 Thornton Transitional Reservoir contributes a capacity to the system, and is expected to contribute when the system is completed in 2014.It is estimated that the reservoir will help protect 500,000 people who live in the surrounding 14 suburbs it serves, and will save the city around $40 million worth of damages each year.The quarry contains Silurian reefs which formed when the Michigan Basin was covered in sea water more than 400 million years ago.