Rio Grande Compact: Elephant Butte Storage Rule Explained

As of 16 April 2026, the U.S. Bureau of Reclamation put available storage in Elephant Butte and Caballo for the Rio Grande Project at about 265,000 acre-feet (news release). The same release put Elephant Butte at about 13% of capacity. On our mirrored Bureau of Reclamation series, Elephant Butte stood at 6.9% on 1 November 2026. The Rio Grande Compact's Article VII trigger is 400,000 acre-feet of usable Project storage.

The Compact was signed at Santa Fe on 18 March 1938 by Colorado, New Mexico and Texas. Congress consented in 1939. It apportions the Rio Grande above Fort Quitman, Texas. When usable water in Project storage falls under 400,000 acre-feet, Colorado and New Mexico may not increase storage of native Rio Grande water in reservoirs built after 1929. Project storage means Elephant Butte plus the other Project reservoirs available below it, principally Caballo.

This is a summary for general information. It is not legal advice. Compact accounting and storage rights are set by the Compact, the Rio Grande Compact Commission, and any decree that binds the parties.

The Compact and why Elephant Butte matters

The Compact's opening states that Colorado, New Mexico and Texas desired "an equitable apportionment" of the waters of the Rio Grande above Fort Quitman. Article I defines the terms the rest of the Compact uses. Two of them fix how Article VII is read:

"Project storage" is "the combined capacity of Elephant Butte reservoir and all other reservoirs actually available for the storage of usable water below Elephant Butte and above the first diversion to lands of the Rio Grande project, but not more than a total of 2,638,860 acre-feet."
"Usable water" is "all water, exclusive of credit water, which is in project storage and which is available for release in accordance with irrigation demands, including deliveries in Mexico."
"Credit water" is "that amount of water in project storage which is equal to the accrued credit of Colorado, or New Mexico, or both."

Usable Project storage is therefore not the same as the raw volume sitting in Elephant Butte and Caballo. Credit water is excluded. Reclamation's figure of about 265,000 acre-feet, as of 16 April 2026, is stated as "Available storage in Elephant Butte and Caballo reservoirs for the Rio Grande Project" and is the official Project figure used here for the Article VII comparison.

On our mirrored Bureau of Reclamation series, Elephant Butte Reservoir Dam and Powerplant stood at 6.9% of capacity on 1 November 2026, and Caballo Reservoir and Dam at 11.2% on the same date. Those fill percentages are calculated by reservoirs.earth: Reclamation storage divided by NID capacity. They are physical storage readings. They are not the Compact's "usable water" account. Live New Mexico figures are on the New Mexico state page; the July 2026 situation piece is New Mexico reservoir levels, July 2026.

Article VII: the 400,000 acre-foot storage rule

Article VII of the Compact states:

Neither Colorado nor New Mexico shall increase the amount of water in storage in reservoirs constructed after 1929 whenever there is less than 400,000 acre-feet of usable water in project storage; provided, that if the actual releases of usable water from the beginning of the calendar year following the effective date of this compact, or from the beginning of the calendar year following actual spill, have aggregated more than an average of 790,000 acre-feet per annum, the time at which such minimum stage is reached shall be adjusted to compensate for the difference between the total actual release and releases at such average rate; provided, further, that Colorado or New Mexico, or both, may relinquish accrued credits at any time, and Texas may accept such relinquished water, and in such event the state, or states, so relinquishing shall be entitled to store water in the amount of the water so relinquished.

What that means in practice, as the Compact and Reclamation describe it:

While usable Project storage is under 400,000 acre-feet, Colorado and New Mexico may not increase native Rio Grande storage in post-1929 upstream reservoirs.
Reclamation's 16 April 2026 release says: "Restrictions under the Rio Grande Compact also currently limit storage in El Vado." It adds that El Vado is limited to about 13% of capacity, about 25,200 acre-feet, for dam-safety reasons.
San Juan-Chama Project water, stored in reservoirs such as Heron, is imported from the Upper Colorado River basin. The NM Interstate Stream Commission overview says it "does not count toward New Mexico's Compact delivery obligations". Compact Article X also deals with imported water.
The same ISC overview names a second condition. Upstream storage of native water in post-1929 reservoirs is also restricted "when New Mexico carries a Compact debt".
The 790,000 acre-foot average-release proviso can shift when the 400,000 acre-foot floor is treated as reached. The Compact states that adjustment. The Rio Grande Compact Commission and its Engineer Advisers do the detailed accounting.
Relinquishment: a state with accrued credits may relinquish them, and if Texas accepts, the relinquishing state may store an equal amount even while Article VII would otherwise bar an increase.

