Riverbed Research Articles

The effect of compound channel shape for local scouring and flow dynamics using NaysCUBE-3D RANS at Downstream Tukad Unda River Bali Province

The prediction of sediment transport and flow dynamics are important issues in channel design as the local scouring has an important effect on the shape of the channel, especially on the compound channel. Tukad Unda River in Bali has river section in the form of compound channel. It consists of two sections with different dimension, the main channel and the flood plain. These dimensional differences cause two different flows. Transformation of flow velocity and turbulence cause movement of sediment transport, generates a complex 3D flow structure in the boundary of main channel and floodplain. This study uses morphology data in Tukad Unda River and simulated by using NaysCUBE. NaysCUBE is a three-dimensional numerical modeling which use the Reynold Average Navier Stoke equation (3D RANS model). The result in this study shows the different pattern of flow dynamics and local scouring in the boundary between main channel and floodplain as the concrete block located in that boundary compare to the nature compound channel. In the 40-minute simulation, the nature compound channel represented significant deformation of the river bed in the interface area, with a decrease in elevation of 0.01 meters higher than the compound channel with concrete blocks. while the increase in elevation in the main channel is around 0.09 meters lower than the compound channel with concrete blocks. Application of concrete blocks can be useful to reduce local scour at the interface as the impact of compound channel flow characteristics.

Influence of Sediment Supply Timing on Bedload Transport and Bed Surface Texture During a Single Experimental Hydrograph in Gravel Bed Rivers

AbstractChannel stability and sediment transport in gravel bed streams depend on temporally and spatially variable fluid forces, bed surface structures, armoring, and sediment supply/storage. Of particular interest here is the influence of sediment supply timing on bedload transport rate and grain size distribution, bed surface composition and channel morphology. We conducted flume experiments in a sediment feed flume with poorly sorted sediment. A symmetrical, identical stepped hydrograph was used with five different sediment feeding schemes: no feed, constant feed, rising‐limb only feed, falling‐limb only feed, and variable feed. The same sediment mass of 800 kg was fed during each experiment. Sediment transport rates ranged over five orders of magnitude regardless of feeding scheme. Clockwise hysteresis was observed for bedload transport rate and bedload grain size, that is, the transport rate was larger and coarser during the rising limb. Counterclockwise hysteresis was observed for the grain size distribution of the bed surface, that is, the bed surface was finest during the rising limb. In all experiments sediment yield during the rising was higher than during the falling limb, indicating that the rising limb is more capable to transport the supplied sediment. Our study provides insight on how timing of sediment supply influences sediment transport and bed surface during a single hydrograph, essential information for artificial sediment supply projects to restore and habilitate gravel bed streams.

Changes and transport of microplastics in the riverbed of the mainstream below the Three Gorges Dam of the Yangtze River

The Yangtze River has always been considered an important river for transporting microplastics into the sea. However, there is still a lack of understanding of the degree of microplastic pollution in the sediment of the middle and lower reaches of the Yangtze River, which has affected the estimation of microplastic flux into the sea. In this study, microplastics in sediments from 55 stations in the middle and lower reaches of the Yangtze River were investigated, including 48 mainstream stations, 5 confluence stations, and 2 lake stations. Microplastics were detected in 34 stations, ranging from 0 to 71.04 n/kg of dry weight. The average concentrations of microplastics in the mainstream, confluence and lake were 6.16 ± 8.87, 23.91 ± 11.2, and 43.95 ± 27.09n/kg of dry weight, respectively. Of all the microplastics found in this investigation, fiber (59.52 %) forms the main type in terms of shape; PET is the most abundant microplastic species, accounting for 51.19 %. Sewage treatment plants are the most likely source of microplastics in sediment, and sediment from tributary estuaries, lake mouths, and lakes is an important sink of microplastics. Terrain, sediment transport load, biofilm, and flow velocity are important factors affecting microplastic settlement. Although there are multiple microplastic enrichment areas, the high flow velocity during the flood season makes it difficult for microplastics to remain in the sediment of the Yangtze River bed. This indicates that microplastics in riverbed sediments have little influence on the flux into the sea during flood season. This study is the first large-scale investigation of microplastics in riverbed sediments in the Yangtze river basin.

