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The goal of the paper is to assess the temperature effect of a large (40 ha) pond with a surface weir, damming a confluence zone of four streams in Limousin (French Massif Central). The research is based on 536,552 water temperature measurements, upstream, downstream and inside the pond. Compared to the most frequent calculation method, which consists in measuring the difference between the inlet and the outlet, two new methods are used. The first consists in weighting the temperature values of each of the four tributaries, in order to construct an overall inlet temperature. The second considers the distance existing between the inlets and the outlet. After reconstitution of the former hydrographic network, the method applies a temperature gradient from upstream to downstream mixing temperatures to each confluence. According to the method of weighting the inlets, the Great Pond Cieux warms the watercourse by 1.8°C for a full year and by more than 4°C from June to September. It also modifies the thermal regime of the watercourse, by reducing its diurnal temperature variation. According to the temperature gradient method, the significant warming during the summer months would be due one third to the natural evolution of the streams from upstream to downstream and two thirds to the pond. During some weather types, in particular periods of forced convection by stormy winds, the responsibility of the pond would even be much less.

Le concept de « frontière lacustre » pose de nombreuses questions quand il s'agit de prendre en compte la diversité des enjeux aquatiques face aux problématiques environnementales et politiques contemporaines. D'une logique de séparation, il faut penser coopération avec un élément aqueux qui se soustrait aux réalités terrestres de la frontière. Délimiter un objet lacustre, marqué par ses mouvements et sa profondeur, peut tout à fait se penser, même en cartographie. Par contre, une cartographie linéaire de la frontière peut avoir comme effet d'ancrer la représentation d'une limite forte, même quand elle peut être imperceptible dans la réalité. Il faut donc sortir des représentations classiques linéaires renforçant l'image d'une limite intangible, plus ou moins épaisse. Dans cet article, il est proposé d'utiliser l'outil de la cartographie mentale pour analyser le regard porté par les individus sur la réalité frontalière du lac Léman. Dans une volonté de proposer un regard géographique original, le public choisi est constitué de jeunes enfants (autour de 10 ans) qui ont participé à la croisière d'été « Eau'tour du Léman ». Cet événement, organisé par l'Association de sauvegarde du Léman, a permis de montrer la diversité des regards entre séparation politique et lieu commun à protéger.

Les littoraux sont des zones de concentration de différentes activités socio-économiques qui sont parfois difficiles à concilier. Le tourisme balnéaire par exemple, exige une plage de qualité et des eaux de baignade propres, ce qui peut entrer en conflit avec d'autres activités comme la pêche et la transformation des produits marins. Cet article vise à examiner comment l'occupation désordonnée des zones côtières par différentes activités socio-économiques impacte le tourisme côtier, et à proposer des solutions pour une gestion plus rationnelle de ces espaces. L’étude s’est focalisée sur le littoral de l’axe Abéné-Kafountine, au sud Sénégal. Une première évaluation de l'occupation des zones côtières entre Abéné et Kafountine a été effectuée pour analyser les conflits d'utilisation et leurs effets sur le tourisme. La méthodologie combine la cartographie des activités et une approche qualitative basée sur des entretiens et des observations. Les résultats de la cartographie de ces installations montrent une occupation anarchique du littoral, avec une centralisation des quais de pêche à Kafountine et à Abéné et la répartition de part et d’autre des aménagements touristiques. Cette situation combinée à un problème d’aménagement entraîne l’insalubrité de la plage. Les résultats des enquêtes qualitatives permettent de constater la frustration des hôteliers et des touristes qui déplorent la prolifération des ordures et la fumée sur la plage, ce qui pénalise le secteur touristique. Des pistes sont enfin explorées pour envisager une gestion durable et concertée de ces territoires.

In recent years, in France, water mills have been rediscovered thanks to their ability to generate hydroelectric energy. As in the past, their operation depends on a weir pool, which nature is very similar to that of a pond during some seasons of the year, especially during summer, when flows aren't strong and the water column has thermal stratification. Thus, the objective of this article is to study whether downstream of this environment we find the same thermal effects generated by other types of reservoirs, such as summer warming or the reduction of thermal amplitudes. To do this, recording thermometers were placed upstream, downstream and in the weir pool of Thévalles (Mayenne, FR) water mill, which is fully operational today and which is inserted in a hydrological context representative of the French reality. The results obtained show that the effects on water temperature are generally weak both when the mill is in operation and when it is not.

