River Gravel Research Articles

An Evaluation of the Physical and Chemical Stability of Dry Bottom Ash as a Concrete Light Weight Aggregate.

Compared to the bottom ash obtained by a water-cooling system (wBA), dry process bottom ash (dBA) makes hardly any unburnt carbon because of its stay time at the bottom of the boiler and contains less chloride because there is no contact with seawater. Accordingly, to identify the chemical stability of dBA as a lightweight aggregate for construction purposes, the chemical properties of dBA were evaluated through the following process of the reviewing engineering properties of a lightweight aggregate (LWA). Typically, river gravel and crushed gravel have been used as coarse aggregates due to their physical and chemical stability. The coal ash and LWA, however, have a variety of chemical compositions, and they have specific chemical properties including SO3, unburnt coal and heavy metal content. As the minimum requirement to use the coal ash and lightweight aggregate with various chemical properties for concrete aggregate, the loss on ignition, the SO3 content and the amount of chloride should be examined, and it is also necessary to examine heavy metal leaching even though it is not included in the standard specifications in Korea. Based on the results, it is believed that there are no significant physical and chemical problems using dBA as a lightweight aggregate for concrete.

Trends in the Use and Recovery of Electronic Waste As Aggregates in Eco-friendly Concrete

The management of electronic waste (e-waste) mainly from televisions and computers, has turned into an environmental issue due to the increased demand in the electronics sector and the highly toxic contents (mercury, lead, or cadmium) of some of these devices that make them almost unrecoverable. Therefore, these valuable devices become wastes disposed of in landfills. Worldwide, some scholars have proposed recycling methods that re-introduce these wastes streams in the manufacturing process of heavy concrete, pavement, concrete blocks, and clay bricks among other unconventional products. The replacement rates of virgin materials with recycled e-waste fluctuate according to the type of waste. Nevertheless, the use of e-waste generates a positive environmental impact due to the less demand for virgin materials such as river sand and gravel. This study aimed to review the current e-waste recycling state-of-the-art such as circuit boards (PCB), high-impact polystyrene (HIPS), cathode ray tube (CRT), and LCD screens. A systematic review of scientific literature published in the last 10 years (2010–2019) was done through the SCOPUS database. The results showed a maximum potential replacement rate of 40% for this type of waste, given the effect on the physical and thermomechanical properties of the concrete.

Migration characteristics of atrazine in porous media during managed aquifer recharge

Abstract To study the influences of sand and gravel layer and groundwater velocity of Yufuhe River on atrazine migration, adsorption-desorption and sand column experiments were carried out. Results show that the adsorption capacity of montmorillonite, raw sand and washed sand to atrazine sequentially weakens. In different media, the time for atrazine concentrations to peak in washed sand with montmorillonite (WSM), raw sand and washed sand is 60, 135 and 105 minutes respectively, and the peak concentration accounts for 84, 90 and 95% of the initial concentrations. Under different flow rates, the peak time in washed sand at flow rates of 100, 150 and 200 mL/min is 135, 105 and 75 minutes, and the peak time in WSM is 90, 60 and 45 minutes, respectively. Results from this study indicate that increasing flow velocity and suspended colloids concentrations can promote the migration of atrazine in aquifers, while the presence of clay minerals in sand and gravel layers can reduce atrazine migration. Thus, during Yellow River water recharging, the sand and gravel layer of Yufuhe River is helpful to protect the aquifer, but the colloids-associated migration of atrazine can contaminate groundwater in underlying karst aquifer.

