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Sediment Bypass Tunnels (SBTs) are proven to be an effective measure to reduce or even stop reservoir sedimentation by bypassing sediment laden flows around reservoir dams to the downstream river reach. They are mostly used in Switzerland, Japan, and Taiwan. However, hydraulic and sedimentological operating conditions and the resistance of the invert materials against hydroabrasive erosion affect their cost-effectiveness. Hydroabrasion is a pressing issue at SBTs, other hydraulic structures and steep bedrock rivers exposed to high sediment transport rates under supercritical flow conditions. The present study was therefore conducted to address this issue by aiming at improving knowledge on abrasion mechanics and calibrating a mechanistic saltation abrasion model enhanced by Demiral-Yüzügüllü (2021). To this end, the abrasion resistance of fourteen different invert materials installed at Solis, Pfaffensprung and Runcahez SBTs in Switzerland was quantified by annual 3D laser scanning and the hydraulic conditions and sediment transport rates were regularly monitored between 2017 and 2021. The analysis of invert scans and hydraulic conditions revealed that Prandtl's first and second kinds of secondary currents occurring in the bends and straight sections of the SBTs, respectively, and the observed abrasion patterns were strongly interrelated. The tested potassium aluminate cement and steel fibre concretes, granite, cast basalt and steel plates had better abrasion resistance against impact of sediment-laden flows compared to other materials. Sediment mineralogical composition i.e., bulk hardness relative to the invert material properties significantly affected hydroabrasion. The enhanced abrasion prediction model was calibrated with the present data and a quasi-constant abrasion coefficient of k v = (4.8 ± 2.2) × 104 was obtained. The enhanced model is well-suited for both laboratory and field scales. The present findings will contribute to the sustainable utilization and operational safety of hydraulic structures, optimization of SBT and reservoir operations regarding bypassing efficiency and reservoir lifetime and modelling of bedrock river erosion. [ABSTRACT FROM AUTHOR]

Deciphering sedimentary provenance in the Okinawa Trough (OT) is vital for understanding the dispersal system from source to sink and the paleoenvironmental evolution in the East China Sea (ECS). Sources include the Huanghe, Changjiang, and Taiwan rivers, as well as the ECS shelf; however, there is controversy over which source has dominated sediment supply since the last deglaciation, and how the tidal currents, shelf circulation, and Kuroshio Current (KC) has controlled the sediment transport. Here, we present a high-resolution record of grain size and clay minerals over the last 14.3 kyrs in an AMS 14C dated piston core from the middle OT. We use these data to reconstruct changes in the KC, identify the provenance of fine-grained sediment, and unravel the impact of paleoenvironmental factors on these provenance changes. A grain size component of 15.6–31.3 μm was extracted to reconstruct the KC changes. These data show that the KC strengthened sharply until 10.2 ka, then kept strong and stable during the Holocene. Clay mineral assemblages indicate that the sediment was mainly derived from the ECS shelf between 14.3 and 8.6 ka, then from the Taiwan rivers after 8.6 ka. The shelf sediment was eroded and transported by intense tidal currents. Taiwan river sediment became the dominant source due to the development of Taiwan Warm Current rather than the strengthening of KC. The ratio of smectite and kaolinite to illite and chlorite content indicates that the sediment contribution from the Huanghe (old Huanghe delta) and Changjiang rivers increased from 7.6 to 5.0 ka and from 3.2 ka to the present. This increase is attributed to the strengthening of East Asian winter monsoon and the consequent intensification of cross-shelf circulation. • Sediment source changed from East China Sea shelf to Taiwan rivers at 8.6 ka. • Tidal reworking controls shelf sediment supply during the last deglaciation. • Taiwan Warm Current induces early Holocene provenance change rather than Kuroshio. • Winter monsoon enhances Huanghe and Changjiang supply at 7.6–5.0 ka and 3.2–0 ka. [ABSTRACT FROM AUTHOR]

• SWAT-Twn 2.0: Enhanced model with adaptable landslide triggers improves sediment simulation. • Dual triggers (PCP: rainfall and FSW: fraction of soil water content) in SWAT-Twn 2.0 show superior performance. • PCP trigger significantly affects landslide identification accuracy. • Lack of particle size leads to channel deposition overestimation. • Incorporate landslide characteristics into HRU (Hydrologic Response Unit) classification to address limitations. Landslides, caused by heavy rainfall, earthquakes, or human development, are likely occur in steeper slopes, while some occur in moderate slopes (15°– 35°). Although landslides can contribute a significant amount of sediment transport in a watershed, landslides are rarely considered in hydrological models. To conduct a thorough investigation into the influence of landslides on sediment transport within rivers, a detailed analysis of landslide characteristics was performed. Subsequently, a dedicated landslide module was integrated into a hydrological model, known as SWAT-Twn 2.0 – an enhanced version of SWAT-Twn, originally developed by Chiang et al. (2021). This integration allowed for the simulation of sediment transport at the hydrologic response units (HRUs) within the Xiuguluan River Basin, a mountainous watershed located in Taiwan. The study explores multiple threshold values for landslide-triggering factors (PCP: rainfall and FSW: fraction of soil water content), emphasizing the influence of the number and locations of rainfall stations on landslide identification. In comparative scenario simulations (S1: no trigger, S2: single trigger, S3: dual trigger), the integration of dual triggers (PCP + FSW) significantly improves sediment simulation results, particularly for peak total load (S3: R2 = 0.83, NSE = 0.74, PBIAS = 23.69 %). It also emphasizes the importance of specifying the particle size distribution of landslides for accurate sediment deposition calculations. In summary, it is necessary to consider landslide-triggering factors in hydrological models to enhance accuracy in sediment yield simulations. To further improve landslide identification and sediment transport modeling, the study recommends incorporating additional triggering factors into HRU classification (i.e., elevation and aspect). [ABSTRACT FROM AUTHOR]

An approach involving data on wave-induced sediment transport estimates is essential for managing coastal environments. Numerical models are powerful tools to understand and investigate many processes responsible for longshore sediment transport (LST) in a systematic way, since direct measurement of LST is a difficult task. This paper presents estimates of longshore sediment transport through numerical modeling of wave-induced sediment dispersion patterns in the Formosa Bay, State of Rio de Janeiro - Southeast Brazil. The analysis was conducted using the computational package Coastal Modeling System/SMC-Brazil and mathematical formulations proposed by Cerc (1984). The results suggest average residual solid discharge (Qsr avg) in the order of 131,442.745 m3/yr in northern sector, −151,908.32 m3/yr in central sector, and 71,987.69 m3/yr in southern sector of investigated area. In addition, it is important to highlight that minor variations in the wave incidence angle may cause changes in the longshore sediment drift, promoting the convergence and divergence zones throughout the investigated area. The results presented contribute to the advancement of knowledge on the topic addressed here and will be useful in future engineering projects related to beach nourishment and the management of coastal areas subject to erosion processes. • Data are presented on simulations of wave-induced longshore sediment transport rates in Baia Formosa Bay, southeastern Brazil. • The Coastal Modeling System SMC/Brazil were used. • Results suggest different solid outflow rates for each sector of investigated area. • The model may provide a basis for planning actions and environmental management in coastal zones. [ABSTRACT FROM AUTHOR]

[Display omitted] • The sediment provenance of North Manila Trench is mainly from Taiwan Island. • Turbidity currents carry biogenic debris and fresh organic carbon into deep ocean. • Turbidity currents bury organic carbon as much as millennium sedimentation. Turbidity currents play a significant role in sediment transport in deep ocean, profoundly impacting sedimentation in the abyssal sea. This study focused on a 375 cm long sediment core collected from the Manila Trench, revealing a distinctive 15 cm turbidite layer characterized by coarse sediment, an upward fining pattern, and a basal erosion surface. Analysis of rare earth elements and Nd isotope indicates that this turbidite layer originated from Taiwan Island. Initiated in the estuarine shelf region of southwestern Taiwan Island, the turbidity current transported substantial biogenic debris and marine fresh organic carbon into the Manila Trench. Consequently, the turbidite layer exhibited an elevated CaO content and more positive δ13C values. Despite lower TOC content in the turbidite layer due to coarse particle size, the mixture of marine fresh organic matter significantly lowered the carbon age of this layer compared to the strata both below and above it. The rapid sedimentation of the turbidite deposit led to an organic carbon burial flux comparable to the rate at which normal deep-sea sediment buries organic carbon over seven hundred years. Notably, finer sediment overlaying the turbidite layer acted as a cap, enhancing carbon sequestration within the trench. In contrast to nearby core GEO6, which documented over 11 turbidity currents, core S02 recorded only one event. Detailed bathymetric analysis highlights the crucial role of local topography in detecting and preserving turbidity currents. The insights gained from this study would advance our understanding of how turbidity currents shape and influence the deep ocean sedimentation. [ABSTRACT FROM AUTHOR]

• Contour currents with different physical natures observed over a drift-moat system • High SSC on the drift due to long-range sediment transport by contour currents • High SSC in the moat due to moat wall erosion by tidal-induced secondary flows • Formation of drifts forced by upslope sediment transport of tidal currents Contourite drifts are ubiquitous sedimentary features in the world′s oceans, and their formation are usually ascribed to sedimentation from contour currents. However, in-situ observations of contour currents and their associated sedimentary processes were inadequate. Here, we present mooring observation results from a drift-moat contourite system in the South China Sea to gain insight into its sediment dynamics and formation mechanism. We found that quasi-persistent contour currents develop in the moat, on and below the drift, yet subject to diverse physical oceanographic processes. High suspended sediment concentrations observed on the drift mainly occur in winter, induced by high levels of sediments transported by contour currents from Taiwan. In the moat, however, high suspended sediment concentrations are mostly caused by erosion of the moat wall during periods of strong tidal currents and low shear variance. Such results underscore the complexity of current patterns and sedimentary processes across various topographic units in the drift-moat contourite system. A novel formation mechanism of the contourite drift is thereby proposed, wherein sediment transport by contour currents brings materials for constructing the drift, while its formation is driven by near-critical reflection and upslope transport of sediments by tidal currents. [ABSTRACT FROM AUTHOR]

