As per the Fort Bend Drainage Criteria Manual (7.3.1.1 –Design Criteria Assuming Coincidental Events), the maximum ponding level within the leveed area should not exceed the maximum water surface elevation associated with the 100-yr coincidental flood event computed in designing the internal drainage system of the levee area, including the required minimum freeboard of one foot and the pumping and storage capacity of the leveed system.
The coincidental ponding is determined from the coincidental probability of interior and exterior flooding and the capacity of pumps, drainage channels, and detention using the precipitation requirements of Atlas 14.