The valley is part of the hydrographic basin of the
Dora Baltea, and has a U-Shape. Just before Cogne, four minor valleys gather to form the Cogne valley: the
Valnontey, leading to the
Gran Paradiso, the Grauson Valley, leading to the Grauson peak, and, eastwards, the
Urtier Valley and the
Valeille. All the streams from these valleys flow into the
Grand Eyvia, which flows into the
Dora Baltea near
Aymavilles.