Search Results (257)

Land subsidence driven by excessive groundwater extraction in the Choushui River alluvial fan of central Taiwan poses a significant threat to the structural integrity of the Taiwan High-Speed Rail (THSR). This study presents an integrated approach combining multi-temporal Interferometric Synthetic Aperture Radar (MT-InSAR), continuous and campaign Global Navigation Satellite System (GNSS) measurements, and precise leveling surveys to characterize both vertical and horizontal surface displacements along the THSR corridor. Sentinel-1 C-band SAR data from ascending (A69) and descending (D105) tracks were processed using the Small Baseline Subset (SBAS) technique over the period of 2015–2021 and decomposed into east–west (EW) and vertical components via 2.5D decomposition. The InSAR-derived EW velocity field was calibrated using GNSS Ordinary Kriging interpolation, improving R² from 0.147 (RMSE = 4.24 mm/yr) to 0.992 (RMSE = 0.24 mm/yr). The vertical velocity field was corrected using a polynomial trend surface fitted to 922 leveling benchmarks and 38 continuous GNSS stations, reducing the RMSE from 6.03 to 4.85 mm/yr (increasing R² from 0.889 to 0.898) and virtually eliminating the systematic bias (a decrease from +3.47 to −0.47 mm/yr). Maximum subsidence exceeding 60 mm/yr was identified in the Yunlin Tuku area, while three secondary subsidence centers were found in Changhua. The horizontal velocity field revealed a convergent pattern directed toward subsidence centers, with magnitudes of 2–10 mm/yr, confirming that aquifer compaction induces significant lateral deformation. Along the THSR corridor, differential EW velocities across the Xizhou and Tuku subsidence zones highlight potential risks to rail alignment and structural safety, with horizontal strain rates reaching approximately 10⁻⁶/yr. GNSS observations additionally provide the north–south velocity component that InSAR cannot detect, enabling a more complete three-dimensional deformation characterization. Full article

Under the background of global warming, high-tide floods pose growing threats to China’s coastal ecosystems, infrastructure and freshwater supplies. Although the occurrence of high-tide flooding events is widely recognized as being related to relative sea-level rise, tides, and residuals, the analysis and attribution of individual events remain relatively scarce. Based on tide-gauge data and numerical simulations, this study conducted a quantitative analysis of the high-tide flooding events along China’s southern coast around 19 November 2024 and provides mitigation recommendations. Results indicate that coastal sea levels south of the Yangtze River Estuary in November 2024 hit the third-highest November value on record. Sea levels south of the Taiwan Strait were 26 cm above those of normal years, with the highest monthly level since that recorded in 1980. Around 19 November, the coastal area levels coincided with the astronomical spring tide period, with the astronomical high water levels in Shanwei (Guangdong), Dongfang (Hainan), and Beihai (Guangxi) reaching 116 cm, 186 cm, and 292 cm above local mean sea level, respectively. Additionally, influenced by the outer circulation of the tropical cyclone Man-Yi and a cold-air process, an extensive coastal surge occurred, with 30~80 cm surges persisting for nearly 30 h. The combined effects of high sea levels, spring tides, and abnormal surges triggered extreme sea levels that broke historical records, with multiple stations reaching once-in-20-year levels. The contributions of astronomical tides to the extreme sea levels in Shanwei, Dongfang and Beihai were 49.5%, 69.3%, and 77.8%, respectively, while the contributions of surges were 23.6%, 6.4%, and 4.6%. This high-tide flooding event affected multiple coastal areas in Guangdong, Guangxi, and Hainan. Developing a comprehensive adaptation strategy encompassing emergency observation and early warning, risk assessment and zoning, coastal protection, coastal adaptive planning, and freshwater resources management is crucial for effectively addressing the risks of high-tide flooding events. Full article

