Sediment Storage Research Articles

Petrography and geochemistry of siliciclastic sediments in Permo-Triassic transition from the southern Pranhita-Godavari Gondwana basin, India: Implications for paleoclimate

The Kamthi Formation, in the intracratonic Pranhita-Godavari Gondwana rift basin, bore signatures of climate change from a warm humid climate in Late Permian to hot arid during the Early Triassic. Sedimentation took place mainly under fluvial conditions. The Kamthi sediments were unaffected by burial diagenesis and the source remained the same, therefore this provides an excellent opportunity to study the climatic influence on petrogenesis in an intracratonic rift basin. Subsurface palynofacies data of Kamthi Formation from the southern part of the basin established the presence of Upper Permian rock units equivalent to the Raniganj Formation, which are overlain by Lower Triassic sediments equivalent to Panchet Formation of the Damodar valley Gondwana basins, and are separated by a gradational contact. QFL and trace element compositions reveal transitional continental to craton interior provenance with dominantly felsic source areas, along with some meta-sedimentary and mafic components. Dominance of kaolinite, coal, alteration of K-feldspar, and biotite in the Raniganj equivalent sandstones attests to a humid climate. The presence of mostly fresh K-feldspar, ferruginous matrices, Fe-carbonate nodules, cutans, and microcrystalline silica cement in the Panchet equivalent sandstones mark a shift from humid to arid/semi-arid. This climatic shift is not reflected in the uniform feldspatho-quartzose to quartzose sandstone compositions and mudstone major oxide compositions. The mudstones are depleted in mobile elements, have low K2O/Al2O3 (0.11–0.18), low ICV (0.35–0.72), high SiO2/Al2O3 (2.3–3.4), high K2O/Na2O and moderately high CIA (80.12–87.05) that collectively suggest moderately intense weathering. Despite the humid climate, the Raniganj Formation equivalent rock units did not attain the highest mineralogical maturity due to proximity to relatively high-relief source areas in a fluviolacustrine environment. This relationship resulted in a lack of short-term sediment storage that favoured rapid erosion and sedimentation.

Sand, wind, paleosols, war: Late Quaternary aeolian dynamics in the Selima Sand Sheet Region, Darb el Arba'in Desert, Southern Egypt

First scientifically documented by the British explorer and soldier Ralph Alger Bagnold, the Selima Sand Sheet is an extensive low-relief area located within the modern hyperarid core of the Eastern Sahara. Field survey and trenching reveal a surface mantle of near ‘pinstripe” laminated aeolian sands that comprise active chevron (or zibar) bedforms, which are apparent on satellite datasets. These active sands cover Quaternary paleosols with morphostratigraphic characteristics that reflect differing degrees of soil development over time as a function of in situ weathering of quartz parent materials, addition of silts and clays via illuviation and eluviation processes, the precipitation of carbonates, rubification, and bioturbation by plants and insects. A relative chronostratigraphy is inferred from the associated archaeological (Neolithic) and historical materials (Late Historic to World War II), and absolute ages for these deposits are provided by optical dates using single aliquot regeneration techniques (SAR). Constraining the timing of aeolian sedimentation provides a basis for reconstructing paleoenvironmental changes and pedogenesis over Late Quaternary timescales in this region of northeast Africa. Accretion of the sand sheet was episodic and occurred during time periods of enhanced aeolian activity at ∼20–14 and ∼5–3 ka years ago. Late Pleistocene deposition of the sand sheet was out-of-phase with the widely recognized period of rainwater-fed “pluvial” playa lake formation and wadi river drainage alluviation documented in the Sahara, which resulted from enhanced monsoonal rains associated with the orbitally-forced precessional insolation maximum in the Northern Hemisphere. Enhanced bioturbation processes associated with wet phases during the Holocene have completely obliterated most primary sedimentary structures in the Pleistocene-aged sand sheet, resulting in the development of a cohesive, coarse sand and granule-dominated deposit exhibiting incipient prismatic soil structural development. The younger sand sheets dating to the Late Holocene (∼4–3 ka years ago) preserve primary sedimentary structures (e.g. planar laminations), and increasing amounts of cohesion and structure with age. Reconstructing the maximum estimated accumulation rates, and assuming approximately uniform rates of sedimentation across the Selima Sand Sheet area, sediment storage within the sand sheet may be on the order of ∼7 km3/1000 years during the time period that has elapsed since the mid-Holocene onset of arid conditions.

