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v 11-15 COMPARISON SUMMARY Table VI 1-7 presents cost benefit comparisons of the various design frequency alternatives for the reoches of Lena Gulch in each entity. The estimated construction cost is given annualized over a 40-year period at 7 percent. Similarly, the estimated land cost is given which includes acquisition of existing structures, and converted to an annual cost by an annual interest rate of 7 percent. This takes into account the fact that the land acquisition is a one-time occur- rence, not to be replaced after 40 years. The annual operation and maintenance (0 & M) costs were ca"lculoted accord;;ng to the costs given earlier. The annual damages are the same as those listed in Table VII-6 for the expected dama~le which wi 11 occur after improve- ments. The annua 1 damage reduct ions a re the d i He '-ences between the present level of expected annual damages and the annual damages to be incurred after improvement. The intangible benefits of TallIes VII.'3 through 5 are shown, along with a tabulation of acres made avail,lble for deve'lopment or con- tinued used, for each alternative. The average market value of struc- tures was determined from Table 1\1-1 and added to a land cost of $6,000 pe r acre. Th is sum waS va 1 uated at 30 percent and taxed at an average entity mi II levy to calculate the tax benefit of lands that would continue to have significant taxes. That is, the unit tax benefits shown in Table VII-8 could be claimed for the area re- moved from the flood plain by the improvements of various alternates. The net tax difference between present taxes and future taxes after flood plain zoning of the area left in flood plain is not considered he,-e to be a loss because such areas shouldn't and probably wouldn't have been bui It upon if flood plain determination had been made. The benefit cost ratios and annual costs are then computed by the "ollowing equations. Without tangibles: Annual Cost = BenefitlCost Ratio Annual Construction Cost + Annua 1 l.and Cost + Annua'l F'robab I e Damages Annu~I...l~~~e Reduc t i on Annual Cost = With tangibles BenefitlCost Ratio Annua'l Damage Reduct i on +Annual Intangibles Annual l~x Benefit -Annu,iT Cost-- = Table VII-9 presents a summary for each alternate for the enti re basin.