The Milandre underground river is recognized as a site of high patrimonial value and is monitored for many parameters since 1990. The recent construction of a highway in-cluding a tunnel portal 50 meters above the cave galleries induced a series of dedicated observations. Among them, was the monitoring of flow conditions at a series of inlets at cave roof in the part of the cave located directly below the road. Water discharge and CO2 concentrations have been monitored for 5 years before the highway construction, 5 years during the road construction and 3 years after. The effects of the removal of the soil and epikarst, as well as the sealing of the surface could be observed in the cave, implying significant changes in the regime of the water inlets in the cave. As this effect was predicted and confirmed by observations, it was decided to build an injection sys-tem below the road in order to artificially feed this part of the cave which is highly dec-orated with active speleothems. The injection system is operating since October 2011 and several tests are being conducted in order to adjust discharge and CO2 concentra-tions of the injected water. Cave inlets clearly react to injections, but the control of CO2 concentrations is still difficult to fix. A modeling of recharge before, during and after the road construction has been attempted. Changes in the recharge parameters accord-ing to the three situation of the construction could be assessed. The model should be improved in order to take CO2 and possibly temperature transfer into account.
Investigations related to the dimensioning and construction of the injection system, as well as experiments, which can be conducted using this system are very valuable for better characterizing diffuse recharge of karst systems.