Oudland area de Poel

The old island core did intersect with large and small tidal creeks in several places. Inside the creeks, stronger currents than outside them swept away some of the peat and deposited sand. Outside the creeks, the flow velocity of the water was lower and mostly clay was transported and deposited on top of the peat. Over the centuries, the peat and clay outside the creeks contracted, causing the land surface there to decrease. Therefore, today the former gullies lie higher in the landscape and form so-called creek ridges. On these are often the oldest roads and settlement centers. The low-lying clay-moorland areas outside the creek ridges are called poelgronden. Poelgronden are nowadays a valuable bird area and are part of Ganzenreservaat de Poel.

De Poel is part of the polder 'Brede Watering Bewesten Yerseke', dating from before the 13th century. It was not constructed all at once, but rather built up from several smaller former polders, each time a new piece of alluvial salt marsh was diked. The dikes that came to lie around the salt marshes within the new sea wall were often removed (demolished) in the past. Dike embankment was banned in 1452 AD. Thus, in land reclaimed later, the inner dikes were preserved.