River incision, 10Be production and transport in a source-to-sink sediment system (Var catchment, SW Alps)

Abstract. Detrital 10Be from continental river sands or submarine sediments has been extensively used to determine the average long-term denudation rates of terrestrial catchments, based on the assumption that the rate of cosmogenic nuclide production by the interaction of source rocks with cosmic radiation balances out the loss of these nuclides by surface denudation. However, the 10Be signal recorded in sediments may be affected at the source by the response time of mountainous catchments to high-frequency forcings. In addition, transient sediment storage in piedmonts, alluvial plains and lakes or near the coast may also induce a difference between the erosive signal and its record in the sedimentary sink. Consequently, a significant part of the signal recorded in shallow-water sediments can be lost, as deep marine sediments may simultaneously record a signal coming from newly eroded source rocks along with one coming from the destabilization of previously deposited sediments. In this paper, we use the landscape evolution model Badlands to simulate erosion, deposition and detrital 10Be transfer from a source-to-sink sedimentary system (the Var River catchment, southern French Alps) over the last 100 kyr. We first compare model-based denudation rates with the ones that would be extracted from the 10Be record of local continental sediments (equivalent to river sands) and from sediments deposited offshore over time in order to examine if this record provides an accurate estimate of continental denudation rates. Then, we examine which conditions (precipitation rate, flexure, ice cover) satisfy published measured river incision rates and 10Be concentration in submarine sediments. Our results, based on the Var catchment cosmic ray exposure dating and modelling indicate that, while river sands do accurately estimate the average denudation rate of continental catchments, this is much less the case for deep submarine sediments. We find that deep-sea sediments have a different and often much smoother 10Be signature than continental ones and record a significant time lag with respect to imposed precipitation rate changes, representing the geomorphological response of the margin. A model which allows us to fit both measured 10Be concentration in marine sediments and river incision rates on land involves an increase in precipitation rates from 0.3 to 0.7 m yr−1 after 20 ka, suggesting more intense precipitation starting at the end of the Last Glacial Maximum.

Using a post-glacial terrace sequence to better understand landscape evolution and paleohydrology in the eastern San Juan Mountains, USA

Terraces provide a unique record of environmental change as they form due to changes in sediment supply and hydrology. In the upper Rio Grande drainage, terraces are post-glacial in age and have not been impacted by tectonics during that period. As such, these terraces are the result of changes to the fluvial system since glaciers retreated. We mapped four terrace units across two sections of the upper Rio Grande. We then examined soil profiles on terrace units, described the sedimentology, and dated the terraces where possible. Our findings indicate that the upper terrace (FT1) formed as an outwash terrace during glaciation and that incision began immediately after glaciers had melted around 12.1 ka. Two intermediate terraces likely formed during brief pauses in post-glacial incision as aggradation of the lowest terrace (FT4, 7–14 m below FT1) had already begun by 9.6 ka. Cumulic soils and fine-grained sediment on FT4, combined with radiocarbon ages, indicate that FT4 aggraded consistently in both rivers throughout the Holocene. Specifically, overbank deposits emplaced during decadal-scale flooding have allowed FT4 to aggrade consistently since 9.6 ka. The main channel appears to have been stable throughout the entire Holocene given that it is pinched between fine-grained deposits. Previous work indicates that other authors have noted similar landforms although they seem to be underreported in the literature. The timing of terrace formation differs from that in nearby headwater streams, indicating that headwater systems are more responsive to hillslope processes while larger trunk streams appear to receive sediment from upstream. Apparent differences in flooding between the two basins may indicate that basins with water managed by reservoirs may flood the FT4 surface less often, thereby highlighting the impact of water management on both fluvial hydrology and sediment storage.