PERBANDINGAN ELEVASI DASAR SUNGAI BERDASARKAN HASIL ANALISIS PADA DEM DRONE, DEMNAS dan DEM SRTM

Digital elevation models (DEMs) are essential to accurately predict river cross-section in the watershed. Technological developments of unmanned aerial vehicles (UAVs) or drone has received a lot of attention in various research field to get the latest information from the area, because of its mobility, high resolution, and low cost, so it can be a competitive alternative to produce maps with precise georeferences. However, this has not been tested so far. In this study, We evaluated the accuracy of the DEMs generated from UAV imagery by comparing it to DEMNAS, DEM SRTM, and direct topographic measurements. We performed regression analysis on the river bed elevation of the Kuranji River Padang, where the river bed elevation is the result of the analysis of each DEM. The result found that for river bed elevation of the DEM Drone performed competitively to DEMNAS with the correlation test value (r) were 0,992 and 0.954, respectively. The result of the DEM SRTM analysis has a wider range of data variations than the DEM Drone and DEMNAS.

Assessment of Turbulent Kinetic Energy Balance within the Boulder Array in Gravel Bed Stream

Assessment of Turbulent Kinetic Energy Balance within the Boulder Array in Gravel Bed Stream

Heat transfer model for moving packed-bed particle-to-sCO2 heat exchangers integrated with metal foams

Particle-to-supercritical carbon dioxide (sCO2) heat exchangers (HXs) play a vital role in coupling heat transfer fluid (HTF) from high-temperature thermal receivers to power cycle working fluids (WF). Heat transfer enhancement is essential for adopting particle-based moving packed-bed heat exchangers (MPBHXs) in next-generation thermal energy storage (TES) systems, as MPBHXs usually exhibit low particle bed-to-wall heat transfer coefficients. High-porosity metal foams have shown their effectiveness in heat transfer enhancement. This work presents a continuum heat transfer model to demonstrate the heat transfer enhancement in MPBHXs when the particle bed channel is filled with high porosity metal foams compared to open channel MPBHXs. The presence of metal foams increases the effective thermal conductivity in the particle channel and enhances the interstitial heat transfer coefficient between the moving particle bed and the stationary metal foams. The present model considers coupled two-dimensional (2D) heat transfer in the particle channel with metal foams and 1D heat transfer in the sCO2 channel and the dividing wall. The temperature profiles for the particle bed, metal foam, dividing wall, and sCO2 stream, as well as the local heat flux profiles between those, are studied in detail for various foam porosities, from which the particle bed-to-wall heat transfer coefficient, overall heat transfer coefficient, and total heat transfer rate for the MPBHX are determined. The effects of major MPBHX design and operating parameters on the particle bed-to-wall heat transfer coefficient and overall heat exchange capacity are thoroughly examined; thus, the MPBHX performance improvement with metal foams is quantified for each case. The present heat transfer model can provide valuable insights into the metal-foam MPBHX design and optimization, scale-up, and operating parameters selection.

