Here's what would likely happen:
A “tsunami-like wave” would rush through Mosul, carrying away everything in its path, including bodies, buildings, cars, unexploded bombs, hazardous chemicals, and human waste. The wave would almost certainly catch most of the people trying to outrun it. Residents of Mosul, scrambling on foot and by car through a citywide traffic jam, would need to travel at least three and a half miles to survive. In less than an hour, those who remained would be under as much as sixty feet of water.
Within four days, the wave would reach Baghdad, depositing as much as sixteen feet of water in many areas of the city, probably including the airport and the Green Zone, the site of government buildings and most of the embassies. The report said the majority of the city’s six million residents would face Hurricane Katrina-like conditions: people forced from their homes, with limited or no mobility and no essential services.