- Compute the runoff rate using Equations 11-1 and 11-2.
- Calculate the outflow rate due to infiltration, in cubic feet per second, using Equation 11-3.
- Calculate the outflow rate, in cubic feet per second per acre, of imperviousness using Equation 11-4.
- Calculate the duration of the design storm in minutes using Equation 11-5.
- Calculate the maximum required detention volume using Equation 11-6.

Where:

Q_{inf} | = | outflow rate due to infiltration in cubic feet per second |

FA_{min} | = | minimum footprint or surface area of the stormwater disposal system |

i _{soil} | = | soil infiltration rate in inches per hour |

Where:

Q _{o } | = | restricted flow rate in cubic feet per second per acre of imperviousness |

Q _{inf } | = | outflow rate due to infiltration cubic feet per second |

C _{w} | = | weighted runoff coefficient for the area tributary to the stormwater system |

Where:

t | = | duration of the storm in minutes |

Q_{o} | = | restricted flow rate in cubic feet per second per acre of imperviousness |

Where:

v | = | maximum required detention volume |

t | = | duration of the storm in minutes |

Q_{o} | = | restricted flow rate in cubic feet per second per acre of imperviousness |

A | = | Area tributary to the detention facility in acres |

C_{w} | = | weighted runoff coefficient for the area of tributary to the stormwater system |