Facts
In 2004, company A. SA (the Company) obtained a concession (the Navizence Concession) to use the waters of the lower Navizence basin and the Fang torrent to produce electricity. However, due to the insufficient capacity of the existing headrace tunnel between Vissoie and Niouc, a portion of the conceded waters (approximately 20 million m3) was discharged and not turbined. The Cantonal Energy and Hydroelectric Power Service of the Canton of Valais included these discharged waters in the tax base of the cantonal special tax on hydroelectric power, which the Company contested. The Federal Tribunal ultimately upheld the Company's appeal.Considerations
According to the Federal Tribunal, Art. 51(3) of the Federal Act on Hydroelectric Power (WRA) must be interpreted to mean that, when granting a concession, the usable flows that are included in the calculation of the determining theoretical power are the usable flows that can be absorbed by the installations that the concessionaire is required to construct, as provided for in the text of the concession. When a concession is granted while existing installations are already in place, the extent of the usable flows depends on what the concession provides. If the concession does not stipulate that the concessionaire has an obligation to carry out work to improve the capacity of the existing installations, the latter remain the "planned"…