Because a river was created in and by nature, we speak of a natural waterway. However, the natural course of a river is not always suitable for the use of the river as a discharge of water or as a waterway. In order to get or keep a river suitable for this, man intervenes. The following four interventions form a classic list of common human measures in rivers:
Regulating a river is to create a spacious winter bed. For this purpose, the dikes are placed well away from the river. Another regulatory measure is the even running of the slope, the gradient. These measures will prevent floods and/or rapids from occurring in the event of major water discharges.
Normalising is bringing and keeping a river to a certain width and depth. The means of achieving this is the construction of groynes and breakwaters. Cribs limit the width of the summer bed (see A in the picture). Due to this river narrowing, the depth in the summer bed is greater. This is beneficial for shipping. The groynes and breakwaters also keep the current away from the bank, thus limiting the natural erosion of the banks). Due to the subsidence in recent years, groynes are much higher than would be strictly necessary. As a result, when the river rises, they keep the water longer between the groynes and the water cannot spread sufficiently. It is therefore being considered to apply groyne reduction on certain routes.
The breakwaters run along the length of the river and direct the stream (see B in Figure 13).
When a river is corrected, annoying and unnecessary bends are generally removed and extended. It shortens the river. With the same outlet, the flow rate will increase as a result of such an intervention. This means that it is not always possible to cut corners if the gradient becomes too large. On Dutch rivers this will not easily be the case, but on the Saar, for example, people were obliged to allow certain bends to exist, because otherwise the decline over a short distance would be too great.
In this intervention, weirs will be built in the river.
Weirs are artificial dams that can let more or less water through at will. This allows the water level to be brought under control, so that the water can be pushed up into a reach. We find weirs on the Meuse and the Lower Rhine. In addition to the weirs we encounter in rivers, there are other weirs in the Netherlands. The storm surge barrier in the Eastern Scheldt is well known, as it ensures that there is a high tide and low tide on the Eastern Scheldt but it can be closed during heavy storms.
Locks have been built next to a weir on a canalised river. When the barrage is in use, shipping must use the lock and lock ‘up or down’.
The dams in the rivers act as control valves. With a lot of outlet the weirs will ‘go out’. The water will no longer be hindered by the weirs and can flow freely. In that case, the ships can use the weir opening and there is no need for locking anymore.