The best known level in the Netherlands is the NAP, but there are also many other areas of comparison. That is what this paragraph is about.
- Channel level and other local interfaces
A ‘pand’ is the canal part between two locks. Often a certain water level is sought in a ‘pand’. This target local water level is called channel level (KP). The responsible waterway manager (Rijkswaterstaat, Provinciale Waterstaat or Hoogheemraadschap/ Watererschap) tries to keep the water level at the channel level as much as possible.
Other local areas of comparison are:
- basin level (BP);
- weir level (SP);
- IJsselmeer summer level (IJZP);
- IJsselmeer winter level (IJWP);
- Frisian summer level (FZP);
- and so on.
The reference points of these levels/comparison areas in relation to NAP are known.
Many of these areas of comparison can be found on the ANWB water charts, the hydrographic charts for coastal and inland waters, in government notices to captains (the so-called shipping reports from the RIZA message centre), in a number of (water sports) almanacs and also in a single computer program, including the PC-Navigo programme. Finally, you can always obtain information about this from the locks and/or the traffic control posts that you will pass on your journey.
- Agreed low river level (OLR)
The OLR plane is a reference plane for the upper rivers. Every 10 years, the Central Commission for Navigation on the Rhine sets the reference points for all 23 reference scales along the Rhine between Rheinfelden (Switzerland) and IJsselkop (the Netherlands). The last amendment was made on 1 January 2003. These adjustments are necessary because the river is eroded, causing the riverbeds and therefore the water to sink.
For you as a captain and waterway user the OLR is of little use, because the OLR is only based on this water outlet and does not say anything about the height of the river bottom. (Because the river bottom in the Netherlands is subject to permanent changes because of its composition, including sand and silt, the altitude of the soil is also constantly changing. Such changes can occur very quickly, sometimes within a few hours.)
If you, as a waterway user, would like to calculate with the OLR, it is necessary that you not only know the water level (this is given in relation to NAP), but also the exact, current altitude of the soil in relation to NAP.
What do you, as a waterway user, have to do with the OLR? The OLR
offers the waterway user a certain minimum guarantee. At the moment, the channel manager aims to keep the channel at a depth of 2.50 metres and a width of 150 metres as much as possible with a water discharge of 984 cubic metres at Lobith (= OLR).
So: for the waterway user, carrying out accurate calculations using the OLR plane is in practice a somewhat tricky business because he never has access to the precise data on the height of the river bottom. On the site www.scheepvaartpagina.nl you will find various sites about tides and water levels, including the site http://waterland.net/rikz/waterstand/ where the current water levels of the rivers are shown.
- Least sounded depth
If the water level falls below a certain level as a result of the decline in the surface water, the waterway user will be informed and the least sounded depths will be passed on. If, for example, the depth in the channel in the Loevestein – Millingen section is 3.50 m or less, the least sounded depth at the water levels is also indicated. All you have to do is deduct the safety margin for your own ship from this least polluted depth.