Does water flow uphill?

The Sông Son River flows directly past our hotel 'Coco Riverside Homestay' in Phong Nha.

Coco Riverside Homestay

Ferry over the Sông Son

It originates in the central Vietnamese highlands and meanders around karst mountains, coming from a narrow valley, until it passes through Phong Nha.

From here, it is about 45 km to the estuary of the Sông Gianh, into which it flows shortly before. This would not be worth mentioning if there were not regularly changing water levels and, consequently, a seeming reversal of the flow direction. At first, we thought it was imagination and lack of precise observation until we looked at a map with an elevation profile.

Surrounded by karst mountains, we did not expect to be moving only minimally above sea level here!

But that explains the fluctuating water levels and the regular reversal of the flow direction, both of which are triggered by the distant sea with its tides. You have to come up with that when the sea is so far away. 😲