Cycles Of Erosion Research Articles

Mechanical properties and sulfate resistance of basalt fiber-reinforced alkali-activated fly ash-slag-based coal gangue pervious concrete

To address the strength deficiencies and enhance the durability of coal gangue pervious concrete while promoting the resource utilization of coal gangue, this study employs alkali-activated fly ash and slag as binding materials, partially replacing natural coarse aggregates with coal gangue to prepare alkali-activated fly ash-slag-based coal gangue pervious concrete (AFSGPC). Basalt fibers are introduced to examine the effects of varying fiber lengths and volume fractions on the mechanical properties, permeability, and sulfate resistance of AFSGPC. Results indicate that incorporating an appropriate amount of basalt fibers improves the mechanical properties and sulfate resistance of AFSGPC, attributed to the high strength characteristics of the alkali-activated fly ash-slag binder and the crack-bridging and toughening effects of the basalt fibers, although it may slightly reduce permeability. When the fiber length is 12mm and the volume fraction is 0.1%, the compressive strength at 28 days reaches 24.12MPa, and the splitting tensile strength is 2.95MPa, reflecting increases of 10.48% and 32.89%, respectively. The permeability coefficient is measured at 2.07mm/s, meeting the standards for pervious concrete in road applications. After undergoing 60 cycles of sulfate wet-dry erosion, the corrosion resistance coefficient of AFSGPC increases by 20.02%. To meet the stringent strength requirements for pervious pavements, it is recommended that basalt fibers with a length of 12mm and a volume fraction of 0.1% be utilized in AFSGPC. In regions characterized by high precipitation, the application of basalt fibers shorter than 12mm, with a volume fraction not exceeding 0.15%, is advisable to minimize the obstruction of interconnected pores. These findings provide valuable insights for the preparation and engineering application of basalt fiber-modified AFSGPC.

Down in the Slumps: Tracing Erosion Cycles in Arctic Permafrost

Climate change is altering permafrost thaw cycles and leading to unique Arctic erosional problems.

Experimental Study on the Physical Properties of Autoclaved Bricks Made from Desert Sand and Their Resistance to Sulfate Attacks

In order to optimize the application of desert sand autoclaved bricks in rural construction in Xinjiang, this study focuses on the research and development of MU15-grade desert sand autoclaved bricks. Experimental investigations were conducted to examine the relationship between the water absorption rate of desert sand autoclaved bricks and the duration of water absorption while analyzing the impact of the water absorption rate on the compressive strength of these bricks. Additionally, experimental research was carried out to evaluate the appearance, compressive strength, and pore structure of autoclaved bricks after sulfate erosion. The results indicate the following. (1) With an increasing immersion time, the water absorption rate of desert sand-based autoclaved bricks initially rises and then declines, reaching approximately 14.74% when immersed for 4 h, which is close to the saturation water absorption rate. (2) The compressive strength of desert sand-based autoclaved bricks gradually decreases with an increasing water absorption rate, reaching its lowest point when saturation is attained, with a strength loss rate of approximately 33.18%. (3) Finally, after sulfate erosion, cracks and detachment appear on the surface of desert sand-based autoclaved bricks, and these cracks extend and propagate with the continuous accumulation of eroded products. Simultaneously, this process leads to an increase in the proportion of harmful pores by 0.96%, thereby causing a deterioration in strength. Through data analysis, a decay curve of the compressive strength erosion coefficient of desert sand-based autoclaved bricks with the number of sulfate erosion cycles was established, with good accuracy. This study provides theoretical references and technical support for the performance characteristics of desert sand-based autoclaved bricks and their application in rural construction in Xinjiang.

