Channel Sediment Research Articles

Numerical investigation of flow behavior at the lateral intake using Computational Fluid Dynamics (CFD)

Hydraulic and environmental engineering projects often utilize side channels. The water flow through the lateral intake of channels and rivers is turbulent including separation zone and lateral eddies. This causes many problems, the transfer and deposition of sediments to the sub-channel, being the most serious. In the current work, a hydrodynamic model using the Navier–Stokes equation for the flow of incompressible fluids was studied. Using the CFD software, ANSYS FlUENT 19.2, 3D flow patterns were simulated at a diversion channel. First, the simulation results were confirmed in this study utilizing the experimental data performed by earlier investigation. The results showed good agreement using the comparison between the experimental and numerical results when the k-omega turbulence viscous model was employed. Simulation of the flow pattern was then done at the lateral channel junction using a variety of geometry designs. These improvements include changing the intake's inclination angle and chamfering and rounding the inner corner of the intake mouth instead of the sharp edge.The flow parameters at the diversion including velocity streamlines, bed shear stress, and separation zone dimensions were computed in the current study. The findings demonstrated that changing the 90° lateral intake geometry can improve the flow pattern and bed shear stress at the intake junction. Consequently, sedimentation and erosion problems are reduced.According to the conclusions of this study, a branching angle of 30° to 45° is the best configuration for increasing branching channel discharge, lowering branching channel sediment concentration and lowering Scour depth at the junction region. It was also discovered that modifying the intake inlet's sharp interior corner with specific conditions has a favorable effect on reducing the size of the separation zone. The intake of chamfered inner edge with 30° angle to flow direction (α) and c value of 0.75b was found to be the best model for lowering separation area in this investigation. In addition, the separation area and stress distribution are negatively influenced by the Configuration E model (chamfered edge at 60° angle with the horizontal), notably the greater chamfer size by increasing chamfered vertical distance (c).

Ancient and modern anastomosing rivers: insights from sedimentological and geomorphological case studies of the Triassic, Neogene and Holocene of Poland

We review the three regional anastomosing fluvial systems, both ancient and modern. The dinosaur-bearing upper Triassic succession in Krasiejów (S Poland) is composed of siltstones and claystones that are divided into three facies associations. One of the fluvial associations is characterized by features typical of a low-energy anastomosing river system in a tropical semiarid climate, interpreted as the result of accumulation in deep, wide and low-sinuosity palaeochannels with pronounced vertical accretion. Deposition from suspension predominated in flows of very low stream power. The upper Neogene muddy succession in a tectonically active area (Kleczew Graben, central Poland) includes a great number of fluvial palaeochannels filled with sand and/or mud. These ribbon-shaped fluvial bodies are deep and wide, and represent channels showing very limited lateral migration. They were filled mostly under low-energy conditions, and their mapped course shows an “anabranching” pattern in plan view. The palaeochannels are transitional from sand- to mud-dominated. The Holocene upper Narew River (NE Poland) represents a modern anastomosing fluvial system. The interconnected channels form an anabranching pattern. The channels are straight to slightly sinuous, relatively deep and wide. Interchannel, low-lying “islands” are covered by peat-forming plants. Despite the low stream power, in-channel deposition is dominated by sand transported as bedload. The channel banks are stabilised by vegetation, which effectively prevents their lateral migration.

Bedrock gorge incision via anthropogenic meander cutoff

Abstract Bedrock river-gorge incision represents a fundamental landscape-shaping process, but a dearth of observational data at >10 yr timescales impedes understanding of gorge formation. I quantify 102 yr rates and processes of gorge incision using historical records, field observations, and topographic and image analysis of a human-caused bedrock meander cutoff along the North Fork Fortymile River in Alaska (USA). Miners cut off the meander in 1900 CE, abruptly lowering local base level by 6 m and forcing narrowing and steepening of the channel across a knickpoint that rapidly incised upstream. Tectonic quiescence, consistent rock erosivity, and low millennial erosion rates provide ideal boundary conditions for this 102 yr gorge-formation experiment. Initial fast knickpoint propagation (23 m/yr; 1900–1903 CE) slowed (4 m/yr; 1903–1981 CE) to diffusion (1981–2019 CE) as knickpoint slope decreased, yielding an ~350-m-long, 6-m-deep gorge within the pre–1900 CE channel. Today, diffusion dominates incision of a 500-m-long knickzone upstream of the gorge, where sediment transport likely limits ongoing adjustments to the anthropogenic cutoff. Results elucidate channel width, slope, discharge, and sediment dynamics consistent with a gradual transition from detachment- to transport-limited incision in fluvial adjustment to local base-level lowering.