How much organic carbon have UK lakes stored in the Holocene? A preliminary estimate

Temperate lake sediments store a substantial amount of organic carbon (OC) over millennia. Despite the importance of quantifying terrestrial carbon budgets for Nature-based Solutions, the long-term accumulation of OC in European temperate lakes is poorly constrained. In this study, we analyzed 30 lake sediment records to generate a preliminary first-order estimate of Holocene OC accumulation rate (OCAR) and OC storage in UK lakes. We also examined the environmental variables that influence OCAR and produced synthesized Holocene records of %OC and z-scores of log-transformed OCAR and sediment accumulation rate (SAR) at 500-year resolution. Based on our estimation, we report an average Holocene OCAR of 7.4 ± 5.5 g C m−2 yr−1 and a Holocene total OC storage of 0.24 ± 0.18 Pg C in UK lakes. Apart from latitude, no relationship was found between the average Holocene OCAR and the various environmental variables (i.e. temperature, precipitation, surface area, catchment area, depth, altitude, and geology type). During the Holocene, OCAR closely resembles variations in SAR, whereas the increase in %OC is likely explained by the warming climate. Early Holocene variations in OCAR were primarily climate-driven. In contrast, the anthropogenic impact on the landscape exerted a predominant influence on OC burial during the middle-late Holocene. Our results improve the current understanding of terrestrial carbon budgets in the UK and demonstrate the under-appreciated importance of lakes as long-term OC stores.

Time‐average stochastic control based on a singular local Lévy model for environmental project planning under habit formation

This study applies the theory of stochastic control to an environmental project planning to counteract against the sediment starvation problem in river environments. This can be considered as a time‐average inventory problem to time‐discretely control a continuous‐time system driven by a non‐smooth jump process under habit formation disturbing project implementation. The system is modeled such that the sediment storage dynamics are physically consistent with certain experimental results. Further, the habit formation is modeled as simple linear dynamics and serves as a constraint related to the replenishment amount of the sediment. We show that the time‐average control problem is not necessarily ergodic. Consequently, the effective Hamiltonian may become a non‐constant. Thereafter, ratcheting cases as extreme cases of the irreversible habit formation are considered, owing to them being unique exactly solvable non‐ergodic control problems. The optimality equation associated with a regularized and hence well‐defined control problem is verified. Furthermore, a finite difference scheme is examined against the exactly solvable case and then applied to more complicated cases.

Anatomy of a diamondiferous gravel barrier spit at the palaeo‐Orange River mouth, south‐western Namibia

ABSTRACTThe sedimentary facies architecture of a Plio‐Pleistocene diamond‐bearing gravel barrier spit within the palaeo‐Orange River mouth in south‐western Namibia has been revealed during onshore mining activities. Four sedimentary facies associations build this ancient coastal landform and have been interpreted, from a seaward to landward direction, as sediments in: (i) the foreshore, represented by an intertidal beach; (ii) a subtidal spit platform on which the spit developed; (iii) storm‐constructed spit head recurves on the landward side of the spit; and (iv) an estuarine back‐barrier. This sedimentary record reflects an evolving spit that grew in response to a combination of marine and fluvial processes in a wave‐dominated, high‐energy coastal regime. Here, the southern Atlantic Ocean aggressively dispersed sediment delivered by a Plio‐Pleistocene Orange River, ensuring that the fine‐grained sediments were removed to allow only the gravel fraction to build up along the coastline. This extreme dispersal of sediment also precluded the construction of a classic delta; hence sediment storage offshore of the river mouth was limited and spit growth was dependent on the direct supply of river sediment. In response to the intermittent supply of sediment, spit growth and decay alternated during periods of sediment abundance and starvation, respectively. During positive sediment budget, the spit extended northward and cut off parts of the mainland to form an estuarine back‐barrier. Foreshore and spit head progradation was sustained under these conditions, and formed a beach‐ridge plain with a topographic expression of several coast‐parallel ridges that curved at the spit head into the back‐barrier. Spit extension and recurve development were controlled by a combination of high sediment supply, a vigorous longshore drift and powerful waves approaching from various directions. This Plio‐Pleistocene coastal landform in Namibia offers a depositional model relevant to gravel‐dominated barrier spits near river mouths along wave‐dominated clastic coasts.

