How have courts interpreted the rule of reasonableness in the context of the reasonable use doctrine?

In Martinson v. Hughey (1988) 199 Cal.App.3d 318, 244 Cal.Rptr. 795, the court assumed that the rule of reasonableness applied to the discharge of [7 Cal.4th 355] irrigation waters and surface waters into a natural watercourse. There a lower owner had blocked a natural watercourse with debris which backed water up onto the upper land. Applying the rule to irrigation waters, the court concluded: "The rule we deduce ... is that the upper owner has the right to discharge reasonable and noninjurious amounts of irrigation water through natural areas of flow onto the lower owner's property. The lower owner has a co-equal burden to receive reasonable and noninjurious amounts of irrigation water through natural flowage channels." (199 Cal.App.3d 318, 328, 244 Cal.Rptr. 795.)

Page 630

[867 P.2d 741] In Weaver v. Bishop (1988) 206 Cal.App.3d 1351, 254 Cal.Rptr. 425, the question was liability for damages for improvements in a natural watercourse constructed for the purpose of protecting the defendants' property. The court held that the reasonable use doctrine articulated in Keys v. Romley, supra, 64 Cal.2d 396, 408-409, 50 Cal.Rptr. 273, 412 P.2d 529, was properly applied in an action predicated on damage caused by the riparian owner's installation of riprap (boulders) along the stream bank to protect the land from erosion. The riprap altered the flow of the stream sufficiently that erosion occurred on the opposite bank, the owners of which sued. Given an instruction that liability depended on the reasonableness of each party's conduct, the jury found by special verdict that defendants' conduct was reasonable, while that of plaintiffs was not.