Late Cenozoic changes in the intensity of the East Asian Summer Monsoon (EASM) are reconstructed using both terrestrial and marine proxy records; however, proxies from terrestrial (e.g., loess, pollen, and pedogenic isotopes) and marine environments (e.g., foraminifer assemblages and geochemistry) commonly display large discrepancies both in the direction and timing of changes in the EASM. In part, these discrepancies reflect long-term changes in paleogeography that are independent of climate variations. We assess the influence of a rapidly uplifting orogen on EASM records by comparing temporally constrained gamma-ray, δ13C org , hematite/goethite, and magnetic susceptibility records from Late Miocene–Early Pleistocene strata of the Taiwan Western Foreland Basin to time-equivalent EASM proxy records in the South China Sea (SCS). Prior to the emergence of modern Taiwan (∼6.3–5.4 Ma), sediment in the SCS was largely derived from Eurasia and transported into the Pacific Ocean. Following its emergence and southwest migration of the collision zone ∼5.4 Ma, proto-Taiwan became a major sediment source to the SCS. The uplift and southwest migration of Taiwan and northwest migration of the Luzon volcanic arc resulted in the formation of southwest-flowing deep- (1500–2500 m water depth) and bottom-water (>2500 m water depth) currents and the SCS Branch of the Kuroshio Current. Together these currents transported sediment from Taiwan towards the SCS. Increased sediment input from Taiwan is recorded as a decline in hematite/goethite values in sediment records from the northern and central SCS. By ∼3.2 Ma, continued southwest migration and growth of the Taiwan orogen resulted in the formation of the Taiwan Warm Current, which remobilized some sediment from Taiwan towards the East China Sea. Despite strengthening of deep-water currents during the Late Pliocene–Early Pleistocene, relative sediment input from Taiwan to the wider SCS decreased. Consequently, relative contributions from Eurasia and Luzon increased. In the southern SCS, where the Mekong River has dominated sedimentation since the Late Miocene, proxy records show no influence from the Taiwan orogen and instead reflect environmental changes in Mainland Southeast Asia driven mainly by monsoon variability. Our results show that a rapidly uplifting orogen has the potential to significantly impact paleoclimate records >1000 km away from the collision zone. This highlights the influence of shifting sediment sources on paleoclimate proxy records, which must be considered in interpreting past climate change from the sedimentary record. • Taiwan orogenesis is linked to South China Sea climate proxies. • Rapid orogenesis can drive shifts in sediment source and ocean currents. • Tectonic activity is the dominant control on proxies prior to ∼3 Ma. • After ∼3 Ma, proxies reflect enhanced monsoon strength related to glaciation. [ABSTRACT FROM AUTHOR]

The Kuroshio Current flows northward along the east coast of Taiwan toward the Okinawa Trough and the East China Sea, but its dynamics and trajectory were probably different during the Last Glacial Maximum (LGM) due to the globally lower sea level that could have caused a (debated) deflection of the current along the eastern edge of the Ryukyu Arc. Core MD18–3532 has been recovered in an intra-slope basin of the Ryukyu accretionary prism, currently disconnected from the Kuroshio Current, but would have been on its trajectory in case of a NE deflection. Measurements of clay mineral assemblages and illite crystallinity revealed that Taiwan has been the main sediment source at this site over the last 26 kyr. The significantly higher sedimentation rate from the Last Glacial Maximum to the Bølling–Allerød compared with the period from the Younger Dryas to the Holocene, coupled with very low δ15N sed during LGM and Heinrich Stadial 1, provide evidence for the transport of sediments and Trichodesmium spp. cyanobacteria by the partially deflected Kuroshio Current toward the eastern edge of the Ryukyu Arc. Combined with δ13C org , TOC, TN, and XRF analyses, an increase in primary productivity has been observed during LGM and Heinrich Stadial 1. This would have been caused by an enhanced East Asian Winter monsoon winds resulting in the deepening of the mixed layer that would have led to the upwelling of the Kuroshio Current nutrient-enriched subsurface waters to the oligotrophic surface waters, and the supply of dust-borne iron from the Chinese Loess Plateau. • The Kuroshio Current deflected partially eastward during the LGM and HS1. • The Kuroshio Current exerts a strong control on the dispersion of hypopycnal flows. • Dust and upwelled nutrients under intensified EAWM control paleoproductivity. • Intensified primary productivity in the NW Philippine Sea during the LGM and HS1. [ABSTRACT FROM AUTHOR]

Sediment source-to-sink processes of river systems have significant impacts on depositional environments in coastal and shelf seas and on long-term climate change. Typically, sediments at the outlets of small mountainous rivers (SMRs) are considered to represent the average composition of particles eroded from the entire river basin due to the fast sediment transfer rate and short residence time in the basins. However, this assumption may be challenged by the significant heterogeneity in sediment erosion and transport processes within the SMRs catchments. In this study, we compare the geochemical and provenance heterogeneity of two typical mountainous rivers in subtropical East Asia, the Mulanxi in Mainland China and the Zhuoshuixi in Taiwan. These two SMRs have similar monsoon climate regimes but different tectonic, geomorphic, and hydrological settings, as well as sediment routing processes. Neodymium isotopes (εNd) and stable elemental ratios of Cr/Th and Sc/Th demonstrate the remarkable intra-catchment geochemical heterogeneity of both rivers. The εNd decreases from −7.1 to −10.0 from non-tidal to tidal reaches in the Mulanxi, while it changes from −11.5 in the upper reaches to −14.1 in the lower reaches of Zhuoshuixi. Apart from the general controls of provenance lithology and weathering processes on sediment geochemical heterogeneities between these two SMRs, the intra-catchment heterogeneity of the Zhuoshuixi is mainly induced by uneven sediment mixing in the flat and low connectivity areas (accounting for ∼36.5% of the downstream area). Meanwhile, the strong tidal influence is the primary control for the intra-catchment geochemical heterogeneity of the Mulanxi sediment, and relatively long sediment residence time in the catchment also plays some role. Our study suggests that samples collected at the river mouths cannot be simply treated as representative of the basin average or fluvial end-member to the sea. The compositional heterogeneity of the SMRs and its environmental effects and responses to rapid climate change require more in-depth investigations. • Distinct geochemical heterogeneity observed between SMRs in subtropical East Asia • Tide-induced sediment mixing accounts for heterogeneity of SMRs in SE China coast • Geomorphic features and climate events explain the heterogeneity of Taiwan rivers • Samples in the river mouth cannot represent the fluvial end-member to the sea [ABSTRACT FROM AUTHOR]

Submarine canyons are the principal conduits for turbidity currents transporting sediments to the deep sea. Thus, turbidites, as sedimentary products of turbidity currents, can be used to trace sediment sources and transport processes and to reconstruct mechanisms of turbidity currents in submarine canyons during the geological past. Herein, clay mineral assemblage of late Holocene turbidites at Core MD18–3565 in the Gaoping Submarine Canyon is investigated to reveal the triggering mechanisms of turbidity currents. High-resolution grain-size analysis of typical coarse-grained layers characterized by basal erosion surface and fining-upward sequence in the core verifies their turbidity current origin. A total number of 318 such turbidite layers, covering ∼30% of the total thickness (19.68 m) of the core, are recognized in the late Holocene sediments (33–3954 cal yr BP). Clay mineral assemblage of the turbidites is composed mainly of illite (52–60%) and chlorite (35–45%), with small quantities of smectite (0–5%) and kaolinite (0–4%), while clay mineral assemblage of the non-turbidite sediments (hemipelagites) is composed of approximately the same contents of illite (51–62%) and chlorite (34–43%), but with slightly higher smectite (0–10%) and kaolinite (1–6%). Despite the small differences in smectite and kaolinite contents, the provenance analysis identifies the Gaoping river as the predominant source of sediments in the turbidite layers, while the hemipelagite layers receive small amounts of sediments from the neighboring Erhjen, Tsengwen, and Pachang rivers besides the Gaoping river in southwest Taiwan. In combination with clay mineral compositions of surface sediments in the adjacent continental shelf and slope, as well as in-situ observational results by subaqueous moorings, we believe that the turbidity currents, in which the Gaoping river directly supplied clay minerals to the submarine canyon to form the turbidites, have been triggered mainly by typhoons passing through Taiwan. The frequency of turbidites generally keeps pace with long-term variations of El Niño-Southern Oscillation (ENSO) events, implying the potential modulation of ENSO on occurrences of late Holocene typhoon activities in the Western Pacific. • Turbidites in Gaoping Submarine Canyon mainly come from Gaoping river in SW Taiwan. • Turbidity currents triggered by typhoons are responsible for turbidite occurrence. • ENSO regulates the occurrence of late Holocene submarine canyon turbidity currents. [ABSTRACT FROM AUTHOR]