Preparation and corrosion resistance of β-Al2O3–MgAl2O4 multiphase materials for synthesising Li-ion battery cathode materials

The sagger, primarily composed of aluminum-silicon, serves as an essential vessel in the sintering process of ternary lithium battery anode materials (LiNixCoyMn1-x-yO2, LNCM). However, the acidic oxide SiO2 in the sagger material readily reacts with Li2O in the cathode material, forming substances such as LiAlO2 or LiAlSiO4, resulting in volume expansion, which makes the sagger spalled and damaged. In this study, β-Al2O3–MgAl2O4 multiphase materials with excellent alkali resistance were prepared using the high-temperature solid-state method. The effects of anhydrous sodium carbonate content and heat treatment temperature on the properties of the composites were investigated, and the thermal shock resistance of the specimens was evaluated by the water-rapid-cooling method, as well as the LNCM corrosion resistance of the specimens was evaluated by the static crucible method. The results showed that the overall performance of the specimens was the best at a anhydrous sodium carbonate content of 6 wt%, with a compressive strength of 57.50 MPa and a flexural strength of 42.49 MPa after firing at 1600 °C for 4 h. The strength retention of the specimens was 33.21 % after one thermal shock at a thermal shock temperature of 900 °C. The specimens showed excellent resistance to erosion as there were no obvious erosion traces on the surface of the specimens after undergoing five cycles of erosion.

Lineage diversification and rampant hybridization among subspecies explain taxonomic confusion in the endemic Hawaiian fern Polypodium pellucidum.

Polypodium pellucidum, a fern endemic to the Hawaiian Islands, encompasses five ecologically and morphologically variable subspecies, suggesting a complex history involving both rapid divergence and rampant hybridization. We employed a large target-capture data set to investigate the evolution of genetic, morphological, and ecological variation in P. pellucidum. With a broad sampling across five Hawaiian Islands, we deciphered the evolutionary history of P. pellucidum, identified nonhybrid lineages and intraspecific hybrids, and inferred the relative influence of geography and ecology on their distributions. Polypodium pellucidum is monophyletic, dispersing to the Hawaiian archipelago 11.53-7.77 Ma and diversifying into extant clades between 5.66 and 4.73 Ma. We identified four nonhybrid clades with unique morphologies, ecological niches, and distributions. Additionally, we elucidated several intraspecific hybrid combinations and evidence for undiscovered or extinct "ghost" lineages contributing to extant hybrid populations. We provide a foundation for revising the taxonomy of P. pellucidum to account for cryptic lineages and intraspecific hybrids. Geologic succession of the Hawaiian Islands through cycles of volcanism, vegetative succession, and erosion has determined the available habitats and distribution of ecologically specific, divergent clades within P. pellucidum. Intraspecific hybrids have likely arisen due to ecological and or geological transitions, often persisting after the local extinction of their progenitors. This research contributes to our understanding of the evolution of Hawai'i's diverse fern flora and illuminated cryptic taxa to allow better-informed conservation efforts.

Sulfate resistance of UHPC during dry-wet cycling and energy dissipation under compression

To study the sulfate resistance of ultra-high performance concrete (UHPC) in saline soil area of western China, four kinds of sulfate solution concentrations (0 %, 5 %, 10 %, 15 %) and 18 dry-wet cycle tests for 540 days were carried out on UHPC specimens. The effects of sulfate dry-wet cycles on the evolution of UHPC strength and energy were studied, the characteristic stress points during uniaxial compression of UHPC under sulfate dry-wet cycle were determined, based on the evolution law of each energy (total energy U, dissipated energy Ud , elastic stress Ue) at the characteristic stress points, the energy storage index was established to measure the damage degree of UHPC. The results show that the energy evolution process and damage mechanism of UHPC samples under sulfate-wet and dry cycle erosion are closely related to macro and micro changes. With the development of sulfate dry-wet cycle, the dissipative energy Ud and elastic strain energy Ue of UHPC at the characteristic stress points increased first and then decreased. The development trend of elastic strain energy Ue and dissipative energy Ud is more severe with the increase of sulfate solution concentration. The ratio of elastic strain energy at damage stress to elastic strain energy at peak stress (Ueib/Uei) is taken as the energy storage index Kib to measure the damage degree of UHPC, under 10%Na2SO4 erosion, Kib can be increased by 21.41 % at the highest and decreased by 29.67 % at the lowest compared with the initial value. It shows that the damage process of UHPC is difficult and then easy, and this index can accurately reflect the external force required for the damage of UHPC under sulfate dry-wet cyclic erosion, and provide a reference for the safe and stable operation of UHPC in saline soil area.

