To adequately protect an outfall system, what storm event must the structural integrity of a sediment basin withstand?

The correct answer is the requirement for a sediment basin to withstand a 25-year storm event. This standard is significant because it is designed to ensure that sediment basins can handle substantial runoff volumes that occur during significant rainfall events.

A 25-year storm event refers to the level of rainfall that has a statistical probability of occurring once every 25 years, which means it is a reasonably high frequency event. Designing for this type of storm helps to ensure that the basin can adequately manage and filter sediment during periods of heavy rain, preventing soil erosion and protecting water quality downstream.

The 25-year standard is specifically chosen because it balances practicality and risk management; it is less frequent than smaller storms while still being likely enough to occur in the operational lifetime of the sediment control measures. This ensures that the integrity of the outfall system is protected not only from everyday weather conditions but also from more severe weather that could lead to overflow and compromise sediment control efforts.

Understanding the magnitude of the storms and the capacity of structural measures in place is crucial in erosion and sediment control design, which is an integral part of maintaining environmental integrity in construction and land disturbance operations.