Flood-Resilient Road Design Standards for the Sudd Wetland Region of South Sudan

The Sudd, one of the world's largest freshwater wetlands, presents extreme hydrological and geotechnical challenges for road infrastructure design in South Sudan. Seasonal and prolonged flooding, expansive clay subgrades, and an absence of current design standards have rendered much of the existing road network structurally deficient, resulting in chronic disruption to humanitarian logistics, trade, and socio-economic development. This study develops and proposes a comprehensive set of flood-resilient road design standards specifically calibrated for the Sudd Wetland Region, integrating hydrological modelling, geotechnical investigation, pavement structural analysis, and multi-hazard risk assessment. A probabilistic flood frequency analysis based on remote-sensing-derived inundation data (2010–2023) was performed using the Log-Pearson Type III distribution. Field investigations across three representative road corridors revealed subgrade California Bearing Ratio (CBR) values ranging from 2% to 8%, necessitating subgrade stabilisation with hydrated lime at 4–6% by dry weight. Proposed design standards include minimum embankment heights of 1.2 m above the 50-year return period flood level, use of geotextile filter membranes, modified asphalt wearing courses with improved moisture resistance, and hydraulically designed culverts incorporating a 25% climate change surcharge on peak discharge. Benefit–cost analysis demonstrates that implementation of the proposed standards yields a net present value (NPV) of USD 4.7 million per kilometre over a 25-year design life compared to conventional earthen roads. The findings provide actionable design guidance for government agencies, development partners, and engineering practitioners working on road infrastructure in the Sudd and com