Normal Amsterdam Water Level
The height of an area is generally indicated by means of a fixed standard level. In the Netherlands, this standard level can be found in its capital, Amsterdam. The Muziektheater, the city’s music theatre, contains a very special bolt. Why is this bolt so special? The top of this bolt indicates the standard level that is used in the Netherlands to compare heights with. This level is known as the Normal Amsterdam Water Level (abbreviated to N.A.P.). The heights of different places in the Netherlands is determined by comparing them with the N.A.P. When a city lies three metres lower than the top of the bolt in the music theatre of Amsterdam, the Dutch say: ‘the city lies three metres below N.A.P.’.
The bolt in Amsterdam is not the only one which is used to determine the N.A.P. Water gauges have been installed at various different locations. But in fact, only the gauge at the Veluwe, a nature reserve in the middle of the Netherlands, is reliable. The soil in and around Amsterdam is settling down by 2 centimetres per century. Therefore, the standard level would also fall by 2 centimetres per century. Since the N.A.P. is supposed to be a fixed standard, it is impossible that it would actually change. It would be logical to make the Veluwe-bolt the new standard, but because a number of inhabitants of Amsterdam agreed the standard level in 1683, the N.A.P. is unlikely to change.