The four polders with their areas of fertile soil would be: (I) North-west polder, area 53,599 acres; fertile soil, 46,189 acres.
But in North Holland and Utrecht on the contrary the polder water has generally to be raised.
It sometimes happens that a polder is not in direct contact with the boezem to which it belongs, but first drains into an adjacent polder, from which the water is afterwards removed.
In the Frederiks Park is a pump-room supplied with a powerful chalybeate water from a spring, the Wilhelminabron, in the Haarlemmer Polder not far distant, and in connexion with this there is an orthopaedic institution adjoining.
Below the level of the polder, and in agricultural polders 21 to 31 ft.
These waters are utilized as the temporary reservoirs of the superfluous polder water, each system of reservoirs being termed a boezem (bosom or basin), and all lands watering into the same boezem being considered as belonging to it.
The roads are divided into national or royal roads, placed directly under the control of the waterstaat and sup- 'ported by the state; provincial roads, under the direct control of the states of the provinces, and almost all supported by the provincial treasuries; communal and polder roads, maintained by the communal authorities and the polder boards; and finally, private roads.
To increase the reservoir capacity of the polder, as well as to conduct the water to the windmills or engines, it is intersected by a network of ditches cut at right angles to each other, the amount of ditching required being usually one-twelfth of the area to be drained.
The level at which it is desired to keep the water in these ditches constitutes the unit of water measurement for the polder, and is called the polder's zomer peil (Z.P.) or summer water-level.
Below A.P. in the Beschotel polder, and in reclaimed lands (droogmakerijen) may be still lower, thus in the Reeuwyk polder north of Gouda it is 214 ft.