Historical analogue...look up the San Francisquito dam (also known as the St. Francis dam). A terrible dam failure where hundreds died downstream. March 12, 1928
http://www.academia.edu/6429492/THE_ST._FRANCIS_DAM_FAILURE_worst_American_civil_engineering_disaster_of_the_20_th_Century_Shlemon_Specialty_Conference_Dam_Foundations_Failures_and_Incidents