## Facts

- Groundwater levels in the San Luis Valley’s unconfined aquifer declined due to increased pumping and drought, creating risks to Rio Grande Compact compliance and alleged injury to senior surface-water rights.
- Groundwater irrigators formed Special Improvement District No. 1 within the Rio Grande Water Conservation District to manage pumping and avoid widespread well curtailment.
- The Subdistrict proposed a Plan of Water Management to govern well operations using fees, incentives, and replacement obligations to prevent “material injury” to senior surface rights and address aquifer sustainability.
- The Plan identified a non-exclusive set of possible actions (e.g., acquiring and retiring irrigated acreage, obtaining surface rights for replacement water, and funding recharge projects) without committing to a single fixed set of projects.
- The State and Division Engineers indicated they would administer wells in reliance on the Plan, rather than broad curtailment, if the Plan received judicial approval.
- Senior surface-rights holders and related entities objected, arguing the Plan was speculative, too indefinite to ensure non-injury, and inconsistent with Colorado water law and the compact.
- The water court approved the amended Plan with conditions, including monitoring, annual replacement planning, reporting requirements, and retained jurisdiction to adjust or terminate the Plan if needed.

## Issues

1. Whether statutes authorizing subdistricts and groundwater management plans permit this Plan and its administration within Colorado’s prior appropriation system.
2. Whether the Plan, implemented through annual replacement plans and decree conditions, provides sufficiently concrete and enforceable protections to prevent material injury to vested senior water rights.
3. Whether the Plan’s flexible, forward-looking structure is unlawfully vague or speculative, and whether retained water-court jurisdiction may be used to supervise and modify the Plan over time.

## Decision

- The Colorado Supreme Court affirmed the water court’s decree approving the amended Plan of Water Management as conditioned.
- The Court held the Plan and the Subdistrict’s operation were statutorily authorized and consistent with prior appropriation and the State Engineer’s administrative duties.
- The Court held the Plan’s annual replacement plan requirement and decree conditions supplied enforceable safeguards against material injury to senior rights.
- The Court upheld retained jurisdiction as a lawful and central mechanism for continued judicial oversight and correction if implementation failed to prevent injury.

## Legal Principles

- Colorado statutes allow basin-scale groundwater management through court-approved plans of water management and subdistricts, functioning as a collective method for junior users to meet replacement obligations.
- A water-management plan may permit continued junior groundwater pumping only if enforceable mechanisms ensure prevention of material injury to senior water rights.
- Specific, enforceable annual replacement plans may supply the operational detail required to quantify depletions and provide replacement water or other measures each year, subject to administrative and judicial oversight.
- A plan need not predetermine every future project if binding performance obligations, monitoring/reporting requirements, and effective enforcement tools ensure non-injury in practice.
- Water court retained jurisdiction may be used to supervise implementation, hear challenges to future annual plans, and modify or terminate an approved plan that fails to meet legal standards.

## Conclusion

The court upheld a subdistrict’s adaptive groundwater management plan because statutes authorize such plans, and the decree’s enforceable annual replacement planning, monitoring, and retained jurisdiction provided legally sufficient assurance that senior surface-water rights would be protected from material injury.


San Antonio, Los Pinos & Conejos River Acequia Pres. Ass’n v. Special Improvement Dist. No. 1, 270 P.3d 927 (Colo. 2011)