Replacement of Sand by Quarry Dust in Concrete

The role of quarry dust in the construction of building and other structures to eliminate the demand of nature sand by using quarry waste to replace the use of natural sand. We are investigating the potential of using quarry waste and its effect on the strength and workability of concrete. Initially cement concrete cube was studied with various proportion of cement concrete +quarry dust (M20 & M25). The experimental result showed that the additional of quarry dust as fine aggregate ratio of 30%, 40% and 50% was found to enhance the compressive properties. The compressive strength of concrete cubes at the age of 7 and 28 days were obtained at room temperature. These raw materials of concrete, i.e., river sand and gravel, are also struggling to cope with the rapidly growing demand in many areas around the globe. The sources of good quality river sand and gravel are depleting very fast. According to United Nations Environment Program (UNEP) report, “Sand-rarer than one thinks”, published in March2014, sand and gravel has now become the most widely used natural resource on the planet after water. These are now being extracted at a rate far greater than their renewal. Crushed sands, fine aggregate produced from stone crushing, has become very popular in areas where natural sand is not abundantly available or where there is scarcity in the supply of natural sand. The Mumbai-Pune express highway was a project, where there is a difficulty in procurement of natural sand. This made the construction company to use crushed sand for making approximately 20 lakh cum of concrete necessary for the construction. However, such type of sands contains a large amount of micro-fines, i.e., particles finer than 75 microns, which can have an adverse effect on properties of concrete. So proportioning of different raw materials at the time of mix design is very important, when crushed sand is used in concrete The availability of sand at low cost as a fine aggregate in concrete is not suitable and that is the reason to search for an alternative material. Quarry dust satisfies the reason behind the alternative material as a substitute for sand at very low costIt is found that 40% replacement of fine aggregate by quarry dust gives maximum result in strength than normal concrete and then decreases from 50%. The compressive strength is quantified for varying percentage and grades of concrete by replacement of sand with quarry dust.

Can use of substrates affect water quality in aquatic organism culture?

The choice of suitable substrates has received special attention in aquaculture and fishkeeping ventures. The aim of this study was to evaluate the influence of different substrates on water quality and the development of lambari fish (Astyanax bimaculatus) and freshwater shrimp (Macrobrachium potiuna). Two experiments were performed sequentially, one with fish and the other with shrimp. In both experiments, three different substrates were evaluated (shell gravel, river gravel, and dolomite), and the control was without any substrate. The water parameters evaluated were as follows: dissolved oxygen, saturation, oxide-reduction potential, temperature, pH, alkalinity, conductivity, ammonia, nitrite, nitrate, and phosphorus. It was observed that both dolomite and shell gravel interfered with the parameters that are related to the acid-base balance of the water and the availability of calcium and magnesium. The productive performance of lambari fish was not affected considering the different substrates evaluated; however, the productive performance of freshwater shrimp was lower in the absence of substrates in relation to the other treatments.

Deformation Properties of Nano-Silica Modified Concrete Mixtures under Uniaxial Compression Loading

The enhancement that nano-silica (NS) constitutes in the microstructure of concrete would affect its deformation behavior. In this work, the pre-peak and post-peak stress–strain diagram characteristics of concrete mixtures with NS (1.5% of cement by wt.) under uniaxial compression were investigated. The results were compared with the mixtures containing micro-silica (MS) (7.3% of cement by wt.). Aggregate characteristics in the range of 16 to 22 mm, as another variable, were also changed by utilizing river gravel (RG II) or crushed sandstone (CS II). Compared to reference concrete, the addition of NS did not improve the compressive strength and modulus of elasticity significantly. However, the addition of only 1.5% NS significantly affected the stress–strain diagram characteristics, such as discontinuity and critical stress limits before the peak load. Relative to the mixtures containing MS, the effect of NS on the pre-peak region was more significant. For example, when the mixtures containing RG II as coarse aggregate are considered, with respect to reference mixture, the increase in normalized discontinuity stress limits at 28 days was found as 52% and 26%, respectively, for the mixtures containing NS and MS. However, in the same order, the increase in 28-day compressive strength was just 8.1% and 5.2%. Post-peak behavior of the mixtures also indicated that the fracture of concrete is more brittle when MS or NS is used. Among these, the effect of NS on the post-peak region was found to be more dominant.