Constructing new reservoirs to ensure a reliable water supply in downstream areas and to alleviate overflow flooding along rivers during floods is an urgent task for the authorities. In this study, we developed a GIS platform that integrates a series of watershed geomorphological and hydrological models to assess the suitability of prospective dam sites. The built-in modules include watershed geomorphological analysis, rainfall analysis, flow analysis, surplus water analysis, and reservoir analysis. Using the digital elevation model, users can obtain the reservoir H-A-V curve at a prospective dam site and the upstream watershed’s geomorphological factors. A topography-based hydrological model was used to estimate available water at the dam site, and surplus water was obtained by subtracting existing water demands and/or environmental flow requirements from the available water series. Exceedance probability analysis was then conducted for the surplus water to evaluate the dam site’s feasibility for new water resources development. The system also provides a reservoir’s useful-life evaluation to determine the time required for sediment accumulation to render the reservoir unable to serve its intended purpose. Moreover, for flood control, the platform includes a built-in module for estimating design discharge for different return periods. The planned Pingxi Reservoir site in New Taipei County, Taiwan, is used as an example in this study. Detailed analytical procedures are presented to demonstrate the use of the proposed integrated GIS platform system to assess the adequacy of prospective dam sites for new water resources development. Full article

This study developed a novel framework integrating UAV-derived orthophotography, deep learning-based substrate classification, two-dimensional hydraulic modeling, Froude number (Fr) analysis, and multispecies habitat suitability assessment to evaluate the effects of channel modification and precipitation on fish habitats in Gaoliao Creek, eastern Taiwan. Habitat changes under baseflow and rainfall-induced high-flow conditions were quantified using Fr-based hydraulic habitat availability and Habitat Suitability Index (HSI)- and Combined Habitat Suitability Index (CHSI)-based habitat suitability. Channel modification transformed the channel from a deep and slow-flowing system into a shallower and faster-flowing environment. Under baseflow conditions, the proportion of available habitat meeting the adopted hydraulic criteria decreased from 81.6% to 73.9%, whereas the CHSI-derived proportion of weighted usable area (PUA) increased from 0.300 to 0.323 due to favorable substrate composition. During rainfall events, habitat availability and suitability declined markedly during peak flows and recovered as discharge receded. Compared with the pre-engineering channel, the modified channel exhibited greater sensitivity to short-term hydrological fluctuations but effectively prevented overbank flooding during the selected extreme rainfall event. These findings highlight the trade-off between flood-control benefits and ecological resilience and emphasize the importance of maintaining habitat heterogeneity in river management. Because the analyses were based on a single typhoon-related rainfall event and lacked direct biological validation, the results should be interpreted as event-specific predictions requiring further verification. Full article

The South China Sea serves as a premier location for investigating sediment provenance and source-to-sink processes within marginal seas. However, the sediment composition and transport mechanisms within the deep-water areas of the Qiongdongnan Basin remain poorly understood. This study analyzed the grain-size distribution, bulk geochemistry, and clay mineralogy of surface sediments to identify their origins and transport controls. Results indicate that the sediments are predominantly silt-sized with a high smectite content. Major element geochemistry suggests derivation from stable ancient terranes, while trace element patterns—characterized by LREE enrichment and negative Eu anomalies—point toward a multi-source contribution. Our analysis suggests that the Red River is the primary sediment source, supplemented by inputs from the Pearl River, the Vietnamese coast, and Hainan Island. We propose that monsoon-driven surface circulation is the primary transport driver, while deep-water currents and a branch of the Kuroshio Current facilitate the influx of Taiwan-derived materials. Our study clarifies the source–sink relationship and transport mechanism in a semi-quantitative manner, offering new insights into sediment dynamics in monsoon-influenced marginal seas. Full article