Harnessing ion beam erosion engineering for controlled self-assembly and tunable magnetic anisotropy in epitaxial films

The engineering of the surface morphology and the structure of the thin film is one of the essential technological assets for regulating the physical properties and functionalities of thin film-based devices. This study presents an easy and handy approach to tailor the surface structure of epitaxial thin films utilizing low-energy ion beam. Here, we investigate the evolution of the surface structure and magnetic anisotropy (MA) in epitaxial Fe/MgO (001) model systems subjected to multiple cycles of ion beam erosion (IBE) after thin film growth. The growth of Fe film occurs in the form of three–dimensional islands and exhibits intrinsic biaxial MA. Following a few cycles of IBE, an induced uniaxial magnetic anisotropy leads to a split in the hysteresis loop, and the film displays almost uniaxial magnetic switching behavior. More distinctly, we present a clear and conclusive evidence of (2 × 2) reconstruction of the Fe surface due to the atomic rearrangement by IBE. Furthermore, 57Fe isotope sensitive nuclear resonance scattering measurement provides insight into the depth-resolved magnetic information due to the modified surface topography. We also demonstrate that thermal annealing can reversibly tune the surface reconstruction and induced UMA. The feasibility of the IBE technique by adequately selecting IBE parameters for surface structure modification has been highlighted apart from conventional tailoring of the morphology for the tuning of UMA and introduces a new dimension to our understanding of self-assembled surface morphology evolution by IBE.

Tracing uplift and erosion in orogenic settings using quartz luminescence sensitivity: Insights from the Northern Andes uplift

The optically stimulated luminescence (OSL) sensitivity of the fast component in quartz has been increasingly used in provenance analysis of Quaternary sediments. Quartz OSL natural sensitization is thought to be mainly controlled by the formation conditions of the source bedrock and surface processes occurring mainly in sediment source areas. Thus, quartz OSL sensitivity can be linked to distinct sediment source regions, based on their tectonic setting and erosion conditions. In this way, changes in quartz OSL sensitivity within siliciclastic successions would track variations in sediment provenance. So far, few works evaluated how the OSL sensitivity of quartz sand grains varies in sedimentary successions that experienced long-term cycles of deep burial, exhumation, and erosion. Therefore, this work aims to characterize the sensitivity of the fast OSL component of quartz sand grains retrieved from the Cenozoic sedimentary rocks of the Northern Andes basins and assess its spatiotemporal changes. We found that quartz grains with the lowest OSL sensitivity are sourced by crystalline and volcanic rocks related to the Andean Continental Arc emplaced in the Colombian Central Cordillera, reflecting the onset of denudation in orogenic sources during the Paleocene. Subsequently, increasing trends in OSL sensitivity are related to the sedimentary recycling during the Andean orogeny, reaching maximum values as a result of the progressive unroofing of Cretaceous rocks in the Colombian Eastern Cordillera, originally sourced from the low-relief Amazon Craton. Changes in quartz OSL sensitivity measured in the Cenozoic sedimentary basin-fill sequences of the Northern Andes vary according to the shifts in sediment provenance related to the orogenic construction and sediment recycling of the Andean range.

Investigation on damage evolution mechanism of various FRP strengthened concrete subjected to chemical-freeze-thaw coupling erosion.

The corrosion resistance of FRP-reinforced ordinary concrete members under the combined action of harsh environments (i.e., alkaline or acidic solutions, salt solutions) and freeze-thaw cycles is still unclear. To study the mechanical and apparent deterioration of carbon/basalt/glass/aramid fiber cloth reinforced concrete under chemical and freeze-thaw coupling. Plain concrete blocks and FRP-bonded concrete blocks were fabricated. The tensile properties of the FRP sheet and epoxy resin sheet before and after chemical freezing, the compressive strength of the FRP reinforced test block, and the bending capacity of the prismatic test block pasted with FRP on the prefabricated crack side were tested. The deterioration mechanism of the test block was analyzed through the change of surface photos. Based on the experimental data, the Lam-Teng constitutive model of concrete reinforced by alkali-freeze coupling FRP is modified. The results indicate that, in terms of apparent properties, with the increase in the duration of chemical freeze-thaw erosion, the surface of epoxy resin sheets exhibits an increase in pores, along with the emergence of small cracks and wrinkles. The texture of FRP sheets becomes blurred, and cracks and wrinkles appear on the surface. In terms of failure modes, as the number of chemical coupling erosion cycles increases, the location of failure in epoxy resin sheets becomes uncertain, and the failure plane tilts towards the direction of the applied load. The failure mode of FRP sheets remains unchanged. However, the bonding strength between FRP sheets and concrete decreases, resulting in a weakened reinforcement effect. In terms of mechanical properties, FRP sheets undergo the most severe degradation in the coupled environment of acid freeze-thaw cycles. Among them, GFRP experiences the largest degradation in tensile strength, reaching up to 30.17%. In terms of tensile performance, the sheets rank from highest to lowest as follows: CFRP, BFRP, AFRP, and GFRP.As the duration of chemical freeze-coupled erosion increases, the loss rate of compressive strength for specimens bonded with CFRP is the smallest (9.62% in salt freeze-thaw environment), while the loss rate of bearing capacity is higher for specimens reinforced with GFRP (33.8% in acid freeze-thaw environment). In contrast, the loss rate of bearing capacity is lower for specimens reinforced with CFRP (13.6% in salt freeze-thaw environment), but still higher for specimens reinforced with GFRP (25.8% in acid freeze-thaw environment).

