Fluvial Processes Research Articles

Quantitative assessment of the erosion and deposition effects of landslide-dam outburst flood, Eastern Himalaya

Both regular flow and infrequent outburst floods shape the mountain landscape, but their relative contributions have been widely debated, in part due to the paucity of quantitative data on historical outburst floods. In June 2000, an outburst flood was triggered by a landslide-dam failure in a rapidly exhumed region of the Eastern Himalaya. To investigate the role of this kind outburst flood on landscape evolution, we employ topographic differencing, satellite imagery, and 2D hydraulic simulations to quantify the equivalent erosion and deposition within ~ 80 km flood route downstream of the breach. The flood lasted for ~ 10 h, with a peak discharge of 105 m3/s, leading to average erosion of 10 m, and contributed ~ 1–2 × 103 times more sediment than over long-term mean fluvial processes. The flood produced extensive lateral erosion, which triggered a threefold widening of the valley floor and abundant subsequent landslides. The ubiquitous boulder bars deposited in the channel inhibited incision, and facilitated lateral erosion after the flood. The resulting channel configuration and extensive bank erosion continue to affect fluvial dynamics until the next catastrophic flood that remobilizes the boulders. Our quantitative findings highlight the profound importance of recurrent outburst floods for gorge development and landscape evolution in Eastern Himalaya.

Increased late Holocene dust activity revealed by loess accumulation rates in Central Asia

Dust from the vast arid and semi-arid regions of arid Central Asia (ACA) makes a large contribution to global-scale dust cycles. However, systematic and regional-scale reconstructions of dust activity in ACA are lacking, thus hindering the exploration of its relationship with climate change. Aeolian loess deposits provide valuable records of past dust activity and its linkages to climate. We constructed a stacked, normalized dust mass accumulation rate (MAR) record from 17 loess sections with high-resolution dating, together with a probability density record based on 189 absolute ages from 39 Holocene loess sections. These records were used to reconstruct the temporal pattern of Holocene dust activity in ACA, which shows a pronounced increase during the late Holocene. After evaluating the temporal variation of moisture conditions at different altitudes in ACA, we conclude that while dust activity during the early and middle Holocene was driven predominantly by climate change, this was not the case in the late Holocene. Taking the mountain-basin system of the Yili Basin in Xinjiang as an example, we propose that dust activity on a large spatial scale was not completely controlled by changes in moisture conditions, and that regional factors, such as fluvial geomorphic processes, played an important role in increasing the materials supply to the areas of dust accumulation. We speculate that dust activity may intensify in ACA under future global warming scenarios.

Reducing uncertainty in source area exploration of mineralized glacial erratics using terrestrial cosmogenic radionuclide dating

Mineral exploration often relies on sedimentary indicators as first signs of a potential nearby mineralization in bedrock. The transportation of sediment by glacial and fluvial processes introduces uncertainty into the tracing of potential source areas of the sediment. This is particularly challenging in areas where glacial erosion has been weak, resulting in reworking of sediments and multiple directions of transportation. In this study we explore the use of Terrestrial Cosmogenic Nuclides (TCN) alongside conventional mineral exploration methods to better link indicators with their potential source areas.The study focuses on a mineral exploration project site in northern Finland in a region with stratigraphic evidence of multiple glaciations. The project targets the source of discovered Au mineralized erratic boulders that have been deposited atop the most recent till unit. The superposition suggests transportation in the latest glacial event. However, the 10Be (35.9 ± 1.3 and 30.3 ± 1.1 ka) and 26Al TCN ages analyzed from the mineralized erratics precede the latest glacial event, suggesting the possibility of multiple stages of transportation. The local bedrock TCN inventories (48.9 ± 1.9 and 85.3 ± 2.8 ka) are well preserved, suggestive of weak glacial erosion and therefore short recent transportation distances for the mineralized erratics. By combining the TCN interpretation and historical ice flow directions derived from the till stratigraphy, we suggest a nearby source locating NNW of the dated erratics.We find that TCN dating can limit some of the transportation related uncertainties in glaciated terrain. Through the analysis of TCN inventories from bedrock and boulders it is possible to characterize glacial erosion and boulder transportation, and to identify repeated exposure events, i.e., the possibility of multi-staged transportation. The method benefits from combined use of stratigraphic investigations that can identify both the local transportation directions and local glacial coverage history. TCN sampling has a minimal environmental impact, can be used in remote areas and can provide information about the transport history already in the early stages of exploration. Although the analysis is time consuming, the survey is light to conduct and informative even with a small number of samples.

