The watershed
Delineated from USGS 3DEP terrain and snapped to the pour point for the kind of point you picked. Large watersheds split into sub-basins at their stream junctions.
Drainage study software · TR-55 on live data
Get a drainage study for any project.
Parcels, roads and culverts, detention ponds: draw the area and get peak flows, pond sizing and a report you can put your stamp on. The answer takes about a minute, and every number behind it stays visible.
Your first study is free. No card to start.
4.82
cfs peak flow, 10-yr storm
Your 12-inch pipe handles it, with 31% capacity to spare.
How a study runs
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01
Pick the point
A culvert, a crossing, an outfall or a parcel. The pour-point snap changes with the kind of point you picked — a road crossing pulls onto the stream, a parcel barely moves. Or draw the area by hand.
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02
Delineate the watershed
USGS 3DEP terrain, priority-flood fill, D8 accumulation, and the contributing area traced upstream. The window grows until the watershed fits, or it tells you it was truncated.
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03
Run it
NOAA Atlas 14 depths and SSURGO soils fetched live for that catchment. Composite CN, time of concentration measured off the longest flow path, TR-55 hydrographs routed by modified Puls.
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04
Read the answer
Peak flow and volume, what it means in one sentence, and a detention pond sized and sited if the site owes one. Every intermediate value stays on screen.
On a real site
What comes out
Rainfall and soils
NOAA Atlas 14 depths and SSURGO hydrologic soil groups, fetched live for that catchment — not typed in from a table.
Road crossings and culverts
Every place a road alignment crosses flowing water, with the culvert sized by FHWA HDS-5 and the headwater checked.
Flow and storage
TR-55 runoff and hydrographs, routed by modified Puls, with a detention pond sized across every storm and placed on the terrain.
Floodplain
FIRM panels and effective dates, SFHA and floodway intersections, and the explicit CLOMR, LOMR and no-rise language the review will ask for.
Criteria and the report
The jurisdiction's criteria applied and each finding stated, then a preliminary drainage study report in PDF and Word.
Methods, not magic
Every number traceable to a published method.
Drainage Study does not invent hydrology. It runs the methods your reviewer already accepts, on data it fetches for your site, and it shows the substituted values behind each result — not just the answer.
It is preliminary and honest by design: every output is labeled, every gap is stated, and nothing is sealed. This is the work that happens before the seal, so the expensive surprises surface while the design can still move.
- NRCS TR-55Runoff curve number, time of concentration, tabular hydrograph
- NEH-630Dimensionless unit hydrograph and convolution
- NOAA Atlas 14Point precipitation frequency by coordinate
- USDA SSURGOHydrologic soil groups for the catchment
- USGS 3DEP1 m elevation where it exists, 10 m everywhere else
- FHWA HDS-5Inlet-control culvert sizing and headwater checks
- FEMA NFHLEffective floodplain, floodway and panel data
Who it is for
Civil engineers
You already know how to do this study. The hours go into delineating the area, chasing rainfall and soils data, and rebuilding the same spreadsheet. Drainage Study does that part in about a minute and hands you every intermediate value, so the judgment stays yours and the clerical work stops being yours.
Developers and land buyers
Before you close on a parcel, you want to know what the drainage will cost you — how much detention the site owes, and how much of the ground you are buying is still developable after it. That answer usually takes a consultant and a week. Here it takes a point and a minute.
Your first study is free.
Create an account, pick a point, and read the answer. A subscription takes over after the first study.