Jamestown Dam

The Jamestown Dam is a rolled-earth dam spanning the James River in Stutsman County in the U.S. state of North Dakota, serving the primary purpose of flood control. It is north of the city of Jamestown, North Dakota. Built from April 1952 to September 1953, the dam measures 1418ft long at the crest and 85ft high. It impounds the James River to form the Jamestown Reservoir. A small islet lies shortly upstream of the dam, where the James River previously split into two channels.The dam and reservoir rest on a wide plain of shale where the James River cut a canyon up to 1mi wide and 100ft deep. The shale (called Pierre Shale) has a dark gray, bedded appearance, and is mostly claystone or siltstone. The valley also contains many traces of alluvium, mainly deposited during the last ice age when the area was heavily glaciated.ConstructionProposal and companies involvedThe dam was proposed in 1951. The site selected offered the required storage with the smallest dam and with close access to embankment materials; however, the underlying rock and soil was both unstable and pervious. The problems were considered minor because the extended storage need of the reservoir only consisted of the lower 30ft of the reservoir. If this had not compensated for the pervious material, the required excavations to stabilize the dam would have been over 120ft to solid bedrock.