Accounting for failure frequency due to natural disasters occurs at the design (initial or retrofit) stage, not the maintenance stage. Should every mom-and-pop dam adhere to the once-in-ten-thousand-year-rule (eg: nuclear powerplants) or once-every-hundred-years (eg: steel framed commercial construction)? Cost effectiveness is also a huge concern.<p>Note that maintenance doesn&#x27;t increase the expected failure frequency, it maintains it at the design spec. And I&#x27;m willing to bet that even with proper maintenance those small dams in SC would not have survived; they were way outside their designed specs.