To calculate the critical velocity of a sedimentation basin, we can use the following formula:
Vc = (Q / A) * (1 / t)
where:
Vc = critical velocity (in ft/min)
Q = flow rate (in million gallons per day, or MGD)
A = cross-sectional area of the basin (in square feet)
t = detention time (in minutes)
First, we need to convert the given values to the appropriate units:
- Flow rate (Q) = 5.77 MGD
- Cross-sectional area (A) = volume / depth = (1,000,000 gallons) / (3 feet) * (1 ft² / 7.48 gallons) = 4479.9 ft²
- Detention time (t) = 3 hours = 180 minutes
Now we can substitute these values into the formula:
Vc = (5.77 MGD / 4479.9 ft²) * (1 / 180 min)
= 0.0225 ft/min
Therefore, the critical velocity of the sedimentation basin is 0.0225 feet per minute.