About
Built for the engineer who seals the plan
CurveNumber is for the civil engineer or site planner who will put a seal on the drawing and then sit across from a reviewer who is paid to doubt it. The arithmetic is TR-55, and there is nothing novel about it. What is different is that every figure arrives with where it came from, so defending it takes an hour rather than an afternoon.
What you can rely on
- Every number says where it came from. It was read from a published source, with the edition; or it is a stated assumption, with what that assumption is worth in your answer; or a person changed it, with their name and their reason.
- It says "not computed" rather than guessing. When the public data cannot support a number, such as an unrated soil under most of the site, the tool stops and tells you what it needs. It does not fill the gap quietly.
- Nothing is rewritten after the fact. Every change to a site is kept in a record that cannot be edited, and each report is stored with the run it came from, so it can be reproduced.
- Your reviewer can check it. The report carries the citations, the assumptions and every override of a default on its face.
What stays with you
CurveNumber supports your judgment and does not replace it. A licensed professional remains responsible for the design. Your local manual is the rule you are reviewed against, and the tool holds only what a person has transcribed from it. Every figure the tool prints should be checked the way you would check any figure you seal; the tool's job is to make that check quick.
What is not finished yet
CurveNumber is in a private pilot with invited engineers, before launch. Here is what an engineer should know before relying on it.
The published curve number tables and the rainfall distributions were transcribed by one person and have not yet been checked by a second. Reports that use them say so. The cover table holds 81 rows from TR-55 Tables 2-2a to 2-2d; a cover type that is not among them is not computed, not guessed. One row of the antecedent runoff condition table looks wrong against its neighbors and is left exactly as transcribed until someone checks it against the published document.
CurveNumber can fit a curve number to an observed rainfall and streamflow record. That figure describes everything that drains to the stream gauge. It is not your site's curve number, and the tool will not print it against a parcel outside that drainage area, or against one too small a part of it.
Two things are still absent. There is no asymptotic fit of curve number against rainfall depth, and there is no confidence label on a calibrated figure. So the assistant cannot explain a calibration yet. That part is not built.
Also not finished
- The peak flow tables are unchecked. Peak flow uses the NRCS unit hydrograph, for one storm or for every storm in the set. The unit hydrograph and rainfall distribution tables behind it have not yet been checked by a second person, and every peak says so. A time of concentration under 6 minutes is raised to the TR-55 minimum of 6 minutes, and the results say that too.
- The storm set is the same everywhere. Water quality, 1, 2, 10, 25 and 100-year, 24-hour. There are no state or county storm sets yet: if your reviewer asks for a different storm, type its depth. The General check (peak with practices at or below the existing peak) is a plain test, not your local rule.
- Suggest a fix resizes one practice. It tries a fixed menu of sizes, 1.25 to 3 times the current one. It does not design a new practice or size a pond.
- Suggested drainage areas read the ground, not the pipes. Where curbs, inlets and pipes decide where water goes, it says so and asks you to draw. The thresholds and citations behind the warnings have not yet been checked by a second person.
- Coverage is the contiguous United States (the lower 48 states), because the public datasets are. Alaska, Hawaii, Puerto Rico and the territories are not covered.
- One meter land cover is located but not read yet.
- Card payment is built and switched off. Nobody has paid for CurveNumber yet. Until card payment is on, payment is by invoice, as the pricing page explains.
- Aerial imagery classification is a guess you accept or reject. It has been checked against an independent published measurement on one site (n = 1), which is one agreement and not a validation. What it costs to use is on the features page.
- The assistant is available, and unreviewed. It is switched on for the live deployment, for invited accounts. It runs on Claude Sonnet 4.6 through Amazon Bedrock in US regions, and writing help in text boxes runs on Claude Haiku 4.5. It cannot produce a number of its own, and a check blocks any answer that tries. It has not yet had the expert review panel that would let anyone call it correct. Using it sends your site's record to a commercial model vendor, which the privacy page describes item by item.
- Accounts are opened by invitation. The access page records a request.
Who is behind it
CurveNumber is operated by CZDTS LLC. Background on the people and the research behind it is at waterdmd.info. How the service is secured, and what your IT department will want to know, is on the security page. Write to support@curvenumber.com with any question.