What a Winter Rio Chama Release Reveals About the Middle Rio Grande
Background: Why the Water Was Stored
Last spring, state and federal water agencies stored approximately 34,000 acre-feet of Rio Chama water to assure a full supply for the six Middle Rio Grande Pueblos’ prior and paramount water rights. Less than 5,000 acre-feet was ultimately used by the Pueblos, about 2,000 acre-feet was lost to evaporation over the storage period, and roughly 26,000 acre-feet remained in storage at the start of winter.
That remaining water was released this month in a planned winter block release.
The Release and River Operations
The release originated at Abiquiu Dam and appears clearly in the Cochiti Dam release as rapid step increases in flow, a sustained six-day release of approximately 1,400 cubic feet per second (cfs), and a more gradual step-down when the release ended. The Rio Chama release flowed into the Rio Grande upstream of Cochiti Reservoir, where Cochiti Dam operations reflected the combined inflows. Cochiti Dam released 2,000 cfs for six days, also. This was by far the highest flow since 2023.
USGS gage data provide a clear picture of the timing and shape of this release as it entered and traversed the Middle Rio Grande system.¹
What these Hydrographs Show
As the pulse moved downstream, it weakened, spread out, and arrived later at each successive river gage below Cochiti Dam. By the time it reached Elephant Butte Narrows, only a small fraction of the released water remained in the river channel.
This behavior is consistent with a river that is hydraulically well-connected to heavily pumped tributary aquifers and dried over extensive distances and durations during the record dryness of early- and mid-2025. Large volumes of groundwater were pumped this past summer by municipal supply wells, domestic wells in and near the floodplain, agricultural wells, and phreatophytic riparian vegetation. Together, those large uses lowered groundwater levels in both the shallow river alluvium and the deeper aquifers beneath metropolitan Albuquerque.
As the surface water of the Cochiti Dam block release moved downstream, increasing portions of the swollen river flow left the river channel. Driven by gravity, it seeped through the river’s bed and banks to recharge the connected but depleted shallow aquifer storage space. The gaps between adjacent upstream and downstream gages illustrate these losses, accumulating reach by reach.²
Why This Winter Releases Is Revealing
Winter conditions make this behavior easier to observe. Irrigation diversions are absent, riparian vegetation is largely dormant, and evaporation from the river surface is small. Under these conditions, losses observed between gages have no plausible destinations other than groundwater recharge and temporary bank storage.
The hydrographs also show delay. Peaks arrive days later downstream, and in some cases downstream flows briefly exceed the contemporaneous Cochiti Dam release. This reflects travel time and temporary storage in the river channel and adjacent aquifers, not the appearance of new inflow.³
What Counts for Compact Accounting
Only water that actually reaches Elephant Butte Reservoir and increases the net volume stored or released from there counts toward New Mexico’s water delivery obligations under the Rio Grande Compact. Compact deliveries are accounted as the sum of the net annual change in Elephant Butte storage and total annual releases from Elephant Butte Dam . Daily reservoir storage volume data needed to complete that calculation are not currently available online so this analysis relies on the reservoir inflow measurement instead. Official accounting results will be available only after the federal agencies approve their provisional data and the Rio Grande Compact Commission approves the accounting. Official results are expected in early spring 2026.⁴
In the meantime, Middle Rio Grande delivery debt continues to accumulate. At the real-time flows shown in the graphic above, today’s under-delivery is approximately 90 acre-feet.
End Notes and Disclaimers
¹ Data limitations.
USGS streamflow data are provisional. Several gage locations on the Middle Rio Grande present difficult hydraulic and sediment conditions that limit measurement accuracy and precision. All observations and interpretations presented here should remain roughly accurate as the provisional data are reviewed and finalized. The author’s judgment is that the data set is internally consistent, which supports confidence in this early interpretation.
² Attribution of losses.
Attribution of observed surface-water losses to groundwater recharge is based on hydrologic inference, system behavior, and the absence of significant winter surface-water diversions. This analysis does not represent a quantified groundwater balance or a formal causal determination.
³ Delay and return flows.
Some delayed return of water from bank storage or groundwater back to the river may occur over time. The timing and magnitude of any such return cannot be determined from the available data. In any case, unless it adds measurably to the volume of water in Elephant Butte Reservoir this year, it won’t be counted in 2025.
⁴ Compact accounting.
Daily or interim delivery estimates reflect the author’s qualifications. Those estimates are published here for timely science- and data-driver reporting to the NM Water Advocates readers. Official results are determined annually and are subject to Commission approval, usually in late March each year.