Hydrologist assesses Lake Delhi failure

Jeff Zogg, the hydrologist at the National Weather Service in Des Moines, offered this take today on the failure of the dam system at Lake Delhi over the weekend:

All ... did some back of the envelope calculations for the Delhi dam in eastern IA.Before the dam breached, the water behind it was exerting a collective force of 7.2 million pounds on the dam. That works out to about 1.2 pounds per square inch or 175 pounds per square foot. These are rough estimates, though.It should be noted that the dam did not breach because of the force of water behind the dam. Instead, the water behind it built up high enough to spill over the top of the dam. When water spills over the top of dams such as the Dehi dam, it is very dangerous as we saw.

Before the dam breached, the water behind it was exerting a collective force of 7.2 million pounds on the dam. That works out to about 1.2 pounds per square inch or 175 pounds per square foot. These are rough estimates, though.

It should be noted that the dam did not breach because of the force of water behind the dam. Instead, the water behind it built up high enough to spill over the top of the dam. When water spills over the top of dams such as the Dehi dam, it is very dangerous as we saw.

The Delhi dam was not designed for water to go over the top. When that happens, there is a high risk of erosion of the top of the dam which is exactly what happened. The water eroded away the road and the underlying earth, which led to the breach.