Hydrohistorian
Lesson A2 · prior appropriation
Paper water and wet water
A water right names an amount — so it is natural to assume that amount is the water the ditch gets. It is not. The decree states the most a right may divert when water is available and the right is in priorityA senior water right demanding its water, which requires everyone junior on that stream to stop diverting until it is satisfied.; what a structure actually diverted, year by year, is a different and usually much smaller number. The gap between them has a name in Colorado water circles: paper water versus wet water.
See it on a real structure
Any ditch, canal or pump in the state — try your own. The numbers below come from DWR's decree and diversion records.
SOUTH PLATTE DITCH on SOUTH PLATTE RIVER
The paper: its 9 absolute decreed rights total 233.6 cfsCubic feet per second, a rate of flow. One cfs running for a day is about 2 acre-feet.. Flowing all 183 days of an April–October season, that rate would move 84,785 AFA volume: one acre covered a foot deep, about 326,000 gallons -- roughly a suburban household's outdoor use for a year..
One more layer of paper: summing 9 decreed rights counts alternate points, refills and exchanges of the same water more than once, so the bar above overstates even the on-paper maximum. Decrees stack; rivers don’t.
The water: in its median recorded year it actually diverted 15,443 AF — 18% of the paper figure.
Every recorded year against the same bar
A bar outlined in green exceeded the seasonal screen — winter diversions and storage movements can lawfully do that, which is itself a lesson in reading records.
The full record behind these figures: SOUTH PLATTE DITCH’s dossier.
Why the gap exists
Three reasons, all structural. The decree states a maximum rate, not a running total — a headgate rarely runs full for a whole season. The right can only divert when it is in priority — in a dry year a junior right may be called outNot entitled to divert right now, because a senior right is calling for the water. for much of the season. And a farm only takes what its crops and its ditch capacity can use.
The gap matters because Colorado law knows it. When a right is sold or its use is changed, the measure of what transfers is not the decreed amount but the right’s historical consumptive use — what was actually, beneficially consumed. Buying the paper number and receiving the wet one is the classic expensive mistake in Colorado water, and the reason change cases are fought over diversion records like the ones on this page.
What this does not let you conclude
The seasonal figure is a screen — the decreed rate run for a 183-day season — not an entitlement or a forecast, and diversions are not consumptive use: a real HCU analysis subtracts return flows and is engineering work this page does not do. Records can be incomplete, and a low year may reflect administration, drought, or simply a farmer’s choice. Advisory reading aid on public data — never a valuation, a title opinion, or a substitute for DWR administration.