# PondSheet

> Site stormwater calcs in your browser, with a report reviewers can check.

Browser-based site stormwater calculations for New York civil engineers: design rainfall, runoff, pond routing, NYSDEC checks and a PDF report.

PondSheet is for small New York sites: commercial pads, retail sites and small subdivisions with one to a few detention ponds or underground chamber systems. The engine is the NRCS TR-55 and TR-20 method (CN runoff, the dimensionless unit hydrograph, storage-indication routing) with the NYSDEC design manual criteria the engineer selects. It runs in the browser and on the server from one Rust crate, and the report comes with a SWMM 5 .inp so a reviewer can rerun the routing in any SWMM tool.

PondSheet checks a design against the criteria the engineer selects. It does not speak for the DEC, a town or a plan reviewer; the engineer who seals the report is responsible for it.

Some reference records are still awaiting their check against the printed source, so results are marked PRELIMINARY.

## Free calculators

No account. Each runs the same engine as the full app, in the browser, and opens on a published worked example with its source cited.

- [Curve number and runoff calculator](https://pondsheet.com/tools/curve-number): Composite CN from cover type and hydrologic soil group, then TR-55 runoff depth for a 24-hr rainfall.
- [Time of concentration calculator](https://pondsheet.com/tools/time-of-concentration): TR-55 Tc from a sheet flow, a shallow concentrated flow and a channel flow segment, in hours and minutes.
- [Rational method calculator](https://pondsheet.com/tools/rational-method): Peak runoff Q = Cf·C·i·A from the runoff coefficient, rainfall intensity and drainage area, with the frequency factor for the storm.
- [Detention volume calculator](https://pondsheet.com/tools/detention-volume): Storage needed to hold post-development runoff to an allowable release rate, by the modified rational critical-duration method.
- [New York water quality volume calculator](https://pondsheet.com/tools/ny-water-quality-volume): WQv = P·Rv·A/12 from the 90th percentile rainfall, impervious cover and contributing area, per the NYSDEC design manual.

## Not in scope

- CAD drawing or grading design
- Storm sewer network design, culverts and channels (a channel appears only as a Tc segment)
- 2D flood modeling and large-watershed studies
- States other than New York
- Desktop or mobile apps

## Pricing

$99 per firm per month, unlimited engineers and projects. 14-day trial, every feature, no card. Plan reviewers open a read-only share link with no account.

## Pages

- [Validation](https://pondsheet.com/validation): how the numbers are checked
- [Pricing](https://pondsheet.com/pricing)
- [Help](https://pondsheet.com/help): the calculators and the source documents
- [About](https://pondsheet.com/about)

Operated by Crux Labs LLC. Contact: hello@pondsheet.com