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All Journal Journal of Degraded and Mining Lands Management
Koichi Yamamoto, Koichi
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Agriculture, Biological Sciences & Forestry Biochemistry, Genetics & Molecular Biology

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Hydrological modeling of small coastal peat island in degraded peatlands of Bengkalis Island, Riau Province Sutikno, Sigit; Yusa, Muhamad; Rinaldi, Rinaldi; Muhammad, Ahmad; Saputra, Hendra; Wardani, Khusnul Setia; Yamamoto, Koichi
Journal of Degraded and Mining Lands Management Vol. 13 No. 1 (2026)
Publisher : Brawijaya University

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.15243/jdmlm.2026.131.9163

Abstract

Small coastal peat islands such as Bengkalis (Riau, Indonesia) are hydrologically sensitive systems where groundwater level (GWL) controls ecosystem stability. Both extremes are hazardous: prolonged low GWL elevates peat-fire, subsidence, and carbon-loss risks, while excessively high GWL can trigger bog-burst. This study developed a simple empirical model to predict daily GWL in degraded peatlands on Bengkalis Island using in situ GWL data from three sites (drained, undrained inland, and undrained coastal) and GPM satellite rainfall (October 2023-April 2025). Calibrated over one year and validated over the next seven months, the model performed well at drained and coastal sites (R ~0.82, MAPE ~14%), capturing seasonal dynamics. In contrast, its performance at the inland site was lower (R ~0.5) due to minimal water table fluctuation. Coefficient values indicate the strongest rainfall response and fastest losses at the drained site, negligible daily loss at the inland site, and intermediate behavior at the coastal site. Scenario simulations highlight management-relevant risks: 15 rain-free days cause GWL to drop below the critical -0.40 m fire-risk threshold at the drained site and coastal site, whereas undrained inland remains just above it; conversely, 60 mm/day of rain for four days can raise GWL to the surface at coastal site (bog-burst risk). The model provides a practical tool for informing rewetting strategies to manage fire and collapse risks in degraded tropical peatlands.
Predictive model for California Bearing Ratio (CBR) in expansive coastal subgrades: a rapid geotechnical assessment for degraded and marginal lowland areas Nugroho, Soewignjo Agus; Satibi, Syawal; Putra, Agus Ika; Zulkifli, Zulkifli; Sutikno, Sigit; Yusa, Muhamad; Rinaldi, Rinaldi; Yamamoto, Koichi
Journal of Degraded and Mining Lands Management Vol. 13 No. 1 (2026)
Publisher : Brawijaya University

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.15243/jdmlm.2026.131.9329

Abstract

In geotechnical engineering, professional actions and expert judgment are often essential in soil investigation methods. In lowland and coastal areas, expansive, fine-grained soils and sandy sedimentation lead to reduced bearing capacity, posing significant challenges for sustainable infrastructure development on marginal and degraded lands. Such conditions are prevalent in post-mining or naturally poor coastal environments, necessitating cost-effective and rapid assessment tools. This study modeled a clayey sand mixture using bentonite and kaolin as fine fractions, which exhibit expansive behavior and poor gradation, simulating worst-case geotechnically degraded subgrades. The mechanical behavior of the soil was evaluated through modified compaction, using the CBR test and CPT test as bearing capacity parameters. Soil mixtures were simulated with sand fractions ?65% and bentonite-kaolin compositions with ?50% bentonite. Compaction was modeled using variations in energy compaction and water content under conditions below the maximum dry density. CBR prediction was conducted using Qc as the primary predictor and dry density as a supporting predictor. A hybrid stepwise regression analysis in the         Z-score scale identified positively correlated predictors: +3.00 (Qc), +0.55 (?dry), and +1.28 (Qc ?dry interaction). The regression model showed strong statistical performance with R² = 0.84 and high significance with the lowest p-values. The resulting regression equation offers an applicable approach to rapidly evaluate the bearing capacity of subgrade soils in degraded coastal or marginal conditions, thereby facilitating geotechnical engineering design and initial site assessment crucial for land management and rehabilitation actions.
Co-Authors Agus Ika Putra Ahmad Muhammad Hendra Saputra Muhamad Yusa Rinaldi Rinaldi Satibi, Syawal Soewignjo Agus Nugroho Sutikno, Sigit Wardani, Khusnul Setia Zulkifli Zulkifli