Influence of Different Particle Sizes of Sediments on the Lower Reaches of the Basin and its Significance in the Liao River Governance

Based on the sand volume and sedimentation volume data for different particle size (PS) groups, the relationship between the annual scouring and silting amount of the Juliu River-Liujianfang section and the yearly sediment volume entering the downstream river channel was established. The critical values of sediment storage and release for the downstream river channel were obtained. It was found to decrease with an increase in the sediment particle size. The correlation coefficient between the annual scouring and silting amount of the Juliu River-Liujianfang section and the annual sediment volume entering the downstream river channel increased with the coarsening of sediment PS. It indicated that the sediment size was proportional to the sediment amount (SA) entering the river channel. As the sediment size increased, the deposition amount increased due to the variation of unit sediment amount. Based on the treatment and achievement of source areas with sediment sizes larger than 0.05 mm, it is significant to concentrate on treatment areas with sediment sizes larger than 0.10 mm.

Modeling anthropogenic affected sediment transport in a mid-sized European river catchment–extension of the sediment rating curve equation

Land use and water resource management influence the suspended sediment concentration (SSC) in rivers. Fine sediments are an important driver for river development, even in coarse-material-rich rivers. In this study, the sediment rating curve approach is modified to predict SSC several river-km downstream of a sampling site. Further, the prediction is improved by adding sediment input, storage, and dilution effects through relevant anthropogenic measures through a model identification approach. Thus, the impact of the most severe anthropogenic measures, damming and changes in the length of a channel section for the Rur River, could be identified. Further, the impact of describing parameter changes for those measures on the SSC can be computed and considered in future water resource management. In this approach, particle swarm optimization was used to fit parameters in permutable test- and training data sets to identify linear extensions to the sediment rating curve. The input data consists of (1) SSC, which was obtained by sampling along the river section four times a year over approximately two years, (2) discharge data from river gauges supplemented by rainfall-runoff modeling between stations, (3) rainfall data from meteorological stations, and (4) sub-catchment characteristics like river section length and erosivity obtained with GIS. Via incorporating the river section length and sediment deposition in response to damming, we reduced the RMSE (root mean squared error) from 152.27 to 131.83% with a p-value of 0.073 in the Wilcoxon Signed Rank Test. Further integration of sub-catchment parameters like erosivity led to overfitting and decreased prediction accuracy. A catchment-wide prediction was achieved, but sub-catchments operate on different spatial scales with different connectivity behavior, which restricts the transferability of the equation. SSC-Q hystereses provide the first indications of characteristic sediment sources and were used to discuss connectivity behavior within the study area. They are recommended as part of a (sub-) catchment characterization for further studies.

Responses of coastal sediment organic and inorganic carbon to habitat modification across a wide latitudinal range in southeastern China

Coastal wetlands are important to the global carbon (C) budget and climate regulation. Plant invasion and aquaculture reclamation have drastically transformed China’s coastal wetlands, but knowledge of the effects on sediment carbon remains limited. We sampled top layer sediments (0–20 cm) in 21 coastal wetlands in southeastern China across the tropical-subtropical climate gradient, that have experienced the same sequence of habitat transformation from native mudflats (MFs) to Spartina alterniflora marshes (SAs) then to aquaculture ponds (APs). We measured the sediment carbon contents and ancillary physicochemical parameters. Landscape change from MFs to SAs increased sediment organic carbon (SOC) but decreased sediment inorganic carbon (SIC) content, whereas conversion of SAs to APs resulted in the opposite changes. Based on stepwise regression analysis, ammonium concentration and particle size distribution were the common factors that affected changes in SOC between habitat types, whereas for SIC it was ammonium and chloride concentrations. Habitat change affected SOC to a larger degree than SIC. Overall, invasion of MFs by SAs increased total carbon storage in the top sediment by 22%, or 6.6 × 106 g C ha−1; conversion of SAs to APs decreased it by 9.7%, or 3.5 × 106 g C ha−1. Our results showed the differential effects of different habitat modification scenarios on the sediment carbon pools and help assess how landscape-scale change affects terrestrial carbon budget and emission in the context of global climate change.