Reconstructing the role of provenance and transport mechanism of sediments deposited in deep-water environments is often complex because of myriad of factors such as variability in sediment sources, tectonics, bottom morphology, climatic changes and sea level fluctuations as well as current regime. The South China Sea (SCS) is situated at the tectonic intersection of the Pacific, Eurasian, and Indo-Australian plates, and provides an excellent natural laboratory for understanding source-to-sink transport processes of fluvial sediments. The Qiongdongnan Basin (QDNB) is located in the northern part of the SCS, and the deep-water area (>300 m) of the QDNB has a good hydrocarbon source and hydrocarbon accumulation conditions with a tremendous thickness since the late Miocene-Quaternary. However, the complex sources and transport mechanisms of sediments in the QDNB are undefined. In previous study QDNB may have a major provenance or a mixture of sources. In this paper, the sediments of two cores from the deep-water area of QDNB have been analyzed using several sedimentological and geochemical approaches, including measurements of grain size distribution(433 samples), the occurrence of minerals, and trace element geochemistry(37 samples)as well as strontium and neodymium isotopes(20 samples).The granularity analysis results first show that the 19S37 core can be divided into three stages while the 19S40 core is divided into two stages by clear vertical variations in grain size characteristics. Chlorite (62.0%) and Muscovite (33.6%) appear to be the predominant minerals in the 19S37 core, while the mineral assemblage of sediments from 19S40 mainly consists of kaolinite (37.4%), muscovite (29.2%) and chlorite (27.1%). The primitive mantle standardization curves and chondrite standardized distribution patterns of 19S37 and 19S40 are consistent and display enrichments in Th, U, Pb, and Nd and depletions in Ba, Nb, Sr, and Eu. In addition, the content of Sr fluctuates greatly with depth, which should reflect the influences of sea level changes and the relative proportion of various provenance components. The 143Nd/144Nd ratios and εNd values of the sediments from 19S37 are higher than those of the sediments from 19S40, and all the εNd values show narrow variations and range from −10.085 to −11.080. We conclude that the sediments of the deep-water area in the upper Pleistocene-Holocene were mainly from the sources of the Red River, Taiwan, Pearl River, Hainan Island, and Vietnam. The transport mechanism of the sediments from Hainan Island can be explained by the short distance between the source region and the sedimentary site, while the large amounts of terrigenous sediment inputs derived from the Red River and advantageous morphology make the Red River the largest sediment source to cores 19S37 and 19S40. The transport distance and amount of Deep Water Current could be even more powerful to make Taiwan be the second largest source of modern sediments in QDNB. • 19S37 core can be divided into three stages while the 19S40 core is divided into two stages. • The sediment of the deep-water area QDNB is mainly from the sources of the Red River. • The Pearl River and Taiwan Island have significant contributions to the whole NSCS. • The deep-water current and shallower Kuroshio current are the main pathways. • Sediments from the Pearl River were mainly transported by the Guangdong Coastal Current. [ABSTRACT FROM AUTHOR]

• Mudstone deposits behave like noncohesive sediments in terms of erosion resistance. • High erosion resistance of laterites cannot be predicted merely by particle size. • Shields' parameter predicted by water content, clay content, and plasticity index. Soil erosion and sedimentation are major factors in landscape evolution and river morphology. The erosion resistance of sediments plays an important role in landscape evolution processes because it determines the threshold of an acting force at the initiative sediment motion, and the amount of sediment transports. This study examined the sediment properties and their correlations to the erosion resistance of mudstone deposits and laterites, which are two representative natural cohesive soils in hill and terrace topography in Taiwan. Soil physical properties and pore water chemical properties, and the erosion resistance were investigated and determined using laboratory tests and hydraulic flume experiments, respectively. Investigations of sediment properties showed that the mudstone deposits and laterites had significant differences in median particle size, soil texture, level of plasticity, internal structure, and pH value and electrical conductivity of their aqueous slurry. Results from the hydraulic flume experiments showed that the laterites had stronger erosion resistance, indicating by larger values of critical shear stress and the Shields' parameter, than the mudstone deposits. Through the stepwise multiple regression analysis, a quantitative equation was proposed to estimate the Shields' parameter using fine sediment properties including water content, clay content, and the plasticity index expressed in decimal fractions, of the two soils. Despite more experiments of the two natural soils with different ranges of the sediment properties are needed to validate the empirical equation for predicting the Shields' parameter, the proposed methodology provides an essential reference in which erosion resistance is an important parameter. [ABSTRACT FROM AUTHOR]

At least 17 subsea telecommunications cables cross the Gaoping Canyon and Manila Trench system in the Strait of Luzon between Taiwan and the Philippines. There, cable breaks record rapid (5–16 ms − 1 ), long run-out (> 300 km) sediment density flows triggered by earthquakes and typhoons. Four major cable-breaking events have occurred in the last decade. In 2006, the Pingtung M L = 7.0 earthquakes formed up to 3 individual flows, some of which ran-out for up to 460 km. In 2009, Typhoon Morakot generated two sediment flows; the first was triggered by hyperpycnal river discharge, whereas a second flow formed 3 days later, possibly due to failure of recently deposited flood sediment in upper Gaoping Canyon. A flow in 2010 formed during a swarm of M L = 3–5 earthquakes that followed the M L = 6.4 Jiashian earthquake. Finally, Typhoon Soudelor of 2015 caused the Gaoping River to form a hyperpycnal plume that failed to break cables at < 2600 m depth, but broke at least 6 cables in deeper water. The 2006 Pingtung earthquakes produced the largest sediment flow(s) that produced 22 cable breaks. The other events were less destructive with each causing 6–9 breaks. Sources of the sediment flows varied with the triggering mechanism: those associated with hyperpycnal discharges probably began near the mouth of the Gaoping River. In contrast, earthquake-triggered landslides and subsequent sediment density flows formed anywhere on the adjacent continental margin. Flow speeds generally declined with increased run-out, lower seabed slope and increased channel width. Most variability (7–20 ms − 1 ) was observed over the 0.4°–1.0° slopes of Gaoping Canyon but speeds were mainly restricted to 5–8 ms − 1 in the 0.3° sloping Manila Trench. The 2006–2015 period of frequent cable-damaging flows is the first for the past two decades or longer. In the absence of evidence for increased seismic or anthropogenic activity, this disruptive period may reflect increased typhoon intensity and fluvial sediment discharge. Such typhoon-related flows may complicate interpretation of palaeo-seismic records derived from turbidites in such settings. [ABSTRACT FROM AUTHOR]

Among many 234U–238U disequilibrium applications, the " comminution age " approach enabled quantitative constraints of sediment transport timescale since the genesis of detrital sediment. This method requires a critical assumption regarding the initial bedrock (234U/238U) activity ratios (A 0), typically assumed to be in secular equilibrium (=1). However, this supposition needs further validation as more authors proposed preferential leaching as a vital mechanism that produces U-series disequilibrium among bedrocks. To address this uncertainty and to examine the extent of impacts responsible for the bedrock (234U/238U) disequilibrium, we compiled the published A 0 covering a wide range of lithologies. In this study, the global A 0 values ranged from 0.700 to 1.280, with an average of only 0.981 ± 0.070 (2σ; n = 160). This widely observed 234U deficiency among global bedrocks cannot be resulted from the direct α-recoil of 234U alone but is attributed to the preferential release of 234U from the microfissures created in rock diagenetic history. To further evaluate the impact of A 0 on comminution age calculation, the Zhuoshui River (Taiwan Island) sediment comminution age was re-calculated using the newly measured A 0 from the Zhuoshui River basin, which is 0.978 on average. The newly derived comminution age was nearly three-fifths shorter than the values estimated using A 0 = 1 in the previous study. Our case study demonstrated that assuming bedrock secular equilibrium could lead to overestimated comminution age, inferring a significantly lengthier sediment transport timescale across the river basin; therefore should be carefully constrained to provide a holistic perspective of catchment-scale earth-surface processes. • Bedrocks are not always in a "closed system" due to the micro-fissures formation. • An "open system" through preferential leaching led to bedrock U-disequilibrium. • Zhuoshui River bedrock (234U/238U) is much more depleted than expected. • Comminution recalculation inferred nearly 3/5 shorter ages than assuming unity. [ABSTRACT FROM AUTHOR]

Small mountainous rivers (SMRs) play a crucial role in the global sediment and carbon cycle by rapid transfer of huge particulate and dissolved loads into the sea. Gaoping river-sea system is a good representative of SMRs in Oceania, having an extreme high denudation rate (15,000 t km − 2 yr − 1 ) and a high burial efficiency of terrestrial particulate organic carbon (POC) in the Gaoping submarine canyon (GPSC). However, it is contentious whether silicate weathering or POC burial plays more important role in long-term carbon cycling in such a high active orogen. Clay minerals of fluvial sediments not only act as an important carrier of POC, but also encode valuable information of weathering regimes on land and dispersal routes in the seas. To uncover these informations, surface and core sediments are systematically collected from the Gaoping river-sea system for clay-mineral analysis. Comparative studies are carried out on the basis of new results and vast published data to better understand weathering processes and products in Oceanian islands and Southeast Asian continent. We find that clay-mineral compositions in the Gaoping River (GPR) and other Taiwan rivers are a legacy from provenance rocks in the alpine reach, characterized by predominant illite and chlorite and limited compositional change throughout the river courses. These sharply contradict the downstream increase in compositional complexity (rich in kaolinite and smectite) and chemical weathering intensity in Southeast Asian large rivers because of strong hydrolysis and active sediment recycling at the lowland reach with extensive floodplains. High consistency of clay-mineral compositions is also observed in the interior and exterior of GPSC. Careful examination shows that a slight offshore decrease in cumulative illite and chlorite content is accompanied by a slight increase in exotic clay-mineral inputs by ocean circulations. The combination of this finding with previously reported data on the offshore change in δ 13 C org and Δ 14 C org values suggests that petrogenic POC predominates in the river-dominated Gaoping continental margin with high preservation efficiency due to its tight bandage with clay minerals. Moreover, a tardy response of chemical weathering fluxes to high elevated physical erosion rates is remarkably examined in the Oceanian and global river gauging data. We therefore postulate that rapid transfer and high burial efficiency of terrestrial POC in the tectonically active high-standing islands and their adjacent continental margins play much more important role in the long-term carbon cycle than silicate weathering. [ABSTRACT FROM AUTHOR]