Chloride Ion Penetration Resistance of Reactive Powder Concrete with Mineral Admixtures

This study employed the rapid chloride ion penetration test and the salt spray erosion method to examine electric flux changes in mineral-admixed reactive powder concrete (RPC). Variations in the chloride ion content and diffusion coefficient under different erosion durations and depths were also investigated. The impact of mineral admixtures on the chloride penetration resistance was explored. Notably, after mixing fly ash (FA) and granulated blast furnace slag (GGBS), the electric flux values of RPC of each group were significantly reduced, and the electric flux values of RPC of the mixed group were significantly lower than those of the single mixed group and the reference group, in which the electric flux of FA10G10 was reduced by 85.2% compared to the control group; at the same erosion cycle and depth, the chloride ion content and diffusion coefficient of the mixed group were significantly lower than the control group. It shows that the reasonable compounding of mineral admixtures can better exert the "superposition effect", improve the compactness inside the matrix, and effectively reduce the chloride ion penetration rate. Considering comprehensively, the FA10G10 group has the best chloride penetration ion resistance effect.

Study on the Freeze-Thaw Resistance of Concrete Pavements in Seasonally Frozen Regions.

In seasonally frozen regions, concrete pavement is exposed to cycles of freeze-thaw and erosion from de-icing salt, which can lead to unfavorable service conditions and vulnerability to damage. This paper examines the compressive strength, flexural-tensile strength, abrasion resistance, permeability, and spacing factor of concrete, taking into account the impact of various curing conditions, de-icing salt solutions, and mass fractions on the concrete's freeze-thaw resistance. Two test methods, the single-face method and the fast-freezing method, were used to comparatively analyze the freeze-thaw resistance of concrete. The analysis was based on the surface scaling, water absorption rate, mass loss rate, relative dynamic elastic modulus, and relative durability index. The results indicate that the presence of salt solution significantly worsened the degree of concrete damage caused by freeze-thaw cycles. The use of freeze-thaw media, specifically sodium chloride (NaCl), calcium chloride (CaCl2), and potassium acetate (KAc) at mass fractions of 5%, 4.74%, and 5%, respectively, had the greatest impact on the surface scaling of concrete. However, their effect on the water absorption rate was inconsistent. When the freeze-thaw medium was water, the concrete's relative dynamic elastic modulus and relative durability index were 9.6% and 75.3% higher, respectively, for concrete cured in 20 °C-95% RH conditions compared to those cured in 0 °C-50% RH conditions. We propose a comprehensive relative durability index (DFw) by combining the results of two methods of freeze-thaw tests. The DFw of concrete cured in 0 °C-50% RH conditions was 83.8% lower than that of concrete cured in 20 °C-95% RH conditions when exposed to a freeze-thaw medium of 5% mass fraction NaCl solution. To evaluate the salt freeze-thaw resistance of concrete pavement, it is recommended to use surface scaling and DFw together.

