Abstract

This project deals with the water management of the ski resort in Puy-Saint-Vincent. An enlargement of the ski resort and tourist facilities is proposed to satisfy the tourism requirement for the coming years. This project will be treated with four main parts which are the hydrological study of the catchment area, the adjustment of the skiing domain, the study of the drinking water distribution network and future needs, and the study of the environmental impacts of these adjustments.

The aim of the first part is to learn more about the watershed’s hydrological behaviour. A simulated water balance needs to be performed. Two softwares are thus used for modeling : CemaNeige will give a relevant discharge estimation and HEC-­HMS will provide snow depth values thanks to a specific template. Both of them will use snowmelt data. Hydrodynamic models calibration and validation are based on four-year meteorological data in order to get an optimal performance. Results show that discharges on the watershed are too low compared to the increasing water needs. This phenomenon is supposed to increase due to climate changes (rise of temperature and precipitation). To balance the upcoming lack of water, the construction of a new reservoir is envisaged (choice of possible localizations, retention basin scaling and safety structures). A particular attention is drawn for snow avalanche fences. Indeed downstream flood risks are high in case of avalanches or landslides. This exposure scenario would lead to a one square metre area affected.

To satisfy the enlargement of the ski resort, it is necessary to use snow­blowers, to fight on one hand against the global warming and on the other to offer better skiing conditions to the increasing tourist demand. In the case of the Puy­-Saint-­Vincent ski resort, the artificial snow coverage will concern two different parts. The first one is the artificial snow coverage of a largest part of the current ski slopes. Today, only 38 % of tracks are equipped with snow­blowers and the objective is to raise up this ratio to 50 %. The second is the creation of a low elevation new ski trail, allowing to connect the domain of Puy­-Saint-­Vincent to the village of Vallouise, located down the valley. Regarding the altitude, an artificial snow coverage is essential for this ski trail. A water conveyance network equipped with snow­blowers was modelled using the software Porteau, and a model validation was performed with season 2013-­2014 data. The 27000 cubic metre reservoir is filled few times a year, to reach a total volume of 90 000 cubic metres per season used for artificial snow production. However, this volume is not enough to satisfy the proposed domain enlargement. Consequently, it is necessary to build a new reservoir. The new water convenyance network was modelled using Porteau. Two choices are proposed for the new network. Thanks to a one season simulation, both of them are conceivable, considering the the volume and the new reservoir feed flow. Water flows and pressures in each snow­blower are in the range of expected values. The decision is finally made on environmental and economic criteria, knowing that the first one is slightly more expensive to install, and the other one causes noise pollutions and ground degradations.

The third part of the project consists in studying the drinking water ressources in Puy-Saint-Vincent. Currently, about 500 people are leaving there permanently and the city is able to host 12 000 tourists during the winter season. In order to increase tourism facilities, an extra 4 000 beds can be provided.
« La source des Mondes » is the main drinking water ressource currently used. According to the French legislation (prefectoral order from 2011), a maximum daily water volume of 3456 cubic metres is allowed to be withdrawn. In 2003, about 2400 cubic metres were daily pumped from the source during the winter season. This quantity represents 70% of the maximum volume allowed to be taken. The daily water consumption is estimated at 120 liters per person. An increase of 4 000 beds in the ski resort will lead to an extra drinking water production of 740 cubic metres per day. As the legislation changes regularly, a new drinking water treatment plant has been chosen as the best solution to provide an extra drinking water volume to the city. The raw water is pumped from a new hill reservoir designed on the first part of the project. Three drinking water treatment steps have been study : slow sand filtration, membrane filtration and disinfection.
Finally, the drinking water distribution system was investigated. It is composed of  five 500 cubic metre tanks. The main one is fed by « la source des Mondes ». The others are supplied with the overflow of the main tank. A study about the variation of the water volume in the main tank within a day showed that no extra water can be stored in it. An extra 300 cubic metre tank is considered to receive the extra drinking water production. 

The fourth part consists in studying the impacts of the different facilities on the natural environment. In a first step, preliminary studies allow to choose four potential construction areas for the new hill reservoir, taking into account regulations applicable in a mountain context (natural parks, protected areas, flora and fauna protected species). Natural hazards that could threat each construction areas are also considered to exclude risk areas or to forecast specific protection facilities.
The impacts of artificial snow are studied in a second part, dealing about climatic, hydrologic, flora and fauna aspects. Because of a greater density, artificial snow may alter soils, decreasing gas exchanges with atmosphere and delaying vegetation process for weeks. These phenomena, in addition of a local overload, promote landscape changes and erosion process, increasing landslide risks. The example of two new track snow cover are treated. They allow to develop compensatory policies. In a third part, the impacts caused by the new hill reservoir construction are envisaged. Two potential construction areas are situated on wetlands, and a third one may dry the downstream wetland. Water intakes in nearby rivers to fill the reservoir may jeopardize aquatic species if ecological instream flow regimes are not respected. Compensatory policies like shore revegetation or artificial wetlands creation should be set up if the project is accepted.