Damp- to dry aeolian systems: Sedimentology, climate forcing, and aeolian accumulation in the Late Cretaceous Liyou Basin, South China

Aeolian desert systems were widely distributed in South China during the Late Cretaceous. These systems developed under the control of subtropical highs and a monsoon climate. They reveal the evolution of palaeoclimate and palaeogeography and the regional palaeowind pattern in the South China interior during this period. Based on the analyses of sedimentology and facies architecture, this study examines and reassesses the aeolian succession of the Upper Cretaceous Daijiaping Formation in the southern Liyou Basin of southeast China. This aeolian desert succession records aeolian dune, dry and damp interdune and aeolian sandsheet sedimentation in streamflow, fluvial channel and overbank settings. Aeolian dune deposits comprise low-angle dune plinth strata and superimposed sets of cross-strata bounded by a hierarchy of bounding surfaces. The deposits record two morphological types of compound crescentic dunes and complex linear dunes. Palaeowind direction in the Liyou desert agrees with the subtropical high-pressure westerly and northeasterly wind pattern that existed in the mid to low latitudes of the Northern Hemisphere, in conjunction with possible monsoon climate conditions during the Late Cretaceous. The fault-bounded basin in which the succession accumulated experienced a high subsidence rate and a high supply and availability of windblown sand, which ensured hundreds of metres of thick accumulation of the dune field system. The occurrence of a near-surface water table and soft-sediment deformation in the aeolian dune foresets indicates that the monsoon rains could have recharged the groundwater system and resulted in episodes of relative water-table rise, which played an important role in the accumulation and preservation of aeolian systems in the Liyou desert basin. Gradual and progressive subsidence of the aeolian succession combined with water-table fluctuations allowed the preservation of the aeolian accumulation system.

Dilution of PAHs loadings of particulate matter in air, dust and rivers in urban areas: A comparative study (Tehran megacity, Iran and city of Tübingen, SW-Germany)

PAHs (polycyclic aromatic hydrocarbons) in urban areas are usually bound to particles. Concentrations are different in different compartments (airborne particles, street dust, suspended sediments in rivers and channels). This study follows concentrations of PAHs from particles in air to street dust and finally suspended sediments in the city of Tehran, Iran compared to Tübingen, Germany. Data sets are based on own investigations (PAHs on suspended sediments), or taken from literature studies (PAHs in street dust and airborne particles). Based on a cross-comparison of concentrations of PAHs on particles, and their congener distribution patterns, the occurrence, interrelation (exchange and mixing processes), as well as possible dilution processes among PAHs in the different particle classes are disentangled. Results show that for Tehran and Tübingen PAHs in airborne particles are very high (in the range of 500 mg kg−1). However, in street dust and suspended sediments PAHs concentrations on particles are around 100 times lower. Surprisingly concentrations in street dust and suspended sediments are 5 to 10 times lower in Tehran (average 0.5 mg kg−1) than in Tübingen (average 5 mg kg−1). Since it is unlikely that PAHs emissions are lower in the Tehran megacity, an effective dilution of the atmospheric signal by uncontaminated (background) particles is hypothesized. Uncontaminated particles may stem from wind erosion of bare surfaces, construction and sand mining sites or even dust from the desert areas, which are frequent in arid climate in Tehran.

Sediment transport modeling in non-deposition with clean bed condition using different tree-based algorithms.