Experimental study on weathering mechanism of ancient bricks in Jiayuguan Wei-Jin tombs, Gansu, China

This study focuses on the ancient bricks of Wei-Jin tombs in Jiayuguan, Gansu, China, analyzing the deterioration of the bricks under the long-term influence of natural environments and human activities. Currently, the ancient bricks exhibit various degradation diseases such as cracks, exfoliation, fracture, weathering, and microbial erosion, severely affecting the integrity of the cultural relics. Through on-site investigation and characterization testing, the physical and mechanical properties, compositional elements, pore size distribution, and thermal characteristics of the ancient bricks were analyzed. Indoor simulation experiments were conducted to study the impact of different types of environmental erosion cycles (such as H2O, HCl, NaOH, Na2SO4) on the performance and structure of the ancient bricks, the patterns and causes of deterioration were also studied. The results indicate that the cyclic effects gradually transform the porosity of the ancient bricks into lateral microcracks, which continue to expand, leading to varying degrees of degradation of performance. The extent of the impact of these cycles on the properties of ancient bricks is in descending order: Na2SO4, HCl, NaOH, H2O. H2O, NaOH, HCl, Na2SO4.

Research on the surface abrasion resistance performance of basalt fiber reinforced concrete

The visual characterization of the surface erosion structure of concrete can serve as an initial analysis method for the overall abrasion resistance performance, providing a reference for the rapid formation of a preliminary understanding of the level of abrasion resistance performance. This research investigates the impact of erosion on the durability of coastal concrete. The "two-dimensional" and "three-dimensional" feature description methods are applied to study concrete damage and its mechanical properties. The findings indicate that increasing erosion cycles have a noticeable adverse effect on the specimen's surface, and higher water-cement ratios decrease strength while increasing quality loss. By categorizing the erosion cycle into three stages based on concrete surface damage, exposed aggregate area, and depth changes, it's observed that Basalt Fiber-Reinforced Concrete (BFRC) exhibit improved abrasion resistance and reduced quality loss during these stages. BFRC demonstrates its best abrasion resistance at a water-cement ratio of 0.3. The inclusion of basalt fibers significantly boosts concrete compressive strength with an enhancement ranging from 10.1% to 17.5% across various curing ages and water-cement ratios.

Experimental Study on the Wind Erosion Resistance of Aeolian Sand Solidified by Microbially Induced Calcite Precipitation (MICP).

Microbially induced calcite precipitation (MICP) is an emerging solidification method characterized by high economic efficiency, environmental friendliness, and durability. This study validated the reliability of the MICP sand solidification method by conducting a small-scale wind tunnel model test using aeolian sand solidified by MICP and analyzing the effects of wind velocity (7 m/s, 10 m/s, and 13 m/s), deflation angle (0°, 15°, 30°, and 45°), wind erosion cycle (1, 3, and 5), and other related factors on the mass loss rate of solidified aeolian sand. The microstructure of aeolian sand was constructed by performing mesoscopic and microscopic testing based on X-ray diffraction analysis (XRD), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). According to the test results, the mass loss rate of solidified aeolian sand gradually increases with the increase in wind velocity, deflation angle, and wind erosion cycle. When the wind velocity was 13 m/s, the mass loss rate of the aeolian sand was only 63.6%, indicating that aeolian sand has excellent wind erosion resistance. CaCO3 crystals generated by MICP were mostly distributed on sand particle surfaces, in sand particle pores, and between sand particles to realize the covering, filling, and cementing effects.

Degradation mechanisms of concrete cold joint surfaces under sulfate cycles and varying pouring intervals

In concrete structures, particularly in arid and saline environments, the cold joint surface often serves as a primary entry point for erosion damage, thus dictating the lower limit of structural durability. This study investigates the erosion and damage mechanisms of cold joint concrete under such conditions, focusing on specimens with varying pouring intervals (0.25 d, 0.5 d, 1 d, 7 d, and 28 d). These specimens underwent 0, 30, 90, and 150 sulfate dry‒wet cycles, with their degradation assessed through compression‒shear tests. The findings reveal a logarithmic relationship between the cold joint surface adhesion and the pouring interval, and similarly, there is a logarithmic relationship between the internal friction angle and the pouring interval. Shorter intervals correspond to a higher rate of decrease in both adhesion and internal friction angle, while longer intervals result in lower, eventually stabilizing, values of these properties. Scanning Electron Microscopy analysis indicates that inherent defects in the cold joint surface expedite sulfate penetration into the concrete. As the number of sulfate cycles increases, ettringite formation in the cracks leads to their expansion and interconnection, diminishing the shear resistance of the cold joint surface. The study shows that the pouring interval significantly influences corrosion resistance, with its effects becoming more pronounced after a threshold of sulfate cycles (approximately 90). Shear strength is found to be more susceptible to sulfate erosion compared to compressive strength, with a faster degradation rate. After 80 to 110 erosion cycles, the adhesion corrosion resistance drops to 75%, while the compressive strength remains above this threshold.

