Des Moines city officials have announced  they will immediately evacuate parts of Des Moines that are in the “500 year” flood plain along both the Raccoon and Des Moines rivers. The water levels are expected to crest along the Des Moines River Friday evening between 8:00 PM and Midnight, at or slightly below the top of the levee system. The evacuation is voluntary and is being done as a precaution in case the water exceeds the levee capacity or in case of levee breaks.
This map  depicts the affected areas.
Police are asking for residents and businesses to evacuate immediately.
Birdland (in the northern part of the city) has already been evacuated.
** Update **
Police Chief Judy Bradshaw said major downtown employers will start releasing employees in stair-step releases to help clear downtown.