The role of the in-plane solidity on canopy flows

Turbulent open channel flows developing above submerged canopies made of slender cylinders mounted perpendicular to the channel bed are known to be largely governed by the solidity parameter$\lambda =dh/\Delta S^2$($d$and$h$being the diameter and height of the filament, and$\Delta S$the average spacing between filaments). When the filaments are sufficiently slender, the ratio between the height of the stems and the spacing sets the hydrodynamic regime developing inside and outside the canopy. This ratio also establishes the conditions leading to the transition from a dense to a sparse canopy flow regime (Nepf,Annu. Rev. Fluid Mech., vol. 44, 2012, pp. 123–142). In a previous, companion numerical investigation, Montiet al.(J. Fluid Mech., vol. 891, 2020, A9) used large eddy simulation (LES) to study the influence of the canopy height on the onset of the different regimes without modifying the average spacing$\Delta S$between the stems. In that LES study, we were looking at the complementary situation in which the height of the stems is constant while the filaments’ number density of the canopy is changed. It was found that for low values of$\lambda$(i.e. sparse or moderately dense canopies:$\lambda \lessapprox 0.26$), the flows sharing the value of the solidity obtained by either varying$h$or$\Delta S$are very similar. Differently, for higher values of$\lambda$(i.e. in denser canopies), the effects of$h$and$\Delta S$start to diverge although sharing the same nominal value of$\lambda$. In this paper, we analyse the different physical mechanisms that come into play for dense configurations obtained by varying either$\Delta S$or$h$. In particular, we focus on the most relevant length scales and carry out a detailed analysis of the flows using a triple decomposition approach. We show that the inner region of dense canopy flows, characterised by tall stems, is dominated by wall-normal sweeps delivering high momentum in the wall vicinity. Here, the impenetrability condition of the bed redistributes the available momentum in the wall-parallel directions re-energising an otherwise stagnating flow. Differently, in densely packed canopies, the penetration of the outer jet and the momentum transfer from the external flow are limited by the decreasing value of the wall-parallel permeabilities leading to different behaviours, including a reduction of the total drag offered by the canopy.

Assessing the threats of small lowland reservoirs under climate change on the example of Supraśl Water System (NE Poland)

The Supraśl River is a stable water ecosystem in North-Eastern Poland. This is indicated by the flow rate over many years, as well as the water quality monitored for years. Despite this, there are periods of oxygen deficiency in the water, causing massive fish kills. Our research shows that climate change resulting in an increase in the frequency of hydro-meteorological extremes may contribute to negative processes taking place in aquatic ecosystems. On the example of Supraśl Water System (SWS), we present an analysis of the phenomenon of suspension caused by the underground inflow, supplying the surface waters with a significant load of organic matter. The accelerated decomposition of peat formations in the Supraśl River catchment after heavy rains makes it easier for organic matter to penetrate into the aquatic ecosystem. Intensive flushing of valley and river bed sediments during summer floods has a particularly negative impact on the ecosystem of inland waters. If there are organic sediments on the bottom, their re-suspension is very dangerous. Then there is the immediate demand for oxygen, which can lead to deoxygenation of the water. Although this is a natural process, alarm and monitoring procedures should be established and countermeasures sought to respond in time and prevent mass fish kills.

Flow structure of the confluence between an open channel and a pipe.

It is common that the sewage is discharged into rivers through a municipal drainage network. The hydraulic properties of the confluence between a lateral drainage pipe and a rectangular open channel are investigated using numerical simulation. The simulation results show that the recirculation zone, the separation area, and the secondary flow are highly influenced by the tailgate height and flow rate ratios. Both the recirculation zone and the separation zone enlarge with the increasing flow rate ratios. The recirculation zone also enlarges with the tailgate height within a certain range. It is worth noting that as the tailgate height increases, two vortices rotating in opposite directions at the same level initially merge into a counter-clockwise rotating vortex, and then one vortex splits into three. Ultimately, one of them dissipates and there are two vortices left on a vertical line. The tailgate can reduce the vertical velocity gradient and the streamwise velocity to moderate the erosion of the channel bed caused by the pipe flow inlet.

Fungal symbionts impact cyanobacterial biofilm durability and photosynthetic efficiency

