Risk Analysis for Flood Mitigation on the Raritan

We have developed a framework for flood mitigation risk analysis that applies generally to floods, and have applied it in this study of flood mitigation risk analysis for the Raritan Basin in New Jersey, USA. The framework we have developed involves a conceptual model of the relation among meteorological activity, hydrological models, infrastructure intervention, fine-grained topography, and economic impact. We have developed a hydrological model of the Raritan Basin. We used the calibrated model to compute the reduction in stream gage height (water level) over time as a result of implementing sufficient Green Infrastructure to reduce runoff depth by 1 inch throughout a relevant Watershed Management Area. Three scenarios of sufficient GI implementation and their associated costs were evaluated. In an econometric effort, we have developed a non-linear, threshold-based model that relates the cumulated or integrated amount of river activity above flood level to the FEMA insurance payouts, using historical data on both. This model was tested for four communities, and it achieves excellent predictive behavior against historical data, and can be used to relate the hydrological model results directly to FEMA payout records. Many possible water-related explanatory variables for FEMA insurance payouts were considered, and the most effective was found to be the aggregated quantity of water above flood level during the time directly associated to the flooding event that caused the claims and payouts. We applied this risk mitigation analysis framework to one community, Manville. The estimated cost savings due to the one inch reduction in runoff depth from Green Infrastructure in the region affecting Manville is about 6.1 million US dollars for a 68% reduction in FEMA payouts. Our effort has demonstrated that linking of meteorology, hydrology, non-linear econometric modeling and sophisticated elicitation can provide a very powerful tool for informing and guiding discussion among all stakeholders.