National Geographic : 1969 Oct
Moving a hillside to tame a river: Hungry scrapers gulp huge loads of earth to build up a North Mankato dike. The region's rich blue gray clay proved ideal for making watertight levees. down with a brick. The explosion would have the force of 10 dynamite sticks. We linked such charges by the dozen and spliced delaying devices between them, so that they would go off successively, a fraction of a second apart. This would produce a wave action under the ice, lifting and cracking. Whoom! Bits of ice sailed 250 feet into the air. Great fissures appeared in the ice. Suc cess! The first ice island detached itself and began drifting downstream. The Blue Earth would unjam gently. On the night of April 9 word came from South Dakota that a very important dike was Ramparts rise atop a high way to protect North Man kato; trucks shuttle more clay eroding fast. This dike, on the Big Sioux River, protected a meat-packing plant that provided 2,500 jobs-a livelihood for one out of every eight wage earners in the city of Sioux Falls. The plant had closed because of the flood danger, and there was fear that if it were badly damaged it might not open again. When I arrived on April 10, I learned that attempts to reinforce the dike had been aban doned at 3 a.m. By dawn that dike was still there, though I could see a 100-foot stretch washing away, bit by bit, into the rushing, foaming river. Two-thirds of the dike's origi nal width was gone.