Influence of Fly Ash Content on the Durability of Mortar Specimens under Dry/Wet Sulfate Attack.

To investigate the durability of cementitious materials under complex environmental conditions in Xinjiang, this study conducted durability tests on mortar specimens with different fly ash contents under dry/wet sulfate attack conditions, with standard curing and steam curing at 70 °C. The appearance loss and flexural and compressive strength variations in the specimens were analyzed, and an evolution model of the mortar strength under a dry/wet sulfate attack was established. Moreover, XRD and SEM techniques were used to characterize the erosion products and microstructure, and to explore the erosion resistance mechanism of fly ash cementitious materials. The results showed that, after 160 cycles of erosion, the flexural strength of the specimens decreased with the increase in the fly ash content. In the context of steam-cured mortar specimens, throughout the entire erosion period, specimens with a fly ash content of 45% exhibited the highest relative compressive strength. The established strength evolution model had a minimum determination coefficient of 0.879, indicating a good agreement between the model and experimental results. Microscopic research showed that fly ash would undergo a pozzolanic reaction under the action of sulfate and calcium hydroxide, which was beneficial to the improvement of the erosion resistance. As the fly ash content increased, the erosion products of the specimens gradually became dominated by gypsum.

Impermeability performance and corrosion resistance mechanism of basalt fiber recycled concrete under the coastal tidal environment

The application of Recycled Aggregate Concrete (RAC) can effectively reduce resource consumption and mitigate environmental pollution. Under the coastal tidal environments, the performance of concrete is significantly impacted by environmental degradation. Incorporating fibers into RAC can enhance its performance in such special conditions. This study investigates the variations in properties of RAC with different Basalt Fiber (BF) volume ratios (0%, 0.5%, 1.0%, 1.5%) under composite salt dry-wet cyclic erosion cycles (0 d, 30 d, 60 d, 90 d). The results from apparent corrosion morphology analysis, internal microstructure examination, and impermeability testing demonstrate that BF can effectively inhibit the expansion of micro cracks and micropores within the test block while improving the overall compactness of the internal structure of RAC. When the BF content reaches 1.0%, it exhibits an optimal toughening effect on RAC with significantly improved impermeability and corrosion resistance properties. Furthermore, this paper comprehensively summarizes and verifies the corrosion damage mechanism of Basalt Fiber Recycled Aggregate Concrete (BFRAC) under composite salt dry-wet cycles through chemical reaction principles. A salt solution erosion model for BFRAC is proposed to elucidate fiber crack resistance mechanisms and explain accelerated corrosion caused by ion crack channels within salt solutions. This proposed model provides theoretical support for understanding salt erosion damage in fiber-reinforced concrete.

Patterns and processes of channel and floodout adjustment in a discontinuous dryland river, semi-arid eastern Australia

