Abstract

     The use of water in rivers in order to produce electricity is nowadays regulated and controlled very closely by the French State. Indeed, even if this kind of electricity is considered as a renewable energy, environmental pressures have put a stop to the hydroelectric estate development. However, before the French Revolution, lords could deliver a French ownership rights as regards the water to a private individual. After 1789, the same rights were delivered by the French State. These rights which are passed down from parent to child, allow to use the force of the water on a precise section of a river.

     This is the case of the private individual Mr. Bonnet, who owns full French ownership rights on a section close to Le Pont de la Taule on the Salat River, in Ariège. A prefectoral decree dating from 1883 defines the characteristics of a facility which was a sawmill for marble at the time. This facility was composed of a weir across the whole breadth of the river, a headwater channel and a tail race. This facility is now derelict but Mr. Bonnet plans to rehabilitate it into a micro-hydropower plant to produce and sell electricity.

     This website presents all the necessary studies for this project, namely a hydrological study, a mechanical and electrical design, an environmental impact assessment with two compensatory measures for both ecological and sedimentary continuity but also an economic study. Therefore, six focal areas were tackled.

     The first step of the project was to lead a hydrological study. This refers to the data collection and to the water resource appraisal. With regard to the water resource, two angles were addressed: the first one about the production and the second one concerning the security. The former involved the assessment of the notable flows and water levels while the latter called for a flood study.
     Thereafter, a technical study was conducted, fulfilling two requirements: the owner's needs and the electrical company’s conditions. Under these circumstances, and with the hydraulic data obtained from the 1st study, the various components to produce electricity and to connect the power plant to the national network were chosen.
     On another hand, the rehabilitation project has to ensure ecological continuity in order to be approved by competent authorities. Therefore, the construction of a facility allowing fish to cross the weir was necessary. For that purpose, the migratory species present in this part of the river were listed to determine the relevant fish pass which was sized afterwards.
     However, the Salat is also classified by the Environmental Code as a river in which sedimentary continuity is compulsory. That's why the weir had to be modified by setting up a type of valve. That valve must be openned during a flood to let the river pebbles pass. After hydrodynamic and sedimentary dynamic numerical modellings, the place and the size of the valve were determined.
     Since the Law of Nature Protection of 16 July 1976, an impact assessment is mandatory on every work, activity or project, whose the layout and the content are set by the law. The assessment is composed by several steps like the diagnosis of the initial state, the evaluation of the project effects on the environment and the ways to reduce or compensate all the effects. Since the project is quite small, only a modest impact assessment about the rehabilitation into a micro-hydropower plant was done.
     Finally, it is important for the owner to determine if his project would be profitable. If it is too expensive, then it will probably not be interesting to bring it to fruition. Consequently, an economic study was completed in order to determine the profitability of Mr. Bonnet's project depending on whether the turbine is a Banki-Mitchell or a hydrodynamic screw. For that purpose, the time of return on investment was calculated to know when the owner would be beneficiary. Therefore, one of the two scenarios considered was retained in light of the financial viability.

     To conclude, all these studies have revealed that the rehabilitation of Mr. Bonnet's facility into a micro-hydropower plant is a feasible project which would be profitable within a few years.