To reduce the problem of sedimentation in open channels, calculating flow velocity is critical. Undesirable operating costs arise due to sedimentation problems. To overcome these problems, the development of machine learning based models may provide reliable results. Recently, numerous studies have been conducted to model sediment transport in non-deposition condition however, the main deficiency of the existing studies is utilization of a limited range of data in model development. To tackle this drawback, six data sets with wide ranges of pipe size, volumetric sediment concentration, channel bed slope, sediment size and flow depth are used for the model development in this study. Moreover, two tree-based algorithms, namely M5 rule tree (M5RT) and M5 regression tree (M5RGT) are implemented, and results are compared to the traditional regression equations available in the literature. The results show that machine learning approaches outperform traditional regression models. The tree-based algorithms, M5RT and M5RGT, provided satisfactory results in contrast to their regression-based alternatives with RMSE = 1.184 and RMSE = 1.071, respectively. In order to recommend a practical solution, the tree structure algorithms are supplied to compute sediment transport in an open channel flow.

Expansion of woody vegetation on a Missouri River reservoir delta‐backwater

AbstractConstruction of dams in the mid‐20th century reduced channel dynamism, sediment transport, and regeneration of riparian trees on the Missouri River. Opportunities for forest regeneration, however, may occur where the Missouri River or tributaries deposit sediments in reservoir headwaters, forming deltaic and associated upstream backwater areas. One such delta‐backwater occurs at the confluence of the Niobrara and Missouri rivers upstream from Lewis and Clark Lake in southeastern South Dakota and northeastern Nebraska. We investigated spatiotemporal patterns of tree recruitment through vegetation sampling in 2017–2018, dendrochronology, and analysis of aerial photography from 2006 to 2016. We sampled woody vegetation in 47 plots and took tree‐ring samples from one to two trees within each plot to determine establishment dates. Woody vegetation was dominated by Populus deltoides (cottonwood) and Salix amygdaloides (peachleaf willow) in the tree layer and Salix interior (sandbar willow) in the shrub layer. Tree establishment occurred primarily in 2010–2012 and was distributed throughout the study area, including at the delta‐reservoir interface. LiDAR data showed that most of the delta‐backwater experienced a 0.5‐m increase in elevation in 2005–2011, a period that included high flows in 2010 on the Niobrara River and 2011 on the Missouri River. Woody vegetation decreased 8% from 2006 to 2012, but doubled from 2012 to 2016, colonizing areas of previous sandbar and herbaceous vegetation. These woodlands represent early successional habitat that is in decline elsewhere along the river. Understanding vegetation dynamics within reservoir delta‐backwaters may be vital for forecasting changes in regulated riverine landscapes, assessing biodiversity values of these ecosystems, and informing sustainable reservoir management.

River sediment geochemistry and provenance following the Mount Polley mine tailings spill, Canada: The role of hydraulic sorting and sediment dilution processes in contaminant dispersal and remediation

The failure of the Mount Polley tailings storage facility (TSF) in August 2014 was one of the largest magnitude failures on record, and released approximately 25 Mm3 of material, including c. 7.3 Mm3 of tailings into Hazeltine Creek, part of the Quesnel River watershed. This study evaluates the impact of the spill on the geochemistry of river channel and floodplain sediments and utilizes Pb isotope ratios and a multi-variate mixing model to establish sediment provenance. In comparison to sediment quality guidelines and background concentrations, Cu and V were found to be most elevated. Copper in river channel sediments ranged from 88 to 800 mg kg−1, with concentrations in sand-rich and clay/silt-rich sediments being statistically significantly different. Concentrations in river channel were believed to be influenced by hydraulic sorting during the rising and falling limbs of the flood wave caused by the tailings spill. Results highlight the importance of erosive processes, instigated by the failure, in incorporating soils and sediments into the sediment load transported and deposited within Hazeltine Creek. In this instance, these processes diluted tailings with relatively clean material that reduced metal concentrations away from the TSF failure. This does however, highlight environmental risks in similar catchments downstream of TSFs that contain metal-rich sediment within river channels and floodplain that have been contaminated by historical mining.