Forestry influences on salmonid habitat in the North Thompson River watershed, British Columbia

Freshwater ecosystems that support juvenile salmonids can be degraded by human pressures such as forestry. Forestry activities can alter water temperatures and the delivery and storage of water, nutrients, wood, and sediment in streams, resulting in changes to the habitat, growth, and survival of juvenile salmon. Previous research on forestry impacts on habitat has focused on small, intensively monitored coastal systems. Here, we examined forestry activities, watershed characteristics, physical habitat, and stream temperature for 28 mid-sized tributaries of the North Thompson River to examine relationships between forestry and juvenile coho stream habitat in interior watersheds. Forest harvest had a positive correlation to maximum summer stream temperature. Streams with 35% of the riparian area harvested since 1970 had maximum summer temperatures 3.7 °C higher on average than those with 5% harvested. Stream gradient explained most of the variation in physical habitat and had negative correlations to pool cover, pool depth, and fine sediment cover. Taken together, these results indicate that watershed characteristics drive physical habitat, but forest harvest can be a primary driver of water temperatures.

Simulating daily sediment transport using the Water Quality and Sediment Model (WQSED)

IntroductionHigh erosion and sediment yield rates continue to pose a significant threat to the environment globally. Information on erosion and sediment rates is key for supporting effective and sustainable mitigation measures. Models that estimate sediment yield are vital in providing information about erosion and sediment yield rates, as empirical studies are prohibitive over large spatial and temporal scales.MethodsIn this study, we simulate daily sediment transport using the WQSED model and assess the effectiveness of the tool in providing crucial estimations of sediment yield. The model structure links the Modified Universal Soil Loss Equation (MUSLE) to a simple sediment storage component. The model was applied to the Odzi River catchment in Zimbabwe and The Rio Tanama River catchment in Puerto Rico, where daily observations of sediment yield exceeding a decade were available for calibration and validation.ResultsIn both catchments, we achieved a coefficient of efficiency and R2 and NSE of > 0.7 during model calibration and > 0.6 during model validation. The percentage bias remained below 45% for both calibration and validation periods.ConclusionThese results indicate that the WQSED model can be applied to provide estimates of sediment yield that are reliable for erosion, sediment yield and water quality management. An effective and relatively simple sediment yield model incorporating sediment storage is essential for catchment management in erosion-prone areas.

A Novel Approach to Quantify Sediment Transfer and Storage in Rivers—Testing Feldspar Single‐Grain pIRIR Analysis and Numerical Simulations

AbstractQuantifying sediment transport and storage in fluvial systems is fundamental for understanding the transfer of eroded materials from source to sink. Here, we investigated the potential of a combined approach using a luminescence measured in modern fluvial sediments and numerical simulations to quantify transport and storage in rivers. We acquired luminescence data at the single‐grain scale on feldspar sediments of Waimakariri and Rakaia braided rivers (New Zealand) using a post infra‐red infra‐red stimulated luminescence protocol. We considered three metrics from the analysis of luminescence equivalent dose (De) distribution: the percentage of bleached and the percentage of saturated grains, and the meanDe. All three metrics show similar longitudinal trends along both rivers. To derive quantitative information on sediment transfer from these data, we developed a numerical model that simulates the longitudinal evolution ofDedistribution of a population of grains during transport and storage in floodplains. The model considers four main parameters: the transport length of grains during floods, their resting time between successive transport events, the bleaching probability (probability of the luminescence signal to be reset due to sunlight exposure during transport or rest), and the likelihood of partial bleaching. Identification of model parameters that best reproduce natural observations allowed estimating transit time of sediments between 2.1 and 10.3 Kyr (mean of 6.9 2.9 Kyr), corresponding to mean virtual transit velocity of 20–95 m.yr−1(mean of 46 28 m.yr−1). Our study illustrates the potential of the combined single‐grain luminescence and modeling approach to quantify sediment transfer in fluvial systems.

