The Mississippi River's flow through the Coon Rapids dam doubled last week after heavy rains June 21, but the height of the pool above the dam remained at the level where it will be maintained during a two-year upgrade of the structure.

The flow after the June 21 rain jumped from 15,000 to 30,000 cubic feet per second, but has been dropping, said Jason Boyle, state dam safety engineer. High flows, and the debris they carry, are considered hazardous for recreation, but boat access in the area has been closed because of construction anyway.

The river height above the dam rose slightly on June 18 because of a broken gate that remained closed, but all gates were opened to manage the flow last week, Boyle said.

The $16 million dam upgrade is part of an effort to prevent the possible spread of Asian carp up the Mississippi. The river elevation above the dam is being maintained at its higher level year-round to help as a barrier to the carp.

Bill McAuliffe