Effect of suspended sediment concentration on local scour around cylinder for clay–sand mixed sediment beds

Suspended sediments present in the flow are known to affect the flow resistance, velocity distribution and turbulent characteristics. Experiments were conducted in the laboratory flume to see the effect of suspended sediment concentration (SSC) on local scour around a cylindrical pier for a wide range of clay–sand mixed sediment beds for SSC up to 2700 mg/L. It has been observed that the effect of SSC on equilibrium scour hole parameters such as maximum equilibrium scour depth, and longitudinal and transverse extent of scour hole can be significant. Present data showed that the presence of SSC in the range 993–1332 mg/L can increase maximum equilibrium scour depth as much as 1.54 times compared to the clear water case. However, tests made for SSC in the range 2456–2700 mg/L showed that the maximum equilibrium scour depth reduced compared to that for SSC in the range 993–1332 mg/L, but these maximum equilibrium scour depths were still larger than that obtained for clear water. The effect of SSC on time variation of scour and equilibrium scour hole geometry was further investigated.     

Spatiotemporal distribution of flood disasters in Asia and influencing factors in 1980–2019

Natural Hazards - Floods are common natural disasters in Asia. Flood datasets from 48 countries in Asia were collected to investigate the spatiotemporal distribution and influencing factors, using...     

U–Pb dating of detrital zircons for sediment provenance studies—a comparison of laser ablation ICPMS and SIMS techniques

New developments in U–Pb dating of zircons by laser ablation (LA) ICPMS are described and, for the first time, a direct comparison of detrital zircons dated by LA ICPMS and SIMS methods is presented. True real-time mass bias correction is made by aspirating a Tl/U tracer at the same time as laser ablation. The method is similar to that described in Horn et al. (2000), except that enriched ²³³U rather than ²³⁵U is used in the tracer solution. Correction for laser-induced Pb/U elemental fractionation is based on a mathematical treatment of time-resolved data that is independent of laser ablation characteristics and does not require external standardisation. Internal corrections for mass bias and elemental fractionation eliminate the effects of variable sample matrix on isotopic ratios and improve the accuracy of U–Pb dating by laser ablation ICPMS. With the proper error propagation, the precision of U–Pb age determinations is only slightly worse than SIMS-based ion probe dating. However, LA ICPMS is capable of much more rapid analysis of the large number of zircons required for sediment provenance studies. There is excellent agreement between concordant laser ablation ICPMS and SIMS analyses of detrital zircons extracted from lower Silurian metasandstone from the Ulven Group (Skarfjell Formation) in the west Norwegian Caledonian nappes. Both LA ICPMS and SIMS U–Pb zircon ages indicate that sedimentary detritus of the Ulven Group was supplied from a terrain containing zircons of Archean, Proterozoic and early Ordovician age.     

Synthesis and nutrient release patterns of a biochar-based N–P–K slow-release fertilizer

Biochar has excellent solute adsorption capacity, yet few studies have investigated its application as a nutrient carrier in the development of slow-release fertilizers. The current study developed a biochar-based N–P–K fertilizer (BSRF) and evaluated its nutrient release patterns relative to a conventional fertilizer. SEM and EDX analyses confirmed the coarse and highly porous microstructure of the biochar (SBC) that enabled it to effectively sorb NO₃ ^?, PO₄ ^3?, and K⁺ and form a nutrient-impregnated BSRF. BSRF had lower NO₃ ^?, PO₄ ^3?, and K⁺ release than the conventional chemical fertilizer, demonstrating its low release behavior. BSRF-amended sandy soil had higher water retention capacity than that amended with a conventional chemical fertilizer. BSRF has potential to reduce nutrient leaching, improve water retention, and hence increase crop nutrient and water use efficiencies. Future research should focus on understanding nutrient release mechanisms, synchronization of nutrient release with plant uptake, and applications of the BSRF in environmental remediation.     

