A polder is an area of low-lying land that has been reclaimed from a body of water and is protected by dyke and pump systems. Once the land to be reclaimed has been selected, dykes are built around the area. The water within the dykes is then pumped out of the area into a system of constructed canals (Figure 1). The land remaining is below the natural water level and pumps are used to continually remove water from the area. The polder is physically separate from the surrounding water system as the inflow and outflow are controlled through pumping stations. Natural seepage from ground water also contributes to maintaining soil moisture.
Figure 1: Side view of a bog (top) turned into a polder (bottom)
The Dutch are well-known for their polders. They have reclaimed sea beds using this technique, holding back the sea with large dyke systems and pumps that were once powered by windmills. Other polders can be built to reclaim land from lakes, rivers, or bogs. Rich, fertile soils reside within these polders; once drained, polders have clay or muck soils, or a combination of the two. The land is largely flat and treeless, which is very suited to agriculture.
Figure 2: Overhead view of the northern end of Holland Marsh where the canals converge with the Holland River at the pumphouse [date unknown]
Draining the Holland Marsh, named for the first Surveyor General of Upper Canada Major Samuel Holland, was a project led by Professor William Day of the Ontario Agricultural College beginning in 1925. The 28 km of canals dug then now protects 7,000 acres of prime muck soil. Pumping stations, one situated at the North Branch and the other at the northern end keep the water level low enough to keep the land dry. There is an additional 2,500 acres in smaller polders along the Holland River as it runs north to Lake Simcoe.
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