Landsliding is one of the primary surface processes shaping the landscapes of active mountain belts. The mobilization (or stabilization) of landslide deposits plays a crucial role in fluvial dynamics, carbon output, and topographic development of active orogens. Despite numerous previous efforts, the controls on erosion or storage of large landslide deposits remain yet to fully understand. Toward this end, we investigated eight large landslides at three locations in Taiwan. Our observations of the Jiufengershan and Tsaoling landslides, the two largest co-seismic landslides of the 1999 Chi-Chi earthquake, indicate that as high as 90 % of the original landslide volume is still preserved in Jiufengershan after two decades, whereas only less than half remains in Tsaoling. The striking difference illustrates the importance of fluvial connectivity in the preservation or removal of landslide deposits. In the longer timescale, our topographic reconstructions of six fan terrace systems along the Laonung River revealed that, even with direct connectivity with one of the largest rivers in Taiwan, approximately 10 % to 30 % of the landslide deposits are still preserved in-situ after millennia of erosion. Their preservation ratio is mainly controlled by their age, their original size, and the river/hillslope processes nearby. Wider riverbeds around these terraces imply the occurrence of large landslides and subsequent deposition on riverbeds as an important mechanism of river lateral erosion. Our results suggest that a substantial portion of large landslide deposits may persist in the hinterland over thousands of years, and such long-term preservation of landslide deposits would be important in the landscape evolution and the mass balance of active orogenic belts. • We analyzed the evolution of landslide deposits in different timescales in Taiwan. • Connectivity to high-transport-capacity rivers controls the landslide removal. • A substantial portion of landslide deposits may be preserved for a long time. • The long-term storage of landslide deposits is important for landscape evolution. [ABSTRACT FROM AUTHOR]

There are many different source-to-sink dispersal systems around the world, and the Gaoping River (GPR)–Gaoping Submarine Canyon (GPSC) provides an example especially as a canyon-captured system. The GPR, a small mountainous river having an average gradient of 1:150, and the GPSC, which links the river catchment to the deep-sea basin, represent two major topographic features around SW Taiwan. Together, they constitute a terrestrial-to-marine dispersal system that has an overriding impact on the source-to-sink transport of sediment in this region. The GPSC extents from the mouth of the GPR through the shelf and slope and into the northeastern Manila Trench, a distance of about 260 km. It is a major conduit for the transport of terrestrial sediment and carbon to the South China Sea and the landward transport of particles of marine and biological origin. In the GPSC the dominant mode of suspended-sediment transport is tidal oscillations and the net direction is up-canyon. In contrast, sediment transport associated with episodic gravity-driven events is down-canyon. The steady sedimentation of the tidal regime results in hemipelagic mud across the canyon floor, whereas the gravity-driven (hyperpycnal) regime causes turbidite erosion and deposition along the canyon thalweg. Typhoon-induced river floods often lead to hyperpycnal plumes at the river mouth, which directly and indirectly ignite hyperpycnal turbidity currents in the canyon forming an effective agent for transporting large amounts of terrestrial organic material (modern and fossil carbon) to the South China Sea basin. Therefore, the GPR–GPSC represents a source-to-sink system in which terrestrial sediment in a mountainous catchment is promptly removed and transported to the deep sea by episodic gravity flows. This is also a pathway by which modern terrestrial organic carbon is quickly and effectively delivered to the deep sea. [ABSTRACT FROM AUTHOR]

When economic expansion started in the late 1970s, Taiwan was in desperate need of better infrastructure. In response, the government began construction along the coasts around the island. Many of these structures were constructed under time constraints, and their possible effects on the environment were not considered. Years later, some of the structures were found to have disrupted littoral sediment transport, resulting in the retreat of shorelines downstream. The Integrated Coastal Zone Management Plan demands the implementation of remedial measures for erosion by the responsible party in the near future. However, as morphological changes are complicated processes involving both natural and human-induced drivers, the liabilities of the parties involved are typically difficult to determine. In this study, bathymetric analysis and numerical simulation were used to assess the effects of coastal structures on coastal erosion. With the former, the rate of change of the bathymetric volume along the shore was used to identify the extent of the structural effect. The latter one is then used to clarify the respective effect of adjacent structures on coastal bathymetry. Three cases with different surroundings were considered to verify the scheme. It is suggested that range of influence of the structure should be determined in terms of coastal cells. In the case of multiple structures existing within a cell, the cost of remedial measures should be proportional to the length of the structure vertical to the coastline. Remedies to restore the continuity of longshore drift are then proposed. These results can be used to promote effective coastal zone management and prevent further deterioration. • Simulations and field surveys were used to assess the extent of the structural effect on coastal morphology. • The limits of responsibilities for each developer should be considered in terms of the coastal cell. In the case of multiple structures within a cell, the cost of remedial measures should be proportional to the length of the structure vertical to the coastline. • The remedial measures are focused on restoring the continuity of longshore drift, and, in the meantime, to reduce environment deterioration. [ABSTRACT FROM AUTHOR]

• Topography can quantitatively describe the uplift amplitude of plate movement. • Concavity index and stream order can be used to extract sediment-prone areas. • Collapse rate and concavity index can show the evolution of landslides and/or debris flows. This study uses topographical factors to quantitatively describe the uplift amplitude of the plate movement, collects and analyzes the long-term series of rainfall, earthquakes, landslides and debris flows in watersheds from 1993 to 2019, explores the evolution mechanism of landslides, and uses conceptual models to map the areas prone to occurrence of potential debris flows in central Taiwan. Results show that the topographic factors of a watershed can effectively reflect the concavity index (θ) of the crustal uplift, and the spatial distribution of the concavity index in the watershed can be easily estimated. Combining the spatial distribution of concavity index and stream order, a watershed-scale potential debris flow map can be obtained. According to the interpretation rate change of the relationship between the concavity index and the watershed collapse rate, we can understand the occurrence time of landslides and/or debris flows, as well as the sediment transport dynamics of the watershed. The change of the interpretation rate of the concavity index to the collapse rate can be used as a guideline for the establishment of a debris flow warning system. [ABSTRACT FROM AUTHOR]

As an important component in East Asia sediment source-to-sink systems, small mountainous rivers in Taiwan deliver disproportionately large amounts of sediments to oceans. Although the modern fluvial sediment transport processes, discharge fluxes and sediment compositions have been well investigated, the drainage evolution of these mountainous rivers remains understudied and sediment fluxes are expected to vary greatly in glacial-interglacial cycles due to the tremendous climatic fluctuations. To define how the drainage of Taiwan mountainous rivers has evolved since the last glaciation, we target a sediment core (98 m in length) from the Zhuoshui River delta, western Taiwan and conduct sediment petrography, heavy mineral analysis, detrital zircon U Pb geochronology and clay mineralogy to investigate provenance variations and river basin evolution since 60 ka. Sediments of the last glaciation show comparatively high illite crystallinity index values, low metasedimentary lithic fragment and stable heavy mineral contents and similar detrital zircon U Pb ages with downstream signatures, indicating prominent sediment contributions from the Coastal Plain and Western Foothills regions (elevation <1 km) during the glaciation. However, characteristics of the deglacial and Holocene sediments indicate high contributions from the higher Hsueshan Range and Central Range regions (elevation >1 km). We suggest that headward extension and drainage capture since the deglaciation, which was most likely due to the increasing monsoon rainfall, account for the provenance variations in the discharged sediments. This implies a climate-driven drainage reorganization of the small mountainous rivers in Taiwan since the last glaciation. Our findings highlight the previously-overlooked, variable provenance information from Taiwan in glacial-interglacial cycles, and the dynamic source signatures are important to East Asia sediment source-to-sink studies. [Display omitted] • The provenance of Zhuoshui River sediments has changed since the last glaciation. • The provenance variation was caused by climate-driven drainage reorganization. • The river system of Zhuoshui River was not developed during the last glaciation. • The Zhuoshui River headward extended and captured other basins in the Holocene. [ABSTRACT FROM AUTHOR]

Abstract: Analysis of typhoon- and earthquake-triggered landsliding and fluvial response in the Tachia River, central Taiwan, documents highly episodic sediment supply over decade to century timescales. Landslide data from the Chi-Chi earthquake (1999) and subsequent typhoons (2001, 2004, and 2005) quantify the sediment supply from these events. Fluvial response was investigated by decadal-scale and century-scale longitudinal river profile data spanning 1904 to 2008 and by sediment delivery recorded in suspended sediment load and reservoir sedimentation data. Our results show that the different time periods of satellite images and aerial photographs used in previous studies make it difficult to unambiguously identify the causes of landslides previously attributed by some studies to the effects of the Chi-Chi earthquake rather than subsequent high intensity precipitation. In response to significant variability in sediment delivery from hillslopes, century-scale profile variation data indicate substantial bed surface elevation change of 2.6±6.7m, and decade-scale bed surface elevation change of 1.1±3.3m. Since 1993, the downstream reaches incised in response to bedload sediment trapping by reservoirs while headwater reaches aggraded in response to increased sediment delivery from uplands. A tremendous increase in reservoir sedimentation after 2000 likely reflects the effects of the highest decade-average daily rainfall since 1900. Suspended sediment load data indicate a post Chi-Chi earthquake increase in sediment concentration in low-flow events but do not exhibit the clear influence on sediment yields at higher flows as (e.g., typhoons) reported by others for fluvial response in the epicentral region. [Copyright &y& Elsevier]

