Evaluating the Effectiveness of Seepage Countermeasures and Retrofitting Strategies for Mitigating Nappe Flow-Induced Reverse Flow and Erosion for Overtopping Flow from a Levee

Abstract

Levee failure due to nappe flow and subsequent erosion presents a significant challenge to flood protection infrastructure. This study evaluates the effectiveness of horizontal drainage layers, a common seepage control method, in mitigating these risks. While many traditional solutions to mitigate overtopping are costly and complex, horizontal drainage layers offer a promising and cost-effective alternative. These layers not only address seepage control but also manage nappe flow-induced erosion, potentially reducing construction and maintenance costs. Despite extensive research on their role in seepage control, a gap remains in understanding their effectiveness against overtopping-induced erosion, particularly in managing reverse flow. Existing studies often address seepage control or nappe flow erosion separately, overlooking the integrated impact of these layers. This study aims to address this gap by evaluating the performance of horizontal drainage layers under simulated overtopping conditions. The research involves two series of experiments, Series I: Focuses on newly built levees equipped with full (HD15L50 and HD25L50, where the thicknesses are 15 and 25 cm, respectively, with a horizontal drainage layer length of 50 cm and a crest length of 40 cm), partial length (HD15L40 and HD25L40), and short/reduced length (HD15L30 and HD25L30). The results showed that full-length layers reduce erosion inside the levee body and foundation by almost 100% and enhance levee stability due to their superior ability to dissipate hydraulic energy. Series II: Investigates practical solutions for retrofitting existing levees using shorter drainage layers with extended crests and gauzed sheets (HD15L15L30C60GH and HD25L30C60GH, where the thicknesses are 15 and 25 cm, the drainage length is 30 cm, and the crest is extended to 60 cm with gauzed sheets). Although shorter layers were less effective than full-length ones, extending the levee crest significantly improved their performance, achieving protection levels comparable to full-length layers, providing a valuable solution for upgrading existing levees. Overall, this study offers valuable insights by systematically evaluating and optimizing seepage control techniques. These findings can be directly applied to guide levee design, maintenance, and risk reduction strategies. This research contributes significantly to improving the resilience of levee systems against water pressure and ensuring their long-term stability.