Physical modeling of vanishing bores in open-channel flows

When an undular bore propagates upstream against a subcritical flow in a flat channel, its leading front may weaken and vanish. The present study physically investigated the entire decaying process of vanishing bores in a relatively large facility. The invert was made of mobile or fixed natural river gravel. Detailed sampling of water surface elevations and velocities was performed in combination with high-resolution photos and video recordings. Despite some increased turbulence characteristics linked to the bore front arrival, no sediment motion was observed underneath the vanishing bores. The quantitative results provide a unique benchmark dataset for further study of later-stage bore propagations.

Investigating the Impact of Reducing the Cementitious Content in Bridge Deck Concrete

Abstract For this research, bridge deck concrete mixtures were investigated in order to lower the required cementitious content while maintaining prescriptive specifications. Cementitious contents of 362, 335, and 307 kg/m3 in conjunction with water-to-cementitious materials ratios of 0.40, 0.44, and 0.50 and fly ash levels of 0, 20, and 30 % were studied. Mixtures were tested for workability, entrained air, drying shrinkage, and the ability to maintain a 28 MPa compressive strength requirement. The compressive strength requirement was met by each mixture investigated and drying shrinkage was reduced as the cementitious content was lowered. A coarse limestone aggregate was used for the majority of this research; however, a smaller investigation indicated that sandstone and river gravel aggregates impacted compressive strength, drying shrinkage, and the static modulus of elasticity. Therefore, aggregate type should be investigated prior to use in reduced cementitious content bridge deck mixtures. Durability testing (such as permeability and freeze/thaw) should also be conducted prior to altering the prescribed cementitious content in concrete mixtures.

Vegetation of the European mountain river gravel bars: A formalized classification

AbstractAimsRiver gravel bars are endangered habitats in Europe. However, classification schemes of their vegetation and habitat types differ among European countries, and they are even ignored in some national schemes. This causes problems in conservation planning, monitoring and management. Hence we aimed at building the first unified vegetation classification for river gravel‐bar habitats across European mountain systems.LocationEurope.MethodsIn total 4,769 vegetation plot records of river gravel‐bar plant communities were collected from national, regional or private databases, digitized from the literature and newly collected in the field. A hierarchical classification expert system with formal definitions of vegetation types was created. The definitions combined the criteria of presence or cover of groups of species with similar ecology or single species narrowly specialized to a particular gravel‐bar habitat. The TWINSPAN classification was applied to early‐successional vegetation types to check whether the classification based on formal definitions was supported by the results of unsupervised classification. Similarity patterns among vegetation types were visualized using the detrended correspondence analysis (DCA) ordination.ResultsEarly‐successional and scrub gravel‐bar vegetation types were respectively classified into two classes: Thlaspietea rotundifolii and Salicetea purpureae. Eleven associations and four alliances (Calamagrostion pseudophragmitae, Epilobion fleischeri, Salicion cantabricae and Salicion eleagno‐daphnoidis) were defined formally. Based on a critical revision, some associations or alliances defined in the previous literature were merged or discarded. The main gradient in variability within the gravel‐bar vegetation is connected with the altitudinal gradient, biogeographical variation, local hydromorphological processes and various successional changes.ConclusionsThe first unified and formalized classification system of the European mountain river gravel‐bar vegetation was created, and species composition, ecology and distribution of these types were characterized. The syntaxonomical nomenclature of these types was checked and revised. This study provides a base for conservation planning of these threatened and rapidly disappearing habitats.

The bioavailability of oil droplets trapped in river gravel by hyporheic flows.

