This dam has been classified as unsafe, non-emergency by the St. Louis District as a result of the application of the following criteria: (1) Spillway will not pass 50 percent of the Probable Maximum Flood; (2) Overtopping could result in dam failure; and (3) Dam failure significantly increases the hazard to loss of life downstream.

This report was prepared under the National Program of Inspection of Non-Federal Dams. This report assesses the general condition of the dam with respect to safety, based on available data and on visual inspection, to determine if the dam poses hazards to human life or property. (Author).

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. This dam is classified as an intermediate size dam with a high downstream hazard potential. The 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 pass 30 percent of the probable maximum flood without overtopping. Deficiencies visually observed by the inspection team were erosion, seepage, and presence of excessive brush and small trees on the downstream embankment slope. Also, the sloughing of the riprap on the upstream embankment slope has contributed to erosion of the embankment material. Seepage and stability analyses are not available as required for dams having the above size and hazard potential as required by the guidelines. There were no observed deficiencies or conditions existing at the time of the inspection which indicated an immediate safety hazard.

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. Inspection and evaluation indicated the spillways do not meet the criteria set forth in the guidelines. The spillways will not pass the probable maximum flood without overtopping but will pass 20 percent of the probable maximum flood. The spillways will pass the flood which has a one percent probability of occurrence in any given year (100-year flood). The spillway design flood recommended by the guidelines is 50 to 100 percent of the probable maximum flood. Considering the hazard zone, the spillway design flood should be 100 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. Based on visual observations, this dam appears to be in fair condition.

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. This dam is classified as an intermediate size dam with a high downstream hazard potential. The 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 pass 50 percent of the probable maximum flood without overtopping. Deficiencies visually observed by the inspection team were minor amounts of seepage at random slab, joints and in abutment drains, minor concrete spalling on the spillways downstream surface, exposed reinforcing steel on vertical supports, and the absence of containment walls on the spillway.

Union Lake Dam 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 spillways do not meet the criteria set forth in the guidelines for a dam having the above size and hazard potential. The spillways will not pass the probable maximum flood without overtopping but will pass 10 percent of the probable maximum flood. The spillways will not pass the flood which has a one percent chance of occurrence in any given year (100-year flood), but will pass the flood with a 10 percent change of occurrence (10-year flood). The spillway design flood recommended by the guidelines is 50 to 100 percent of the probable maximum flood. Considering the damage zone, the spillway design flood should be 100 percent of the probable maximum flood.