Cyanobacteria contribute to over 25% of the world's net primary photosynthetic production and are pivotal in mitigating greenhouse gas emissions.1 This study unveils a previously unobserved symbiotic relationship between benthic cyanobacteria and fungi that have also adapted to life as a plant endophyte. The interaction suggests an initial phase of lichenization. We isolated Leptolyngbya frigida from the Naracauli stream, which emanates from abandoned Zn industrial waste in Sardinia. Seasonally, L.frigida participates in a biomineralization processes, mitigating the Zn transfer to rivers and, subsequently, the sea.2,3,4L.frigida is a benthic cyanobacterium that establishes a biofilm on the stream bed. Notably, the area predominantly features Juncus acutus. From these roots, endophytic fungi were predominantly isolated as Clonostachys rosea, a fungus recognized for its biocontrol capabilities against plant pathogens. An intriguing observation was made when L.frigida was cultured with C.rosea on a low-carbohydrate agar medium: the fungal mycelium transformed into wall-less forms, a phenomenon not documented previously. In liquid environments, the resulting biofilm first settled at the container's bottom. Even upon rising to the surface, this biofilm remained pigment rich. Concurrently, a secondary biofilm began its formation at the bottom. These fungal-integrated biofilms displayed enhanced resilience and superior photosynthetic performance compared to those without fungal presence. Moreover, the symbiotic relationship significantly amplified O2 emission and CO2 sequestration by the biofilm.

Evaluation of different machine learning algorithms for LULC classification in heterogeneous landscape by using remote sensing and GIS techniques

Remote sensing land cover classification plays a crucial role in detecting changes, urbanization planning, mapping and monitoring land cover on earth surface. It is very challenging to get accurate result in remote sensing data because different classifiers are very much area dependent. Different classifiers such as decision tree (DT), K-nearest neighbor (KNN), artificial neural network (ANN), support vector machine (SVM), boosted decision tree (BDT), random forest (RF), classification and regression tree (CART) and maximum likelihood classifiers (MLC), have different accuracies for the same classes. Several studies have utilized remote sensing and GIS tools to investigate changes in land use and land cover (LULC) using different classifiers. Seasonal rivers which should be classified as water bodies are mostly classified as urban area with the conventional land cover classification schemes because spectral reflectance of these river bodies is similar to urban area due to stones present in their river bed. It is very difficult to distinguish between these river beds (which are mostly found in various districts of Uttarakhand, India) and urban area in remote sensing images. In this paper, we present a new method to distinguish these river beds with the urban area and to separate other classes easily. First of all different spectral indices such as NDVI, NDBI, EVI and MNDWI are extracted from a high resolution Sentinel-2 MSI image then these indices are integrated with Sentinel-2 MSI image for classification of different land cover classes by using four different machine learning classifiers such as RF, SVM, DT and CART. The obtained results confirm the performance strength of the suggested method as there is much improvement in accuracy.

Microplastics attenuation from surface water to drinking water: Impact of treatment and managed aquifer recharge – and identification uncertainties

River water can be used to recharge aquifers exploited for drinking water production. Several recent studies reported microplastics (MPs) in river water, and therefore, the potential contamination of groundwater by MPs is a growing concern among stakeholders and citizens. In this research, we investigate the fate of MPs (> 20 μm) along six different stages of a major Managed Aquifer Recharge (MAR)-water supply system in Switzerland. About 20 l of water were filtered using steel meshes at each location in triplicates. In the laboratory, MPs deposited on the anodisc filters were identified using Focal Plane Array (FPA) micro-Fourier-Transform-InfraRed (μFTIR) spectroscopy. The obtained hyperspectral data were processed using the imaging software Microplastics Finder for MPs identification and classification. Our results revealed a 20-fold decrease in MPs concentration from the Rhine River bed water (112 ± 27.4 MPs/l) to after the coagulation, flocculation and sedimentation (5.5 ± 2.2 MPs/l), a further 3-fold decrease to after the sand-filtration system (1.8 ± 0.9 MPs/l), corresponding to an overall removal efficiency of 98.4 %. The MPs concentrations remained low following MAR (2.7 ± 0.7 MPs/l) through a Quaternary gravel aquifer. Activated carbon filters did not substantially further reduce MPs concentrations. The percentage of fragments (≈95 %) prevailed over fibers (≈5 %) at all locations, with fibers being longer and more abundant in the river water. Overall, this study demonstrates the effectiveness of the treatment systems to remove MPs larger than 20 μm. Finally, we calculated an uncertainty in MPs concentrations of one order of magnitude depending on the user-defined parameters inside the MPs identification and classification model. The Quality Assurance/Quality Control approach followed during laboratory analysis highlighted an accumulation of surrogate particles at the edges of the disc, which would have an impact for MPs number upscaling.