Coastal regions played a key role in the emergence of Early Neolithic cultures. Fluctuating sea levels shaped prehistoric human migration, settlement patterns, and adaptation strategies. The lower reaches of the Min River in Fujian were a major centre of activity. During the Middle to Late Neolithic, marine communities such as the Keqiutou (6500–5500 cal. a BP) and Tanshishan (5500–4300 cal. a BP) cultures flourished. However, the scarcity of earlier remains has limited understanding of Early Neolithic life before 8000 cal. a BP. We dated stratigraphic layers at the newly excavated Niutoushan site using radiocarbon dating and optically stimulated luminescence (OSL). OSL results indicate the site’s Neolithic culture layer between 9.3 ± 0.7 ka and 8.1 ± 0.5 ka, with radiocarbon dates clustering around 8300–7000 cal. a BP. Based on the younger bounds of the dating results and kernel density estimation, the Neolithic remains at the site are dated to approximately 8000–7000 cal. a BP, identifying Niutoushan as one of the earliest Neolithic sites in the region. Combined with sea-level reconstructions, the findings suggest that the rapid Early Holocene sea-level rise drove human migration along China’s eastern coast before 8000 cal. a BP. The Niutoushan culture was influenced by Neolithic cultures from northern coastal regions and potentially by those located to its south across the exposed Taiwan Strait from the Last Glacial Maximum to the Early Holocene. This points to complex interactions among Early Neolithic cultures in both northern and southern coastal China, warranting further investigation for validation. Full article

River levees in Taiwan are exposed to typhoons, earthquakes, and long-term erosion and scour, which often cause subsurface voids of varying severity within the levee body. This study conducted a quantitative physical analysis of 0.15 m-thick concrete specimens containing voids of different dimensions (widths of 0.10–0.40 m and sizes of 0.06–0.15 m). The specimens were scanned using ground-penetrating radar (GPR) antennas with center frequencies ranging from 750 MHz to 2.3 GHz. Variations in electromagnetic-wave reflection amplitude within the material were used to determine void size along the X-axis, whereas the depths corresponding to the reflection points were quantified along the Y-axis. The void area was then estimated based on the X-Y coverage. The results showed that absolute amplitude differentiation provided distinct quantitative features that reflected the presence of voids of various sizes. The proposed method was further validated using an actual river-levee scour case. The findings of this study offer a practical reference for the inspection, maintenance, and repair of river levees. Full article

Wind energy is an important form of clean energy, and its rational utilization represents a crucial solution for mitigating the energy crisis and global warming. In this study, wind energy potential and its long-term changes in the South China Sea (SCS) are evaluated using ERA5 100 m wind data from 1944 to 2023, validated against ASCAT observations. High wind speeds and high wind power density (WPD) are concentrated southwest of Taiwan and southeast of Vietnam. Annual wind availability exceeds 6457 h across most regions, reaching up to 8283 h in optimal locations. WPD and capacity factor peak in winter (up to 2.4 × 10⁸ Wh·m⁻² and >50% capacity factor), with the most stable conditions occurring in the southwestern Taiwan Strait, southeast of the Pearl River Delta, and the Beibu Gulf. Empirical orthogonal function analysis reveals that the first mode of winter WPD accounts for 65.7% of the total variance, with a statistically significant increasing trend since 1990. The interannual variation in wind energy resources in the SCS during winter is controlled by the combined effects of sea surface temperature (SST) anomalies in the tropical Pacific and the Arctic Barents Sea. Specifically, in the years with strong wind anomalies in the SCS, mega-La Niña-type SST patterns in the tropical Pacific trigger anomalous cyclonic circulation in the SCS and the eastern Philippine Sea, while warm anomalies in the Arctic Barents Sea surface drive a wave-like structure of “anticyclone–cyclone–anticyclone” from Siberia to South China. The coupling of the two systems jointly promotes the strengthening of the South China Sea monsoon, leading to increased wind speeds and elevated WPD in the northern SCS. These findings provide a scientific basis for wind farm siting and long-term operational planning in the region. Full article