Abstract: The Fangliao submarine canyon cuts across the shelf and slope of southwest Taiwan. Unlike other canyons along this margin, there is no obvious connection to an individual fluvial sediment source on land. Two recent cruises to Fangliao Canyon provide insight into sedimentation associated with a major typhoon. Box and piston cores were retrieved from Fangliao Canyon in early January 2007, after a local earthquake and an extended period of low-to-moderate river flow in streams that are suspected of contributing sediment to the canyon. Similar cores were collected from the canyon in early October 2009, following one of the largest typhoons to hit Taiwan in the past several decades. Typhoon Morakot delivered several meters of rain to Taiwan, with the largest river floods occurring in the south and southwest regions. In addition, the coastal ocean environment was energized by significant wave heights (>12m). Comparisons of textural, radioisotopic, and geochemical data reveal likely sediment transport and depositional processes within and surrounding Fangliao Canyon. Typhoon Morakot caused a layer ~10cm thick (and greater) throughout the canyon. X-radiographs of the 2007 cores show limited physical structure in most cases, and the 2009 radiographs display obvious changes in sediment density relative to the underlying sediment, as well as distinct physical lamination. Examining signals from different geochemical and radiochemical tracers for terrestrial sediment source indicates that the flood layer deposited by Typhoon Morakot came from several small mountainous rivers. By comparing the results of the 2007 cruise with those from 2009, we gain significant insight to the close linkage between a line source of fluvial sediment and deposition in a submarine canyon, as well as the role that tropical-storm events can play in delivering sediment to these environments. [Copyright &y& Elsevier]

Abstract: Landslides play an important role in the evolution of mountain topography and are a major source of sediment in tectonically active mountain belts. For the active orogeny of Taiwan, erosion rates have been assessed by various methods. The discrepancies observed between erosion rates integrated over modern and Quaternary time scales may result from various effects related to surface processes. More process-oriented research on the spatio-temporal distribution of hillslope processes and coupling relationships with the fluvial system is needed to reconcile the temporally heterogeneous data in the future. This paper assesses and describes the processes of subsequent erosion on hillslopes via a time series of topographic surveys of hillslopes after the initial failure in order to better understand the temporal and spatial variability of landslide erosion, sediment fluxes, and storage of landslide sediment within channels. The results demonstrate that hillslope-channel coupling is controlled by the relative frequency of erosive flooding events and the magnitude of rainfall-driven hillslope processes. The latter is assumed to be disproportionately high on larger failures in periods with less rainfall. Mass wasting may only affect part of the total failure’s area. Volumes of eroded sediment from gullies on the landslide scar may be as high as the volume estimated for the initial failure. The geometry of the sliding masses eroded after the initial failure appears to be uniform, and their depths average 6.1 ± 2.2 m. [Copyright &y& Elsevier]

Abstract: Typhoon Morakot, which first made landfall in central Taiwan on Aug. 7th and then in Fujian on Aug. 9th after crossing through the Taiwan Strait was the strongest typhoon to impact the East China Sea (ECS) in 2009. Two surveys were conducted, respectively on Aug. 1st and Aug. 12th, in the mud deposition center off the Zhejiang–Fujian coast to study the impacts of the typhoon on the marine environment and sediment transport. Continuous in-situ hydrographic data (water temperature, salinity, depth and turbidity) were recorded at 29 stations during the first survey and 23 stations during the second survey. The water and surface sediment samples were collected at the same time. A comparison of the measurements from the two surveys shows that significant variations in temperature, salinity and turbidity distributions occurred in the water column. The upper water layer was well-mixed after the passage of Morakot. The water temperature and salinity dropped approximately 0.2–1.4°C and 0.3–3.3psu, respectively, while the water turbidity increased from less than 1FTU to 1–30FTU. In the bottom layer, the temperature increased approximately 2.5–4.0°C, and the salinity dropped approximately 0.2–0.6psu due to the water mixing. The water turbidities generally increased to greater than 50FTU (greater than 150FTU in some locations), which were several times to more than tenfold greater than those in the first survey, which were generally between 10 and 60FTU. The thermocline, which existed at a depth of approximately 10m during the first survey, disappeared after the typhoon. A halocline appeared at approximately 10m depth in the near-shore area due to abundant fresh water supply, whereas the salinity was generally homogeneous during the first survey. Concurrently, the relatively warm and fresh water extended downward to the whole medial water layer due to the water mixing. The turbidity and volume of the bottom turbid layer was greatly increased at the second survey compared with the first survey. The intrusion of the low-temperature and high-salinity deep water (below 50m depth) was significantly reduced at the same time. [Copyright &y& Elsevier]

Abstract: Landslides have both immediate and extended-duration effects on sediment discharge. Examining the role of post-failure soil loss/sediment yield of landslides is essential for basin management purposes. The comprehensive measurement of sediment production of existing landslides could provide a better understanding in this aspect. This study investigated the post-failure sediment yield of 13 landslide sites in the Shihmen reservoir watershed, Taiwan, during the rainy seasons of 2006 and 2007 using a total station. Our study showed that soil loss is mainly controlled by rainfall conditions, and the geometric and geographic characteristics of each landslide can significantly influence the efficiency of sediment delivery. We also observed that rainfall is important in determining landslide retrogression/enlargement, although vegetation in the landslide area increases with time. We obtained a large amount of landslide measurement data, which could be useful for future landslide modeling. We suggest two regression models for estimating gross soil loss using cumulative rainfall. The estimated gross soil loss values of 0.78 to 1.06myr−1 are equivalent to 18,096 to 24,592tha−1 yr−1. Using these estimates, we assessed the sources of sediment in the watershed, and found that the ratio of landslide erosion, soil loss after landsliding, and soil erosion from other parts of the watershed was approximately 66:31:3. This study implies that remedying existing landslides is more effective than any other solution in reducing sediment production in the watershed. [Copyright &y& Elsevier]

Abstract: Important factors for the initiation of debris flows include available loose sediment, torrential rainfall, and topographic conditions. The objective of this study is to identify topographic features of debris flows and conditions favorable for debris-flow initiation based on geomorphological analyses of 11 river basins in northern and central Taiwan. Morphometric indices were derived from 10-m grid digital terrain models before and after debris flow events using GIS. The indices include the stream power index (SPI), topographic wetness index (TWI), sediment transport capacity index, elevation–relief ratio, form factor, effective basin area, and slope gradient. The results show that debris flows tend to initiate from steep slopes or landslides with higher TWI values. Debris flows are expected in basins with higher SPI and TWI. Basins with lower slope gradients and SPI but higher TWI may also have a high potential for debris flow. SPI changes most significantly due to a debris flow event particularly in steep basins. [Copyright &y& Elsevier]

Abstract: Large earthquakes deform the Earth''s surface and drive topographic growth in the frontal zones of mountain belts. They also induce widespread mass wasting, reducing relief. The sum of these two opposing effects is unknown. Using a time series of landslide maps and suspended sediment transport data, we show that the MW7.6 Chi-Chi earthquake in Taiwan was followed by a period of enhanced mass wasting and fluvial sediment evacuation, peaking at more than five times the background rate and returning progressively to pre-earthquake levels in about six years. Therefore it is now possible to calculate the mass balance and topographic effect of the earthquake. The Choshui River has removed sediment representing more than 30% of the added rock mass from the epicentral area. This has resulted in a reduction of surface uplift by up to 0.25m, or 35% of local elevation change, and a reduction of the area where the Chi-Chi earthquake has built topography. For other large earthquakes, erosion may evolve in similar, predictable ways, reducing the efficiency of mountain building in fold-and-thrust belts and the topographic expression of seismogenic faults, prolonging the risk of triggered processes, and impeding economic regeneration of epicentral areas. [Copyright &y& Elsevier]

Abstract: The shear wave velocity of shallow sediments is very important in seismic wave amplification and thus Vs30 is a well-known parameter for site classification. Based on the relationship between Vs and soil indexes, the empirical regression equations were evaluated using more than 600 data sets from the Ilan area and the Taipei Basin. Multivariable analysis, which can increase the accuracy of regression equations, was used in this study. Three extrapolations were compared, and then the most accurate bottom-constant extrapolation was adopted to estimate Vs30 at 16 boreholes, none of which reached a depth of 30m. Ultimately Vs30 was derived for 110 free-field strong motion stations, and the stations in northeastern Taiwan were reclassified according to the Vs30-based NEHRP provisions. Regression equations of Vs and the extrapolation of Vs30 were also applied to boreholes with only N-values and corresponding depths of less than 30m for assessing the Vs30 and NEHRP class. [ABSTRACT FROM AUTHOR]