Genetic diversity of the submerged macrophyte Ceratophyllum demersum depends on habitat hydrology and habitat fragmentation.

The adaptability of plant populations to a changing environment depends on their genetic diversity, which in turn is influenced by the degree of sexual reproduction and gene flow from distant areas. Aquatic macrophytes can reproduce both sexually and asexually, and their reproductive fragments are spread in various ways (e.g. by water). Although these plants are obviously exposed to hydrological changes, the degree of vulnerability may depend on the types of their reproduction and distribution, as well as the hydrological differences of habitats. The aim of this study was to investigate the genetic diversity of the cosmopolitan macrophyte Ceratophyllum demersum in hydrologically different aquatic habitats, i.e. rivers and backwaters separated from the main river bed to a different extent. For this purpose, the first microsatellite primer set was developed for this species. Using 10 developed primer pairs, a high level of genetic variation was explored in C. demersum populations. Overall, more than 80% of the loci were found to be polymorphic, a total of 46 different multilocus genotypes and 18 private alleles were detected in the 63 individuals examined. The results demonstrated that microsatellite polymorphism in this species depends on habitat hydrology. The greatest genetic variability was revealed in populations of rivers, where flowing water provides constant longitudinal connections with distant habitats. The populations of the hydrologically isolated backwaters showed the lowest microsatellite polymorphism, while plants from an oxbow occasionally flooded by the main river had medium genetic diversity. The results highlight that in contrast to species that spread independently of water flow or among hydrologically isolated water bodies, macrophytes with exclusive or dominant hydrochory may be most severely affected by habitat fragmentation, for example due to climate change.

Downward seepage effects on flow near a L-shape spur dike and bed morphology

Spur dikes are structures built along riverbanks that serve two purposes: stabilizing the banks and minimizing erosion risk by controlling water flow in the river channel. The current study used L-shaped spur dikes in an alluvial channel to analyze the bed morphology and flow pattern in the spur dikes zone with the influence of no-seepage and two distinct seepage velocities, VS1 = 0.075 mm/s and VS2 = 0.15 mm/s near the channel bed z/h < 0.2. The experimental study was also done to examine and compare the transformation in the local scour depth for the seepage condition. According to the study results, downward seepage movement causes significant modification in the channel's bed elevation and the development of scour depth. Observations indicate that the maximum local scour occurs at the first spur dike's leading edge. Seepage velocity VS1 results in a 16.1% increase in the maximum scour depth compared to the no-seepage scenario. In comparison, seepage velocity VS2 causes an increase of 25.2% in the maximum scour depth. Due to downward seepage, the flow distribution is shifted down near the channel's boundary. With an increase in the seepage rate, the magnitude of velocity, Reynold shear stress, turbulent kinetic energy, and bed shear stress also rise close to the channel's boundary. The current study also examined bursting events near the channel's bed under seepage and no-seepage conditions. These events included outward interaction, inward interaction, ejection, and sweep. Quadrant analysis of velocimeter data revealed that ejection and sweep were the dominant events contributing to the production of Reynolds shear stress in seepage and no-seepage flows. Meanwhile, outward interactions and inward interactions made minor contributions compared to ejection and sweep events to the Reynolds shear stress.

