FLOOD04820 - Laserfiche WebLink

Home Browse Search

the capacity with channelization. For example, the stream under study has a capacity of 2,000 cfs. Channelization will increase that capacity to 5,000 cfs--an increase of 3,000 cfs. The 100-year flood damages are now the equivalent of (20,000-3,000) = 17,000 cfs, or $1,200,000. Flood damages will also be reduced for the other recurrence intervals and can be estimated by shifting 3,000 cfs on the peak discharge scale. A new damage probability curve can be constructed and the equivalent annual flood damage potential calculated for the channelization alternative. If flood damages within the existing channel cannot be neglected, then an overbank flood damage versus probability curve must be constructed by subtracting the amount of the damage within the channel before this procedure can be used. Step 10 - Compute Flood Damages and Average Annual Flood Damage Poten- tial for Alternatives Repeat Steps 8 and 9 for each flood control alternative under consideration. Step 11 - Compute the Benefits for Each Flood Control Alternative The reduction in the annual flood damage potential is the principle bene6~ realized if the flood control improvement is constructed. The average annual benefit is illustrated graphically in Figure 111-2 which compares the damage probability curves of the future situation with the curve for the first alternative. Quantify the other tangible benefits identified in Step 6 and tabulate as in Table 111-7. Step 12 - Compute the Costs of the Various Flood Control Alternatives Costs considered in this step should include at least all of those listed in Step S. Prepare a table that reflects end-of-the-year costs over the project life. Such a table might resemble Table 111-8 which follows. 77