Think of it this way.  There's a valley with a dam above it.  The builders of the dam could have built it as high as they want to, but instead, they only built it to a height where it would keep the water back until 2013.  When they built the dam, they knew for a fact that it would overflow on January 1, 2013.  In the valley is a bunch of valuable historic artifacts that the dam owners thought were important to save.

Over the years, the board of directors has some changeups, and some on the new board think the valley isn't worth protecting, because they would like to see the river flow its natural course so that it can provide other resources.  The board decides to allow the water to flow over the dam instead of building the dam higher.