New Probable Maximum Precipitation (PMP) for Dam Safety – the case of North Carolina

This study delivers new grided PMP and Temporal Distributions for NC and adjacent regions. ArcGIS Pro based PMP Evaluation Tool is developed that enables users to generate PMP and temporal distribution outputs for a user-defined basin. Local Storm PMP (1-hr to 24-hr durations, 5-minute interval), General and Tropical Storms PMP (1-hr to 72-hr durations, 15-minute interval) were developed. Given that over 70% of NC dams have watershed areas under 1 square mile, significant attention was given to short-duration, high-intensity rainfall patterns and developing PMP depths for these smaller basins. Compared to HMR51, results of PMP depths show range of reductions in western NC and increases in eastern NC. The Tool has been tested on several specific sites and few HEC-HMS analysis results reveal that the shorter duration of 2-hr PMP is more critical in some sites in western NC, while the 12-hr PMP is more critical in some sites in central NC. Additionally, the study provides Annual Exceedance Probability (AEP) analyses for 6-hour and 24-hour durations for 18 different probabilities (or return periods).