The Vorderrhein (German; English: Anterior Rhine; Sursilvan: ; Sutsilvan: Ragn Anteriur; Rumantsch Grischun, Vallader, and Puter: Rain Anteriur; Surmiran: Ragn anteriour) is one of the two sources of the Rhine. Its catchment area of 1,512 square kilometres (584 square miles) is located predominantly in the canton of Graubünden (Switzerland). The Vorderrhein is about 76 kilometres (47 mi) long, thus more than 5% longer than the Hinterrhein/Rein Posteriur (each measured to the farthest source). The Vorderrhein, however, has an average water flow of 53.8 m3/s (1,900 cu ft/s), which is less than the flow of the Hinterrhein. According to the Atlas of Switzerland of the Swiss Federal Office of Topography, the source of the Vorderrhein—and thus of the Rhine—is located north of the Rein da Tuma an