Marine Geological Studies of the Bay of Naples (Southern Tyrrhenian Sea, Italy): Revised Applications of the Seismo-Stratigraphic Concepts and Evolving Technologies to a Late Quaternary Volcanic Area

Marine geological studies of Naples Bay are discussed and reviewed, focusing on the application of the seismo-stratigraphic concepts to a Late Quaternary volcanic area. The Naples Bay represents an active volcanic area in which the interactions between volcanic and sedimentary processes controlled a complex stratigraphic architecture during the Late Quaternary period. While the volcanic processes took place in correspondence with the activity of the Somma–Vesuvius, Campi Flegrei Ischia, and Procida volcanic complexes, the sedimentary processes were controlled by the fluvial processes in the Sarno-Sebeto coastal plain and by the tectonic uplift in correspondence with the Sorrento Peninsula’s structural high Key geophysical and stratigraphic studies of the three active volcanic complexes are revised and discussed. The seismo-stratigraphic concepts applied in the geological interpretation of seismic profiles of Naples Bay are reviewed and discussed: here, the classical concepts of seismic and sequence stratigraphy have been successfully applied, but only partly, due to the occurrence of several buried volcanoes and volcanic seismic units and tephra layers, calibrated by gravity cores.

Identifying geomorphic domains using hierarchically clustered drainage area‐slope scaling

AbstractArea‐slope scaling is an important tool for analysing geomorphic processes. In this study, we used hierarchical clustering to sort the area‐slope scaling data for both the numerical landscape created using the LandLab model and real landscapes. Random forest analysis was used to explore the effect of hierarchical clustering. We aimed to illustrate the heterogeneous features of area‐slope clustering and their influencing factors and to test whether they can be used to distinguish geomorphic domains. Our results showed that hierarchical clustering can easily detect the heterogeneous features of area‐slope scaling constrained by tectonic uplift and fluvial erodibility but not those constrained by the diffusion coefficient. The slope gradients over the inflection/transition zone of the colluvial and fluvial domains play a key role in identifying area‐slope scaling from different geomorphic domains. Case studies show that area‐slope scaling of clusters would be affected by different lithology and distance away from the trunk channel. In the high erosion circumstance, the fluvial process caused by tectonics leads to increasing slope gradients over whole geomorphic domains, as well as to retreating inflection between the colluvial and fluvial process domains. In low erosion circumstances or steady state, the fluvial process caused by nearby rivers cannot effectively change the slope gradients but can retreat the inflection. The real landscapes suggest that basins should be carefully selected for area‐slope scaling analysis to ensure that they are representative of the entire study area. Before geomorphological research, more basins of a specific research region need to be selected to conduct hierarchical clustering to select representative basins. Our study could be helpful in the identification of area‐slope domains, the extraction of geomorphic metrics and geomorphic process research.

Outcomes of control and monitoring of a widespread riparian invader (Tamarix spp.): a comparison of synthesis approaches