The Step Pyramid of Djoser in Saqqara, Egypt, is considered the oldest of the seven monumental pyramids built about 4,500 years ago. From transdisciplinary analysis, it was discovered that a hydraulic lift may have been used to build the pyramid. Based on our mapping of the nearby watersheds, we show that one of the unexplained massive Saqqara structures, the Gisr el-Mudir enclosure, has the features of a check dam with the intent to trap sediment and water. The topography beyond the dam suggests a possible ephemeral lake west of the Djoser complex and water flow inside the 'Dry Moat' surrounding it. In the southern section of the moat, we show that the monumental linear rock-cut structure consisting of successive, deep compartments combines the technical requirements of a water treatment facility: a settling basin, a retention basin, and a purification system. Together, the Gisr el-Mudir and the Dry Moat's inner south section work as a unified hydraulic system that improves water quality and regulates flow for practical purposes and human needs. Finally, we identified that the Step Pyramid's internal architecture is consistent with a hydraulic elevation mechanism never reported before. The ancient architects may have raised the stones from the pyramid centre in a volcano fashion using the sediment-free water from the Dry Moat's south section. Ancient Egyptians are famous for their pioneering and mastery of hydraulics through canals for irrigation purposes and barges to transport huge stones. This work opens a new line of research: the use of hydraulic force to erect the massive structures built by Pharaohs.

The subject proposed in this article concerns the intersection of the hydrodynamics of lakes and ponds with the economic development of their territory. It will be a question of understanding the interactions between these water bodies and territorial actors evolving on these limnic territories. Different managements are therefore imposed on each of the parties present. These managements are organized according to the limnological mechanisms specific to each environment (ponds and lakes), their temporality, their spatiality, and their risks for the human activities integrated into these water bodies. We will focus in this article on water and sediment movements not yet studied to interact with local managements. These phenomena constitute a base on which the actors around these water bodies can rely to guide the measures used to protect their activities. The purpose of this article is to provide scientific insights for decision support to actors evolving in the federation of municipalities of the Great Lakes, in the Landes, in New-Aquitaine (France).

In Senegal, in the agricultural perimeters of the Gorom-Lampsar axis (middle delta of the Senegal River), small agricultural farmers are faced with secondary soil salinization resulting, on the one hand, from the consequences of neoliberal policies initiated in the 1980s, and, on the other hand, of the effects of the absence of assistance from the State in agricultural policy. This situation leads to an absence of an operational management framework, and consequently to poor water management at the small scale of the perimeters. Such management, added to poor development policies which further weaken the control of water use as well as poor drainage and poor disposal of agricultural waste, cause, beyond salinization and the abandonment of land, the destruction of the fragile state of this agricultural space. In this context, farmers use vernacular indicators for recognizing soil salinity and mobilize associated agronomic and hydraulic practices, which are dominated using chemical fertilizers. This promotes better yields in the short term but does not necessarily ensure good management of saline land, which is inherent in water management, which is intended to be operational and strategic.

The weir pools are the spaces formed by the raising of the water line and the slowing of the current caused by weirs, overflowing hydraulic structures, generally of small dimensions, very widespread in contemporary rivers. The nature of these environments is still poorly understood and water sciences struggle to classify them in known continental aquatic environments. Some see them as degraded segments of watercourses, which have totally or partially lost the typical features of lotic environments; others consider them as ecosystems as such, with their own functionalities and their own role to play in environmental dynamics. In a research that we have recently published, we equate weir pools operation with ecotones operation and we would like to explore this hypothesis in further detail in this paper. Indeed, weir pools and ecotones are controlled by environmental gradients and seem to have the same functionalities, such as the ability to filter matter, to store and redistribute substances and to provide a real habitat for different types of organisms. This new vision of weir pools can even be extended to other man-made aquatic environments, ponds for example. Thus, new research and management outlook arise as this type of environment will no longer be considered as a mere obstacle within rivers, but as environments which are fully integrated into today’s fluvial landscapes with their own functionalities.