Incorporating Regional Rainfall-Frequency into Flood Frequency using RMC-RRFT and RMC-BestFit

Accurate estimates of flood frequency and magnitude are a key component of nationwide flood risk management programs. Quick estimates of at-site flood frequency curves have been historically limited to readily available data, such as historical gauge records, or documented historical floods. Most project sites in the U.S. have limited flood information, with most sites having fewer than 100 years of gauged flow data. Incorporating regional information can be used to effectively substitute space for time, increasing the effective record length and reducing statistical uncertainty in the flood frequency curve. However, incorporating regional information to an at-site flood frequency study has historically been a difficult, laborious, and computationally intensive.
The Risk Management Center (RMC) developed a web-based rainfall-runoff frequency tool (RMC-RRFT) that provides an intuitive step-by-step process for developing flood hazard curves using regional precipitation-frequency information. The RRFT allows engineers, who are not necessarily stochastic modeling experts, to rapidly develop flood hazard curves. After a user uploads a calibrated HEC-HMS hydrologic model of a watershed, the RRFT automates the extraction of NOAA Atlas 14 precipitation-frequency information and performs a stochastic flood event simulation to construct flood frequency curves. The Bayesian estimation and fitting software, RMC-BestFit, provides a framework for merging the RRFT results with at-site flow records, historical and paleoflood data, and regional skew information, resulting in a better understanding of the flood frequency relationship.
This paper will discuss the implementation of RRFT that allows engineers to incorporate regional precipitation-frequency information into at-site flood frequency curves. We will discuss the scalable framework that provides for a wide range of user demands from simple to complex stochastic analysis, and how the results are incorporated into BestFit to produce flood frequency curves. Finally, case studies that apply RRFT and BestFit to develop regionalized at-site flood frequency curves are evaluated.