Measure/Site drainage before acquisition
For developers, engineers and acquisition teams
Site drainage analysis before you buy the land
The ground is the one thing about a parcel you cannot negotiate later. A site drainage analysis measures remotely, before an offer goes in, where water concentrates on the site, where it stands, and what it does at any structure already there — without site access, a landowner's permission, or a survey crew's calendar.
It is a diligence instrument, not a design instrument. It sharpens the question you take to your engineer, and it will occasionally kill a deal early, which is the cheapest place to kill one.
What it establishes
The bare-earth surface
The ground measured in 3D, with the trees and buildings stripped out, leaving the shape of the ground. This is the layer that matters on a wooded parcel, where a canopy-height surface tells you nothing about what a bulldozer will find.
The surface is gated before it is used: the median step between adjacent elevations must clear 0.004 m. Below that the surface is a coarse source stretched onto a fine grid, and every channel computed from it would be interpolation presented as measurement. The engine refuses the parcel rather than drawing on it, and ships the measured step with the refusal.
Where flow concentrates
Water is routed downhill and accumulated, spreading the way overland flow actually behaves — near-single-channel in a gully and dispersive across open ground. That distinction decides whether a natural drainage line is a constraint on your layout or a feature of it.
Existing buildings — on the parcel and adjacent to it — stand as walls in the model, so flow routes around structures rather than through them.
Where water is stored
Every closed depression is filled to its spill point, and the fill depth is kept rather than discarded. That depth is depression storage, and on a flat parcel it is often the single most consequential number in the diligence.
Millimeters matter more than intuition allows. On real ground, 282,572 m² of contributing area in Chicago and 201,312 m² in Pittsburgh drained into interior pits two to four millimeters deep and simply stopped, against largest surviving channels of 1,034 m² and 33,931 m². Water spills over a 2 mm lip; an unconditioned model does not, and any analysis built on one is reporting noise.
The arithmetic is checked against ground where the answer is known: a bowl cut into a 2% slope fills to its spill point at 0.28 m predicted against 0.289 m measured.
Grade at any structure already on the parcel
Slope measured 0.75 m to 3.25 m out on each wall's own outward normal, repeated and combined so no single reading decides it, against a 5% fall over 3 m target — with the direction printed only when it survives displacing the footprint one meter in each of sixteen directions.
An independent check on the routing
Where a city digs its storm drains is a yardstick nobody here tuned. Against Pittsburgh Water's published inlets: the 73 inlets in the frame fall within 10 m of a modeled channel 3.99× as often as the frame's own base rate at the 260 m radius the product ships — the control being the share of the frame that sits that close to a channel anyway. Pittsburgh is the only municipality publishing inlets in a form we can consume, so this is a one-city check.
The limits on that check
Pittsburgh is the only municipality that publishes its inlets in a form we can consume, so this is a one-city check and not a national one. Published inlet positions carry one to two meters of georeferencing error of their own. And an inlet sits where a crew could dig, which is not always where the water goes — agreement is evidence the routing is sane, not proof that it is right.
What it is explicitly not
- Not a stormwater design. Detention sizing, permitting, discharge agreements and design-storm modeling stay with your civil engineer. This measures existing conditions.
- Not a flood determination. No riverine or coastal inundation, no return period, no regulatory zone.
- Not a geotechnical report. Soil type, infiltration rate, bearing capacity and water table are not observed.
- Not a boundary survey. Parcel lines, easements and legal elevations require a licensed surveyor.
- Not a claim about any structure. Ground falling toward a foundation raises the risk of water reaching it — ordinary building science. That a particular building has water was not measured and is not claimed.
Where it earns its place in a diligence file
The value is timing rather than depth. A topographic survey is better than this, at a scale and cost that arrives after you are committed. This runs on public data before the offer, which means:
- You can screen several parcels and take one forward, instead of surveying the one you already liked.
- You arrive at the engineer with the drainage question already framed, rather than paying to have it discovered.
- You can price a constraint into an offer instead of discovering it in the entitlement period.
- On the Pro plan ($399 a month, 200 lookups) you can drop candidate buildings onto vacant land and re-run the terrain with them standing as walls.
Send us a site
Tell us what you are evaluating and where. We will run it, show you what the engine measured and what it refused, and be honest about whether the coverage supports the question you are asking.
A refusal is never billed. You can also run an address free to see the shape of the output.
Does this replace a civil engineer's stormwater design?
No. It measures existing terrain and where water goes on it. Design, sizing and permitting stay with your engineer.
How quickly can a parcel be measured?
It is measured remotely, so it needs no site access, no landowner permission and no survey crew calendar. That is why it fits a diligence window.
What if there is no usable elevation data?
The engine refuses and ships the measured step with the refusal, rather than interpolating. A refusal is never billed.
Can you model a proposed building on vacant land?
Yes — the development analysis tool on the Pro plan drops buildings onto vacant ground and re-runs the terrain with them standing as walls.