The inundation sluices were the most important part of the New Water Line. Several types were designed to suite the local conditions. One type was designed around 1815 by Jan Blanken. At first sight it is quite complicated, but it could be opened and closed against the pressure of the water. The sluice consists of two L-shaped doors. The smallest part of the L blocks the sluices. attached to them are the larger side parts, 6/5 the size of the smaller doors. Normally the sluices doors are closed because the water pushes against both sides of the large side parts and against the smaller doors. To open the doors they let the water out of the large niches next to the large side doors. This way the water pushes these doors to the outside, opening the small doors. To close the valves to the niches were opened against, so the water pushed again against the large side parts.

The indundations sluices allowed the defenders to regulate the height of the water.Contrary to popular ideas you cannot easily blow up a dike to flood a polder. When the water level is too high the enemy would be able to cross the inundations by boat. Therefore the Dutch prefered a water level of 40 cm. This way boats couldn't cross the inundations while the crossing infantry men could not sea the many ditches. In those days the soldiers carried a heavy equipment and most of them couldn't swim, so they would easily drown.