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<br />26 <br /> <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />The next step is to determine the variation of benefits, or flood <br /> <br />damage reduction, with design frequency. This is done by preparing <br />damage-frequency curves for the reach for several alternative design <br />frequenci es, <br /> <br />Figure 11-6 shows four damage frequency curves for the reach <br />corresponding to no change and designs for 2, 10 and 100-year designs. <br />(See Appendix A for instructions regarding preparation of damage- <br />frequency curves). Essentially these curves show the damage which <br />will still occur after installation of flood protection if floods <br />greater than those designed for occur. <br /> <br />ur <br />w <br />(lI <br />~ <br /><l: <br />o <br /> <br /> <br />:- _ <NO CHANGE <br />~ '" <br />. "" ""- <br />\ 2-YEAR~ '\ <br /> <br />~IO- YEAR . \\ <br />I \ <br />IOO-YEAR <br /> <br />'" <br />g <br />..... <br />"* <br /> <br />o 0.1 <br /> <br />Q2 0.3 0.4 0.5 0.6 0.7 <br /> <br />EXCEEDANCE PROBABILITY <br /> <br />Figure 11-6 <br /> <br />The areas under the curves give "average annual damages." Damages <br /> <br />prevented by the systems may be found by subtracting as shown by <br /> <br />Table 11-8. <br />