Characterizing the response of the coastal Rio Grande to upstream damming

Dams are major obstructions to the flow of water and the transport of sediment in rivers. Much work has shown the construction of dams, and storage of sediment in reservoirs, can lead to significant changes in the morphodynamic behavior of alluvial rivers; however, in most cases, the effect of damming has a finite downstream limit as sediment is supplied back to the river through channel bed/bank erosion and/or tributary inputs. Here we present a study of a natural experiment that isolates one source of sediment downstream of a dam – the lower Rio Grande, which has no major tributary inputs of sediment over a ~450 km reach, from Falcon Dam to the coast. Analysis of the morphology and topography of the Rio Grande shows that prior to damming in the 1950s the coastal Rio Grande was a kinematically active channel with large, subaerial point bars. Subsequent to damming, lateral migration of the river shut down and exposed point bars shrunk in size, becoming static and vegetated. Bathymetric survey data show meter-scale incision of the channel bed for hundreds of kilometers downstream of the dam. Entrenchment of the river is also evidenced by the development of steep banks on the inner portions of channel bends. Damming also impacted the interaction between the river and the floodplain, resulting in the formation of persistent gullies incised into the channel banks, suggesting transport of water and sediment is net positive into, not out of, the channel. Based on all of these observations we conclude that the full ~450 km reach of the Rio Grande, from Falcon Dam to the coast, became net degradational following dam closure. We conclude that the presence of such a long degrading reach is caused by the exposure of bedrock in the Rio Grande channel for nearly 100 km downstream of the dam, which, combined with the lack of tributaries, limits downstream sediment supply to the river. Our results provide new insights into the response to damming for rivers with no tributary sediment input and thin alluvial cover, and more broadly to the kinematic and channel geometry responses to a major drop in water discharge and sediment supply for coastal meandering rivers.

Benthic Invertebrates on the Move: A Tale of Ocean Warming and Sediment Carbon Storage

AbstractOngoing effects of climate change create a dual challenge of shifting distributions of organisms and concerns about the fate of organic carbon in nature. Marine sediments store vast amounts of organic carbon, but the fate of that material hinges on the biology of organisms associated with the seafloor and how they influence rates of carbon decomposition and burial. Shifts in large megafauna that disturb and thus help to oxygenate sediments could have important ramifications regarding whether sediments release or store carbon for long periods of time. We consider snow crab and lobster, two commercially important seafloor species in the Northeastern Atlantic, and the potential effects of ongoing changes in their distributions and that of their fisheries for future climate scenarios. These ongoing biogeographic shifts, considered in tandem with areas of seabed legislatively protected from fishing impacts and thus not confounded by cumulative effects of fishing gear disturbance, offer an opportunity to study how newly arrived species that disturb large areas of the seafloor might influence the global carbon cycle.

