"Article I, section 19 (formerly art. I, 14) of the California Constitution requires that just compensation be paid when private property is taken or damaged for public use. Therefore, a public entity may be liable in an inverse condemnation action for any physical injury to real property proximately caused by a public improvement as deliberately designed and constructed, whether or not that injury was foreseeable . . . ." (Chatman v. Alameda County Flood Control etc. Dist. (1986) 183 Cal. App. 3d 424, 431 [228 Cal. Rptr. 257], quoting Souza v. Silver Development Co. (1985) 164 Cal. App. 3d 165, 170 [210 Cal. Rptr. 146].) "A storm drainage system constructed and maintained by a public entity is such a public improvement. [Citations.] An action in inverse condemnation will lie when damage to private property is proximately caused by use of a storm drainage system for its intended purpose. The fact that a part of the system may have been actually constructed by a private person will not insulate a public entity from liability, if the system has been accepted or otherwise approved by the public entity. " (Souza v. Silver Development, supra, 164 Cal. App. 3d at p. 170; accord, Chatman v. Alameda County Flood Control etc. Dist., supra, 183 Cal. App. 3d at pp. 431-432.)