Abstract: Clay mineralogy of surface samples throughout the northeastern South China Sea (SCS) and surrounding fluvial drainage basins has been investigated to reveal source and transport of detrital fine-grained sediments. Three characteristic end-members in clay mineral compositions were observed from three major provenances, respectively: major kaolinite and moderate illite and chlorite from the Pearl River, predominant illite and chlorite from Taiwan, and principal smectite from the Luzon arc system. The transport of four clay mineral species in the northeastern SCS is influenced by various mechanisms. Smectite derived from the Luzon arc system is transported mainly by surface current with significant influence of the Kuroshio intrusion, illite and chlorite from Taiwan are mainly carried by deep water current, while kaolinite from the Pearl River is affected obviously by the westward Guangdong Coastal Current and longshore current. A westerly tongue-shaped distribution of high contents of illite and chlorite mainly from Taiwan on the eastern shelf may result from the westward Guangdong Coastal Current during the winter. The results suggest that clay mineral assemblages in the northeastern SCS are mainly controlled by provenance supply and current transport and their downcore records do not bear contemporaneous paleoclimatic features. The implication of clay minerals for proxies of the late Quaternary East Asian monsoon evolution is realized through both the provenance supply and current transport processes. [ABSTRACT FROM AUTHOR]

Summary: Polycyclic aromatic hydrocarbons (PAHs) are usually loaded through atmospheric deposition into a water body and eventually into sediments. We study the PAHs from a 22-cm sediment core collected from the subtropical Feitsui Reservoir in Taiwan, and find the PAHs deposition characteristics in the reservoir, the man-made water body, is different from those in natural water bodies. The surficial sedimentary PAH fluxes are significantly higher than those in the European high altitude mountain lakes and those in the northeastern USA urban/industrial lakes. However, the catchment-corrected PAH fluxes normalized by the ratios of the catchment area to the water surface area are comparable to those of remote lakes in Europe and USA, suggesting the sedimentary PAHs in the reservoir is fluvial dominated, i.e., the reservoir system concentrated the atmospheric PAHs from the catchment area into the sediments. PAHs distribution found in the Feitsui Reservoir indicates both biogenic and anthropogenic origins. We also find the vehicular transport upstream of the reservoir is likely one of the PAHs sources to this reservoir. [ABSTRACT FROM AUTHOR]

Abstract: Development of fan terraces in incision-dominated river settings documents episodic increases of sediment supply from upland catchments. In the non-glaciated, active mountains of Taiwan, such increases in sediment supply result typically from increases in landslide/debris flow activity. Studying fan terraces, therefore, helps understand the history and nature of mass-wasting processes eroding the mountains. This study explores fan-terrace successions developed at tributary mouths of the Chen-yeo-lan and Lao-nung Rivers in central-southern Taiwan. Judging from the spatial variations of sizes, heights, sequences and sedimentation of the fan terraces, the magnitude and frequency of mass-wasting activities appear to vary from tributary catchment to catchment. Two types of tributary catchment are differentiated, which can be located in close proximity to each other. One has been subject to extremely large but infrequent mass-wasting events, as a result of which high and/or large fan terraces with 100–200 m thick debris-flow/fluvial gravels have been formed. Seven examples of this type of fan terrace have yielded radiocarbon dates of >40ka, ∼18.4ka, ∼13.9ka, 8.9–9.5ka, 3.9–4.8ka, ∼3.3ka, and ∼1.4ka in age. With the availability of multiple dates, this type of fan terrace can be shown to have been created in no more than 1000 years, from the aggradation of thick gravel sequences to subsequent incision. The second type of catchment has been subject to relatively minor but frequent mass-wasting events. Due to repeated incision after each such event, the resultant fan terraces are relatively low and limited in size but have formed over lengthy periods. Although located in the same geological and geomorphic setting, the dated fan-forming mass-wasting events in the Chen-yeo-lan catchment do not appear to have occurred synchronously with those in the Lao-nung catchment. Nor could the succession of these events, or their origins, be clearly linked to known paleo-climate data. These findings highlight the importance of internal factors (e.g., rock-mass strength) in determining the timing, magnitude, and frequency of mass-wasting events in the studied mountains, which are subject to active rock uplift, highly active seismicity, and intense rainfall. [Copyright &y& Elsevier]

Abstract: In an active fold-and-thrust belt, sediment is commonly transported in the form of debris and colluviums, and the ages of such deposits can be important for seismic hazard assessment. These sediments are mainly transported by high concentration flows that travel very short distances before burial, and therefore have very few opportunities for daylight exposure and bleaching, which limits the application of luminescence dating in such environments. Luminescence studies on modern debris flow deposits and channel sediments in central Taiwan indicate a mixed population of bleached and unbleached grains. The well bleached grains constitute a small proportion of the sediments and could only be identified using the single grain dating technique; doing single aliquot analysis may result in overestimation of the age of such sediments by 3–25ka. The data reveal that outwash sediments are better bleached than debris flow sediments. Our results show that quartz that has experienced partial resetting can be used for luminescence dating only through the use of the single grain technique. [Copyright &y& Elsevier]

Abstract: We use the two-dimensional (2D) electrical resistivity imaging (ERI) method to detect the contact between sediment and bedrock in a modern fluvial system. We performed eight 2D electrical resistivity surveys along the Peikang River in Kuohsing area, central Taiwan, with a pole–pole array of 1-m electrode spacing to produce a spatial resolution of about 1 m. The resistivity data were inverted into subsurface electrical structures using the least-squares inversion techniques. Then, the contact between the bedrock and sediment was found by using an image processing technique called Laplacian edge detection (LED), which represents an objective approach in interpreting various geophysical images. Numerical modeling demonstrates that isoresistivity lines are not in good agreement with the hypothetical interfaces between the bedrock and sediment, but the zero-lines of the Laplacian operation are strikingly accurate. Our results indicate a well-defined boundary in the resistivity structure that can be used to estimate the quantity of sediments covering bedrock, thus highlighting the utility of this technique in studies of landscape evolution, sediment transport, and sediment budgets. [Copyright &y& Elsevier]

Abstract: Sediment transport and sedimentation processes in the Gaoping submarine canyon were studied using sediment trap and current meter moorings deployed at a location during the winter (January–March) and the summer (July–September) months in 2008. At the end of each deployment, sediment cores were also collected from the canyon floor at the mooring site. Samples from sediment traps and sediment cores were analyzed for 210Pb and 234Th by gamma spectrometry. In conjunction with particle size and flow measurements, the datasets suggest that sediment transport in the canyon is tidally-modulated in the drier winter season and flood (river)-dominated in the wetter summer season. From the magnitude and temporal variation of sediment flux in the canyon with respect to the burial flux and sediment budget on the open shelf and slope region, we reaffirm that, on annual or longer timescales, the Gaoping submarine canyon is an effective conduit transporting sediments from the Gaoping River''s drainage basin (the source) to the deep South China Sea (the ultimate sink). [Copyright &y& Elsevier]

Abstract: X-ray diffraction (XRD) mineralogical and grain-size analyses indicate that inner continental shelf sediments in the East China Sea (ECS) represent a unique mixing of clays derived from the Yangtze River and silts/sands from small western Taiwanese rivers. Taiwanese (e.g., Choshui) clays (<2μm) display no smectite but the best illite crystallinity and are only distributed along southeastern Taiwan Strait. Both Yangtze and Taiwanese river clays are illite-dominated, but the poor illite crystallinity and the presence of smectite and kaolinite indicate that Taiwan Strait clays are mainly Yangtze-dominated. In contrast, medium silts (20–35μm) and very fine sands (63–90μm) in the Taiwan Strait are characterized by low feldspar/quartz, low K-feldspar/plagioclase and high kaolinite/quartz, indicating their provenance from Taiwanese rivers. Taiwanese silts and sands are introduced primarily by the way of typhoon-derived floods and transported northward by the Taiwan Warm Current during summer–fall months. Yangtze clays, in contrast, are widely dispersed southward about 1000km to the western Taiwan Strait, transported by the China Coastal Current during winter–spring months. Since most Taiwan Strait samples were collected in May 2006, clay results in this paper might only represent the winter–spring pattern of the dispersal of Yangtze sediments. [Copyright &y& Elsevier]

Abstract: The purpose of this study is to analyze variability in rainfall threshold for debris flow (critical rainfall for debris flow triggering) after the ML 7.3 Chi-Chi earthquake in central Taiwan in 1999. Two study sites with different geological conditions were surveyed in the earthquake area. Streambed surveys were conducted to continuously monitor debris flows between 1999 and 2006. During the 7-year study period, every debris flow event was identified, and the streambed characterized. Results show that the rainfall threshold for debris flow was remarkably lower just after the Chi-Chi Earthquake, but gradually recovered. To date, this rainfall threshold is still lower than the original level prior to the earthquake. This variability in rainfall threshold is closely related to the amount of sediment material in the initiation area of debris flow, which increased rapidly due to landslides resulting from the earthquake. With the increase in sediment material, the rainfall threshold was lowered severely during the first year following the Chi-Chi earthquake. However, heavy rainfalls mobilized the sediment material, causing debris flows and transporting sediment downstream. With the decrease in sediment material, the rainfall threshold recovered gradually over time. Furthermore, debris flows occurred only in the subbasins that had sufficient sediment material to cause significant movement. Hence, these results confirm that the sediment material in the initiation area of debris flow is a crucial component of the rainfall threshold for debris flow. [Copyright &y& Elsevier]