Effective ecological restoration requires empirical assessment to determine outcomes of projects, but conclusions regarding the effects of restoration treatments on the whole ecosystem remain rare. Control of invasive shrubs and trees in the genus Tamarix and associated riparian restoration in the American Southwest has been of interest to scientists and resource managers for decades; dozens of studies have reported highly variable outcomes of Tamarix control efforts, as measured by a range of response variables, temporal and spatial scales and monitoring strategies. We conducted a literature search and review, meta-analysis and vote count (comparison of numerical outcomes lacking reported variances and/or sample sizes) on published papers that quantitatively measured a variety of responses to control of Tamarix. From 96 publications obtained through a global search on terms related to Tamarix control, we found 52 publications suitable for a meta-analysis (n = 777 comparisons) and 63 publications suitable for two vote counts (n = 1,460 comparisons total; 622 comparisons reported as statistically significant) of response to Tamarix control. We estimated responses to control by treatment type (e.g. cut-stump treatment, burning, biocontrol) and ecosystem component (e.g. vegetation, fauna, fluvial processes). Finally, we compared results of the various synthesis methods to determine whether the increasingly stringent requirements for inclusion led to biased outcomes. Vegetation metrics, especially measures of Tamarix response, were the most commonly assessed. Ecosystem components other than vegetation, such as fauna, soils and hydrogeomorphic dynamics, were under-represented. The meta-analysis showed significantly positive responses by vegetation overall to biocontrol, herbicide and cut-stump treatments. This was primarily due to reduction of Tamarix cover; impacts on replacement vegetation were highly variable. We found concordance amongst our varied synthesis approaches, indicating that increased granularity from stricter quantitative techniques does not come at the cost of a biased sample. Overall, our results indicate that common control methods are generally effective for reducing Tamarix, but the indirect effects on other aspects of the ecosystem are variable and remain understudied. Given that this is a relatively well-studied invasive plant species, our results also illustrate the limitations of not only individual studies, but also of reviews for measuring the impact of invasive species control. We call on researchers to investigate the less commonly studied responses to Tamarix control and riparian restoration including the effects on fauna, soil and hydrogeomorphic characteristics.

A Pliocene lacustrine system in the Nellis basin, southern Nevada, USA: implications for the Colorado River drainage system

ABSTRACT Lacustrine basins and the sediments in them provide a critical component of regional tectonic development and climate history. Each sub-basin in the landscape records the interplay between active tectonism and shifting climate. Many of the basins in southern Nevada that contain deposits of the Muddy Creek Formation were closed fluvio-lacustrine systems during the latest Miocene and into the Pliocene. They were subsequently integrated into the regional Colorado River system. Lacustrine deposits of the Muddy Creek Formation are exposed along the trace of the Las Vegas Valley shear zone in the Nellis Dunes Recreation Area (NDRA), northeast of Las Vegas, Nevada. The Muddy Creek Formation in NDRA consists of approximately 130 m of mixed carbonates and clastics, and new tephrochronology suggests an early to late Pliocene age (∼ 4.7 to ∼ 2.6 Ma) for the lowermost lacustrine deposits and an unknown, but younger, age for the uppermost spring-fed lacustrine deposit. These sediments were deposited in an arid to semiarid lake (Lake Nellis) and alluvial floodplain system based on the interpretation of lithologies and facies associations. The stratigraphic succession coarsens upward and reflects establishment of a lacustrine carbonate system overlain by a clastic succession of peripheral lake sediments of alluvial and floodplain origin. The peripheral lake deposits consist of spring-fed and fluvial wetland mudflats of brown claystone and siltstone. This brown claystone is capped by a succession of yellow and red sandstones deposited by fluvial and minor eolian processes. The second, and youngest, freshwater limestone, likely disconformably, overlies the yellow and red sandstones, and is thought to be temporally and depositionally distinct from the underlying Muddy Creek deposits. The transition from the lower lacustrine carbonates to clastic fluvial channel and flood-plain deposits indicates desiccation of Lake Nellis and possibly occurs soon after ∼ 2.7 to ∼ 2.6 Ma based on the ages of tuffs occurring in the uppermost limestone and marl beds. This is consistent with an interpreted increase in regional aridity after ∼ 2.8 Ma (Smith et al. 1993). The second limestone deposit at the top of the section represents an even younger spring-fed lacustrine deposit of unknown age. Throughout the lower carbonate section, three tuffs were identified, and geochemically correlated, using a discriminant-function analysis, to the tuff of Napa (≤ 4.70 ± 0.03 Ma), the Putah Tuff (∼ 3.3 Ma), and the lower tuffs of the Badlands (∼ 2.7 to ∼ 2.6 Ma). The timing of deposition of Lake Nellis sediments postdates the integration of the three major lake systems in this region (Lake Grand Wash, Lake Hualapai, and Lake Las Vegas) into the Colorado River drainage (5.6–4.9 Ma), and also postdates the full integration of the river to sea level (4.8–4.63 Ma) (Howard et al. 2015; Crow et al. 2021). Lake Nellis represents an isolated lake basin that was one, and maybe the last, lacustrine system to be fully integrated into the Colorado River drainage in this region.

