SUMMARY
Some forest nurseries, qualified as modern, were the site of several failures related mainly to irrigation management which disadvantages the production of plants of good quality and consequently their installation and their ability to overcome transplanting crises. This study is a contribution to the program of Oued El Bir forest nursery (which is belonging to the delegation of El Haouaria, Nabeul governorate in the North East of Tunisia) rehabilitation. In this work, we carried out a diagnostic study of the existing hydraulic infrastructure in addition to irrigation network sizing in order to reveal existing dysfunctions and then propose possible remedies. Diagnosis study revealed some anomalies throughout the irrigation network such as water losses and equipments wear (valves, sprinklers, pipes, head station equipment and electrical cabinet). The sizing calculation has shown that existing network is oversized and adopted irrigation strategy is not strictly appropriate to the network characteristics.