07-09-18 Drainage and Flooding Committee Meeting

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MAIN GFAA WNDTH (FUG'") FIGURE 1 - TAXIWAY DESIGN GROUPS IML Specific Drainage Design Criteria A more stringent limit of keeping runoff from the 10-year storm event clear of the runways and taxiways was used for this study for the following two reasons: 1) With the recent rain events in Houston and surrounding areas, National Oceanic and Atmospheric Administration (NOAA) along with Harris County and City of Houston is in the process of updating the rainfall data. These updates are expected to release in the near future and expected to increase by as much as 15%. In order to avoid immediate short coming on the design, the 10-year storm event is suggested. 2) During the kick off meeting, Public Works Director indicated the capacity of the receiving system should be considered for selecting the design event. All drainage improvements on the site were designed such that all linear detention on site, including natural channels could drain within 48 hours, as required by the FAA. This will also minimize the risk of wildlife attraction to the area. The FAA AC permits the application of rational methods and hydrograph methods as applicable to determine the peak runoff. This study utilizes the allowable methodologies in conjunction with the state and the local intensity duration frequency (IDF) parameters to develop peak flows and the hydrographs for runoff simulation. Texas Department of Transportation (TxDOT) Design Criteria Per the TxDOT Hydraulic Design Manual Chapter 4 Section 12, revised July 2016, the Rational Method was used to calculate peak discharge values for each drainage basin on the site. TxDOT values for Harris County were used for the "b", "d", and "e" rainfall intensity coefficients, as shown in Table 1 below. Page 16