Entin Hidayah, Yeny Dhokhikah, Hari Sulistyowati, Jojok Widodo Soetjipto, Joko Widodo, Alexander Agung Santoso Gunawan, Henny Herawati, Azmeri Azmeri, Juliastuti Juliastuti
Steep-gradient rivers such as the Jompo Watershed in Jember Regency, East Java, are highly prone to flash floods. This study assesses four mitigation scenarios using Hydrologic Engineering Center–Hydrologic Modeling System and Hydrologic Engineering Center–River Analysis System: (i) existing conditions, (ii) grey infrastructure, (iii) Nature-based Solutions (NbS) involving land restoration and retention ponds, and (iv) a hybrid grey–NbS approach. Among these, the hybrid scenario produced the strongest risk reduction, decreasing peak discharge by 37%, flood depth by 42%, and inundation area by 39% (from 4.81 to 2.91 km2). Grey infrastructure primarily reduced flow velocity, whereas NbS increased infiltration, storage, and runoff delay. Their combined effects generated greater attenuation than either strategy alone. The magnitude of reduction reflects the watershed's steep slopes and limited spatial availability, which constrain mitigation performance relative to wider or low-gradient basins. Overall, the results suggest that relying solely on conventional grey infrastructure is insufficient for steep tropical watersheds. Hybrid solutions offer a more cost-effective and ecologically sustainable alternative, enhancing both hydraulic performance and catchment resilience. The study provides an evidence-based framework that supports SDG 11 on resilient urban development and can be applied to similar flash-flood-prone tropical catchments facing heightened climate risks. © 2026 The Authors.
Department of Civil Engineering, Universitas Jember, Jl. Kalimantan Tegalboto No.37, Krajan Timur, Sumbersari, East Java, Jember, 68121, Indonesia; Department of Environmental Engineering, Faculty of Engineering, Jember University, Jember, 68121, Indonesia; Biology Science Department, Faculty of Mathematics and Natural Science, Universitas of Jember, Jember, 68121, Indonesia; Department of Civil Engineering, Faculty of Engineering, Jember University, Jember, 68121, Indonesia; Research Center for Geoinformatics, National Research and Innovation Agency (BRIN), Jakarta, 10340, Indonesia; Computer Science Department, School of Computer Science, Bina Nusantara University, Jakarta, 11480, Indonesia; Department of Civil Engineering, Faculty of Engineering, Tanjungpura University, Pontianak, 78124, Indonesia; Department of Civil Engineering, Faculty of Engineering, Syiah Kuala University, Banda Aceh, 23111, Indonesia; Department of Civil Engineering, Faculty of Engineering, Bina Nusantara University, Jakarta, 11480, Indonesia
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