The Archer exception provides that, if a public entity's improvement falls within either of two narrow categories of "privileged" activities, the public entity's liability is subject to a reasonableness test rather than a strict liability standard. This exception owes it name to its origin in Archer v. City of Los Angeles (1941) 19 Cal.2d 19. In Belair v. Riverside County Flood Control Dist. (1988) 47 Cal.3d 550, the California Supreme Court applied the Archer exception to a public flood control improvement and held that a reasonableness test applied when a public improvement fell within the Archer exception. The damage in Belair was caused when a "flood control levee" gave way after heavy storms causing flooding of property belonging to the plaintiffs. (Belair at pp. 554-555.) The levee had been built by the flood control district to protect the plaintiffs' land from periodic flooding to which it had been subject prior to the construction of the levee. (Belair at p. 556.) The California Supreme Court again considered the parameters of the Archer exception. "The doctrine of the common law 'right to inflict damage,' emanating from the complex and unique province of water law, has been employed in only a few restricted situations, generally for the purpose of permitting a landowner to take reasonable action to protect his own property from external hazards such as floodwaters. Frequently referred to as the 'common enemy' doctrine, the notion is that the owner of land subject to flooding has the right to erect defensive barriers and that any injury caused thereby to lower landowners as the result of the increased discharge or velocity of water is considered damnum absque injuria." (Belair at pp. 563-564.) The court noted that "the common law privilege, however, does not permit a property owner to obstruct or divert a stream from its natural channel, or to collect and discharge surface waters so as to increase the natural servitude." (Belair at p. 564, fn. 4.) The Belair court distinguished cases where "the public improvement resulted in a diversion of surface or flood waters from their natural channel or drainage." (Belair at p. 566.) Although it declined to address the validity of these diversion cases, it suggested in dicta that strict liability might not be applicable in such cases either. "It is doubtful, however, whether evidence of an unintended 'diversion' -- an elusive concept to begin with -- would elevate the test of inverse condemnation liability to absolute liability, rather than a reasonableness standard. As earlier discussed, the purposes of the Constitution, rather than the rules emanating from the complex and unique province of water law, must fix the extent of a public entity's responsibility. It is sufficient for our purposes here to hold that when a public flood control improvement fails to function as intended, and properties historically subject to flooding are damaged as a proximate result thereof, plaintiffs' recovery in inverse condemnation requires proof that the failure was attributable to some unreasonable conduct on the part of the defendant public entities." (Belair at p. 567.) Thus, the California Supreme Court held that a public improvement that falls within the Archer exception subjects the public entity to liability only if the public entity acted unreasonably in creating or maintaining the public improvement. (Belair at pp. 565.)