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The mechanics of a structural failure in an earthen dam. or any other dam, are important to downstream communities because they deter- mine the amount of warning time the community will have and the magnitude of the peal, flow that will be experienced, The mechanics depend on the type of dam and the cause and type of failure, By determining what type(s) of dam(s) is(are) upstream of their communI- ty, local floodplain administrators can evaluate what type of failure, if any, could occur and what flood characteristics would result. The dis- tance of the dam from the community and the variety of dam monitor- ing in place will also a1fect community response to a dam failure, Most dam failure floods are similar to thunderstorm floods, There is a rapid increase In flows creating a sharp peak, with a somewhat slower decrease in flows following the peal,. In June 1965, a flood occurred on Clay Creek in Prowers County from U,e overtopping (Ilydrologic failure) of an earthen dam constructed by Colorado Game, Fish, and Parks Commission. (The dam held.) This dam failure flood resulted in an important legal controversy known as the Barr Case. This case was finally decided in 197;~ by the Colorado Su- ~reme Court which recognized the concept of probable maximum f"ood (PMF) as a predictable and foreseeable standard for spillway design purposes. Two dam failures in Colorado have resulted in Pres- idential Maior Disaster Declarations. These were the failure of the Lower Latham Reservoir Dam in 1973 and subsequent flooding in t1e town of Kersey, and the failure of Lawn Lake Dam on July 15. 19B2 which caused 3 deaths and $31 million worlh of damages in t1e Estes Park/Rocky Mountain Park area. "Major River Basins in Colon:.do" - - _.._-~- -.... -----~l $1.,lIng ( \' ~,\'t" ;J ,.1 . . f <1" , NJ." I II#~I HirtH o '1. Morgon Wh;/t' filII.' M......, MISSOURI - I I J 5