If a structure with a useful life period N year is designed for a Tr year flood, then risk in the design is given by
1
\(\frac{1}{{{T_r}}}\)
2
\({\left( {\frac{1}{{{T_r}}}} \right)^N}\)
3
\(1 - {\left( {1 - \frac{1}{{{T_r}}}} \right)^N}\)
4
\({\left( {1 - \frac{1}{{{T_r}}}} \right)^N}\)