Marsh-induced backwater: the influence of non-fluvial sedimentation on a delta's channel morphology and kinematics

Abstract. We investigate the interaction of fluvial and non-fluvial sedimentation on the channel morphology and kinematics of an experimental river delta. We compare two deltas: one that evolved with a proxy for non-fluvial (“marsh”) sedimentation (treatment experiment) and one that evolved without the proxy (control). We show that the addition of the non-fluvial sediment proxy alters the delta's channel morphology and kinematics. Notably, the flow outside the channels is significantly reduced in the treatment experiment, and the channels are deeper (as a function of radial distance from the source) and longer. We also find that both the control and treatment channels narrow as they approach the shoreline, though the narrowing is more pronounced in the control compared to the treatment. Interestingly, the channel beds in the treatment experiment often exist below sea level in the terrestrial portion of the delta top, creating a ∼ 0.7 m reach of steady, non-uniform backwater flow. However, in the control experiment, the channel beds generally exist at or above relative sea level, creating channel movement resembling morphodynamic backwater kinematics and topographic flow expansions. Differences between channel and far-field aggradation produce a longer channel in-filling timescale for the treatment compared to the control, suggesting that the channel avulsions triggered by a peak in channel sedimentation occur less frequently in the treatment experiment. Despite this difference, the basin-wide timescale of lateral channel mobility remains similar. Ultimately, non-fluvial sedimentation on the delta top plays a key role in the channel morphology and kinematics of an experimental river delta, producing channels which are more analogous to channels in global river deltas and which cannot be produced solely by increasing cohesion in an experimental river delta.

PREDICTIVE NUMERICAL GEOFILTRATION MODEL OF GROUNDWATER INFLOW INTO THE GOREVSKY GOK QUARRY

Gorevskoe zinc-lead ore deposit is located within a unique terrain: it follows the left bank of the Angara River and lies underneath its current river bed, starting 38 km far from the Angara River mouth. This plays a significant role in the ore field hydrogeology and has a great impact on its further development. The complexity of ore field hydrogeology is defined by a number of natural factors, i.e., the occurrence of both aquifers as well as low-permeable and water-proof layers; tectonic failures (if any) and their functioning in terms of hydrogeology dynamics; variability in terms of water-bearing rocks hydraulic properties; water bodies on the surface and their connection with groundwater flows. All the above mentioned features allow us to classify Gorevskoe deposit hydrogeology as rather complex and complicated. The main task of the work performed was to evaluate and forecast the water inflow to Gorevskii open-pit mine and to determine the groundwater level at the end of mining operations. Because of the deposit rather complex hydrogeology, it was decided to perform the task on the basis of numerical geohydraulic modelling using finite difference method (FDM) in the environment of Visual MODFLOW software tools. The paper describes the following steps of works performed within the project: input data acquisition, processing and analysis; creation of concept-based hydrogeology model; development of hindcasting numerical model; model calibration in the context of environmental conditions and actual mining operations hosted within the open-pit; sensitivity analysis and advanced simulation to develop the forecasting numerical model. When performed, the forecast value in terms of groundwater inflow to the pit has been calculated. Thus, pit groundwater level at the end of mining operations has been developed. Following a number of scenarios applied, model sensitivity analysis has been made and this provided the basis to identify the factors that have the most essential impact on water inflow to the pit.

Applicability of environmental DNA metabarcoding for the hyporheic zone of a stream bed

AbstractHyporheic zones play a crucial role in ecological processes primarily orchestrated by hyporheic organisms, known as hyporheos. Our understanding of riverine biodiversity, encompassing hyporheic zones, remains limited. Therefore, the development of a method for the facile and accurate detection of hyporheic communities is imperative. Thus, we evaluated the applicability of environmental DNA (eDNA) metabarcoding surveys in the hyporheic zone in a small stream in Japan. We conducted simultaneous direct sampling and eDNA surveys at two different locations (head and tail of a rapid and a bar) and during two different seasons (less and more disturbed periods). Subsequently, we compared the outcomes of these sampling methods, locations, and seasons. Through eDNA metabarcoding targeting the cytochrome‐c oxidase subunit I (COI) regions, we successfully identified a diverse array of hyporheic and benthic taxa in all samples. Remarkably, the performance of eDNA metabarcoding was comparable to the identification of directly sampled benthos and hyporheos. We observed a 62%–78% concordance between direct sampling and eDNA metabarcoding. Notably, eDNA metabarcoding revealed a higher number of hyporheic taxa compared to direct sampling. Moreover, the relative detectability of hyporheos by eDNA metabarcoding differed between the seasons, unlike direct sampling. Our findings underscore the importance of conducting both eDNA surveys and direct sampling to comprehensively assess the composition of the stream community while accounting for seasonal variations. This study demonstrates the utility of eDNA metabarcoding as a non‐destructive approach for investigating the hyporheic zone, enabling a more effective assessment of riverine biodiversity.

