Multiobjective Optimization of Relief Well Operations to Improve Levee Safety

Abstract

The factor of safety (FS) of levees and floodwalls with relief wells to underseepage is predicated on the blanket thickness and relief well performance. In urban environments with limited right of way, relief wells are an option for addressing underseepage and sand boil development. Instead of adding more wells if problems persist, this study investigates the potential of active pumping at relief wells as an alternative to increase levee and floodwall factor of safety against underseepage. Optimization of relief well operations is achieved by a multiobjective mixed-integer nonlinear programming (MOMINLP) approach. The relief well operations optimization is demonstrated at the Inner Harbor Navigation Canal (IHNC), New Orleans, Louisiana, near the Seabrook Bridge at Lake Pontchartrain. Relief well evaluation at the water level corresponding to the 500-year return storm shows high total head at most IHNC West relief well sites. Relief well operations optimization provides decision makers useful tradeoffs between averaged FS deficit, total pumping rate, and the number of pumping wells for making pumping decisions. This study found that the Pareto-optimal solutions provide reasonable pumping rates, where all of the midway between relief wells in the IHNC West may meet the requirement FS>1.5. The study also found that minimizing the number of pumping wells and minimizing the total pumping rate are influential objectives for deriving efficient pumping strategies. Sensitivity analysis on IHNC water stage found that FS improvement becomes marginal after total pumping rate reaches a threshold, especially at low IHNC water stages.