The North Dakota State Water Commission retained the services of Apex Engineering in May of 2016 to study the hydrology of Queen City Dam. Queen City Dam was classified as a high-hazard dam owned and maintained by the City of Dickinson. The purpose of the project was to provide a hydrologic analysis of the dam to determine dam safety and to perform subsequent dam-break modeling.

The primary use of Queen City Dam is as a recreation facility. The principal spillway is an uncontrolled drop inlet. The riser structure is a 9 foot by 5-foot concrete box, with a headwall against the upstream face of the dam, resulting in a weir length of 23 feet.

Apex’s tasks included:

• Developing a hydrologic model of the watershed above Queen City Dam using HEC-HMS.
• Simulating the inflow to the dam resulting from the Probable Maximum Precipitation.
• Determining the percent of the PMP the dam can pass without overtopping.
• Determining the capacity of the principal spillway, and evaluate the effect of high tailwater on the principal spillway capacity.
• Determining if the dam meets current spillway criteria for a class IV, high hazard dam.

The Queen City Dam study resulted in the following:

• Urbanization has increased the drainage area from 3.82 mi² to 4.13 mi².
• A survey of the crest of the dam, shows that most of the dam is lower than the design elevation.
• The principal spillway does not meet the criteria for a Class IV dam as required by the North Dakota Dam Design Handbook.

The dam does not meet the auxiliary spillway criteria for a Class IV dam as required by the North Dakota Dam Design Handbook.