Impact of anthropogenic activities on morphological and deposition flux changes in the Pearl River Estuary, China

The evolution of the Pearl River Estuary (PRE), China in recent decades has been dominated by human activities. Historical admiralty charts and remote sensing images indicated that from 1936 to 2017, the tidal flat area and water area decreased by 23.6 × 107 m2 and 60.7 × 107 m2, respectively. The average advancing rate of the coastline of the PRE to the sea from 1972 to 2017 reached approximately 64.8 m/year, which is several times or even dozens of times that since the mid-Holocene. Land reclamation was the main reason for the dramatic changes in the water area and coastline. Although the water volume of the PRE showed a decreasing trend from 1936 to 2017, the water volume reduction rates for 1996–2005 and 2005–2017 were only 29% (1.27 × 107 m3/year) and 12% (0.53 × 107 m3/year), respectively, of that for 1936–1972. The combined influences of channel dredging, sand mining, and sediment load reduction caused by dam construction have contributed to this change. From the perspective of the filling up of the estuary, channel dredging, sand mining, and dam construction in the river basin are beneficial for prolonging the life of the estuary.

Coarse sediment supply sets the slope of bedrock channels in rapidly uplifting terrain: Field and topographic evidence from eastern Taiwan

AbstractThe incision rate and steepness of bedrock channels depend on water discharge, uplift rate, substrate lithology, sediment flux, and bedload size. However, the relative role of these factors and the sensitivity of channel steepness to rapid (>1 mm yr−1) uplift rates remain unclear. We conducted field and topographic analyses of fluvial bedrock channels with varying channel bed lithology and sediment source rock along the Coastal Range in eastern Taiwan, where uplift rates vary from 1.8 to 11.8 mm yr−1 and precipitation is relatively consistent (1.5–2.7 m yr−1), to evaluate the controls on bedrock channel steepness. We find that channel steepness is independent of rock uplift rate and annual precipitation but increases monotonically with sediment size and substrate strength. Furthermore, in reaches with uniform substrate lithology (mudstone and flysch), channel steepness systematically varies with sediment source rock but not with channel width. When applied to our data, a mechanistic incision model (saltation‐abrasion model) suggests that the steepness of Coastal Range channels is set primarily by coarse‐sediment supply. We also observe that larger particles are mainly composed of resistant lithologies derived from volcanic rocks and conglomerates. This result implies that hillslope bedrock properties in the source area exert a dominant control on the steepness of proximal channels through coarse‐sediment production in this setting. We propose that channel steepness may be insensitive to uplift rate and flow discharge in fast‐uplifting landscapes where incision processes are set by coarse sediment size and supply. Models assuming a proportionality between incision rate and basal shear stress (stream power) may not fully capture controls on fluvial channel profiles in landslide‐dominated landscapes. Processes other than channel steepening, such as enhanced bedload impacts and debris‐flow scour, may be required to balance rock uplift and incision in these transport‐limited systems.

Morphodynamics of an erodible channel under varying discharge

AbstractAlluvial channels arise through the interaction between morphology, hydraulics, and sediment transport, known as the ‘fluvial trinity’. Over relatively short timescales where climate and geology are fixed but discharge and sediment supply may vary, this process facilitates adjustments towards steady state, where the system oscillates around a mean condition. The relationship between changes in conditions and geomorphic response may be highly complex and nonlinear, especially in systems with multiple modes of adjustment. This study examines the adjustment of an erodible channel with fixed banks and a widely graded sediment mixture to successive increases in discharge. With each increase in discharge, components of the fluvial trinity adjusted towards a steady state. Particularly at relatively low discharges, adjustments were controlled by intrinsic thresholds and highlighted important morphodynamic processes. Notably, there was a strong interplay between channel morphology and sediment transport, and an effect whereby larger‐than‐average grains controlled channel deformation. These two processes occurred at the bar scale and were highly spatialised, which has two important implications: (1) reach‐averaged representations of process provide only partial insight into morphodynamics; and (2) models of rivers that suppress these process feedbacks and size‐dependent transport may not replicate morphodynamics that typically occur in field conditions. The experiments provide quantitative evidence for conceptual models describing exponential approaches towards steady state and the potential for transiency if disturbance frequency exceeds the recovery time. They also highlight how in natural rivers, particularly those with greater degrees of freedom for adjustment (notably, lateral adjustment and meandering), continuous changes in discharge may lead to nonlinear rather than steady‐state behaviour. In these settings, more holistic analytical frameworks that embrace different aspects of the system are critical in understanding the direction, magnitude and timing of channel adjustments.

