Abstract
The hydrological information is the basis of any management of the water resources, of which the relevant scale is the watershed. In addition to direct use of the measurements themselves or derived data, this information is useful for many uses and its "added value", at the trans-boundary level, is multiple: risk prediction in a country located downstream, cross-border planning, management and sharing of benefits between countries. The importance of the operational hydrology is put forward in the undertaken' actions. Then, in partnership with the basin organizations, the transfer of experience in hydrometry with countries is led through expertise, through practical training when implementing modern tools for measurement network management, and through information systems. Decision-support tools give the opportunity to simulate the hydrological processes and the resources allocation depending on the uses and the geographical areas in the basin. Using this type of tool allows optimizing economical investments, which facilitates the profit sharing between countries. The examples of Niger, Mekong and Congo basins are presented. The French experience, coming from many trans-boundary projects of hydrological monitoring systems, shows that: their sustainability, once the foreign support is completed, is difficult to guarantee; it must be ensured by a financial commitment of the countries considering its benefits; the issues related to the use of hydrological measurements are major; only their knowledge allows an economical analysis of both heavy investments and environmental services; the National Hydrological Services play an essential role for the provision of data and the use of the hydrological information with the support of the trans-boundary basin organizations, which organize the valorisation of this information at the basin scale; France can pursue its support and a group of experts can be set up to develop and valorise the accumulated experience.