Little is known about the fate of oil spills in rivers. Hyporheic flows of water through river sediments exchange surface and groundwater and create upwelling and downwelling zones that are important for fish spawning and embryo development. Risk assessments of oil spills to rivers do not consider the potential for hyporheic flows to carry oil droplets into sediments and the potential for prolonged exposure of fish to trapped oil. This project assessed whether oil droplets in water flowing through gravel will be trapped and whether hydrocarbons partitioning from trapped oil droplets are bioavailable to fish. Columns packed with gravel were injected with oil-in-water dispersions prepared with light crude, medium crude, diluted bitumens, and heavy fuel oil to generate a series of oil droplet loadings. The concentrations of oil trapped in the gravel increased with oil loading and viscosity. When the columns were perfused with clean water, oil concentrations in column effluents decreased to the detection limit within the first week of water flow, with sporadically higher concentrations associated with oil droplet release. Despite the low concentrations of hydrocarbons measured in column effluent, hydrocarbons were bioavailable to juvenile rainbow trout (Oncorhynchus mykiss) for more than three weeks of water flow, as indicated by strong induction of liver ethoxyresorufin-o-deethylase activity. These findings indicate that ecological risk assessments and spill response should identify and protect areas in rivers sensitive to contaminant trapping.

Isochron 26Al/10Be burial dating of Xihoudu: Evidence for the earliest human settlement in northern China

The mainstream school of human evolution posits that Homo erectus was the earliest species to leave Africa at ∼1.85 million years (Ma) ago. Recent discoveries from the Shangchen loess-palaeosol sequence near the Lantian hominid site in northern China, however, show lithic artifacts up to 2.12 Ma, pre-dating the fossil record of H. erectus. Here we apply the recently established isochron 26Al/10Be burial dating, whose reliability has been verified by intercomparison with 40Ar/39Ar dating, to two locations at the Palaeolithic site of Xihoudu ∼100km east of Shangchen. The results show that the stone tools found within river gravels there are 2.43±0.06 Ma (1σ) old, making them the earliest radio-isotopically dated evidence for human occupation in Eurasia. The new date is supported by relative dating of the associated fauna, by consistent simple burial ages of quartz sand from deep cores, and by agreement between the two isochrons. Although the validity of the Xihoudu artifacts has been previously debated because of marked fluvial abrasion, there is clear evidence of intentional flaking. In particular, in addition to two cores with small amounts of cortex, a number of flakes lack original rock cortex, which indicate multiple and sustained removals that do not occur naturally. The great antiquity of the Xihoudu artifacts renders firm support to an earlier “Out of Africa I” that approaches the emergence of the genus Homo and the Oldowan industry.

Drainage integration of the Salt and Verde rivers in a Basin and Range extensional landscape, central Arizona, USA

The Salt River and Verde River watersheds provide downstream metropolitan Phoenix, Arizona, USA with much of its water supply, and this paper explains how these rivers integrated in an extensional tectonic setting. Near the end of the Pliocene, segments of the proto-Salt and proto-Verde watersheds of central Arizona consisted of local drainage networks supplying water and sediment into internally drained basins, including depressions occupied by late Pliocene natural lakes occupying the Verde Valley and Tonto basins. A key location, the lower Verde River valley (LVRV), is where the modern-day drainages of the Salt and Verde now meet downstream of these Pliocene lakes. At the time of the Nomlaki tuff deposition ~3.3 Ma, a condition of sediment overfill existed in the LVRV, although there was no exoreic drainage and a playa was still maintained. A fanglomerate unit, named here the Rolls formation, spilled over a bedrock sill and an alluvial-fan ramp transported sediment into the Higley Basin that underlies the eastern part of metropolitan Phoenix. Lithologies of preserved remnants of this Pliocene alluvial-fan system match well cuttings of buried sediment in the Higley Basin with a cosmogenic burial isochron age of 3.90 ± 0.70 Ma. Based on cosmogenic burial isochron ages, ancestral Salt River gravels started depositing on top of this fan ramp between 2.8 and 2.2 Ma. Deposition of Salt and Verde river gravels in the Higley Basin continued for ~2 million years and eventually led to an aggradational piracy event that overtopped a bedrock ridge immediately east of Phoenix's Sky Harbor Airport. A cosmogenic burial age of 460 ± 23 ka is a rough maximum age for this river avulsion that relocated the Salt River into the Luke Basin that underlies western metropolitan Phoenix. Available chronometric data are not precise enough to determine whether the Salt River or Gila River integrated first. All of the exoreic rivers of western North America's Basin and Range Province — the lower Colorado, Gila, Rio Grande, Salt, and Verde rivers — employed lake overflow to integrate across half-graben, graben, rift and supradetachment tectonic settings.