The Escarpão Plateau (South of Portugal)—a Study Case of Nested Geosites from the Aspiring Algarvensis Geopark

Located along the southern limit of the Algarvensis aspiring UNESCO Global Geopark (aUGGp), the Escarpão Plateau is a singular geomorphological structure sculpted by fluvial, karst, and tectonic processes. The plateau is deeply scarved by the Quarteira Rivulet, forming a valley that crosses the most complete Upper Jurassic sedimentary sequence of the Eastern Algarve (Southern Portugal). This sequence includes five geological formations representing different depths of carbonate ramp deposition from the Tethys Sea: Peral Formation, Jordana Formation, Cerro da Cabeça Formation, Escarpão Formation, and the upper Limestone Formation with Anchispirocyclina lusitanica (foraminifera), respectively from the oldest formation to the most recent at the top. Throughout the Quaternary Period, the karst processes shaped a landscape of sparse and poor soils, based on which successive generations adapted their subsistence agriculture and way of life. The geomorphology of the plateau and the rivulet valley, the sequence of the carbonated formations, and the diversity of sedimentary and paleontological records can be considered possible sites of diverse geological interest and with different scales that are embedded in each other, forming thus nested sites. To promote and preserve these sites, the Algarvensis aUGGp shaped an 8-km-long interpretative walking path, passing through 11 points of interest, including biosites and geosites. Their interpretative boards highlight not only the different spatial and temporal geological diversity but also its relationship with surrounding cultural and historical heritage. Finally, this work allowed the creation of new products for outreach and public awareness towards an effective geoconservation.

River plastic transport affected by tidal dynamics

Abstract. Plastic is an emerging pollutant, and the quantities in rivers and oceans are expected to increase. Rivers are assumed to transport land-based plastic into the ocean, and the fluvial and marine transport processes have been relatively well studied to date. However, the processes controlling the transport in tidal rivers and estuaries, the interface between fluvial and marine systems, remain largely unresolved. For this reason, current estimates of riverine plastic pollution and export into the ocean remain highly uncertain. Hydrodynamics in tidal rivers and estuaries are influenced by tides and freshwater discharge. As a consequence, flow velocity direction and magnitude can change diurnally. In turn, this impacts the transport dynamics of solutes and pollutants, including plastics. Plastic transport dynamics in tidal rivers and estuaries remain understudied, yet the available observations suggest that plastics can be retained here for long time periods, especially during periods of low net discharge. Additional factors such as riparian vegetation and riverbank characteristics, in combination with bi-directional flows and varying water levels, can lead to an even higher likelihood of long-term retention. Here, we provide a first observation-based estimate of net plastic transport on a daily timescale in tidal rivers. For this purpose, we developed a simple Eulerian approach using sub-hourly observations of plastic transport and discharge during full tidal cycles. We applied our method to the highly polluted Saigon River, Vietnam, throughout six full tidal cycles in May 2022. We show that the net plastic transport is about 20 %–33 % of the total plastic transport. We found that plastic transport and river discharge are positively and significantly correlated (Pearson's R2 = 0.76). The net transport of plastic is higher than the net discharge (20 %–33 % and 16 %, respectively), suggesting that plastic transport is governed by factors other than water flow. Such factors include wind, varying plastic concentrations in the water, and entrapment of plastics downstream of the measurement site. The plastic net transport rates alternate between positive (seaward) net transport and negative (landward) net transport as a result of the diurnal inequality in the tidal cycles. We found that soft and neutrally buoyant items had considerably lower net transport rates than rigid and highly buoyant items (10 %–16 % vs. 30 %–38 %), suggesting that transport dynamics strongly depend on item characteristics. Our results demonstrate the crucial role of tidal dynamics and bi-directional flows in plastic transport dynamics. With this paper we emphasize the importance of understanding fundamental transport dynamics in tidal rivers and estuaries to ultimately reduce the uncertainties of plastic emission estimates into the ocean.

