Sioux Falls, S.D. ? The commercial barge season on the Missouri River will be shortened by 47 days because of new water conservation measures in a revised operating manual, the Army Corps of Engineers said.

Runoff above Sioux City, Iowa, in June was 56 percent of normal and runoff from mountain snowmelt has been disappointing, said Larry Cieslik, chief of the water management office in the corps’ Omaha, Neb., office.

Runoff into six upstream reservoirs this year is forecast to be 15.7 million acre-feet, down from the normal of 25.2 million acre-feet. Water releases from the reservoirs will remain at minimum service levels.

The commercial navigation season will end between Oct. 6 at Sioux City and Oct. 15 at the river’s mouth near St. Louis, the corps said.

The level of the three northernmost reservoirs — Lake Oahe, Lake Sakakawea and Fort Peck — will fall even more in July, the corps said.