What data is used when no site survey or DEM is provided?

Terrain and elevation auto-fill from an open DEM (SRTM ~30 m); rainfall uses regional IDF presets; land cover comes from Sentinel-2. These are coarse open-data inputs shown as indicative ranges, not exact values — override any field with survey data for higher accuracy.

Beta · Screening only ≈ 60 seconds No sign-up to run

Know your flood risk before spending on detailed studies.

Draw your site for a preliminary flood-risk screening — not a design or approval basis.

Run a screening How it works

Most teams spend two to three days on a desk-study screening like this — done here in about a minute.

What you get when you run it — about 60 seconds

Flood risk band

Low / Medium / High, with a confidence score and the drivers behind it.

Recommended next steps

Which studies you'll likely need, and roughly how many days each takes.

Auto Curve Number + workings

Composite CN (AMC I/II/III) from satellite land cover & soil, plus Tc, peak flows and hydrograph — every assumption shown.

Downloadable PDF report

Take the screening summary to your team, client or the relevant authority.

This tool IS

A rapid screening estimate
A guide to which studies + roughly how long
Labelled by data source (measured vs. assumed)

This tool IS NOT

A hydraulic / inundation model
A substitute for DEM, survey or municipal IDF
A design, permit or approval basis

How this screening works

From polygon to hydrology in three steps

Inputs

Site polygon, terrain class, land cover, region, return period.

Method

Auto Curve Number (land cover × soil), Kirpich/NRCS Tc, Rational + SCS-CN, regional IDF, risk scoring.

Output

Risk band + gauge, indicative ranges, study scope, full audit trail.

Draw your site boundary using the toolbar in the map's top-left corner — draw the site/parcel itself, not the surrounding catchment (the tool derives that automatically). For exact geometry, upload GeoJSON / KML / SHP in the form below.

Layers

Catchment Depth bands Site depth grid r.lake extent Low-lying zones (DEM) Drainage paths (DEM) Streams + site entrance (DEM) ML flood susceptibility

Basemap

100% of design depth

Map legend

Your site boundary Contributing catchment (conceptual) Conceptual flood depth bands Site flood-depth classes (conceptual, see readout for ranges) r.lake flood extent (bathtub approx.) Flood-risk cells (Low/Med/High) Building within flood extent Low-lying / pooling-prone (DEM) Natural drainage path (DEM) DEM stream network Stream entrance (outlet) Stream exit ML flood susceptibility (low→high)

All layers except your site boundary are conceptual/indicative — derived from coarse open data, not survey.

Site boundary

Or upload / paste boundary (GeoJSON · KML · zipped SHP)

Region & return period

Region

Return period

Terrain — used only if no DEM (auto-detected on run)

Terrain & land cover

High elev. (m)

Low elev. (m)

Flow length (m, opt.)

Elevation & terrain type are auto-filled from the open DEM (SRTM ~30 m) on run. Edit either field to override with survey data.

Land cover mix (%) — auto-detected from satellite on run

Paved/roofs

Landscape

Desert/bare

Land-cover year (Sentinel-2)

Curve Number is auto-derived from this year's land cover + SoilGrids soil. Edit the mix above only to override.

Catchment context

Wadi / major channel near or through site

Contributing catchment (km², opt.)

Flow direction (°, opt.)

Your screening results will appear here

Draw a polygon with the toolbar (top-left of the map) or upload a boundary, set the inputs, then run the screening.

Common questions

Flood screening — FAQ

Is this a hydraulic or inundation model?

No. It's a preliminary screening tool — an indicative flood-risk band, a recommended study scope and screening hydrology. It is not a hydraulic / inundation model and not a design, permit or approval basis.

What does the screening produce?

A Low / Medium / High risk band with a confidence score, an automated composite Curve Number (AMC I/II/III) with full workings (time of concentration, Rational and SCS-CN peak flows), a recommended list of studies with rough durations, and a downloadable PDF report — in about 60 seconds, no sign-up.

How is the Curve Number calculated?

The composite TR-55 CN is derived from satellite land cover (Sentinel-2 10 m, Impact Observatory/Esri) combined with the hydrologic soil group from SoilGrids (USDA texture cascade, WRB fallback), then adjusted for antecedent moisture (NEH-630 AMC I/II/III). Every assumption and source appears in the audit trail.

Can I use the result for design or authority approval?

No. It's a screening estimate to scope the work ahead. Design and submission require measured survey/DEM, jurisdiction-specific rainfall (IDF) and full hydrology/hydraulic modelling. Each result is labelled by data source, so measured and assumed inputs stay clearly separated.

What data is used when no survey or DEM is provided?

Terrain and elevation auto-fill from an open DEM (SRTM ~30 m); rainfall uses regional IDF presets; land cover comes from Sentinel-2. These coarse open-data inputs are shown as indicative ranges, not exact values — override any field with survey data for higher accuracy.