Pemanfaatan Sedimen Sungai Untuk Bahan Baku Unfired Bricks (Bata Tanpa Bakar)

The land use change in a watershed cause erosion resulting in sedimentation in river channels. Physically treatment of sedimentation requires a considerable cost, hence it is necessary to find another alternative treatment, i.e. by utilizing river sediment for building materials. Brick is a building material that is widely produced and used by the society. To provide solutions for sediment reduction, it is necessary to do a research on the utilization of river sediment for brick raw materials. In this study, the utilization of sediment into bricks was proposed in the form of Unfired Bricks. Raw sediment material will be mixed with cement and sand with a certain composition to increase the compression strength of brick in order to meet one of the SNI requirements, i.e. 15-2094-2000 or SNI 03-0349-1989. Results found that the addition of cement and sand treatment can increase the compressive strength of the brick up to 44,176 kg/cm² at the age of 14 days. However, the compression strength test results are still below the compression strength of Red Brick requirements in accordance with SNI 15-2094-2000 where the minimum compression strength of brick is 50 kg /cm², but it qualify for the compression Strength Concrete Brick SNI 03-0349-1989 for the quality level of grade III with a minimum of 40 kg / cm² and grade IV with a minimum of 25 kg / cm²

Alteration of gravel-bed river morphodynamics in response to multiple anthropogenic disturbances: Insights from the sediment-starved Parma River (northern Italy)

The alteration of sediment transport regime represents one of the key factors controlling the response of fluvial systems to human impacts. Additional research efforts are required to define sound cause-effect relationships between the human pressures and the morphodynamic responses of sediment-starved gravel-bed rivers. This work deals with the evolution of the Parma River, a large Italian gravel-bed river affected over the last 160 year by multiple anthropogenic disturbances (i.e., land-use changes, in-channel mining and, more recently, the construction of a detention basin), which strongly limited the sediment availability to the high-plain portion of its course. The data collected allowed us to reconstruct the history of the impacts, the river morphological evolutionary trajectory, the sedimentological characteristics of the bed, and to estimate, leveraging a morphological approach, the variation in coarse sediment regime over the most recent period. After the cessation of intense in-channel mining in 1990s, the study sector located upstream from the detention basin shifted from a degrading (i.e., narrowing and incising) to a recovery phase, characterized by a mean coarse transport of 15,000–31,000 m3yr−1. These results demonstrate that the in-channel mining was the most impactful historical pressure acting on the river, and that a channel preserving some natural characteristics and passing from a condition of sediment-starvation to one of increasing sediment availability can recover an active morphodynamics within a short time period. The downstream sector was greatly affected by the reduction of sediment transfer that occurred in the 2000s caused by the construction of a detention basin. Its degradation continued over the most recent period and the coarse transport is currently very low (up to about 3000 m3yr−1 4 km downstream from the basin). This sector is characterized at the present by a morphodynamics defined as “slack”, a condition induced by the complete evacuation of the mobile channel sediments, leading to extremely low bed material mobility and transport, and, consequently, to morphological degradation up to the achievement of a new quasi-equilibrium. We hypothesized that such an extreme state of alteration is relatively limited in space, affecting a gravel-bed river only at the reach scale in response to multiple overlapped impacts or because of an extremely severe perturbation (i.e., reduction) of the sediment availability and dynamics.

Water Management Evaluation for Upgrading Tidal Irrigation System, Katingan, Kalimantan

Due to channel sedimentation, water deficits and flood still becomes problems in Katingan tidal irrigation system, while the stakeholder plans to reclaim new area in the presence of pyrite soil. This research aims to overcome these problems through four water management scenarios simulated using HEC-RAS to meet the needs of water supply, flushing and drainage. The result shows that water leaching requirement for existing area is 2.48 million m3 and could only be fulfilled by canal normalization. Moreover, extended network with narrow intake canal supplies less than 4.3 million m3 water leaching, so that wide canal connected to the river is required to facilitate more water flowing into the system. Related to flushing, installing pumps in the middle intake could increase canal circulation with one-way outflow during ebb tide, while the inflow depends on flap gates at the same position. Furthermore, the volume of rainwater is generally able to be discharged for every rainy day by all scenario designs. However, existing condition and network expansion with narrow intake canal have less rainwater deficit duration. In conclusion, leaching and drainage aspects require more water storage and wide canal intake, where flushing criterion need the use of pumps and gates.

