into a polygon; water that leaves the survey opens into a shoreline.

Water is found on the orthophoto and then grown against the point cloud itself, so the boundary follows the water surface rather than a colour edge in a photograph. Water fully enclosed inside the surveyed area closes into a polygon; water that runs out of coverage opens into shoreline lines instead — a river gets two banks, a coast gets one.

Water body polygons, with islands carved out as holes
Shoreline lines wherever the water leaves the surveyed area
The detected water surface written back into the classified cloud as class 9
Driven by your orthophoto, or by satellite imagery when you allow it

Classify a point cloud

Colourised aerial LiDAR point cloud of a rocky coastline, with the shallow seabed visible through the water

CAD

On the Drawing, Not Only in the Viewer

Hydrography arrives as its own layers in the topographic map.

Drainage axes, depressions and sub-basins each land on their own layer in the topographic-map DXF, beside the shoreline, the water body and the contours. The sheet legend is generated with them, and the printable PDF comes out of the same drawing.

Dedicated stream, depression and basin layers in the DXF
Shoreline and water body on their own layers, in hydrography blue
A legend row generated for every layer that carries geometry
Printable PDF sheet produced from the same drawing

See terrain and contours

Extracted shoreline vector in blue running through orange terrain contour lines

Reference

What each layer carries

Layer	Geometry	Attributes	Formats
Flow accumulation	Raster	Catchment area per cell, plus the conditioned surface	GeoTIFF
Drainage axes	3D lines	Order, upstream area, length, slope, edge flag	GeoJSON, SHP, DXF
Depressions	3D rings	Max and mean depth, area, volume, spill level, treatment, edge flag	GeoJSON, SHP, DXF
Sub-basins	3D rings	Area, outlet order, outlet X/Y/Z, edge flag	GeoJSON, SHP, DXF
Water body	Polygons	Type, islands as holes	GeoJSON, SHP, DXF
Shoreline	Lines	Type	GeoJSON, SHP, DXF

GeoJSON is written in WGS 84; shapefiles and DXF stay in your project CRS. On a survey in feet, areas and lengths are converted with the file.

How it works

Your hydrology workflow

01

Upload

Drag and drop LAS or LAZ files, with your orthophoto if you have one. No conversion, no preprocessing.

02

Choose

Tick the layers you need — flow accumulation, axes, depressions, sub-basins, water body, shoreline — and pick a level of detail.

03

Deliver

Inspect everything in the 3D viewer, then download the vectors, the rasters, the CAD drawing and the report.

Outputs

What lands in your download

GeoJSON

Every vector layer in WGS 84, ready for web maps and for GIS.

Shapefile

SHP with its DBF, SHX and PRJ, in your project CRS, attributes included.

DXF

One drawing per layer, plus the merged topographic map with all of them on it.

GeoTIFF

Flow accumulation and the conditioned terrain surface, georeferenced.

3D viewer

Every layer standing on the terrain in the browser, attributes on hover.

Project report

A hydrology section in the PDF: counts, lengths, volumes and the parameters used.

Use cases

Hydrology use cases

Runoff & flood studies

Concentration paths and contributing areas measured on the surveyed ground, not on an open-data terrain model.

Drainage & earthworks

Where water reaches a road, a platform or a trench, and which hollows will hold it afterwards.

Ponds, wetlands & storage

Depth, area and volume for every closed hollow, with the level at which it spills.

Rivers, canals & coasts

Shorelines and water bodies as survey vectors, with the water surface classified in the cloud.

Questions

Frequently asked questions

Do I need to supply a terrain model?

No. The hydrology stage builds its own ground surface from the classified point cloud, at a resolution chosen from the size of the surveyed area. You do not have to run the DTM first, and turning the DTM off does not turn hydrology off.

What does "conditioned terrain" mean, and does it change my DTM?

A raw ground surface has hollows that water cannot leave, so a flow algorithm stalls in them. The hydrology stage first breaches a hollow where a genuine outlet lies close enough, then fills whatever is left, and runs the flow analysis on that surface. It is delivered as its own raster beside the flow accumulation. Your DTM deliverable is untouched, and no watercourse is ever burned into the terrain.

How is the threshold between a slope and a stream chosen?

From your site rather than from a default. It scales with the surveyed area, drops on steep ground and rises on flat ground, and is bounded at both ends so a very small or very large survey still gets a sensible network. The Finer and Coarser settings halve and double it. The value actually used is written into the report and into the layer metadata.

Why are some axes and basins marked as edge features?

Because a survey has a boundary and water does not. A stream that enters from outside the flown area carries a catchment we cannot see, and a basin touching the boundary is only the part inside it. Those features are flagged so you can tell a measured catchment from a truncated one instead of quietly under-reporting it.

Does water detection need an orthophoto?

It works best with one. Water is detected on imagery and then grown against the point cloud, so an orthophoto of your own survey gives the sharpest result. When you have none, you can allow the use of open satellite imagery for the detection step, and the extraction still runs against your cloud.

Can I edit the layers afterwards?

Yes. The vectors are editable in the viewer like every other vector deliverable, and regenerating the report and the topographic map after an edit rebuilds the drawing with your changes on it.

Documentation

Learn the hydrology workflow

How to process water and drainage layers with Lidarvisor.

User Documentation
Guides, workflows and output reference

Ready to see where the water goes?

Upload a survey, tick the layers you need, and get the drainage network, the hollows and the catchments back with the rest of your deliverables.

Get started free

No software to install. No thresholds to guess. View pricing or contact our team

Where the Water Goes,Straight from the Point Cloud