Hydrohistorian
Lesson C1 · The Ledger · records & administration
How to read a diversion record
Everything in Colorado water argument eventually lands on one artifact: the diversion recordWhat a structure reported taking from the stream, as recorded by DWR. It is a record of reporting, not a meter reading. — the water commissioner’s account of what a headgate actually took, day by day, kept since the 1880s in some districts. Change cases are fought over it, yields are computed from it, and it rewards knowing how to read it.
The columns that matter
The daily value is a rate (cfs, a daily mean), not a volume — volume comes from summing rate × time (1 cfs for a day ≈ 1.98 AFA volume: one acre covered a foot deep, about 326,000 gallons -- roughly a suburban household's outdoor use for a year.). The water class says what movement the row describes: a Total (Diversion) row is water taken at the headgate; a Total (Release) row is storage water let out. They are different movements — summing them as one series double-counts, which is a real mistake we have made and now test against. Days recorded matters as much as volume: 40 days of diversions and 200 days of diversions are different stories at the same AF.
Zero is ambiguous. A year with no recorded volume can mean a dry ditch, a closed headgate, an unmeasured take, or a record nobody kept — the record alone cannot say which. That ambiguity is why yield analysis is careful work, and why abandonment is never concluded from zeros alone.
AGRICULTURAL DITCH’s record, read that way
DWR’s record for this structure runs 1950-05-02 to 2025-10-31 — 15,960 daily values, peaking at 120.0 cfs.
| Year | AF | Against its own record | Days | Peak cfs |
|---|---|---|---|---|
| 2018 | 4,474 | 6th lowest of · 77% of median | 208 | 35.9 |
| 2019 | 9,534 | 9th lowest of · 164% of median | 217 | 38.2 |
| 2020 | 10,593 | 15th lowest of · 182% of median | 228 | 58.1 |
| 2021 | 10,138 | 13th lowest of · 175% of median | 216 | 48.5 |
| 2022 | 10,451 | 14th lowest of · 180% of median | 276 | 39.4 |
| 2023 | 9,710 | 11th lowest of · 167% of median | 311 | 40.8 |
| 2024 | 9,868 | 12th lowest of · 170% of median | 216 | 39.2 |
| 2025 | 9,536 | 10th lowest of · 164% of median | 215 | 39.4 |
The middle column is the reading skill this lesson teaches: a year means little as a number and a lot as a rank.
The full record, downloadable with a citable README: its dossier.
See it on a real structure
Pick a structure and read its actual record the way the columns above describe.
What this does not let you conclude
A diversion record measures what passed a headgate — not what a crop consumed, not what returned to the river, and not what the right was entitled to; and record-keeping practice varied across a century of commissioners. 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.