Bart Schultz
On the American continent, I have identified 18 countries with polders, with an identified area of 1.15 million hectares. The total area of polders is considerably larger, but very difficult to determine.
The vast majority of polders are reclaimed low-lying land. Only in Canada and the United States there are lands gained on the sea. These are primarily agricultural polders along bays. In Canada, Mexico, and the United States, there are a few drained lakes: the Sumas Polder in Canada, the polders in Lake Texcoco in the Mexico Valley in Mexico, and Lake Mattamuskeet in the United States. The polders in Lake Texcoco are special because, to my knowledge, they are the highest polders on earth, at 2,236 metres above mean sea level.
The land use in the vast majority of the polders is agriculture, including the growth of rice in a few of the polders. Along the northern coast of South America – Guyana, Suriname, and French Guiana – there are several plantation polders. Most of these polders were reclaimed using slave labour. Their location is generally favourable for water management, as sufficient irrigation water can be supplied from the hinterland under natural gradient, and drainage can be achieved through discharge sluices, if necessary in combination with pumping. In Ecuador, there are several polders for shrimp farming at the mouth of the Guayas River.
Polders with multiple land use can only be found in Canada and the United States. Urban polders can be found in Canada, Guyana, Mexico, and the United States. In Canada, these include a polder in Toronto; in Guyana, a polder in Georgetown; in Mexico, Mexico City and polders in Lake Texcoco; and in the United States, primarily New Orleans and Houston.
The Bolivar Coast Polders in Venezuela represent a special type of polders, having been created by the subsidence associated with oil extraction along the east coast of Lake of Maracaibo. When oil extraction began, these areas were approximately two metres above mean sea level, but the deepest parts now lie about six metres below mean sea level, but the deepest parts now lie about six metres below mean sea level, as described in an earlier contribution to Flevolands Geheugen about the Bolivar Coast Polders in Venezuela.
The water management situation in and around New Orleans is quite unique, as described in two previous contributions to Flevolands Geheugen about the Mississippi Delta and the Mississippi Delta seventeen years after Hurricane Katrina. Flooding can occur upstream during high discharges from the Mississippi River, and downstream due to hurricanes from the Caribbean Sea. Since the construction of the Bonnet Carré Spillway in 1931, water from the Mississippi River can be diverted to Lake Ponchartrain on the east side of New Orleans and from there to the Caribbean Sea. This bypass has now been used 12 times.
Hurricanes are now more risky, as demonstrated, for example, during the Katrina floods. While the dikes and related provisions were repaired at that time, the safety level was not increased, meaning the risk of another flooding has not decreased, and may even have increased due to climate change.
