PLT21 - North Carolina Statewide PMP-Modernizing the Process for Dam Safety

Abstract Description: Applied Weather Associates (AWA) has completed the statewide PMP update for North Carolina in partnership with North Carolina Department of Environmental Quality (DEQ). This study incorporated many of the recommendations from the Modernization of PMP findings, released in June 2024. This statewide study included the traditional storm-based PMP development that AWA has completed for several other states. Recently completed statewide studies for New Jersey and Maryland to the next steps of incorporating Annual Exceedance Probability (AEP) analysis and climate change assessments specifically related to PMP. This North Carolina study built on those processes and included all three aspects into one study. Each of these analyses (deterministic PMP, AEP, and climate change) were developed to support dam safety evaluations and many other rainfall-runoff evaluations and water management needs. This is critical for North Carolina, which has experienced extreme flooding and infrastructure damage in recent years and includes a diverse range of climatological and topographic settings.

The development of deterministic PMP along with probability assessments combined critical aspects that support each other to confirm the PMP depths are reasonable and appropriate for all levels of dam safety applications. The AEP development subsequently provides detailed information on precipitation accumulation over a wide-variety of recurrence intervals. These can be used to evaluate rainfall-runoff information at locations which do not require the full PMF. In addition, these can be used for risk informed analyses, EAP scenarios, and other water management process. Importantly, NOAA Atlas 14 (and likely NOAA Atlas 15) do not include recurrence intervals beyond 1000-years. There is a need to understand and model recurrence intervals between 1000-years and PMP and this information provides those data.

These outputs were then evaluated in context of climate change projections. Projections were evaluated using several processes unique to AWA which determine whether projected changes would exceed the range of uncertainty in the data. This information can then be used to understand if the current design inputs are adequate or if not what range of outcomes are they resilient against. Decisions can then be made rwhether a given dam or other infrastructure is safe or if modification or other factors of safety should be applied.

This presentation will detail the technical analysis used to develop the PMP, AEP, and climate change projections, provide comparisons and results, and discuss how those results are consolidated into a database and provided to DEQ and the user community application.