Enhancing Near Confluence Infrastructure Resilience using Copula based Joint Probability Design Criteria

Hydraulic Structures on tributaries near river confluences are impacted by extreme events on both mainstream and the tributary that drains into the mainstream. The design criterion for such hydraulic structures need to take into account the coincident events at both the mainstream and the tributary while also accounting for backwater flows from the downstream river. The traditional design method outlined in HEC-22 manual is simplistic and its validity for individual regions is unknown. Therefore, there is a need to develop robust design criteria for hydraulic structure near confluences. This study implements a copula-based approach to develop the joint probability of coincident flows at confluences. The study uses streamflow time-series from SWAT model of the Upper Wabash River basin in Indiana to estimate the joint probability of streamflow at confluent reaches. It then analyzes the dependence of the joint probability distribution on stream characteristics and validates the findings using observed gauge locations to expand this method for ungauged locations. Findings from this study are expected to lead to a more resilient design criteria for designing/renewing critical hydraulic infrastructure near confluences.