relationships. Total damages for each flood event were determined by summing the predicted damages for each individual dwelling. The AAD was then calculated. The AAD is the average damage in dollars per year that would occur in a designated area from flooding over a long period of time. In many years there may be no flood damage, in some years there will be minor damage (caused by small, relatively frequent floods) and, in a few years, there will be major flood damage (caused by large, rare flood events). Estimation of the AAD provides a basis for comparing the effectiveness of different management measures (i.e. the reduction in the AAD). The AAD is the area under the probability-damage graph. Ideally the probable maximum flood damages are included in the AAD analysis, and it is also necessary to assume a flood AEP in which no damages occur. As no flood larger than the 1% AEP event was modelled, the graph was extrapolated, and it was assumed that no damages would occur in the 50% AEP event. Existing Conditions Flood Damages The total existing conditions damages for each design flood event are presented in Table 61. They are also illustrated in Figure 61. The existing conditions AAD for the Highton study area, as presented in Table 61, is $389,000. Table 61 Existing Conditions Damages Summary Event Existing Case Commercial / Incremental (Years Residential Total Indirect Industrial AEP Total Damages Average Annual ARI) Damages Damages Damages Damages PMF* 0.0% $3,430,000* 100 1% $2,284,000 $77,000 $708,000 $3,069,000 $32,000 20 5% $1,206,000 $45,000 $375,000 $1,626,000 $94,000 10 10% $816,000 $28,000 $253,000 $1,097,000 $68,000 5 20% $519,000 $17,000 $161,000 $697,000 $90,000 2 50% $105,000 Average Annual Damage $389,000 *PMF damages are an extrapolation of the 1% AEP data, i.e. they were not calculated using PMF flood levels. Figure 61 Existing Conditions Damages Probability Curve
relationships. Total damages for each flood event were determined by summing the predicted damages for each individual dwelling. The AAD was then calculated. The AAD is the average damage in dollars per year that would occur in a designated area from flooding over a long period of time. In many years there may be no flood damage, in some years there will be minor damage (caused by small, relatively frequent floods) and, in a few years, there will be major flood damage (caused by large, rare flood events). Estimation of the AAD provides a basis for comparing the effectiveness of different management measures (i.e. the reduction in the AAD). The AAD is the area under the probability-damage graph. Ideally the probable maximum flood damages are included in the AAD analysis, and it is also necessary to assume a flood AEP in which no damages occur. As no flood larger than the 1% AEP event was modelled, the graph was extrapolated, and it was assumed that no damages would occur in the 50% AEP event. Existing Conditions Flood Damages The total existing conditions damages for each design flood event are presented in Table 61. They are also illustrated in Figure 61. The existing conditions AAD for the Highton study area, as presented in Table 61, is $389,000. Table 61 Existing Conditions Damages Summary Event Existing Case (Years ARI) AEP Residential Damages Commercial / Industrial Damages Total Indirect Damages Total Damages Incremental Average Annual Damages PMF* 0.0% $3,430,000* 100 1% $2,284,000 $77,000 $708,000 $3,069,000 $32,000 20 5% $1,206,000 $45,000 $375,000 $1,626,000 $94,000 10 10% $816,000 $28,000 $253,000 $1,097,000 $68,000 5 20% $519,000 $17,000 $161,000 $697,000 $90,000 2 50% $105,000 Average Annual Damage $389,000 *PMF damages are an extrapolation of the 1% AEP data, i.e. they were not calculated using PMF flood levels. Figure 61 Existing Conditions Damages Probability Curve
8d2a95337a000c2-HightonDrainageFloodStudyAdoptedbyCouncil.docx