National Dam Safety Program. Johnson County Dam A-1 (MO 20020), Missouri - Kansas City Basin, Johnson County, Missouri. Phase I Inspection Report.

Johnson County Dam A-1 was inspected by a team of engineers. The purpose of the inspection was to make an assessment of the general condition of the dam with respect to safety, based upon available data and visual inspection, in order to determine if the dam poses hazards to human life or property. Our inspection and evaluation indicates the spillway does not meet the criteria set forth in the guidelines for a dam having the above size and hazard potential. The spillway will not pass the probable maximum flood without overtopping but will pass 25 percent of the probable maximum flood and will pass the 100-year flood (one percent probability flood). The spillway design flood recommended by the guidelines is 50 to 100 percent of the probable maximum flood. Considering the small volume of water impounded behind the dam, the valley below the dam and the estimated hazard zone, the spillway design flood should be 50 percent of the probable maximum flood. The probable maximum flood is defined as the flood discharge which may be expected from the most severe combination of critical meteorologic and hydrologic conditions which are reasonably possible in the region.