sonnel are available to put a plan into successful operation, must 

 exist before the protective devices X'Jhich have been installed can 

 be fully utilized, 



c. Normal recovery . Reciirring losses also reflect changes 

 in the affected areas resulting from the complete destruction of 

 property in the flood of 19?U» Vlhere property was destroyed in 

 195U, an allowance has been made for normal recovery. Based on 

 evidence of recovery noted in the damage surveys and on the rate 

 of reconstruction in the area in the years following the hurri- 

 cane of 1938, a 30 percent recovery of loss potential, with addi- 

 tional allowance for increased costs, has been incorporated in 

 the computation of recvirring losses, 



d. Normal growth . The future growth in the flood areas of 

 Narragansett Bay was estimated on the basis of population growth 

 between 1930 and 19^0, and population pro.iections to 1970. A 20- 

 year projection was adopted in order to reflect economic condi- 

 tions near the mid-point of the project life. It was asstuned 

 that urban growth (residential, commercial, public), which was 

 taken as an index of the rate of growth in the affected areas of 

 the bay, would proceed at only one-half the rate of growth out- 

 side the flood areas, on the basis that (l) the shore areas of 

 Narragansett Bay are already hi/^ly developed, and that (2) less 

 urban growth could be expected in areas threatened by tidal 

 flooding. 



Population raoveBients and a heavy concentration of urban de- 

 velopment in the flood area indicated there would occur little 

 or no growth in the flood area of the city of Providence, An- 

 nual losses and benefits in the protected areas below Fox Point 

 barrier were increased by six percent in order to reflect an in- 

 creased loss potential due to increased growth, 



D-U. ANNUAL LOSSES AND BENEFITS 



a. General . The benefits of the plan to control tidal 

 flooding in the Narragansett Bay area consist of flood damage 

 prevention benefits and benefits from the elimination of scare 

 costs. 



Ihe flood damage prevention benefits are by far the most 

 important. Inasmuch as derivation of annual losses and benefits 

 for hurricane flooding and flood protection measures is a new 

 venture, annual benefits have been derived by two methods. The 

 basic method utilizes the standard practice of the Corps of Engi- 

 neers of correlation of stage-damage and stage-frequency to de- 

 velop a damage-frequency curve. Benefits derived by this method 



D-12 