The Bronze Age occupation of the Black Sea coast of Georgia—New insights from settlement mounds of the Colchian plain

AbstractAlong the lower course of the Rioni and several minor rivers, more than 70 settlement mounds (local name: Dikhagudzuba) have been identified by field surveys and remote sensing techniques. They give evidence of a formerly densely populated landscape in the coastal lowlands on the Colchian plain (western Georgia) and have been dated to the Bronze Age. As yet, limited information is available on their internal architecture, the chronology of the different layers and their palaeoenvironmental context. Based on archaeological sources, remote sensing measurements of three mounds and sediment cores from one mound and its closer surroundings, our study presents a review of the relevant literature and reveals the internal structure, distribution and spatial extent of the mounds. Geochemical and sedimentological analyses of element contents (X‐ray fluorescence) and granulometry helped to identify different stratigraphical layers and differentiate between natural facies and anthropogenic deposits; using the Structure‐from‐Motion technique the mounds' dimensions were calculated. The studied settlement mounds had relatively small dimension (varying from 30 to 100 m in diameter) and were similar in their stratigraphy. Measurement of elements that can identify types of human activity, notably metals and phosphorus, suggest changing intensities of human occupation, pastoral agriculture and metalworking through the occupation sequence. According to the 14C chronology, the formation of the settlements occurred during the first half of the second millennium B.C., which confirms the archaeological interpretation of their Bronze Age origin. The narrow age difference between the lowermost and uppermost anthropogenic layers indicates an intentional construction of the mounds, rather than a successive accumulation of construction debris due to the disintegration of loam bricks by weathering. Therefore, they are indeed mounds and not tells. It is most likely that the characteristic circular moats that surround them were the source of their construction material. Fluvial and alluvial processes in a warm and humid climate dominated the environment of the mounds.

Permafrost extent sets drainage density in the Arctic

Amplified warming of high latitudes and rapid thaw of frozen ground threaten permafrost carbon stocks. The presence of permafrost modulates water infiltration and flow, as well as sediment transport, on soil-mantled slopes, influencing the balance of advective fluvial processes to diffusive processes on hillslopes in ways that are different from temperate settings. These processes that shape permafrost landscapes also impact the carbon stored on soil-mantled hillslopes via temperature, saturation, and slope stability such that carbon stocks and landscape morphometry should be closely linked. We studied [Formula: see text]69,000 headwater basins between 25° and 90 °N to determine whether the thermal state of the soil sets the balance between hillslope (diffusive) and fluvial (advective) erosion processes, as evidenced by the density of the channel networks (i.e., drainage density) and the proportion of convex to concave topography (hillslopes and river valleys, respectively). Watersheds within permafrost regions have lower drainage densities than regions without permafrost, regardless of watershed glacial history, mean annual precipitation, and relief. We find evidence that advective fluvial processes are inhibited in permafrost landscapes compared to their temperate counterparts. Frozen soils likely inhibit channel development, and we predict that climate warming will lower incision thresholds to promote growth of the channel network in permafrost landscapes. By demonstrating how the balance of advective versus diffusive processes might shift with future warming, we gain insight into the mechanisms that shift these landscapes from sequestering to exporting carbon.

Sediment Deposits Texture Analysis of Besuk Kobokan River in the Northern Slope Semeru Volcano Lumajang

The flow of volcanic material from Semeru Volcano as one of the most active volcano on Java Island is still flowing and deposited along the Besuk Kobokan River which empties into Bambang Beach, Lumajang. The sediments as volcanic products are transported through the river environment with water as its transport agent. This transportation and deposition process has certain grain texture characteristics that can be identified through granulometry analysis. Geological observations and sediment sampling were carried out at 8 points along the Besuk Kobokan River. Granulometry analysis aims to identify the grain texture distribution of Semeru Volcano sediments that have been transported. The results of granulometric analysis that can identify the distribution of grain texture show that the first point to the fifth point at the sampling location was influenced by lahars flow and pyroclastic flow, resulting in randomness in grain size and rock texture. While the sixth to eighth points show the fluvial sedimentation process.