Innovative Multistage Constructed Wetland for Municipal Wastewater Treatment and Reuse for Agriculture in Senegal

This paper reports on the performance of using a multistage constructed wetland (CW) to treat municipal raw wastewater and an analysis of its suitability for agricultural irrigation. The pilot plant consists of two stages of vertical flow CWs plus one stage of a horizontal CW built in 2018 with different local materials at the Gaston Berger University Campus, Saint Louis (Senegal). Each CW stage is composed of several filters with different type of media (silex, granite, or river gravel), filtering media depths, and macrophytes (Phragmites and Typha). The physicochemical and microbiological indicators were monitored over six months at each bed inlet and outlet to evaluate the efficiency and achievements of the Senegalese, European, and WHO regulations/recommendations for disposal or reuse in irrigation. This study demonstrates the viability of this new multistage CW design to treat raw municipal wastewater and produce an effluent of good quality suitable for reuse in agriculture. The removal of organic matter, suspended solids, and nutrients was very high (>95% for SS, BOD5 and N-NH4+, >90% for COD and P-PO43−), as was the reduction of microbiological indicators (fecal coliform reduction >5 log units and helminth egg removal of 100%). First, trends related to the influence of design (the type of gravel, filter depth, and type of macrophyte), operational modes, and the CW treatment efficiency were determined. The use of non-crushed gravel and Typha spp. seemed to provide better removal rates. On the contrary, no differences were found between the use of silex or granite gravel. For the studied Senegalese conditions under dry and hot climates, the preliminary results indicate that no resting periods are necessary for vertical flow CWs (VFCWs), thus resulting in a reduction in construction and operation costs. The main outcome of our study is evidence that multistage CWs can provide robust, cost-effective treatments, as well as allow for safe water reuse, which is imperative in areas with severe water scarcity and endemic microbiological waterborne diseases.

Characterization of SWOT Water Level Errors on Seine Reservoirs and La Bassée Gravel Pits: Impacts on Water Surface Energy Budget Modeling

The Surface Water and Ocean Topography (SWOT) space mission will map surface area and water level changes in lakes at the global scale. Such new data are of great interest to better understand and model lake dynamics as well as to improve water management. In this study, we used the large-scale SWOT simulator developed at the French Space National Center (CNES) to estimate the expected measurement errors of the water level of different water bodies in France. These water bodies include five large reservoirs of the Seine River and numerous small gravel pits located in the Seine alluvial plain of La Bassée upstream of the city of Paris. The results show that the SWOT mission will allow to observe water levels with a precision of a few tens of centimeters (10 cm for the largest water reservoir (Orient), 23 km2), even for the small gravel pits of size of a few hectares (standard deviation error lower than 0.25 m for water bodies larger than 6 ha). The benefit of the temporal sampling for water level monitoring is also highlighted on time series of pseudo-observations based on real measurements perturbed with the simulated noise errors. Then, the added value of these future data for the simulation of lake energy budgets is shown using the FLake lake model through sensitivity experiments. Results show that the SWOT data will help to model the surface temperature of the studied water bodies with a precision better than 0.5 K and the evaporation with an accuracy better than 0.2 mm/day. These large improvements compared to the errors obtained when a constant water level is prescribed (1.2 K and 0.6 mm/day) demonstrate the potential of SWOT for monitoring the lake energy budgets at global scale in addition to the other foreseen applications in operational reservoir management.

