## Facts

- Plaintiffs owned downstream riparian properties along Reliez Creek, a natural watercourse in Contra Costa County, California.
- The City of Lafayette, Contra Costa County, and other public entities approved or built upstream streets, storm drains, culverts, and drainage facilities that collected, concentrated, and discharged runoff into Reliez Creek.
- Plaintiffs alleged the improvements increased the volume and velocity of water entering the creek and altered the method of discharge, causing erosion, bank instability, landslides, and loss of land on their properties.
- Plaintiffs claimed the entities knew increased runoff from development was causing, and would continue to cause, downstream damage.
- Plaintiffs sued for tort damages and inverse condemnation under article I, section 19 of the California Constitution.
- The Court of Appeal applied *Archer*’s “natural watercourse rule” to bar liability for discharging surface water into a natural watercourse; the California Supreme Court granted review.

## Issues

1. Whether an upstream landowner, including a public entity, is categorically immune from tort liability for downstream damage when it discharges surface water into a natural watercourse.
2. Whether article I, section 19 requires compensation (inverse condemnation) for downstream property damage caused by increased flow and velocity traceable to public improvements and runoff.
3. What standard governs liability when upstream alterations increase stream flow and harm downstream riparian property.

## Decision

- The California Supreme Court reversed the Court of Appeal’s categorical bar on liability and remanded for further proceedings.
- The court rejected *Archer* to the extent it stated a categorical “natural watercourse” immunity for upstream landowners who increase and discharge runoff into a natural channel.
- The court held an upstream landowner’s liability—public or private—turns on whether its conduct was reasonable under all the circumstances when its improvements increased flow volume/velocity or altered the method of discharge and caused downstream damage.
- The court held inverse condemnation liability is not categorically foreclosed in these circumstances; subsequent decisions permit compensation where public improvements unreasonably cause downstream damage.

## Legal Principles

- When upstream alterations discharge an increased volume of surface water into a natural watercourse, and the increased volume/velocity or method of discharge causes downstream property damage, an upstream landowner (including a public entity) may be liable if its conduct was unreasonable under all the circumstances.
- The reasonableness inquiry may consider the extent of increased volume/velocity attributable to the improvements, the manner of discharge (e.g., concentrated or channelized), foreseeability and magnitude of downstream risk, and the relative utility of the improvements compared to the severity of the harm.
- Public entities are evaluated as property owners for drainage impacts; discharge into a “natural” watercourse does not by itself eliminate liability.
- Article I, section 19 may require compensation when public improvements, as planned and constructed, proximately and unreasonably cause damage to private property, including substantial damage from drainage and runoff increases without physical occupation.

## Conclusion

The court replaced a categorical “natural watercourse” immunity with a fact-specific reasonableness standard and held that public entities can be liable in tort and inverse condemnation when their upstream drainage-related improvements unreasonably increase stream flow or change discharge conditions and thereby damage downstream riparian property.


Locklin v. City of Lafayette, 867 P.2d 724 (Cal. 1994)