Abstract: Ninety-two box cores collected during 2004–2006 from an area of ~3000 km2 off the Gaoping (formerly spelled Kaoping) River, SW Taiwan, were analyzed for fallout radionuclides (210Pb, 137Cs and 7Be) to elucidate sedimentation rates and processes, and for the calculation of a sediment budget. The study area is located at an active collision margin with a narrow shelf and a submarine canyon extending essentially into the river''s mouth. The results indicate fairly constant hemipelagic sedimentation in much of the open margin and for most of the time except in the inner shelf and along the axis of the canyon where sediment transport is more dynamic and is controlled by tidal current and wave activities constantly, and by fluvial floods or gravity-driven flows episodically. Sedimentation rates in the study area derived from 210Pb and constrained by 137Cs vary from 0.04 to 1.5 cm/yr, with the highest rates (>1 cm/yr) flanking the Gaoping canyon over the upper slope (200–600 m) and the lowest rates (<0.1 cm/yr) in the distal basin beyond the continental slope. The depocenter delineated from 210Pb-based sedimentation rates overlaps with the area covered by a flood layer resulting from super-typhoon Haitang in July 2005. Such correspondence supports the notion that the processes operating on event timescale have bearing on the formation of the sediment strata over centennial or longer timescales. From the distribution of sedimentation rates, sediment deposited in the study area annually is estimated to be 6.6 Mton/yr, accounting for less than 20% of Gaoping River''s sediment load. The calculated budget, coupled with the presence of the short-lived 7Be and non-steady-state distribution of low levels of 210Pb in sediments along the canyon floor, suggests rapid transport of sediment from Gaoping River''s mountainous watershed (the source) via the Gaoping (Kaoping) Submarine Canyon and adjacent channels (as the conduit and temporary sink) to the abyssal plain and the Manila Trench in the South China Sea (the ultimate sink). [Copyright &y& Elsevier]

Abstract: The river–sea system consisting of the Gaoping (new spelling according to the latest government''s directive, formerly spelled Kaoping) River (KPR), shelf, and Submarine Canyon (KPRSC) located off southern Taiwan is an ideal natural laboratory to study the source, pathway, transport, and fate of terrestrial substances. In 2004 during the flood season of the KPR, a system-wide comprehensive field experiment was conducted to investigate particle dynamics from a source-to-sink perspective in the KPRSC with the emphasis on the effect of particle size on the transport, settling, and sedimentation along the pathway. This paper reports the findings from (1) two sediment trap moorings each configured with a Technicap PPS 3/3 sediment trap, and an acoustic current meter (Aquadopp); (2) concurrent hydrographic profiling and water sampling was conducted over 8 h next to the sediment trap moorings; and (3) box-coring in the head region of the submarine canyon near the mooring sites. Particle samples from sediment traps were analyzed for mass fluxes, grain-size composition, total organic carbon (TOC) and nitrogen (TN), organic matter (OM), carbonate, biogenic opal, polycyclic aromatic hydrocarbon (PAH), lithogenic silica and aluminum, and foraminiferal abundance. Samples from box cores were analyzed for grain-size distribution, TOC, particulate organic matter (POM), carbonate, biogenic opal, water content, and 210Pbex. Water samples were filtered through 500, 250, 63, 10 µm sieves and 0.4 µm filter for the suspended sediment concentration of different size-classes. Results show that the river and shelf do not supply all the suspended particles near the canyon floor. The estimated mass flux near the canyon floor exceeds 800 g/m2/day, whose values are 2–7 times higher than those at the upper rim of the canyon. Most of the suspended particles in the canyon are fine-grained (finer than medium silt) lithogenic sediments whose percentages are 90.2% at the upper rim and 93.6% in the deeper part of the canyon. As suspended particles settle through the canyon, their size-composition shows a downward fining trend. The average percentage of clay-to-fine-silt particles (0.4–10 µm) in the water samples increases from 22.7% above the upper rim of the canyon to 56.0% near the bottom of the canyon. Conversely, the average percentage of the sand-sized (>63 µm) suspended particles decreases downward from 32.0% above the canyon to 12.0% in the deeper part of the canyon. Correspondingly, the substrate of the canyon is composed largely of hemipelagic lithogenic mud. Parallel to this downward fining trend is the downward decrease of concentrations of suspended nonlithogenic substances such as TOC and PAH, despite of their affinity to fine-grained particles. On the surface of the canyon, down-core variables (grain size, 210Pbex activity, TOC, water content) near the head region of the canyon show post-depositional disturbances such as hyperpycnite and turbiditic deposits. These deposits point to the occurrences of erosion and deposition related to high-density flows such as turbidity currents, which might be an important process in submarine canyon sedimentation. [Copyright &y& Elsevier]

Abstract: The Fu-shan long-term ecological site is one of Taiwan''s mid-altitude forest drainage basins. This study provides an estimation of the denudation rate for two small catchments within that site. Data upon which the estimation is based include topographic maps, site surveys, and measurements on bed, dissolved, and suspended loads over the period from 1998 to 2000. The result indicates that typhoons and storm rainfalls, as well as geomorphic and ancestral conditions, have major impacts on hydrological and sediment regimes of these drainage basins. The total sediment output measured at Weir No. 1 indicates a denudation rate of ∼2.7mm per year, which is 53% of the figure calculated from the data measured at Weir No. 2. Since the geological settings in these basins are similar, the result is a demonstration of the nonlinear relationship between basin areas and sediment production. In Basin No. 1, 90% of the total sediment output is dissolved load. However, this figure plunges to 42% in Basin No. 2, in contrast with the fact that the runoff per unit area in Basin No. 2 is 35% higher than that in Basin No. 1. The denudation rates of these two drainage basins are relatively high in comparison with those from other areas around the world. [Copyright &y& Elsevier]

Abstract: Modal analyses of 31 sand samples collected by piston coring document variations in sediment composition along and across the developing collision zone off southern Taiwan and help constrain sediment transport paths and, by inference, of sediment sources. Overall, sand composition from this region is dominated by lithic-fragment populations, with a QtFL average of Qt27F21L52. Three geographic domains are based on morphotectonics and variations in sand composition: (1) South China Sea and the adjacent slope of the accretionary prism; (2) suture zone south of southern Taiwan and north of the Luzon forearc; and (3) the Luzon forearc basin (North Luzon Trough) and immediate adjacent slopes. Sands from the accretionary prism and the suture zone contain subequal amounts of sedimentary and metamorphic lithic fragments (Ls51Lv5Lm45 and Ls47Lv5Lm48), respectively, whereas sands from the forearc basin are dominated by volcanic lithic fragments (Ls29Lv49Lm22). In addition, compositions of individual sand beds vary dramatically in the forearc basin. This heterogeneity indicates that sediments from different sources have been deposited sequentially, but do not typically mix during transport and deposition. Similar, but less dramatic, within-core variations occur over the accretionary prism. The major sediment input for the accretionary prism is from western Taiwan and is dominated by sedimentary and low-grade metamorphic lithic fragments. There appears to be a second sediment source, however, from southeastern China. This implies that a significant amount of sediment is the input from China to this region. The major component of sands in the suture zone is derived from Taiwan, but medium-grade metamorphic lithic fragments are rather sparse in these sands, considering the extensive and high-relief exposures of metamorphic rocks on the island of Taiwan. The major source of sands in the forearc basin is the active volcanoes of the Batan islands. Episodically, minor components appear to be fed to the forearc basin from the arcward slope of the accretionary prism, presumably by submarine mass wasting. This observation provides support for the hypothesized olistostromal origin for the Lichi Mélange of eastern Taiwan. [Copyright &y& Elsevier]

A laterally averaged two-dimensional numerical model is used to simulate hydrodynamics and cohesive sediment transport in the Tanshui River estuarine system. The model handles tributaries as well as the main stem of the estuarine system. Observed time series of salinity data and tidally averaged salinity distributions have been compared with model results to calibrate the turbulent diffusion coefficients. The overall model verification is achieved with comparisons of residual currents and salinity distribution. The model reproduces the prototype water surface elevation, currents and salinity distributions. Comparisons of the suspended cohesive sediment concentrations calculated by the numerical model and the field data at various stations show good agreement.The validated model is applied to investigate the tidally averaged salinity distributions, residual circulation and suspended sediment concentration under low flow conditions in the Tanshui River estuarine system. The model results show that the limit of salt intrusion in the mainstem estuary is located at Hsin-Hai bridge in Tahan Stream, 26 km from the River mouth under Q75 flow. The null point is located at the head of salt intrusion, using 1 ppt isohaline as an indicator. The tidally averaged sediment concentration distribution exhibits a local maximum around the null point. [Copyright &y& Elsevier]

This study examines the influence of a submarine canyon on the dispersal of sediments discharged by a nearby river and on the sediment movement on the inner shelf. The study area includes the head region of the Kao-ping Submarine Canyon whose landward terminus is located approximately 1 km seaward from the mouth of the Kao-ping River in southern Taiwan. Within the study area 143 surficial sediment samples were taken from the seafloor. Six hydrographic surveys along the axis of the submarine canyon were also conducted over the span of 1 yr. Three different approaches were used in the analysis of grain-size distribution pattern. They include (1) a combination of ‘filtering’ and the empirical orthogonal (eigen) function (EOF) analysis technique, (2) the McLaren Model, and (3) the ‘transport vector’ technique. The results of the three methods not only agree with one another, they also complement one another. This study reveals that the Kao-ping Submarine Canyon is relatively a stratified and statically stable environment. The hydrographic characteristics of the canyon display seasonal variability controlled primarily by the temperature field and the effluent of the Kao-ping River. The hydrographic condition and the bottom topography in the canyon suggest the propagation of internal tides during the flood season (summer) of the Kao-ping River. The submarine canyon acts as a trap and conduit for mud exchange between the Kao-ping River and offshore. Near the head of the canyon there is a region of sediment transport convergence. This region is also characterized by high mud abundance on the seafloor that coincides with the presence of high suspended sediment concentration (SSC) spots in the bottom nepheloid layer. Outside the submarine canyon on the shelf where the evidence of wave reworking is strong, the northwestward alongshore transport dominates over the southeastward transport, which is a common theme on the west coast in southern Taiwan. [Copyright &y& Elsevier]