The district of North Vancouver’s landslide management strategy: role of public involvement for determining tolerable risk and increasing community resilience

This paper examines the public involvement processes contained within the Landslide Management Strategy for the District of North Vancouver in British Columbia, Canada. Following a fatal landslide in the Berkley neighborhood in 2005, the District of North Vancouver convened a community-based Natural Hazards task force to establish risk-tolerance criteria for natural hazards. This paper describes the community task force approach and evaluates it against four criteria for successful public involvement: representative participation; early involvement; information availability; and impact on policy. It is identified that the District could have incorporated a broader understanding of risk, allowing public perspectives to influence the initial framing of the risk issue before charging the Natural Hazards task force to arrive at quantitative risk-tolerance criteria. The District could also have sought to engage a somewhat more representative portion of the population to serve on the Natural Hazards task force, seeking to incorporate a broader set of public values and types of knowledge. Notwithstanding, the Natural Hazards task force successfully utilized social, legal, and scientific information for informed decision-making, and their recommended risk-tolerance criteria were enacted into policy by the District of North Vancouver as a result of the process. The paper also investigates the District’s ongoing public involvement and education efforts with respect to landslide risks, considering information accessibility and its usefulness for increasing individual capacity and community resilience. Overall, the District’s ongoing, dynamic approach to risk management promises to empower individuals and foster resilient communities in the aftermath of the tragic Berkley landslide.     

Single-grain apatite geochemistry of Permian–Triassic granitoids and Mesozoic and Eocene sandstones from Chiapas,southeast Mexico: implications for sediment provenance

ABSTRACT

This article reports single-grain multi-elemental results (Sr, Y, Th, U, and rare earth elements) obtained in 966 apatites from 18 rocks (sandstones and granitoids) that were sampled from the Mesozoic (Todos Santos and San Ricardo Formations) and Eocene (the El Bosque Formation) successions as well as from the Permian–Triassic Chiapas Massif Complex (CMC), all of which are exposed within the Sierra de Chiapas (SCH), SE Mexico. The objectives of the present study are (1) to establish changes in provenance between the Mesozoic and Eocene sedimentary sequences using single-grain apatite geochemistry, and (2) to identify source areas for siliciclastic materials from the Todos Santos, San Ricardo, and the El Bosque Formations. The results of the present work strongly suggest that apatites from the Todos Santos and San Ricardo Formations were mainly derived from intermediate to felsic I-type granitoids as well as from arc-related volcanic rocks, indicating that the CMC basement was the most important source area for the Mesozoic sandstones in the SCH. An abrupt change in provenance from Mesozoic to Eocene units was identified based on single-grain apatite geochemistry. Detrital apatites of the Ypresian–Lutetian El Bosque Formation were derived from diverse source rocks such as mafic–ultramafic rocks, intermediate to felsic I-type plutons, strongly fractionated S-type granites and pegmatites, as well as from different metamorphic source lithologies (including high-pressure rocks) such as gneisses, migmatites, metapelites, and/or eclogites. It was proposed, therefore, that most Eocene sediments of the SCH were derived from the Guatemala Suture Complex, which involves all the rock types mentioned above. A minor portion of the El Bosque Formation sediments was derived from the CMC area and/or from recycled sandstones from the Mesozoic Todos Santos and San Ricardo Formations. Some advantages and disadvantages of provenance studies based on detrital apatite chemistry were also observed and briefly discussed.     

Groundwater–river interaction and management in the context of inter-basin transfers

This study is focused on the management of coupled groundwater–river interaction (GRI) in the context of inter-basin transfers. The semi-coupled models, HEC-RAS and MODFLOW, were utilized in this study to replicate the River Tees experiment that had been conducted in 1976. Then the ‘surrogate’ models were applied to two “what if” scenarios in order to understand and manage GRI behavior and the nature of the reservoir control system. The results on the River Tees showed that the total temporary bankside storage volume was up to 17.5 % of the total reservoir release, given about 22 h of travel time. In addition, zones 4 and 5 of the river model with significant alluvium deposits were the best storage sites with values of 4.5 and 6.7 % of the total reservoir release, respectively, estimated as temporary losses. The final direct runoff received downstream at broken scar was about 95 % of the Cow Green total reservoir release. Furthermore, the closure rate proved to be vital to compute the effective return flow in respect of this study area. Finally, with careful reservoir and groundwater management, the River Tees proved to be an ideal natural aqueduct for inter-basin transfers when used as part of a major regional water resources scheme.     

