Multi-Event calibration versus single event calibration results in better interaction with design storms

Ken Orie and Nina Caraway


In its earliest days, Fort Eustis served as an Army training facility, a prison and a work camp. One hundred years later 20,000+ Air Force, Army and civilian personnel work and/or live at Joint Base Langley-Eustis (JBLE), as it is now known. 

Just as JBLE is committed to providing high-quality combat airpower, training, support, operation and maintenance services, Old Dominion Utility Services, Inc. (ODUS) is required to keeping the base’s utilities running as a contracted service provider.

To identify basins in need of immediate attention and meet that “three-times” goal—which would require removing over 2 million gallons of inflow/infiltration—ODUS and McKim & Creed created a calibrated dynamic sewer model of the base’s collection system. The calibrated dynamic hydraulic model includes sewer loading allocations, extended period analysis, multi-event model calibration and system evaluation. Fifty-two sub-basins, 824 manholes, 834 pipes and 20 pump stations were modeled.

The model exceeded all standards for the 21 wet weather calibration events and the 18 extended dry weather events modeled. However, there were two events that led to a little head scratching. These two events were verified to have peaks of over 51 times average flow levels.

If single event calibration was used, as initially required by Federal Facility Technical Standards (FFTS), then we would have calibrated to a completely unrealistic event that would have resulted is massive budgets and overly conservative designs.

The multi-event calibrated model helped narrow down the search for the inflow source to a very uncommon cause. The possible solution will require cooperation between the US Military, ODUS and consultants.

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