A theory of stochastic fluvial landscape evolution

Geometries of eroding landscapes contain important information about geologic, climatic, biotic and geomorphic processes. They are also characterized by variability, which makes disentangling their origins challenging. Observations and physical models of fluvial processes, which set the pace of erosion on most continents, emphasize complexity and variability. By contrast, the spectral content of longitudinal river profiles and similarity of geometries at scales greater than approximately 100 km highlight relatively simple emergent properties. A general challenge then, addressed in this manuscript, is development of a theory of landscape evolution that embraces such scale-dependent insights. We do so by incorporating randomness and probability into a theory of fluvial erosion. First, we explore the use of stochastic differential equations of the Langevin type, and the Fokker–Planck equation, for predicting migration of erosional fronts. Second, analytical approaches incorporating distributions of driving forces, critical thresholds and associated proxies are developed. Finally, a linear programming approach is introduced, that, at its core, treats evolution of longitudinal profiles as a Markovian stochastic problem. The theory is developed essentially from first principles and incorporates physics governing fluvial erosion. We explore predictions of this theory, including the natural growth of discontinuities and scale-dependent evolution, including local complexity and emergent simplicity.

Reservoir Modelling to assess the Releases and Energy Generation for a Projected Scenario of Tarbela Reservoir in Pakistan

Reservoirs are normally formed by the construction of dams across rivers, but off-channel reservoirs may be provided by diversion structures and canals or pipelines that convey water from a river to natural or artificial depressions. The behaviour of the flow due to construction of dam leads to change in a fluvial process leads to deposition of sedimentation in reservoir. In this research, reservoir modelling has been carried out by using HEC-ResSim for Tarbela reservoir in Pakistan. In Pakistan, the Tarbela Reservoir is the largest reservoir on Indus River and it is the backbone of Pakistan’s agriculture sector and economy. The model was calibrated for year 2014 and validated for year 2020 in terms of outflow and power generation. The results show close comparison between simulated and observed outflow and power values for different scenarios. On the basis of 30-year histogram cycle, the future prediction of releases/outflows, power/energy generation in year 2035 has also been made. After 2035, Tarbela reservoir is expected to become the run-off the river type project due to decrease in the gross storage capacity. As per simulated results of the projected scenario (2035), the releases/outflows from reservoir and energy generation will increase in summer season by 7% and 36% respectively and decrease in winter season by 50% and 37% respectively. Further, the reduction in gross storage capacity due to sedimentation would result in the reduction of annual energy generation by 6.5% in year 2035.

Impact of Levee-Breach Width on the Channel–Levee–Floodplain: A Case Study in the Huaihe River Basin, China

Breach geometry is one essential feature for flood modelling in the channel–levee–floodplain system. It is hard to accurately predict the breach geometry because of its high uncertainty. However, due to the fact that breach geometry direct impacts the flow through the breach, the water surface profile in the channel and the flood hazard factors within the floodplain are changed with the breach geometry. To explore the impacts of breach width (one feature of the breach geometry) on the channel–levee–floodplain system, we took the Cinan Feiyou Flood Control Protection Area (CNFY-FCPA) in the middle reach of the Huaihe River Basin as the study area. We constructed a coupled 1D-2D hydrodynamic model to simulate the flooding with a series of breach-width scenarios. According to the simulation results of the models, we quantitatively analyzed the impacts of breach width on the inflow through the breach, fluvial flood process, and flood hazard factors in the CNFY-FCPA. The results indicate that (i) the relationship between the peak discharge (and inflow volume) and breach width was approximate to an S-shaped curve, while the peak discharge, inflow volume, and duration per unit width decreased with the wider breach; (ii) the breach caused a decrease in the water surface profile along the entire river sections; and (iii) while the breach width exceeded a certain width, the inundation area was nearly stable without changing with wider breach. The certain width was not the same in different rivers of 300 m in the Yinghe River and of 500 m in the Huaihe River. The research results can provide a scientific basis for flood-control and disaster-reduction decision making.