In Taiwan, many floodplains are used for agriculture because flood discharge cannot be blocked, and farmers must be willing to accept the noncompensation offer from the government should their plants be destroyed by floods. Moreover, a scour problem has been observed in floodplains with some kinds of plant, such as bananas. Through a series of laboratory experiments, physical modeling was conducted to develop a planting design to reduce the erosion problem. Five different interval spacings between successive plant models were designed to observe the three-dimensional flow field and sediment transport. The results showed that four low-velocity zones formed around plants when a flood bent them. Among them, the fourth low velocity had the largest influence range. However, if the length of the interval spacing was less than the length of the bent plant, it would cause a shelter effect. This effect would limit the appearance of the fourth low-velocity zone and diminish downstream erosion. In addition, it is suggested that plants be planted using the half length of bent plants as an interval spacing to reduce soil loss. The transverse distance between plant rows should be larger than the half length of the bent plant to avoid contraction scour effects on floodplains. This practical planting method could meet human needs (through added profits) and prevent environmental damage (reduce erosion) simultaneously, making it an effective management strategy for ecological engineers in floodplains. • Overlapped plants create a shelter effect that limits the appearance of the fourth low-velocity zone. • The existence of bent plants does not significantly hinder drainage efficiency in floodplains. • Planting using a half length of bent plant interval spacing in the streamwise direction has the slightest downstream erosion. • A practical planting method is suggested for floodplain management. [ABSTRACT FROM AUTHOR]

The Kenting Plateau is characterized by unusual low relief surfaces that straddle the topographic crest of the northern Manila accretionary prism off southern Taiwan at 400–700 m water depth. Multibeam bathymetric data, reflection seismic data, Acoustic Doppler Current Profiler (ADCP) data, surface grab samples, and sediment cores were collected in and around the Plateau to identify evidence of erosion in the Kenting Plateau and understand how the morphological evolution has been influenced by submarine erosion over geological time scales. The most distinctive feature on the Kenting Plateau is a 3 km × 7 km bean-shaped flat elevated platform (Kuroshio Knoll) revealed by multibeam bathymetry. Seismic data show almost no reflections beneath the seafloor and erosional truncations at the seafloor, especially in the Plateau's eastern half, evidencing widespread erosion. The P-wave velocity of the gravels recovered from the top of the Plateau ranges from 2.2 to 4 km/s. After comparing the velocity with the borehole data from nearby basin the burial depth of the parent rocks was found to be around 2 to 4 km below the seafloor, indicating that the parent rocks have been uplifted and gravels were formed due to erosion of the Plateau. The truncation of the seafloor shown on seismic sections suggests significant erosion on the Plateau. Sand content of the sediment cores decreases away from the Plateau, suggesting that sediment transport is effective in this area with high energy deposition, thereby accumulating coarse sediments on the Plateau and removing fine particles away from it. The presence of a dune field migrating northward of the Plateau, parallel to the Kuroshio Current also evidences active sediment transport in the area. Flow velocity of the Kuroshio Current observed from the ADCP data is very high, reaching up to 1.8 m/s on top of the Kuroshio Knoll (SE domain). We thus interpret that the observed intense erosion is caused by the Kuroshio Current, while the uplift of the Kenting Plateau is partially due to isostatic rebound caused by sediment removal through erosion and compression of the accretionary wedge. The higher sedimentation rate and coarser in grain size during sea level lowstand (20,000–12,000 yrs. BP) suggests that the erosion was more intense during the glacial period compared to that of deglacial period (< 12,000 yrs. BP) as seen from the MD97–2145 core. Submarine erosion is predominant throughout the Plateau, and it controls the geomorphology of the Plateau, especially the Kuroshio Knoll. • Ocean current plays an essential role in shaping ocean floor. • Observed Kuroshio Current in the Kenting Plateau is up to 1.8 m/s. • Intense Kuroshio Current shaped the Kuroshio Knoll into flat topped elevated surface. • The parent rocks of the gravels were buried 2 to 4 km below the seafloor. • Decrease in grain size and sand content away from the Plateau indicates the Plateau acts as source for the sand. [ABSTRACT FROM AUTHOR]

Sediment provenance and transport, together with the forcing mechanism behind provenance changes in the middle Okinawa Trough over the past 16 kyr, were reconstructed using records of elemental and Sr–Nd isotopic compositions within the chronological framework of accelerator mass spectrometry radiocarbon dating. Results clearly revealed four notable phases of change in the sediment provenance those are closely related to sea-level fluctuations, the development of the Kuroshio Current (KC), magnitude of tidal bottom stress, and climatic variability of the East Asian monsoon. The sediments of Unit 1 (16–13.8 kyr BP) originated primarily from Changjiang, with a small degree originating from paleo-Huanghe as a result of low-stand sea-level deposition. The sediments of Unit 2 (13.8–11.6 kyr BP) originated from Taiwan the strengthening of because of the KC and the gradual landward retreat of the river mouth; the contribution of Changjiang sediments was reduced. The dominant provenance of Unit 3 (11.6–8.3 kyr BP) changed to seafloor erosion or resuspension and Taiwan sediments with an admixture of Changjiang-derived sediments. After that period, currents, especially the intense KC-dominated deposition, led to dominant sediment supplies from Taiwan during the enhanced KC interval of 8.3–5.4 kyr BP. A prominent decrease in Taiwan-derived particle supply at 5.4–2.8 kyr BP resulted from the suppression of the KC related to the Pulleniatina minimum event. This study suggests that Sr–Nd isotope compositions are useful proxies for understanding the linkage between river sediment source-to-sink processes and paleoenvironmental changes in East Asian marginal regions. • Kuroshio Current reentered at 13.8 kyr BP and suppressed after 5.4 kyr BP. • Sediment provenance changes in the middle Okinawa Trough over the last 16 kyr were characterized by four-phase pattern. • Sediment provenance changes reflect the competing effects of sea-level, the Kuroshio Current, and East Asian monsoon climate. • Paleo-Huanghe was an important source of sediment in middle Okinawa Trough during early-middle Holocene. [ABSTRACT FROM AUTHOR]

The Zhe-Min mountainous rivers in SE China are characterized by stable tectonics, small–mesoscale drainage basins, relatively homogenous bedrocks, dense vegetation cover and high rainfall conditions. These rivers deliver loads of sediments and nutrients to the oceans and always indicate considerably high variability of sediment flux on short-term timescales. However, short-term sediment compositional variations and transport mechanism by these mountainous rivers remain poorly understood. Here we target the Minjiang River, use mineralogical and trace element geochemical data of suspended particulate matters (SPMs) within a one-year hydrological cycle (from October 2016 to October 2017), riverbed sediments (<0.063 mm fractions) and SPMs from the mainstream and major tributaries, to investigate their provenance and transport process. The results indicate that the SPMs in different seasons have strong seasonal geochemical heterogeneity, with highly positive correlations between several trace element ratios (e.g. La (CN) /Yb (CN) and Th/Sc) and runoff of the river. Riverbed sediments and SPMs collected in pairs have distinct geochemical compositions. The riverbed sediments have relatively low La (CN) /Yb (CN) (ca. 10–15) and Th/Sc (ca. 2–5) ratios, whereas the SPMs have La (CN) /Yb (CN) and Th/Sc ratio ranges of ca. 14–17 and ca. 4–7, respectively. These findings suggest a predominant hydrologic control on the Minjiang River sediment transport and geochemical compositions on a seasonal timescale. We conclude that exposed riverbed sediments are probably selectively recycled in dry-season sediment transport, whereas the flood-season SPMs are less mixed with riverbed sediments and are likely dominated by particulates directly from those tributaries and the upper mainstream. We favor that the Zhe-Min mountainous rivers are featured by rapid sediment delivery in response to hydroclimatic changes and have similar sediment transport behaviors with those small mountainous rivers in tectonically active regions of the subtropical East Asia (e.g. Taiwan). This case study also highlights the importance of multi-spatio-temporal scale, heterogeneous river input of chemical elements to the oceans. • Minjiang River sediments are investigated for mineralogy and geochemistry. • Riverbed sediments and SPMs in pairs have distinct geochemical compositions. • La/Yb and Th/Sc ratios of SPMs correlate positively with the river runoff. • Riverbed and overbank sediments are selectively recycled in dry season transport. • The river shows a hydrologic control on sediment geochemical compositions. [ABSTRACT FROM AUTHOR]

After the 2015 Typhoon Soudelor, large boulders and mixed sediments deposited extensively across the beach along the east coast of Taiwan. Field measurements of these storm-related sediments provide the first-hand evidence to document the impacts of extreme waves induced by Typhoon Soudelor. Although the maximum inundation distance is only 170 m due to the lack of beach buffer zone, the weight of the largest boulder was estimated over 1 t and the maximum run-up was estimated up to 11.9 m. The clast distribution of the washover and the beach face sediments exhibited reverse directions of coarsening, reflecting different stages of wave propagation. Our field records show that a super typhoon like Soudelor can potentially leave footprints of extreme values in the geologic records. Therefore, a comprehensive understanding on the occurrence of the sediments and the depositional environment should be carefully considered to pin down the origin of the archived extreme events. In addition, the formation of the higher extreme wave berm and the destruction of the lower swell berm at the Yen-liao Beach displayed the power of the storm surges, suggesting the important role of the run-up on the evolution of the berm. • Field measurements of sediment transport dictate the power of storm surges. • Grain distributions of overtopping and beach face sediments show reverse trends. • Run-up is the key threshold to develop the storm berm. [ABSTRACT FROM AUTHOR]