Dealing with uncertainty in estimating average annual flood damage for ungaged watersheds

Abstract

Average annual damage (AAD) is a key central component of the hydrologic, hydraulic, and economic information developed in the evaluation of flood damage reduction plans. AAD or the expected value of annual damage, in dollars, is a probabflityweighted average of the economic losses associated with the full range of possible flood magnitudes. The Corps of Engineers and others have developed procedures for evaluating AAD that have been applied to numerous feasibil4 studies over the past several decades. A new risk-based analysis approach, currently being adopted in the United States, is based on modifying the conventional procedures to explicitly model the uncertainties involved in developing the required hydrologic, hydraulic, and economic relationships. This research evaluates the uncertainties involved in developing the three basic relationships required to estimate AAD and performs related damage analysis. Also, within this research an approach is developed for explicitly incorporating uncertainties in the basic relationships for the risk-based approach in an ungaged watershed. In addition, this research performs a sensitivity analysis on the risk-based approach AAD estimates and compares the conventional versus explicit uncertainty analysis approaches for evaluating average annual damages of an ungaged watershed. A case study was performed on a local watershed where the physical and economic systems were estimated and analyzed. Based on the case study, the new risk-based approach provides several advantages over the conventional AAD evaluation methods. Primarily, the risk-based approach provides more quantitative information to support decision-making processes such as capabilities for developing an AAD versus frequency relationship for a specified period-of-analysis rather than a single point estimate of AAD. In addition, the riskbased approach should provide more accurate AAD estimates.