Grein

Grein is the easternmost town of Upper Austria, set on the left bank of the Danube at kilometre 2079.06, where the valley narrows into the Strudengau. The Danube water level at Grein is read on a gauge whose zero has stood at 219.43 metres since 1959, with a catchment of 92,082 square kilometres above it. Low water is marked at 668 centimetres, high water at 860, while the navigation threshold known as HNWL climbs to 1,497.

The Town in the Plant's Backwater

The gauge, which records level and water temperature, has stood since 1958 in the backwater of the Ybbs-Persenbeug plant; the plant itself lies 19 kilometres downstream, at kilometre 2060.42, and was the first Austrian power plant built on the Danube, modernised between 2012 and 2022. Low water therefore reads differently here than on free-flowing reaches: in 2018 the year's minimum was 695 centimetres, in 2022 it was 706, and on 3 September 2026 it was 697, each time above the low-water mark. At 08:15 on 25 October 2026 the gauge showed 707 centimetres, an ordinary figure for a town held by a dam. Fifteen kilometres upstream, the Wallsee-Mitterkirchen plant, at kilometre 2094.50, regulates the flow that enters the gorge.

The 2002 Flood and the Mobile Dike

August 2002 remains the highest value of the series that starts in 1976: 1,494 centimetres, reached on 14 August at 03:15. In June 2013 the river stopped at 1,491, three centimetres lower, and carried 11,000 cubic metres a second — a hundred-year flood. The mobile dike, 15.10 metres high, held, although waves occasionally ran over its crest; further downstream the Machland dike, built after the 2002 flood, kept the catastrophe away.

Upstream, Downstream and Greinburg

Thirty-two kilometres upstream, the Mauthausen gauge shows what comes down from Linz; sixty-four kilometres downstream, the Kienstock gauge opens the Wachau, and 138 kilometres on, the gauge at Korneuburg gathers the water before Vienna. Above the old town stands Greinburg, built between 1491 and 1495 and now a museum of Danube navigation. Grein itself is the third-oldest town in the Mühlviertel, was granted its charter in 1491, lies at 239 metres and has about 2,930 inhabitants.

The daily series starts in 1976 and counts 17,537 station-days, with a mean of 736 cm; no day stayed below low water, and 247 rose above high water. The highest daily value, 1,480 cm, dates from 4 June 2013, the lowest, 676 cm, from 14 March 1996. On the evening of 25 October 2026 the gauge stood at 705 cm, five below the day's normal of 710.