Least Sounded Depth (MGD)
This is a service from the Dutch government that reports the actually measured channel depth in the marked fairway, as the depth below OLR (which is actually an international agreement that is thus simply being violated) is not maintained. Its practical use is often seen as limited, much like the guaranteed depth below GlW or OLR, because it does not specify the exact locations of the shallow spots. For example, in the spring of 2025, a shallow was discovered on the Waal in the fairway. The Least Sounded Depth was immediately adjusted by 70 centimeters, while the remaining width of the channel was still more than sufficient. However, this also means that valuable information, such as the depth at the dangerous shallow hard layer near Nijmegen, is lost. This makes it more of a tool to shift responsibility onto the skipper. Dutch regulations are such that a captain can get into legal trouble if they load deeper than the published MGD and subsequently run aground, even if that was caused by someone else's fault and even if they were to adhere to the guaranteed depth below OLR with a 30cm margin, just like in Germany. The peculiar thing, however, is that no safety margin is recommended: as long as you are not loaded deeper than the MGD, it is considered acceptable, which in practice does not really make sense, since a ship always experiences squat. A grounding is therefore still theoretically possible when navigating a stretch that is no deeper than the MGD.
On the (Upper) IJssel the MGD is also very confusing, and it is unclear how it is calculated. At normal discharges, a draught of Doesburg -220 or -230 puts you roughly 15 to 20 cm deeper than the Least Sounded Depth. You still keep a safe margin to the actual shallows in the deepest gully.
At (extremely) low water the MGD only gets deeper and deeper relative to the IJsselkop and Doesburg gauges. During the extreme low water of 2026 the MGD was at one point 140 cm at a Doesburg reading of 344 cm, which means that at a draught of 140 cm you are working to a rule of thumb of Doesburg - 204, which was seriously deep. It was done downstream with an 80 m vessel, but it does mean stopping properly at every shallow.
I would therefore advise against basing a rule of thumb on the MGD, because it scales so oddly and unpredictably with the water level, and not with the real channel depth we actually sail in.
At such draughts you also have to know the shallows well and possibly use the bow thruster regularly to get through the deeper outer bend, as well as waiting for downstream traffic below bends where there is officially no ban on meeting. The IJssel depth charts mark, at every bend, where meeting is advised against, following simulator research by Marin.
Ultimately this is possible because less channel width is needed at low water than follows from the standard calculations for waterway dimensioning. With an empty ship you need more room again, but in that case the shallow inner bends are less of a problem.