Map Scale Question/stage storage curve

[Redskinsdb21]

I have a mapscale question....I am trying to calculate surface area of a pond and creat a stage storage curve from this info.....The question says my map scale is a 500 scale...it tells me I have a 42.34 square inch surface area....what would be the surface area in acres...?

I tried ((500)squared)/43560 which equals 5.73 acres per square inch....then 42.34 square inches multiplied by 5.73 equals 242.60 acres...is this the correct way to do it? The answer in my book says 233.5 acres...so it makes me feel as if I am doing something wrong.

ALso, it ask to determine storage in acre-feet at this elevation...any help is appreciated, thanks!

 

[cvg]

square root of 42.34 is 6.5
6.5 times 500 is 3253
3253 squared is 10585000
10585000 divide by 43560 equals 242.6

use the conic method/equation for calculating the volume you can find in the HEC1 user manual