Lanterna Rally

Author: Arthur L. Johnson

Publisher:

Published: 1978

Total Pages: 37

ISBN-13:

The inspection and evaluation indicates that the spillway of the Ziske Dam 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 a one percent chance flood without overtopping. The Ziske Dam is a small size dam with a spillway that will pass 15 percent of the Probable Maximum Flood (PMF) without overtopping the dam. The guidelines require that a dam of this hazard potential (high) and size pass one-half of the Probable Maximum Flood without overtopping the dam. Since the spillway for Lake Ziske Dam is not capable of passing a minimum of one-half (50 percent) of the Probable Maximum Flood without overtopping the dam and causing failure, the spillway is considered seriously inadequate and the dam is accordingly considered unsafe. Also, our evaluation indicates it will not pass the one percent chance flood. A one percent chance flood is a flood that would have a one percent chance of being exceeded in any given year. Other deficiencies visually observed by the inspection team were the need for cutting the tall grass and brush (some small trees) on the dam slopes, and the need for riprap protection on the upstream face of the embankment to prevent erosion and an erosion resistant spillway. The lack of stability and seepage analysis on record is a deficiency that should be corrected.