Evaluation de l'impact de l'urbanisation sur la réalimentation des nappes d'eau souterraines au nord-est de Paris (France)

Résumé

Les sources localisées en bordure du plateau de Romainville au nord-est de Paris (France) ont été exploitées, au minimum, depuis le Moyen Age et jusqu'au dix-neuvième siècle pour l'approvisionnement en eau de la capitale. La synthèse des débits spécifiques (c'est à dire les débits par unité de surface de bassin versant) mesurés entre le dix-septième siècle et le vingtième siècle montre que ceux-ci sont de l'ordre de 2 à 3 l s^–1 km^–2 (en unités S.I., 2 à 3 10^–3 m³ s^–1 km^–2) et n'indique pas d'atténuation significative que l'on pourrait lier logiquement à l'urbanisation. Celle-ci entraînant l'imperméabilisation de 90% environ des sols, cet article conclut à un apport artificiel lié aux activités urbaines évalué entre 1,7 et 2 l s^–1 km^–2 ce qui représente environ 80% du débit total de l'aquifère.

Abstract

 The plateau of Romainville which spreads over the district of Belleville in Paris (France) to the town of Fontenay-sous-Bois has a surface area of about 12 km² and constitutes a geological and hydrogeological unit because at its base there exists an almost impervious formation, known as the "Glaises Vertes" (green clays of the Sannoisien stage). Above this formation, two water tables exist in two formations: the "Marno-calcaire de Brie" (siliceous limestone) and the "Sables de Fontainebleau" (sand). These two formations are separated by a clay layer: the "Marnes à Huîtres" (marl). In the past (before significant urban development), both waters flowed out naturally from the top of the Glaises Vertes on the edges of the area. Today, most of the springs are directed to the sewer network. Because they are close to Paris, these springs have been harnessed very early, through a very difuse and developed network of drains called "pierrées" and aqueducts. The different archives that have been used for this study provide much information regarding these springs, and the flow rate in particular. The first information available dates from the Middle Ages. This type of water supply was strategically important for Paris for at least six centuries (from the fourteenth to the nineteenth centuries). Having defined the different methods of harnessing the underground water this study shows the evolution of the flow rate through over 50 measurements. These date from the Middle Ages to today. The figures relating to the nineteenth century are surprisingly precise The data have been compared to the rainfall figures where these were available. In 1998 the flow rates were computed over a period of 9 months from the only remaining spring that is in use. A study of the piezometry has also been carried out in the town of Les Lilas which is a part of the plateau of Romainville. The information is compared with a piezometric map of 1882 known as the Map Delesse, drawn up before significant urban development occurred. Comparisons of the data available show that there has been no significant decrease in the specific yields of the springs during the twentieth century, although the catchment area has been totally urbanised with up to a 90% impermeability. Analysis of the piezometric values of 1882 and 1998 leads to the same conclusion. It is considered that, apart from the remaining rain which infiltrates to the water table, there must be another supply that compensates for the loss in catchment capacity. The compensation could be attributed to leaks in different underground networks such as the drinking water supply, the sewer network and the rainfall runoff network. The extensive use of water in public areas for cleaning roads and for irrigation purposes is also likely to contribute to the water table flow rate. The compensating flow of water is assessed at 1.7 to 2 l s^–1 km^–2 (i.e. 1.7 to 2 10^–3 m³ s^–1 km^–2), i.e. about 80% of the total flow of the aquifer.