Phosphorus supply and floodplain design govern phosphorus reduction capacity in remediated agricultural streams

Abstract. Agricultural headwater streams are important pathways for diffuse sediment and nutrient losses, requiring mitigation strategies beyond in-field measures to intercept the transport of pollutants to downstream freshwater resources. As such, floodplains can be constructed along existing agricultural streams and ditches to improve fluvial stability and promote deposition of sediments and particulate phosphorus. In this study, we evaluated 10 remediated agricultural streams in Sweden for their capacity to reduce sediment and particulate phosphorus export and investigated the interplay between fluvial processes and phosphorus dynamics. Remediated streams with different floodplain designs (either on one side or both sides of the channel, with different width and elevation) were paired with upstream trapezoidal channels as controls. We used sedimentation plates to determine seasonal patterns in sediment deposition on channel beds and floodplains and monthly water quality monitoring. This was combined with continuous flow discharge measurements to examine suspended sediment and particulate phosphorus dynamics and reduction along reaches. Remediated streams with floodplains on both sides of the channel reduced particulate phosphorus concentrations and loads (−54 µg L−1, −0.21 kg ha−1 yr−1) along reaches, whereas increases occurred along streams with one-sided floodplains (27 µg L−1, 0.09 kg ha−1 yr−1) and control streams (46.6 µg L−1). Sediment deposition in remediated streams was five times higher on channel beds than on floodplains and there was no evident lateral distribution of sediments from channel to floodplains. There was no effect from sediment deposition on particulate phosphorus reduction, suggesting that bank stabilization was the key determinant for phosphorus mitigation in remediated streams, which can be realized with two-sided but not one-sided floodplains. Further, the overall narrow floodplain widths likely restricted reach-scale sediment deposition and its impact on P reductions. To fully understand remediated streams' potential for reductions in both nitrogen and different phosphorus species and to avoid pollution swapping effects, there is a need to further investigate how floodplain design can be optimized to achieve a holistic solution towards improved stream water quality.

Weathering and River Erosion: Insights from the Variation of Intact Rock Strength in Rhyodacites

The relationship between weathering and fluvial erosion is important in shaping the incisions of bedrock channels. In rhyodacites from Paraná Volcanic Province, plucking and macro-abrasion processes are predominant in the fluvial incision process, according to field observations. Using the intact rock strength as a proxy for the weathering, this paper analyzes how the strength of rhyodacites behave along a cross section of a bedrock channel and seeks to understand how this affects erosion. Topography and intact rock strength were surveyed continuously along a 30 m cross section using a Schmidt hammer, model N. Mean, median, and standard deviation were calculated for each meter of the section. The topographic amplitude of the bed in the section is 30 cm, featuring an almost flat geometry. The average strength values range from 30 to 59 R (7.65 to 58.15 MPa). Despite the small topographical amplitude, the general behavior of the rock strength follows the macrotopography of the bed, increasing in the high zones and decreasing in the low zones. The standard deviation, interpreted as directly proportional to the degree of weathering, follows the microtopography of the bed (amplitude ≈ 10 cm), being greater in low areas and smaller in high areas. This association between standard deviation of strength and microtopography reveals the seasonal variation of the water level in the channel, whereby higher moisture in low-lying areas intensifies the weathering of the rock. Weathering affects the density of rhyodacites in the area with a minimum reduction of 11.2% being calculated. This enhances the erosion processes by plucking and macroabrasion by reducing the intact rock strength. The susceptibility of the rhyodacites to weathering, despite the differences within the section, favors the maintenance of the rectangular geometry of the channel and shows how erosive processes are affected by the condition of the rock. The study revealed that the notion of decreasing the intact rock strength towards the banks associated with greater weathering in higher areas, cannot be generalized, as it depends on the geometry of the channel section, the lithological nature of the bed, and the frequency of flows.

How does landslide debris grain size control sediment transport and dynamics?