Lake-islands: A distinct morphology of river systems

Islands are important morphologies in multichannel fluvial systems for maintaining secondary channels, increasing flow efficiency in the widest stretches, and hosting important ecological environments. This study presents a hitherto unclassified, distinct type of fluvial island that occurs in large rivers: the lake-island. We analyzed islands from large rivers, particularly from South American rivers, the Negro (Amazon Basin) and Paraná (La Plata Basin) Rivers. Satellite images were used for identification and morphometric analysis, while morphometric indices were used to compare island morphologies. Sedimentary facies analysis and dating were also conducted to characterize the island deposits. Lake-islands are differentiated from typical fluvial islands by their lenticular morphology, and frontal and lateral levees that protect and isolate the lake or allow it to be partially connected to the channel. Lake-island morphology can be elongated or circular, based on their morphometric indices and their relationship with channel width. Lake-island lengths varied from hundreds of meters to tens of kilometers. They are formed by in-channel deposition on preexisting sand bars or fluvial islands. Their sedimentary characteristics are relatively simple and comprise basal sandy facies capped by finer-grained deposits. The permanence of lake-islands depends on the flow regime and sedimentary load of the fluvial system. The lake-island's age ranges from 101 to 103 years. A comprehensive understanding of the formation processes and dynamics of lake-islands is of fundamental importance in the management of large fluvial systems, and studies of fluvial ecology.

Analysis of lead (Pb) levels in water, sediment and mollusks in secondary irrigation channels in Gorontalo Province, Indonesia

Abstract. Tahir IA, Lamondo D, Baderan DWK. 2020. Analysis of lead (Pb) levels in water, sediment and mollusks in secondary irrigation channels in Gorontalo Province, Indonesia. Intl J Bonorowo Wetl 11: 1-6. This study was conducted in July-August 2020 in the secondary irrigation channels of Gorontalo Province, aimed to determine the lead content in the water, sediment and gastropods in the channels. The sampling points were located in four sub-districts, i.e., North Bulango Sub-district, Sipatana Sub-district, Central City Sub-district and Hulonthalangi Sub-district. The samples were analyzed using Atomic Absorption Spectrophotometer (AAS). The data were analyzed qualitatively by comparing them with the contamination thresholds set by the government of Indonesia. The results showed that the levels of lead in water in the four stations were 0.37 mg/L, 1.30 mg/L, 1.69 mg/L and 0.38 mg/L, respectively, in the sediment 1.1268 ppm, 0.9719 ppm, 0.7602 ppm, and 0.5290 ppm, respectively, and in each mollusk species, i.e., Bellamnya sp. 0.2924 mg/kg, Pomacea canaliculata 0.2413 mg/kg and Pomacea canaliculata 0.1873 mg/kg. The lead levels in the water, sediment and gastropods in the study sites exceeded the contamination thresholds set by the Indonesian government.

Nitrogen/phosphorus behavior traits and implications during storm events in a semi-arid mountainous watershed

Seasonal rainfall events reinforce the link between terrestrial and fluvial domains and are crucial for assessing hydrological control over riverine nutrient dynamics and pollutant source behaviors, especially in a semi-arid watershed. Taking the Qingshuihe river basin, a semi-arid mountainous basin in China, as an example, this paper investigated storm effects on riverine nitrogen (N) and phosphorus (P) dynamics (i.e. concentration, load, and composition changes) through continuous sampling of four storm events of the 2019 rainy season, including one small storm, two moderate storms, and a large storm. Pollutant sources and transport pathways were then examined over the storm sequence via hysteresis analysis. The results revealed a strong linkage between N/P dynamics and hydrological processes. Storm runoff caused a 6-fold increase in particulate-P (PP) and a 4-fold increase in ammonia-N (NH4-N) fluxes through four storms (most sensitive nutrients to storms). On average, PP shared 86% of P exports, and nitrate-N (NO3-N) contributed 79% of N exports. PP and NH4-N were delivered primarily from overland sources and transported by surface runoff. Nonetheless, mobilization of channel sediment reserves was also an important way of PP supply during storms. The results suggested groundwater as the principal NO3-N source in the watershed, and subsurface flow was important for NO3-N and total dissolved-P (TDP) delivery during storms. The large storm (>20 mm) often registered the highest N/P load exports. However, there were other influencing factors/processes on stormflow N/P dynamics in the semi-arid watershed, which complicate/override the effects of different storm magnitudes. Total suspended solids (TSS)/PP source availability and inter- and intra-storm export trends influenced P behaviors through storms. Moreover, impacts of mobilization processes on NO3-N behavior appeared over the storm sequence. These findings enhance our understanding of storm events induced N/P exports in water-scarce regions and provide references for water quality predictions and control in flood seasons.

