Involved in the biosynthesis of (+)-O-methylkolavelool. Catalyzes the biosynthesis of (+)-kolavelool from (+)-kolavenyl diphosphate via the release of the diphosphate moiety through the nucleophilic addition of a water molecule. (+)-kolavenyl diphosphate + H2O = (+)-kolavelool + diphosphate Belongs to the diterpene synthase family.