Answer:
minimum required detention depth is 20.233 ft
Explanation:
given data
volume = 0.7 ac-ft = 0.7 × 43560 ft = 30492 ft³
dimension = 30’ x 30’
two sides = 1:1 (H:V)
solution
we get here area of square = 30 × 30
area = 900 ft²
we consider height is y
so volume will be triangular volume
v2 = 2 × { 0.5 × y² × 30 }
v2 = 30y²
and volume = area × height
v1 = 900 y
so total volume v1 + v2
total volume = 900 y + 30y²
30492 = 900 y + 30y²
y = 20.233 ft
so minimum required detention depth is 20.233 ft