Hydrohistorian
Lesson A5 · The Line · prior appropriation
Reading an administration number
Every decreed right in Colorado carries one number that settles every argument about who waits for whom: the administration numberDWR's numeric encoding of a water right's seniority. Smaller is more senior; the integer part counts days from 1849-12-31 to the date that ranks the right.. It looks like an ID. It is actually a date — two dates, packed into one sortable value — and once you can read it, a rights table stops being a wall of digits.
Decode one
12696 . integer part — 12,696 days after December 31, 1849 → 1884-10-04, the date that ranks this right (its adjudicationWhen the water court confirmed the right. A use decreed in 1975 was not a decreed use in 1955, however old the appropriation is., or its appropriation when no earlier adjudication exists).
.03774 fractional part — 3,774 days after the same epoch → 1860-05-01, the appropriation dateWhen water was first put to beneficial use. It sets seniority unless a prior adjudication date is later.. A fraction appears only when the water was first put to use before the right was adjudicated — which is most of the 19th century.
Smaller number = earlier date = more senior. Sorting any rights table by admin number IS sorting it by who diverts first.
Why two dates
Colorado ranks rights by adjudication rounds, not appropriation alone: a right decreed in a later round ranks behind everything from earlier rounds, even if its water was put to use first. The integer part carries that controlling date; the fraction preserves the older appropriation date so it can still break ties inside a round. The worked default above — 12696.03774 — is a real pattern: adjudicated October 4, 1884, for water first used May 1, 1860.
This decoder is the same function the rest of the site uses (legal.admin_number_to_dates), with hand-computed test vectors behind it, and the convention is checked against HydroBase’s documentation. See a whole table of these on any structure dossier.
What this does not let you conclude
The admin number ranks; it does not adjudicate. Whether a specific right is administered at its number on a given day involves calls, futile-call judgment, plans and exchanges that no single number carries. Advisory reading aid on public data — never an administrative or legal conclusion, and never a substitute for DWR administration or an engineer’s analysis. Our methodology has not yet had outside expert review: how this is built.