Rising Water, Rising Concerns: Levee Residual Risk in the Susquehanna River Basin

Levees in the Susquehanna River Basin (SRB) play a significant role in mitigating flood-related damage. Despite this, over 65% of these levees are non-accredited, meaning they do not meet federal requirements and may not be able to withstand 100-year flood events. Future floods in the SRB will be impacted by climate change, as studies indicate that there may be a 71% increase in extreme precipitation in the Northeast region of the SRB. This study develops an approach for estimating the levee residual risk, which is the risk that remains after implementing a levee, given the levee's probability of failure. The approach is implemented on a section of the Luzerne County levee system in the SRB. Using USGS streamflow gauge data at the study location, the frequency of flood events was calculated and used as boundary condition to run a 1D/2D hydrodynamic floodplain model. We found that the expected annual residual risk from levee failure is approximately $0.5 million. Furthermore, the results indicate that the expected annual cost associated with the levee residual risk is approximately 40% of the expected annual benefit, calculated as the avoided flood damages due to the levee. We conclude that levee residual risk is an important cost factor. Thus, it is critical to improve estimates of levee residual risk integrating data and models to inform better levee design and decision-making, given a rapidly changing climate.