Detection and Quantification of Cracking in Concrete Aggregate through Virtual Data Fusion of X-ray Computed Tomography Images.

In this work, which is part of a larger research program, a framework called “virtual data fusion” was developed to provide an automated and consistent crack detection method that allows for the cross-comparison of results from large quantities of X-ray computed tomography (CT) data. A partial implementation of this method in a custom program was developed for use in research focused on crack quantification in alkali-silica reaction (ASR)-sensitive concrete aggregates. During the CT image processing, a series of image analyses tailored for detecting specific, individual crack-like characteristics were completed. The results of these analyses were then “fused” in order to identify crack-like objects within the images with much higher accuracy than that yielded by any individual image analysis procedure. The results of this strategy demonstrated the success of the program in effectively identifying crack-like structures and quantifying characteristics, such as surface area and volume. The results demonstrated that the source of aggregate has a very significant impact on the amount of internal cracking, even when the mineralogical characteristics remain very similar. River gravels, for instance, were found to contain significantly higher levels of internal cracking than quarried stone aggregates of the same mineralogical type.

Symbiosis between river and dry lands: Phycobiont dynamics on river gravel bars

River gravel bars are dynamic and heterogeneous habitats straddling the transition between aquatic and terrestrial environments. Periodic flooding, low nutrient concentrations, frost, lack of stable sites, drought, and ground surface heat significantly influence the biota of these habitats. Mutualistic symbiosis may be a successful strategy for organisms to survive and proliferate under such harsh conditions. The lichen genus Stereocaulon was selected as a model symbiotic system from among the organisms living on river gravel bars. The goal of the current study was to determine the effect of this dynamic environment on phycobiont (i.e., green eukaryotic photobiont) community structure. We analyzed 147 Stereocaulon specimens collected in the Swiss Alps using Sanger sequencing (fungal internal transcribed spacer (ITS) rDNA, algal ITS rDNA, and algal actin type I gene) and analyzed 8 selected thalli and 12 soil samples using Illumina metabarcoding (ITS2 rDNA). Phytosociological sampling was performed for all 13 study plots. Our analyses of communities of phycobionts, lichens, bryophytes, and vascular plants indicated a gradual change in the phycobiont community along a successional gradient. The particularly large phycobiont diversity associated with Stereocaulon mycobionts included algae, here reported as phycobionts for the first time. Each of the two Stereocaulon mycobiont operational taxonomic units had a distinct pool of predominant phycobionts. The thalli selected for Illumina metabarcoding contained a wide range of additional algae, i.e., they showed algal plurality.

Correction to: Natural habitat and vegetation types of river gravel bars in the Caucasus Mountains, Georgia

Correction to: Natural habitat and vegetation types of river gravel bars in the Caucasus Mountains, Georgia

Horizontal subsurface flow constructed wetland for tertiary treatment of dairy wastewater: Removal efficiencies and plant uptake

There are different physicochemical and biological methods to treat effluents. However, their efficiency is not enough to meet the effluents discharge limits. For this reason, it could be possible to employ a polished treatment. A suitable alternative for this goal could be constructed wetlands (CWs). The aim of the present research was to evaluate contaminants removal efficiency of a pilot scale horizontal subsurface flow constructed wetland (HSSFW) for tertiary treatment of dairy wastewater. A vegetation study was also conducted in order to determine the role of plants on nutrient removal. A pilot scale HSSFW planted with Typha domingensis was built in a dairy factory, after the biological treatment. The substrate used was river gravel. During a seven-month research period, thirty-two samples (influent and effluent) were taken and analyzed to determine physicochemical and microbiological parameters as well as removal efficiencies. Biomass, TP, TKN and organic matter content in plants was determined at the beginning and end of the monitoring period. Suspended solids showed significant differences between inlet and outlet, with a mean removal efficiency of 78.4%. For BOD and COD, mean removal efficiencies were respectively 57.9 and 68.7%. Removal percentages for TKN, Nitrates and TP were lower than other parameters (25.7%, 47.8% and 29.9%, respectively). Fecal Coliform bacteria decreased one order of magnitude in final effluent. In the case of Escherichia coli and Pseudomona aeruginosa results were variable. Total biomass increased 4.6 times at the end of the monitoring period. The study of plants indicated its important contribution in terms of contaminant uptake and retention. HSSFW would be an advisable alternative as a tertiary treatment of dairy wastewater.