The Effect of Shear Stress on Armor Layer Thickness Under Steady Uniform Flow

The armor layer is essential for maintaining stability on riverbed surfaces. This layer forms when bedload sediment moves until the bed's surface erodes, resulting in a stable layer that reaches an equilibrium state where no further sediment transport occurs. Therefore, the objective of this study is to investigate the effect of grain size and shear stress on armor layer thickness using evenly mixed sand and gravel with five different grain size variations. The research methodology consists of laboratory experiments and optimization analysis. The main instrument used is a sediment-recirculating flume constructed from plexiglass, measuring 10, 0.60, and 0.45 m in length, width, and height, respectively. Bed slope varies across gradients of 1%, 1.4%, 1.8%, 2.2%, and 2.6%. The constant flow rate is set at capacities of 25 l/s, 30 l/s, 40 l/s, and 45 l/s. The results show the consistent behavior of the channel bed surface under different flow rate variations. Meanwhile, the variables affecting armor layer thickness are the uniformity coefficient (Cu), the difference in shear stress on the bed surface (τo-τc)/τc), beds shear stress, and the critical shear stress of the sediment grain. The primary novelty of this research is a formula to determine armor layer thickness. It showed that both shear stress and the proportion of sand-to-gravel materials play significant roles in the armoring process and subsequent changes in the riverbed. Doi: 10.28991/CEJ-2023-09-11-012 Full Text: PDF

Two Innovations for Critical Infrastructure Protection from Natural Disasters

The article elaborates on two innovations developed for the purpose of protecting critical infrastructure facilities from two specific natural disasters – kinematic system for early warning of earthquakes applicable for the Bulgarian nuclear power plant (NPP), and a system for early warning of floods along the river beds near artificial lakes barrages. Both developments are part of the execution of p.1.1.6 from National Scientific Programme (NSP) “Security and Defence” – “Analysis of risk and threats, design and development of conceptual generating models and software for improvement of efficiency of control of forces and means for critical infrastructure influence during natural disasters, accidents and crises, on the territory of Republic of Bulgaria”.

Deposition areas: An effective solution for the reduction of the sediment volume transported by stony debris flows on the high‐sloping reach of channels incising fans and debris cones

SummaryThe main approach to managing the volume of sediment transported by stony debris flows routing along channels is through retention basins and open check dams, usually built in the lower reach just upstream of inhabited areas where slopes are gentler. In some cases, these measures are not sufficient to retain all the volume of sediment transported by debris flows. Works for trapping the sediments should also be placed in the upper reach of debris‐flow channels. In this area, where the channel bed is characterized by very high slopes and vertical variability over time, constructing and maintaining transversal embankments for sediment retention is difficult. In addition, they could also be susceptible to failure, potentially increasing the magnitude of the phenomenon instead of mitigating it. On the other hand, other types of works, such as solid‐body check dams or net barriers, have a decreasing efficiency over time in reducing the volume of sediment transported by debris flows. An alternative solution could be a retention basin open on the downstream side, that is, without the ending transversal embankment or berm. Therefore, it can be designated as a deposition area because the retention effect of the downstream embankment is missing, and sediment deposition only occurs due to the flatness of the basin. For sizing purposes, here, we derive two relationships between the deposition area and the volume of the deposit. These two relationships are derived from a physically based geometrical approach and empirical approach, respectively. After analyzing the morphology of the depositional processes that occurred in an existing deposition area during debris‐flow events, we test the validity of the two relationships. Overall, these can be used independently or in combination for designing a deposition area. At last, we introduce the necessary geomorphological conditions for the construction of the deposition area and guidance for its placement.