Mierspenaeopsis hardwickii (Miers, 1878) represents an important economic resource for coastal artisanal fishers and small-scale fisheries operations. However, very little is known about the distribution patterns related to environmental factors and migration routes of M. hardwickii. In this study, we employed research vessels to obtain CPUE_w (weight in catch per unit effort) and CPUE_n (abundance in catch per unit effort) data in 2018–2019. Our results showed that the largest number was found at 20–40 m in spring and summer, extending in autumn (40–90 m) and shrinking in winter (40–60 m). The scattered distribution pattern of M. hardwickii was observed in spring with sea bottom temperature (SBT) 11–18 °C and sea bottom salinity (SBS) 32–34 and winter (SBT 9–19 °C, SBS 32–35); most individuals were observed in summer (SBT 26–28 °C, SBS 30–31) and autumn (SBT 19–22 °C, SBS 32–35). The annual mean CPUE_w and CPUE_n were 3624 g·h^–1 and 799.4 ind·h^–1, respectively. We hypothesize that in spring, most parent cohorts aggregate in Dasha in the southern Yellow Sea, while many cohorts gather in the coastal waters of the East China Sea, with sharply reduced abundance in the offshore deeper waters. In summer, the parent cohorts produced offspring in Lvsi in the southern Yellow Sea, the Yangtze River estuary, and coastal water areas of the East China Sea. In autumn, juveniles in the coastal waters migrated to the offshore water area. In winter, a few individuals were sparsely distributed in the offshore water areas of the southern Yellow and East China Seas, and part of the recruitment in the Taiwan Strait might migrate northward to Yushan and Wentai fishing grounds for the nursery. The present investigations provide baseline data that will enable fishers and policymakers to better manage and conserve this resource for future use. Full article

Extreme rainfall events can trigger widespread landsliding and fluvial erosion, exerting a disproportionate influence on sediment production and landscape evolution in mountainous watersheds. However, hillslope–channel coupling during individual extreme events remains poorly quantified due to the scarcity of event-scale topographic observations. This study investigates event-scale hillslope–channel coupling by quantifying landslide-driven hillslope erosion and channel incision associated with Typhoon Morakot (2009) in the Sinwulu River watershed, southeastern Taiwan. High-resolution pre- and post-event digital surface models (DSMs) were reconstructed using an aerial structure-from-motion multi-view stereo (SfM–MVS) photogrammetry workflow and corrected for canopy height to derive meter-scale topographic changes. Hillslope and channel domains were delineated, and linked hillslope–channel units were used to examine spatial relationships between erosion processes and topographic and hydraulic factors. Results indicate that landslide erosion dominated sediment production during the event with watershed-average erosion of 544.35 mm, while channel responses exhibited strong spatial contrasts, with pronounced incision in upstream reaches and substantial deposition downstream of major knickpoints. Event-scale analysis provides evidence for a strong correspondence between channel incision and hillslope landslide erosion, whereas correlations with commonly used hydraulic proxies such as unit stream power are comparatively weaker. These findings highlight the value of event-scale topographic measurements for elucidating transient hillslope–channel coupling processes during extreme rainfall events. Full article

The Danshuei River Estuary (DRE), located in northern Taiwan, is severely polluted by dissolved N (ammonium exceeding 500 μM) and P (dissolved phosphate exceeding 10 μM) due to the domestic wastewater discharging into the river system. However, the knowledge of nutrient pollution in the estuarine sediment is very limited. Three sediment cores (SCs) were collected from the DRE to study P pollution status, and five fractions of sedimentary P, Fe, and Mn were analyzed by Ruttenberg’s sequential extraction method. The analyzed results indicate that the total P concentrations and P fractions in the sediment core of the upper estuary differed significantly from those of the lower estuary. The total p-values in the SC of the upper estuary generally exceeded 2000 mg/kg and were dominated by ferric iron-bound P (PCDB), accounting for 80% of total P pools. This result indicates that the mobilization of the PCDB fraction in the SC was significant and dominated the geochemical P cycle rather than the remineralization of organic P. Meanwhile, the corresponding values decreased to 650 mg/kg and 50% in the SC of the lower estuary. The dominance of the PCDB fraction decreased seaward. Meanwhile, the other four fractions, especially for the PDET fraction, increased seaward. The transformations of the P fractions differed across the different depth intervals in the three sediment cores. The sequence of the dominant fractions of sedimentary P and Fe was similar but differed from the Mn fractions in the three sediment cores. Full article

