Orne (Moselle)



The Orne is a river in Grand Est, north-eastern France, which is a left tributary of the Moselle and sub-tributary of the Rhine. Its source is in the hills northeast of Verdun. It flows east and joins the Moselle near Mondelange, between Metz and Thionville.

Name
"Orne" may originate from autura (a river, cf. Eure), or onna (a river) as mentioned in Endlicher's glossary of Gallic names De nominibus Gallicis, in which these words are translated into Latin as flumen.

If so, then there is no relationship with the name of the Orne river in Normandy, which is referred to as the Olina by Ptolemy, a homonym of Fluvius Olne, the Orne saosnoise in Sarthe, which Xavier Delamarre traces back to the Celtic olīnā (elbow).

Geography
The Orne is 85.7 km long. It rises at an elevation of 320 m in the Côtes de Meuse, in the commune of Ornes. It flows through Étain, Conflans-en-Jarnisy, Auboué, Homécourt, Jœuf, Moyeuvre-Grande, Rosselange, Rombas, Clouange, Vitry-sur-Orne, Gandrange and Richemont, where it joins the Moselle at an elevation of 155 m.

The people of the Pays Orne-Moselle and Pays de l'Orne communes have formed an association for the creation of a riverside trail named "Fil Bleu" ("Blue Thread") or "Promenade des Berges de l'Orne" ("Promenade of the banks of the Orne"), which will extend the length of the riverbed. Currently the trail extends about 22 km between the communes of Rombas/Clouange and Valleroy, and is either concrete or macadamised over all of this length. Between Rombas/Clouange and Rosselange, it exists on both sides of the river.

The section of about 2 km from Joeuf to the naval base at Homècourt is marked by a number of bridges and footbridges permitting passage from one bank to the other. Two of these footbridges are however no longer passable: the "passerelle de Moyeuvre Grande" (for which a detour via road bridge exists) and the "passerelle de la base nautique d'Homècourt".

The trail is frequently used by both pedestrians and cyclists, as well as by those on rollerblades. It crosses the communes of Rombas, Clouange, Rosselange, Moyeuvre Grande, Joeuf, Homècourt, Aubouè, Moineville and Valleroy. Since 2011, the trail has been extended from its prior endpoint to the commune of Amnéville-les-Thermes. Between 500 and 600 m of it have been built and are being maintained by the municipality of Rombas.

Tributaries
The Orne's principal tributaries and subtributaries are:

The Orne is also fed by water pumped out of the mines at 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 1226 km2, almost its entire watershed of 1268 km2.

The mean annual flow rate, or discharge of the river at Rosselange is 12.6 m3/s.

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 20.2 and 26.9 m3/s 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 2.81 m3/s in September. These monthly figures, however, are just averages, and conceal even more pronounced short-term variation.

'''Monthly average flow rate in m$3$/s measured at Rosselange hydrological station Data taken over a 41-year period '''

At low water, the 3-year low instantaneous flow rate can drop to 0.56 m3/s, 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 318 m3/s on 22 December 2003, while the maximum recorded daily average was 292 m3/s on the preceding day. The Orne's instantaneous maximum flow rate for 2 and 5 years (IMFR2 and IMFR5) are 170 and 230 m3/s respectively; the IMFR10 is 280 m3/s, the IMFR20 is 320 m3/s, and the IMFR50 is 370 m3/s. 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 190 m3/s as against 280 m3/s for the Orne, and its IMFR50 reaches only 270 m3/s as against 370 m3/s 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 326 mm annually, which is almost equal to the average of all France, but clearly less than the average in the French part of the Moselle basin, 445 mm at Hauconcourt. The specific flow rate reaches 10.3 litres per second per square kilometre of watershed.