Debits, credits and relinquishments

Articles VI and VIII set the debit/credit system that runs beside Article VII.

Annual credits and debits. Article I defines annual debits as the amounts by which actual deliveries in a calendar year fall below scheduled deliveries, and annual credits as the amounts by which they exceed those schedules. Accrued debits and accrued credits are the running balances over a common period. In a year of actual spill, Article VI says no annual credits or annual debits are computed for that year.

Caps. Under Article VI:

Colorado's annual debit and accrued debit shall each not exceed 100,000 acre-feet, except as caused by holdover storage in post-1937 reservoirs above Lobatos.
New Mexico's accrued debit shall not exceed 200,000 acre-feet at any time, except as caused by holdover storage in post-1929 reservoirs between Lobatos and San Marcial.
New Mexico shall not be charged with any greater debit in any one year than the sum of 150,000 acre-feet and all gains in storage in that year.
Within physical storage limits, each state "shall retain water in storage at all times to the extent of its accrued debit."

Calls for release. Article VIII lets the Texas commissioner, in January, demand release from post-1929 storage of the accrued debits of Colorado and New Mexico (and lets New Mexico demand the same of Colorado), limited by those debits, "sufficient to bring the quantity of usable water in project storage to 600,000 acre-feet by March first and to maintain this quantity in storage until April thirtieth," toward a normal Project release of 790,000 acre-feet that year.

2025 accrued-debit figure as published. A Rio Grande Compact overview PDF hosted by the Middle Rio Grande Conservancy District and attributed to New Mexico Interstate Stream Commission Compact administration (PDF created 14 January 2026) states: "2025 Status: New Mexico's accrued underdelivery, or debt, is approximately 124,000 acre-feet." The same document says a debt exceeding 200,000 acre-feet "constitutes a violation" under Article VI.

Texas v. New Mexico (Original No. 141)

Texas filed the original action in January 2013. The Supreme Court docket for the case is No. 22O141 (Texas v. New Mexico and Colorado, Original No. 141).

Dated status from that docket, read on 4 November 2026:

6 February 2026: Fourth Interim Report of the Special Master received.
2 March 2026: Fourth Interim Report ordered filed; exceptions schedule set.
26 May 2026: "The proposed final decree, Appendix A to the Fourth Interim Report of the Special Master, is entered." Special Master D. Brooks Smith is discharged.
8 June 2026: "The United States' claims in this case are hereby dismissed with prejudice."

The TCEQ news release of 5 June 2026 states that on 26 May 2026 the Court adopted the proposed final decree and discharged the Special Master, ending more than 13 years of litigation.

The decree is Appendix A of the Special Master's Fourth Interim Report (filed February 2026; decree entered 26 May 2026). It is titled "Consent Decree Supporting the Rio Grande Compact". It says it "specifies procedures to ensure the proper apportionment of Rio Grande water between Texas and New Mexico below Elephant Butte Reservoir". The tool is the Effective El Paso Index. The split below Elephant Butte follows the Project's irrigable acreage in each state at the time of the Compact, "approximately 57% in New Mexico and 43% in Texas". The decree does not amend Article VII. Article VII appears in the report only in the reproduced Compact and Commission rules.

Mexico delivery under the 1906 Convention

Article XVI of the Compact says nothing in the Compact "shall be construed as affecting the obligations of the United States of America to Mexico under existing treaties." Article XIV adds that Compact schedules "shall never be increased nor diminished by reason of any increase or diminution in the delivery or loss of water to Mexico."

The separate Convention of 1906 between the United States and Mexico, summarised by the International Boundary and Water Commission (IBWC), allotted Mexico 60,000 acre-feet annually of Rio Grande water, delivered on a monthly schedule at the headgate of Mexico's Acequia Madre above Juárez. The IBWC history page states that the United States constructed Elephant Butte Dam to facilitate those deliveries, and that in extraordinary drought or serious accident to the U.S. irrigation system the Mexican delivery "shall be diminished in the same proportion" as deliveries to U.S. lands under that system downstream of Elephant Butte. Compact "usable water" expressly includes water available for release for deliveries to Mexico.