Delineation of recharge patterns and contaminant transport using 3H–3He in a shallow aquifer contaminated by chlorinated solvents in South Korea

Stable isotopes of water and ³H–³He were used to delineate recharge patterns and contaminant transport for a granitic regolith aquifer in an industrial complex in Wonju, South Korea, that has historically been contaminated with chlorinated solvents including trichloroethene (TCE) and carbon tetrachloride (CT). Groundwater recharge mainly occurred in upgradient forested areas while little recharge occurred in the downgradient industrial areas covered with extensive sections of impermeable pavement and paddy fields. δ¹⁸O and δD data indicated that groundwater was mainly derived from summer precipitation. The apparent groundwater ages using ³H–³He ranged from 1 to 4 yrs in the upgradient area and from 9 to 10 yrs in the downgradient area. Comparison of groundwater flow velocities based on Darcy’s law and those calculated with simple mass balance models and groundwater age supported the presence of preferential pathways for TCE movement in the study area. Measureable TCE was observed in groundwater irrespective of groundwater age. Considering the 3-yr duration of the TCE spill, 14 yrs before sampling, this indicates that TCE plumes were continuously fed from sources in the unsaturated zone after the spill ended and moved downgradient without significant degradation in the aquifer.     

Human perturbations on the global biogeochemical cycles of coupled Si–C and responses of terrestrial processes and the coastal ocean

We present a model of the global biogeochemical cycle of silicon (Si) that emphasizes its linkages to the carbon cycle and temperature. The Si cycle is a crucial part of global nutrient biogeochemistry regulating long-term atmospheric CO₂ concentrations due to silicate mineral weathering reactions involving the uptake of atmospheric CO₂ and production of riverine dissolved silica, cations and bicarbonate. In addition and importantly, the Si cycle is strongly coupled to the other nutrient cycles of N, P, and Fe; hence siliceous organisms represent a significant fraction of global primary productivity and biomass. Human perturbations involving land-use changes, burning of fossil fuel, and inorganic N and P fertilization have greatly altered the terrestrial Si cycle, changing the river discharge of Si and consequently impacting marine primary productivity primarily in coastal ocean waters.     

Significance of river–aquifer interactions for reach-scale thermal patterns and trout growth potential in the Motueka River, New Zealand

To assess whether reaches of the Motueka River (New Zealand) that gain water from groundwater were likely to represent significant cold-water refugia for brown trout during periods of high water temperatures, water temperature was monitored for more than 18 months in two gaining reaches of the Motueka River and three reaches that were predicted to be losing water to groundwater. These data were used to predict brown trout (Salmo trutta) growth in gaining and losing reaches. Groundwater inputs had a small effect on water temperature at the reach-scale and modelling suggests that the differences observed were unlikely to result in appreciable differences in trout growth. Several coldwater patches were identified within the study reach that were up to 3.5°C cooler than the mainstem, but these were generally shallow and were unlikely to provide refuge for adult trout. The exception was Hinetai Spring, which had a mean water temperature of close to 16°C during the period January–March, when temperatures in the mainstem regularly exceeded 19°C. Trout were observed within the cold-water plume at the mouth of Hinetai Stream, which would allow them to thermoregulate when mainstem temperatures are unfavourable while still being able to capitalise on food resources available in the mainstem.     

A cost–benefit analysis of mitigation options for optimal management of risks posed by flow-like phenomena

We analyzed the fractal and multifractal properties of the earthquake time series occurred around the Enguri dam in West Georgia by applying the methods of detrended fluctuation analysis and multifractal detrended fluctuation analysis. We examined the interevent time series in two periods: (1) 1960–1980, in which the investigated area was characterized by the natural seismicity; and (2) 1981–2012, in which the quasi-periodic change of the reservoir water level affected the earthquake generation. Our findings show that the water level variation may influence the fractal properties of earthquake temporal distribution in the local area around the Enguri dam. In particular, it is observed that the time distribution features of seismicity occurred in the second period are more persistent than the natural seismicity occurred in the first period. Furthermore, the seismic process of the second period shows a lower multifractal degree than that of the first period, indicating that the influence of quasi-periodic fluctuation of water level features the seismicity as more regular compared to the natural seismicity.