Metals bioavailability and toxicity in sediments of the main channel and subchannel of a tropical (Mandovi) estuary, Goa, India

Metals bioavailability and toxicity in sediments of the main channel and subchannel of a tropical (Mandovi) estuary, Goa, India

Habitat changes in the most important stopover sites for the endangered red-crowned crane in China: a large-scale study.

The red-crowned crane (Grus japonensis) is an endangered bird species that has been listed as one of the Class I National Key Protected Wild Animals of China. This study analyzed the habitat changes in the two most important stopover sites for red-crowned crane (Liao River Estuary and Yellow River Delta National Nature Reserves) from 2000 to 2015. The results showed that the landscape patterns of the important stopover sites of red-crowned crane changed obviously and the potential suitable habitat area (tidal flats and marshland) for the red-crowned crane decreased by 183.3 km2, while the area of human activities (including aquaculture waterbodies, farmland and artificial facilities) increased by 140.3 km2. Landscape fragmentation intensified, which could has negative impacts on the survival of the red-crowned crane during migration. A comparative study confirmed that the reduction in marshlands and increasing landscape fragmentation caused by human activities were the main threats in the Liao River Estuary National Nature Reserve, while human activities and natural factors (such as channel flow, rainfall, and sediment discharge) were the jointly driving factors for the reduction in suitable habitats for red-crowned cranes in the Yellow River Delta National Nature Reserve. We suggest there are some loopholes in the management of the two nature reserves, which need to be strengthened urgently in China.

The Effect of Phragmites australis Dieback on Channel Sedimentation in the Mississippi River Delta: A Conceptual Modeling Study

Phragmites australis is a globally distributed wetland plant. At the mouth of the Mississippi River, P. australis on natural levees of the network of distributary channels appears to increase the flow in the deep draft navigation channel, which, in turn, may reduce the sedimentation and benefit the navigation dredging. For several years, P. australis has been dying in the Mississippi River’s Bird’s Foot Delta, which appears to be shortening the distributary channels and increasing the lateral flow from the remaining portions. A conceptual model based on D-FLOW FM was applied to calculate channel sedimentation in a series of idealized deltaic systems to predict the consequences of P. australis dieback and other factors that diminish the delta complexity, such as sea-level rise and subsidence, on sedimentation in the distributary channels. Channel complexity in each system, which was quantified with an index ranging from 0 to 10 that we developed. Model results indicate that sedimentation was insensitive to the channel complexity in simple deltas but was sensitive to the channel complexity in complex deltas, such as the current Mississippi River Delta with extensive P. australis. Channel sedimentation remains stable from 0 until the channel complexity index reaches 6. In more complex deltas, the sedimentation decreases rapidly as the channel complexity increases. The sedimentation is also affected by waves, river discharge, sediment concentration, grain sizes, and bed level. River managers in Louisiana may benefit from new models based on bathymetric data throughout the Bird’s Foot Delta; data on the effects of the P. australis belowground biomass on bank erodibility across a range of current velocities; and data on the effects of P. australis stem density, diameter, and height on the lateral flow across a range of river stages and tidal stages to help them decide how much to respond to Phragmites dieback. Options include increased navigation dredging, increased restoration of the channel complexity via a thin layer of sediment deposition on natural levees and the planting of more salt-tolerant vegetation on natural levees.