Jarny, Giraumont, Auboué and Orne-Roncourt. Hydrology The Orne is a substantial river, similar to its neighbours in the West Lorraine region which rise in the Côtes de Meuse. Flow rates of the Orne at Rosselange The Orne's flow rate has been measured over a period of 40 years (1967–2007) at Rosselange, in the Moselle department a short way upstream of the confluence. The watershed of the Orne at Rosselange is , almost its entire watershed of . The mean annual flow rate, or discharge of the river at Rosselange is . The Orne exhibits strongly marked seasonal fluctuations, such as are very often found in the east of France, with high water in winter/spring bringing the monthly average up to between from December to March inclusive, with a maximum in February. Summer low waters are quite prolonged, from June to early October, with a low monthly average of in September. These monthly figures, however, are just averages, and conceal even more pronounced short-term variation. Monthly average flow rate in m/s measured at Rosselange hydrological stationData taken over a 41-year period At low water, the 3-year low instantaneous flow rate can drop to , as is seen frequently for rivers of the region. Flooding of the Orne can be very significant. The maximum instantaneous flow rate ever recorded was on 22 December 2003, while the maximum recorded daily average was on the preceding day. The Orne's instantaneous maximum flow rate for 2 and 5 years (IMFR2 and IMFR5) are respectively; the IMFR10 is , the IMFR20 is , and the IMFR50 is . These figures indicate that the flood of December 2003 was, roughly speaking, a 20-year event and thus not particularly unusual. The Orne's IMFRs are over half that of the Meurthe, the Moselle's most significant French tributary and whose basin is almost 2.5 time larger. To compare with a significant river in the Paris basin, the Loing, a river known for its substantial flooding, has an IMFR10 of as against for the Orne, and its IMFR50 reaches only as against for the Orne. This is despite the Loing's watershed being three and a half times larger than the Orne. The Orne is fed by heavy rainfall in the western part of its watershed. The runoff curve number in its watershed is annually, which is almost equal to the average of all France, but clearly less than the average in