The Dutch boezem, a dispersed reservoir

	Boezemstelsel of Rotterdam and The Hague

A boezemstelsel in the Netherlands is a regional, dispersed reservoir system that holds excess water at a level above that of a polder bottom. It awaits evacuation toward the sea until its release is timely, and it can augment groundwater in a drought.

A boezemstelsel, each of which buffers the flow of water from several polders, normally comprises diverse bodies of water that are openly connected - canals, lakes, ditches, shipping waterways. A local authority determines the aspirational level of each boezem system. The true level fluctuates in response to the level at polder-bottom where strict management is important. From the boezem outward, water quality and quantity is monitored for environmental safety and regulatory compliance.

Electric pumps elevate water from the polder floor to the boezem. (This was originally done by wind power, then steam engines, then deisel.) The boezem holds the water until its release is timely, when it's pumped upward again, usually into a river by which it goes out to sea.