An apparatus is described that allowed to estimate flow rates at the interface of compacted clay-geomembrane composite liners in the laboratory in presence of a geotextile. Thank to the results obtained in terms of flow rates some values of interface transmissivities could be deduced. Obtained values were compared to results obtained with ISO 12958 standard for single geotextiles. The results allow to study the influence of the normal stress applied on top of the composite liner, of the type of geotextile and topography of the soil liner surface. It can be deduced that on a flat compacted clay surface, the presence of a geotextile may increase advective transport in interface and thus through the composite liner, especially for thick non-woven needlepunched geotextiles. On an uneven surface, the implementation of a geotextile reduces the flow rate and thick geotextiles seem to act as resistant media. An increase in the mechanical load in the range 50-100kPa does not modify these results and the compacted clay liner surface quality could be the most influent feature.