IDENTIFIKASI KONDISI EKSISTING DAN DAMPAK SEDIMENTASI PADA SUNGAI KREO DAN KALIGARANG KOTA SEMARANG

The Garang watershed which includes the Kreo River and the Kaligarang River is an ecosystem unit that is limited by topographical separators and functions as a collector, storage, and distributor of water, nutrients, and sediment through the river's hydrological system. Garang watershed plays an important role in achieving Sustainable Development Goals (SDGs) 6 related to clean water, namely supplying drinking water raw materials in the city of Semarang experiencing environmental damage due to sedimentation common in river systems in Indonesia. Sedimentation occurs due to the deposition of fragmental material by water caused by erosion. Erosion consists of three phases, namely the release of soil particles and then transport by erosion agents (wind and water). Sediment deposition occurs which is influenced by natural and anthropogenic factors. The impact of sedimentation causes siltation which affects the decreasing capacity of river flow and decreases river water quality. This study aims to identify and analyze the existing conditions of the Kreo River and Kaligarang River related to the impact of sedimentation with qualitative descriptive methods and literature studies of previous studies. The Kreo River and Kaligarang River experience sedimentation due to suspended solids in the form of soil and sand mixed with household waste, resulting in decreased river flow and water quality. This is in line with the results of literature studies from previous studies, in 2008 sedimentation in the Kaligarang River was 124.944.13 tons/year with an erosion rate of 1,064.260.08 tons/ha/year. In 2009-2014 sedimentation in the Kreo River increased from 2,781 to 4,083 tons/year with an erosion rate of 17,827 - 26,171 tons. It can be concluded that the Kaligarang River and the Kreo River are currently experiencing increased sedimentation, so they are threatened with silting and damage to the river's natural functions.

Using fallout 137Cs and OSL as sediment tracers in badlands: a case study of Tepezalá volcano (Central Mexico)

ABSTRACT Badlands are dynamic landforms that cause soil loss over extensive areas. In this study, we analyze recent sediment mobilization in a badland area by using a novel approach that integrates fallout 137Cs and optically stimulated luminescence (OSL). We assess how erosion and sediment storage operate over the Tepezalá volcano, a tephra cone located in central Mexico. We analyzed a set of sediment samples extracted from the surface of an altitudinal sequence with different land uses to explore how landscape management practices relate to erosion and, depth profiles from local sinks, to detect patterns of sediment mobilization and sedimentation. We compared 137Cs and OSL results with reference values to evaluate whether erosion or deposition is predominant and to assess how deep the erosive processes in the landscape are. Results from fallout 137Cs values indicate that in those badlands with implemented actions to mitigate erosion, sediment is retained. The high luminescence values show that the edaphic soil has been flushed away, and subsoil crops out in some of the sampled sites. For the case of depth profiles, maximum values of 137Cs coincide with high luminescence values, suggesting that in such sites, the sediment was mobilized during rapid incision episodes that caused widespread erosion of the landscape. We detected at least three episodes of rapid incision in 10 years of sediment record. We propose that using 137Cs and OSL together can provide valuable information of the sediment transport in settings dominated by fast erosion as do occur for the case of badlands.

Sediment Dynamics and Bed Stability in Step‐Pool Streams: Insights From 18 Years of Field Observations

AbstractStep‐pools are a common morphology in gravel‐bed streams with gradients between 3% and 30%, where coarse sediment and wood are present. Recent experimental work has offered insight on the formation of step‐pools, flow resistance, and interactions between sediment transport and channel morphology. However, field observations are sparse and often limited by short observation periods. Using an extensive 18‐year data set, we examine controls on sediment mobility, step stability, and sediment storage in East Creek, a step‐pool reach in British Columbia. Event bedload yield correlated with peak flow and ranged over two orders of magnitude. For most events, bedload grain‐size was finer than the grain size distribution of the sediment found in pools. Fractional sediment mobility was independent of the flow magnitude and controlled by sediment supply. The large stones that comprise the steps were generally mobile during large events (>10‐year recurrence interval), although the largest ones were not. Despite the movement of large stones, the skeleton of the steps remained in place even during an event with a near 125‐year recurrence interval. Temporal trends in sediment storage in pools show that most events cause negligible changes in sediment storage. Our field observations indicate that the step‐pool morphology of East Creek is stable, as the morphology and shape of the steps persisted under a wide range of flows. The overall stability of the reach is confirmed by observed trends in bedload yield and particle mobility.

Examining sediment accumulation pattern and storage capacity loss of Lake Ziway, Ethiopia

Examining sediment accumulation pattern and storage capacity loss of Lake Ziway, Ethiopia

Examining sediment accumulation pattern and storage capacity loss of Lake Ziway, Ethiopia

Examining sediment accumulation pattern and storage capacity loss of Lake Ziway, Ethiopia