Reliable, real-time river flow monitoring is essential for disaster prevention, but traditional in situ methods are costly and high-risk. Large-scale particle image velocimetry (LSPIV) offers a non-contact alternative, though its accuracy is often compromised by noise and non-water pixels, requiring intensive manual data processing. This study proposes an integrated framework for enhancing non-contact river surface velocity estimation by combining deep learning-based water surface segmentation with optimized LSPIV, using accessible smartphone imaging. The framework was tested on two urban rivers in Taichung, Taiwan. DeepLabV3+ was identified as the superior segmentation model based on MPA/PA and MIoU metrics. The DeepLabV3+-derived mask was integrated into the LSPIV workflow, which was optimized using a 32 × 32 pixels interrogation area (IA), reducing processing time by approximately 44%. By removing non-water pixels, the masked LSPIV yielded a 7% increase in mean surface velocity. This suggests that the inclusion of non-water elements diluted the average, underscoring their tendency to introduce a low-velocity bias in unmasked calculations. The overall validation showed mean absolute percentage errors below 6% compared to the radar velocimeter. Consequently, this integrated smartphone-based framework offers a cost-effective and precise solution for future large-scale deployment in urban flood monitoring and smart city hydrological management. Full article

River water is a vital component of the hydrological cycle, sustaining ecosystems and serving as the most accessible freshwater resource for human use. Beyond elemental concentrations, isotopic tracers such as boron (δ¹¹B) and radiogenic strontium (⁸⁷Sr/⁸⁶Sr) provide insights into weathering processes and anthropogenic impacts. This study examines spatial and temporal variations in the chemical composition of the Erren River to distinguish natural contributions from human-derived inputs and assess recent pollution. Samples collected from upstream to downstream were processed by micro-sublimation or column chromatography, with isotopes measured using MC-ICP-MS. Results show δ¹¹B values from +4.8‰ to +30.4‰ (variation ~26‰) and ⁸⁷Sr/⁸⁶Sr ratios from 0.709679 to 0.710446. Major ion and isotopic data indicate upstream waters are dominated by silicate weathering, while downstream areas reflect seawater and salt spray influence, consistent with regional geology and hydrology. Furthermore, δ¹¹B patterns combined with Cl⁻/Na and NO₃⁻/B ratios suggest that tributaries in the mid-to-lower basin remain affected by anthropogenic pollution, likely linked to agricultural and urban activities. These findings highlight both natural controls and ongoing human impacts on the Erren River system. Full article

River health assessment frameworks play a critical role in guiding restoration planning and watershed management, yet conventional index-based approaches often rely on fixed weighting schemes that limit diagnostic sensitivity and interpretability. This study proposes an integrated assessment framework that enhances the traditional Index of Stream Condition (ISC) by incorporating data-driven structural information while preserving transparency and regulatory relevance. Rather than replacing existing indices, the framework recalibrates sub-index contributions based on intrinsic data patterns derived from nonlinear embedding and density-based clustering. The proposed methodology is applied to the Zhuoshui River basin in Taiwan to demonstrate its capability to improve internal consistency, reduce metric redundancy, and clarify dominant environmental drivers. Results indicate that the recalibrated index provides clearer differentiation among ecological conditions and improves explanatory consistency compared with the original ISC formulation. By balancing methodological innovation with interpretability, the proposed framework offers a practical pathway for strengthening river health assessment and supporting restoration-oriented decision-making. Full article

This study proposes a framework, the RA_WLTE_River model, for quantifying the reliability of flood-altering water-level thresholds, considering rainfall and runoff-related uncertainties. The Keelung River in northern Taiwan is selected as the study area, and associated hydrological data from 2008 to 2016 are applied in the development and application of the model. According to the results from the model development and demonstration, the average and maximum rainfall intensities, roughness coefficients, and maximum tide depths exhibit a significant contribution to the reliability quantification of the estimated water-level thresholds. In addition, empirically based water-level thresholds can achieve the goal of rainfall-induced flood early warning, with a high likelihood of nearly 0.95. Additionally, the probabilistically based water-level thresholds derived from the described reliability can efficiently ensure consistent flood early warning performance at all control points along the river. Full article