A polder is a low-lying tract of land that forms an artificial hydrological entity, enclosed by embankments known as dikes. The three types of polder are:Land reclaimed from a body of water, such as a lake or the seabed
Flood plains separated from the sea or river by a dike
Marshes separated from the surrounding water by a dike and subsequently drained; these are also known as koogs, especially in Germany
Aerial view of Flevopolder, the Netherlands
Satellite image of Noordoostpolder, the Netherlands (595.41 km2)
Pumping station in Zoetermeer, Netherlands: The polder lies lower than the surrounding water on the other side of the dike. The Archimedes' screws are clearly visible.
The Yser river and West Flemish polders near Diksmuide
A levee, dike, dyke, embankment, floodbank, or stop bank is a structure used to keep the course of rivers from changing and to protect against flooding of the area adjoining the river or coast. It is usually earthen and often runs parallel to the course of a river in its floodplain or along low-lying coastlines.
The side of a levee in Sacramento, California
A reinforced embankment
Broken levee on the Sacramento River
A levee keeps high water on the Mississippi River from flooding Gretna, Louisiana, in March 2005.