The grain size of sediment delivered to a river by hillslope processes is an important factor which could impact fluvial erosion, sediment transport, and associated geomorphic changes. Grain size distribution (GSD) is increasingly recognised as an important factor for the impact of landslides on sediment pulses and long-term erosion rates. Therefore a better comprehension of grain size control on landslide-generated sediment transport and dynamics will help with understanding post-seismic fluvial processes and landscape evolution. In this study, we modelled the recovery of the Hongxi River basin affected by the Wenchuan earthquake under different landslide GSD scenarios. The CAESAR-Lisflood (CL) model was first modified to enable the spatial input of sediment GSD, which allows the model to distinguish the grain size composition of landslide sediment and the background sediment sourced from other areas. Using the modified CL model, we simulated three different landslide GSD scenarios (Original, Coarser, Finer) by altering the original landslide sediment GSD observed from a post-earthquake basin. In particular, we analysed the fate of landslide-generated sediment using a new sediment tracing function embedded in CL. This enabled us to evaluate the role of landslide GSD variation on the spatio-temporal heterogeneity of sediment transport. Our results show that the GSD of landslide material exerts a clear control on both sediment yield and channel deposition, the sediment transport of landslides disconnected to the fluvial system is more sensitive to grain size variation, while the GSD of landslides connected to the fluvial system has less impact on sediment dynamics. The duration of landslide disturbances on basin sediment dynamics can largely be dependent on the period of time (e.g., 20 years in this study basin) taken for grain coarsening (the grain size is increasing upward), which is dominated by the evacuation of fine sediments. The modelling results and findings highlight the importance of grain size distribution of landslide material and provide information to support basin sediment management and environmental risk mitigation.

Non-pollen palynomorph assemblages in mid- to late Holocene wetland deposits and their palaeoenvironments of deposition: Microfossil signatures in sediment sequences of the Yangtze Delta coastal lowlands, East China

Fluvial processes such as sediment deposition within drainage channels and seasonal overbank flooding, and fluvial events such as occasional high intensity floods all leave particular sedimentary signatures in terms of their lithology and also in their contained microfossil assemblages, which represent different environments of deposition. Over several thousand years the Yangtze River in eastern China has developed a coastal lowland plain around its delta that is mainly composed of stacked fluvial sediment facies, but also includes many marine or estuarine layers in some areas, as well as deposits of limnic and semi-terrestrial pool, marsh and mire origin, some of which are highly organic. The fluvial facies are dominantly clastic sequences of sands, silts and clays that reflect a range of deposition from quiet water to high energy conditions and in varying water depths, mainly governed by fluvial input from the Yangtze and the many other, smaller, rivers and streams of the deltaic lowland. The limnic and marshland sediments reflect autochthonous deposition in a range of freshwater wetland types of varying water depth, from lake through marsh/fen to surface peatland. Allied to lithological and pollen data, non-pollen palynomorph spore assemblages and abundances within these complex sedimentary sequences, particularly from algal communities, provide signatures of floodplain wetland depositional history and hydrodynamic patterns. We have used groupings of these microfossil data to characterise the sedimentary facies of the lower Yangtze coastal plain and to reconstruct hydrological history across the area at a range of spatial scales. Fluctuations in the relative taxa abundances are good indicators of changes in water levels at the site scale from surface waterlogging through reedswamp and fen to deeper open water. While some changes seem to be site specific, the data show flooding and increased water depths that correlate with known phases of climatic deterioration.

Anthropogenic impacts on watercourses in the region of the Labe (Elbe) and Jizera confluence

The impact of human activities on watercourses has significantly changed throughout history. Anthropogenic impact on the evolution of the middle Labe (river-km 854−882) and the lower Jizera (river-km 0–17) is documented in this paper, together with its influence on the dynamics of fluvial processes. The historical change analysis of the watercourses was based on the historical maps of the Second and the Third Military Survey. The most significant shortening of the studied sections of the Labe and Jizera occurred during the nineteenth century for flood protection purposes. During the last 200 years, the Labe was shortened by 20.6% and the Jizera by 7.4%. In more recent years, the lower reaches of the Jizera show a curving tendency caused by fluvial processes. The reinforcement of the Labe’s banks limits the natural evolution of its channel. These conclusions are confirmed by trends in the curvature index of the Labe and Jizera.