Example 112 Determining Pump Capacity with Influent

Problem: A wet well is 8.2 ft x 9.6 ft. The influent flow to the well, measured upstream, is 365 gpm. If the wet well rises 2.2 in. in 5 minutes, how many gallons per minute is the pump discharging?


Influent = Discharge + Accumulation (112)

365 gpm = Discharge + Accumulation

We want to calculate the discharge. Influent is known, and we have enough information to calculate the accumulation:

Volume Accumulated = 8.2 ft x 9.6 ft x 2.2 in. x 1 ft x 7.48 gal = 108 gal

5 min 1 min

Using Equation 11.2:

Influent = Discharge + Accumulation 365 gpm = Discharge + 21.6 Subtracting from both sides:

365 gpm - 21.6 gpm = Discharge + 21.6 gpm - 21.6 gpm 343.4 gpm = Discharge

The wet well pump is discharging 343.4 gpm.

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