Flood experts and emergency officials say backed-up water channels in South Dakota and Missouri have already caused flooding at points where they meet the Missouri River. In Hamburg, Iowa, work crews are keeping close watch on the Nishnabotna River to their east, as they battle the Missouri River from the west.
Last week, Platte County, Missouri saw a dramatic example of this when the Platte River, north of Kansas City, rose 15 feet in 12 hours. It was the result of f heavy rain and the swollen Missouri River.
Hydrologists say tributary backups generally do not stretch more than a few miles from the point where rivers meet. But with floodwaters expected to stay through at least August, forecasters say the lesser-known tributaries could pose a significant threat as well if Missouri River flows increase or an intense storm strikes.