Waterways: Water levels and gauges – what they reveal and what they don’t

​There should always be a hand’s breadth of water under the keel – at the very least. Unfortunately, that is no longer always the case. The Record low water levels The current situation clearly shows that there are limits to how far the water can reach. But where exactly are they? Out at sea, it’s simple: a glance at the nautical chart will usually keep you on the safe side.

Water levels on all navigable waterways

And inland? There are free-flowing rivers, waterways regulated by locks and weirs, canals and, to top it all off, hybrid forms too. During prolonged rainfall and snowmelt, the water rises; during droughts, it falls – as is currently the case in many parts of Germany.

Sometimes water is drained off, sometimes it is let in. A stable water level that remains constant throughout the year is virtually non-existent. Consequently, measurements are taken several times a day – using the water level gauge. These gauges, which are usually yellow and black, can be found on every navigable waterway.

No direct indication of the water depth

The district control centres publicise the current water levels via noticeboards, on the radio and by radio, on television and on the internet. However, there is a rather significant catch when it comes to the water level:

The reading taken from it does not, in fact, tell us anything about the actual water depth. This has to be calculated first – and the skipper almost always has to do this himself. Furthermore, there is no standardised procedure for this across the country.

The depth of the navigation channel is crucial

Sufficient water depth is particularly important for commercial shipping. Vessels therefore stick to the navigation channel. According to DIN, this is the term used to describe the part of the fairway in which “there are specific widths and depths intended for continuous shipping traffic, the maintenance of which is the objective”.

In other words: the navigable depth is the key factor, not the water level. That is why efforts are made to keep it constant – for example, by dredging – and why the term ‘guaranteed minimum navigable depth’ is used.

The measurement is taken at the flattest point

For safety reasons, measurements are taken at the shallowest point of the navigation channel, known as the highest channel bed level. As already mentioned, however, the water level fluctuates and, with it, the actual depth of the navigation channel – this is where the gauge comes into play.

The exact water level is usually measured using a float gauge and automatically recorded in the gauge house. In addition to the measuring rod, analogue or digital counters are often used as a visual aid for boatmen.

The daily level is always displayed

The daily water level is always displayed; measurements are taken from zero level, the lower end of the gauge. It is important to note that this point is not at the same height as the riverbed or the design low-water mark of the waterway. In the case of rivers, for example, the course of the current and the riverbed change far too frequently for the water levels themselves to be readjusted each time.