Summary table

Rule	Threshold as stated	Body	Consequence	Source date
Article VII storage limit	Usable water in Project storage < 400,000 acre-feet	Rio Grande Compact (CO, NM, TX); administered with Reclamation Project storage	Colorado and New Mexico shall not increase storage in post-1929 reservoirs (relinquishment exception)	Compact signed 18 March 1938; federal consent 31 May 1939; text as in NMSA § 72-15-23 / TCEQ Compact PDF
Article VII release adjustment	Average actual usable releases > 790,000 acre-feet per annum since spill / effective date	Rio Grande Compact	Timing of the 400,000 acre-foot minimum stage is adjusted	Same Compact text
Article VII relinquishment	Accrued credits relinquished and accepted by Texas	Rio Grande Compact	Relinquishing state may store an equal amount	Same Compact text
Article VI New Mexico debit cap	Accrued debit ≤ 200,000 acre-feet (with stated holdover exception)	Rio Grande Compact	Debit above that level is a Compact violation as described by NM ISC overview	Compact text; NM ISC / MRGCD overview PDF (created 14 January 2026)
Article VI Colorado debit cap	Annual / accrued debit ≤ 100,000 acre-feet (with stated holdover exception)	Rio Grande Compact	Colorado must retain storage to the extent of its accrued debit	Compact text
Article VIII January call	Bring usable Project storage to 600,000 acre-feet by 1 March and hold through 30 April	Rio Grande Compact	Texas (and NM vs CO) may demand release of accrued debit water from post-1929 storage	Compact text
Project available storage (operations)	About 265,000 acre-feet in Elephant Butte + Caballo for the Rio Grande Project, as of 16 April 2026	U.S. Bureau of Reclamation, Albuquerque Area	Below Article VII's 400,000 acre-foot usable-storage floor as published	Reclamation news release, 16 April 2026
Physical fill (mirrored gauges)	Elephant Butte 6.9%; Caballo 11.2%	Calculated by reservoirs.earth: Reclamation storage divided by NID capacity	Physical fill only, not Compact usable water	Reading date 1 November 2026
NM accrued underdelivery (2025 status)	Approximately 124,000 acre-feet	New Mexico Interstate Stream Commission Compact overview (via MRGCD host)	"Narrow margin" before the 200,000 acre-foot threshold, in the ISC's words	PDF created 14 January 2026; labelled "2025 Status"
Texas v. New Mexico final decree	Decree entered; U.S. claims dismissed with prejudice	U.S. Supreme Court, Original No. 141 (22O141)	Consent decree entered; Special Master discharged	Docket entries 26 May 2026 and 8 June 2026
1906 Convention Mexico delivery	60,000 acre-feet per year (pro-rata cut in extraordinary drought)	IBWC / 1906 Convention	U.S. delivery at Acequia Madre above Juárez	IBWC history page (Convention of 1906); Compact Arts. XIV and XVI

Sources and methodology

Sources were read on 4 November 2026 unless a source carries its own earlier date.

Rio Grande Compact text: NMSA 1978, § 72-15-23; TCEQ, The Rio Grande Compact (PDF).
U.S. Bureau of Reclamation: News release, 16 April 2026 ("Available storage in Elephant Butte and Caballo reservoirs for the Rio Grande Project is currently about 265,000 acre-feet"; Elephant Butte at about 13%; El Vado Compact and dam-safety limits).
reservoirs.earth mirrored BOR readings: Elephant Butte Reservoir Dam and Powerplant and Caballo Reservoir and Dam, reading date 1 November 2026.
New Mexico Compact administration overview: Rio Grande Compact and Administration (PDF) hosted by MRGCD (created 14 January 2026; 2025 accrued-underdelivery figure, storage restriction conditions, San Juan-Chama water).
U.S. Supreme Court: Docket 22O141 (entries 26 May 2026 and 8 June 2026); Fourth Interim Report of the Special Master, Appendix A (PDF); TCEQ release, 5 June 2026.
IBWC: History: Convention of 1906 (60,000 acre-feet annual allotment to Mexico).

How this page was put together: each rule, threshold and figure is quoted from the body that publishes it, with that source's date. Compact text comes from NMSA 1978, § 72-15-23 and the TCEQ Compact PDF. Nothing has been converted or projected.

Cite this page: reservoirs.earth, "Rio Grande Compact: Elephant Butte Storage Rule Explained", data as of 4 November 2026, https://reservoirs.earth/the-reservoir/rio-grande-compact-elephant-butte-storage-rule.