Tributary groundwater is the river

1969: the hinge

For a century wells sat largely outside priority administration — drilling was a way to take stream water without standing in the line. The Water Right Determination and Administration Act of 1969 ended that: tributary groundwater came into the priority system, wells became junior diverters like any other, and the well-versus-ditch conflict became the defining fight of the next half century. Most tributary wells could only keep pumping under augmentation plans that replace their stream depletions. A curriculum that skips 1969 leaves you unable to follow any modern groundwater dispute in the state.

The delay is the hard part: a well’s depletion of the stream arrives lagged and smeared — months or years after pumping, spread over years (lesson D3). A well pumping nothing today can owe the river water for years, which is why plans and their accounting exist.

See the system underground

The Groundwater tab maps 34,000 monitored wells statewide, charts any well’s water-table history back as far as 1883, pools stream-corridor trends, and runs an advisory Glover stream-depletion screen with its assumptions printed beside the number. The water table’s ups and downs are the river’s slow-motion shadow.

What this does not let you conclude

Not all Colorado groundwater is tributary: designated-basin water and the Denver Basin bedrock aquifers answer to different allocation rules entirely (lesson D2), and whether a specific well is tributary — and how much it depletes which reach — is an engineering and legal determination, not something a map can settle. 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.