Alluvial rivers in semi-arid and arid landscapes are prone to episodic geomorphic adjustments related to long-term sediment accumulation and occasional reworking by flash floods. However, few studies document the rates, patterns and processes leading to channel breakdown, particularly avulsion and floodout. These intrinsically driven adjustments may pose a risk to water resource availability through redistribution of water and sediment on the floodplain. To address this knowledge gap, channel change associated with avulsion and flooding in the last ∼30 years were quantified for Little Faulkenhagen Creek, a dryland river of the Murray-Darling Basin, Australia. The semi-arid, low gradient catchment promotes transmission losses, which with loss of valley confinement leads to channel adjustment and contraction to occur where water, sediment and energy are spread across the floodplain. Pronounced downstream changes occur in channel capacity (i.e., reductions in bankfull width, depth and area) and hydrology (i.e., reductions in bankfull discharge and stream power) as the river enters the floodout zone. Vegetation roughness increases in and around the floodout, where shrubs and river redgum trees line and encroach upon the channel. Mapping and analysis of hydro-geomorphological parameters using cross sections from 1991 to 2021 reveal recent changes in channel capacity, discharge and stream power. The upper reach has experienced substantial channel widening from erosion, while the lower reach leading into the floodout has contracted because of sediment deposition within the channel. Unchannelised floodwaters are deflected around a raised alluvial ridge and over the floodout eventually dropping into several migrating upstream knickpoints (head-cutting gullies) with retreat rates up to 32 m a−1. Therefore, both the existing channel slope (i.e., decline) and potential avulsion courses (i.e., increase) are affected by reduced energy and enhanced sedimentation. The net result of upstream in-channel sedimentation and aggradation on the floodout and downstream incision and gullying is that the floodout has migrated ∼1 km upstream and the river is at risk of a secondary avulsion as gullies retreat towards the main channel, potentially circumventing the floodout within ∼11 years. An erosion cell conceptual model is suitable for this system, where sediment from the local upstream production (erosion) zone is transferred downstream to a sink (deposition) zone. Erosion and deposition will fluctuate over the long-term, leading to periods with dominantly incisional or aggradational processes. Cycles of erosion and deposition will vary over time and external forces may influence a wholesale shift to a new fluvial state. Understanding the context and patterns of recent dryland river adjustments, as well as the dominant processes and their variability, can assist water and land management.

Holocene sedimentary history of the Silala River (Antofagasta Region, Chile)

AbstractAssessing past and ongoing climate change in the central Andes is critical for understanding the impact of future environmental changes under anthropogenic warming. Emerging from springs located in Bolivia and flowing into northern Chile's Atacama Desert, the Silala River contains inset, terraced wetland (or in‐stream) deposits that provide a unique opportunity to study the impact of past hydroclimate change in a sensitive groundwater system with a small catchment area. After an initial (late Pleistocene) period of deep incision to form the present ravine, in‐stream wetland fine‐grained deposits formed during three phases of aggradation dated to >8.5–1.9 ka (Unit 1), >0.65–0.2 ka (Unit 2), and <0.2 ka to the recent 20th century (Unit 4). These phases of accumulation were coeval with periods of well‐dated records of elevated groundwater tables throughout northern Chile. Phases of abrupt downcutting occurred due to a lowering of the water table after 1.9 ka and before 0.2 ka. The cycle of erosion and deposition clearly continues to the present as evinced by the very recent (21st century) incision of Unit 4 (>1.5 m in some areas) throughout sectors of the Silala where dried‐out standing vegetation can be seen. Such recent incision may be due to multiple different factors, including recent climate change coupled with intense extraction of groundwater resources by the copper mining industry.This article is categorized under: Human Water > Water Governance Science of Water > Hydrological Processes Science of Water > Water and Environmental Change

Assessing the importance of hypsometry for catchment soil erosion: A case study of the Yanze watershed, Rwanda

Implementing a watershed erosion control programme requires resource-intensive and time-consuming preliminary studies to prioritize such interventions and to focus on those sub-catchments where they are most likely to yield the most effective results.
 In this study, we explore and document the effectiveness of using hypsometric analysis as a method to prioritize erosion control measures and apply it to the Yanze watershed located in central Rwanda.
 Based on a 30m-resolution DEM of the watershed and using ArcGIS and R software, we made estimates of hypsometric integral values and calculated soil loss estimates through RUSLE modelling and by using data from different sources, namely the Rwanda Meteorological Agency (rainfall data), ISRIC (soil data), and Sentinel-2 images (land cover maps).
 The hypsometric integral values of the Yanze sub-catchments were high, ranging from 0.5 to 0.936. This, combined with the overall convex upward hypsometric curves, indicates that the Yanze watershed is still at a youthful stage in its erosional cycle.
 The results of the RUSLE model showed that the average potential soil loss in the Yanze watershed is 55.63 tonnes.ha-1.year-1, which is comparable to the national average estimated at 62 tonnes.ha-1.year-1.
 The correlation analysis that we conducted between the hypsometric integral values of the Yanze sub-catchments and their respective mean soil loss values revealed no correlation between the two variables. From the results of this study, we conclude that in watersheds where lithology affects soil erosion significantly, morphology can indeed indicate the potential for erosion. However, we further concluded that future studies to characterize erosion potential using morphometry should employ additional morphometric parameters in the regression model.