Isaccea

Isaccea holds the right bank at kilometre 103, thirty-two kilometres before the ceatal where the Danube splits into the delta arms. The Danube water level at Isaccea is read off a staff whose zero sits 0.688 metres above the Black Sea; the absolute height is 0.688 m plus the staff reading, so 10 centimetres give 0.788 metres and 100 centimetres give 1.688 metres. Two pairs of marks matter: AFDJ sets low water at 73 centimetres and high water at 481, while the page prints the Danube Commission's older 72 and 478, beside the county plan's 380 centimetre attention level.

A Position, Not a Depth

The figure says nothing about depth: it fixes where the surface stands against a survey mark. Under 73 centimetres, the navigation threshold, barges lighten their cargo; 481 opens the high-water chapter, and 508 and 520 are the flood and danger levels of the county plan. Four metres separate the outer marks. High water lifts islands out of the minor bed, low water leaves ribbons of sand, and since 1980 a new island has been growing off the port.

Two Floods and a Dike Year

The river climbed to 524 centimetres in 2006 and to 537 in 2010, when peak discharge reached 16,240 cubic metres a second against 14,325 four years earlier. Both passed the printed high-water mark, by 46 and by 59 centimetres. In April 2013 the sector Vadu Oii–Isaccea stood under a yellow warning and SGA Tulcea crews worked on the Isaccea–Ciulineț dike, with the river at 14,500 cubic metres a second. No reading from the staff that month was published.

Low Water, Noviodunum and the Crossing

In August 2022 the fall exposed collapsed walls of Noviodunum, the Roman fortress two kilometres from town at Pontonul Vechi; the site's archaeologist said twenty-two years of work had never shown him such levels. The Danube water level at Isaccea has an AFDJ series from 3 January 2011: 5,729 station-days, 773 below the low-water mark, a peak of 496 centimetres on 3 April 2018, a mean of 192, and a -932 that is a sensor fault. The ferry covers 900 metres to Orlivka on the Ukrainian bank in seven or eight minutes. Downstream, the Tulcea gauge marks the entry to the delta; upstream, the Galați staff holds its zero 17 centimetres higher, and the gauge at Brăila stands 67 kilometres away.