Copula-Based Flood Frequency Analysis at Ungauged Basin Confluences: Nashville, Tennessee

Abstract

Many cities are located at or near the confluence of streams where availability of water resources may be enhanced to sustain user needs while also posing an increased flooding risk from multiple tributaries. An accurate flood-frequency estimator that models the joint flood potential at a basin confluence is needed. Given that long-term flow observations are often unavailable, estimating flood-frequency at ungauged basin confluences proves challenging. Through the use of copulas, this case study demonstrates how an improved flood-frequency analysis can be performed for stream confluences at Nashville, Tennessee. The approach involves four major steps: initial data quality control, fitting of marginal distributions of tributary peak flows, construction of a suitable copula dependence structure, and identification of flood-frequency at the confluence point based on synthesized peak flows. This case study may help researchers and practitioners develop a better understanding of joint flood-frequency with consideration of upstream dam regulation among several contributing watersheds.