Compressive deformation of prefabricated geocomposi(e drains (GCDs) affects the flow capacity and is therefore a significant design issue for many applications. Conceptually, it is understood and recognized that deformation is a function of compressive stress and time (i.e., load duration). This paper presents a methodology for evaluating the combined effect that compressive stress and load duration have on the flow capacity of GCDs. The methodology is used to calculate a “compressive creep reduction factor” that is used as a critical component in evaluating the factor of safety against drainage failure. Compressive creep test data from two commercially available GCD products are presented with a design example to demonstrate the methodology.