The sediment record of the Unicorn Cave, southern Harz Mountains, Germany

We demonstrate the utility of a multi-pronged approach to geomorphological studies. We show how the synthesis of results from 3-D imaging, varied geotechnical methods, and dating, reveals hitherto unknown features of a cave and of its sediment infill, and elucidates its geomorphological history. The Unicorn Cave (Einhornhöhle, southern Harz Mountains, Germany), long famous for its cave bear, lion, and mammoth fossils, is a dry vadose trunk cave high above base level, characterized by large rooms connected by shallow passages, and filled with sediments up to 40 m thick. The sediment is an archive for natural and anthropogenic environmental change: the succession of river gravels, breccia, and silts and sands provides a paleo-geomorphic and climatic archive; while human artefacts from the Paleolithic period provide information about early settlement phases. Here we derive a detailed description of the Unicorn Cave and its sediment infill by utilising several sources: (i) We synthesise data from the literature into a comprehensive picture of the sediment infill; (ii) We present new geophysical measurements of the sediments in the large room Leibnizhalle, and discuss these new measurements in view of our older findings; (iii) We map the larger chambers with the photogrammetric structure-from-motion method to build three-dimensional models; (iv) We present new age estimates from speleothem samples in the cave and discuss them with other, published, age estimates. Finally we use our newly collected evidence to reconstruct the evolution of the entire Unicorn Cave (including the newly-revealed, not-yet-accessible passages and their pristine sediment infill, as yet undisturbed by fossil hunters). The main period of speleogenesis ended with base-level incision in the mid-Pleistocene; the deposition of basal river gravels, probably in the late Cromerian, was followed by a sequence of clays and loams, capped by speleothem at ~MIS 3; the dates suggest at least two bone beds (MIS 3, and MIS 5e), along with bone material older than MIS 7.

Natural habitat and vegetation types of river gravel bars in the Caucasus Mountains, Georgia

River gravel-bar habitats are highly endangered. They are still well-preserved in the Caucasus, but developing conservation strategies is burdened by the lack of data from this region. We studied vegetation and habitat types on gravel bars of 22 rivers in Georgia, including successional stages from open early-successional herbaceous vegetation to scrub. We distinguished five vegetation types based on vegetation physiognomy and β-flexible clustering of species composition, and described them as phytosociological vegetation units: Early-successional herbaceous vegetation at higher elevations was described as the new association Epilobietum colchici and that at lower elevations as the Petrorhagia saxifraga–Crepis foetida community. The grassland dominated by Calamagrostis pseudophragmites and scrub vegetation were assigned to the associations previously described from Central Europe (Tussilagini farfarae-Calamagrostietum pseudophragmitae, Salici purpureae-Myricarietum germanicae and Salici incanae-Hippophaetum rhamnoidis). We established diagnostic plant species for each type using the fidelity calculation and related these types to environmental variables. We further compared them with the previously published data on gravel-bar vegetation from the Russian part of the Caucasus and with European systems of habitat classification. This study demonstrates that vegetation and habitat types occurring in Georgia correspond to those recognized earlier in Europe, and can be easily linked to the European systems of habitat classification. Unlike in other parts of Europe, these habitats are still well-preserved on rivers with natural hydrological dynamics, but they are threatened by plans of dam building and other river regulations. Our study provides baseline data for developing conservation strategies for the Caucasian gravel-bar habitats.