Clay Banks Research Articles

Dynamic Analysis of Changes in Jambu Riverbed and Banks: Case Study Around Cikuya Bridge

Several cross-sections of the Jambu River, particularly around the Cikuya Bridge, have experienced bank collapse phenomena. This paper interprets the issues related to bank collapse and its impact on the flow capacity of the Jambu River, especially around the Cikuya Bridge. Morphological changes were simulated using a sediment transport model implemented in the Hydrologic Engineering Center's River Analysis System (HEC-RAS) 6.3.1, integrated with the ARS-USDA Bank Stability and Toe Erosion Model (BSTEM). The simulation results indicate that over a period of 10 years, the thalweg elevation (the lowest point of a riverbed) of the Jambu River around the Cikuya Bridge is predicted to experience deposition in 17 cross-sections and erosion in 15 cross-sections. The highest deposition occurs at the cross-section below the Cikuya Bridge, with a thalweg elevation change of 0.59 m. This warrants attention as the storage capacity of the cross-section decreases by 7% from the initial condition. Predictions indicate that bank collapse will occur in 7 cross-sections over the next 10 years. This is attributed to the steep slopes of silt and clay banks, exceeding 45 degrees, and the reduced safety factor of bank stability due to groundwater pressure influenced by river discharge fluctuations and tidal effects reaching the Jambu River. Bank collapse impacts the elevation change of the riverbed and adds load to the sediment transport model from the collapsing cross-sections to the downstream sections. Keywords: Jambu River, Cikuya Bridge, Cilacap, sediment transport, bank stability and toe erosion model

Geophysical investigation of hydrocarbon in the southern part of Douala Kribi Campo basin, Cameroon

Well logging analysis and 3D seismic method are combined to evaluate the nature of fluids and reservoir characteristics in the southern part of the Douala/Kribi-Campo basin (DKC). Scientifiques researches that exhibit the important geological and geophysical settings of this basin are lacked. The successful investigation of these areas is possible if the stratigraphical and petrophysical properties of reservoir are properly evaluated. Extracting facies types from 3D seismic sections is a rapidly evolving discipline that facilitates the development of reservoir prediction models. So, a 25m × 25m seismic grid associated with Gamma-Ray log (GR), Neutron (Nphi) log, resistivity log, sonic log and density (RHOB) log have been performed. The results highlight the sedimentary environment and facies, porous-permeable clay banks, clay content, the porosity, saturation and the nature of the fluids in the reservoir. The petrophysical evaluations indicates the presence of potential petroleum reservoirs, mainly sandy-clay with 3.81–29.47% volume, 17.37–27.85% porosity and 47.74–56.02% water saturation. The nature of fluids present in the reservoir is oil, gas and water. This research work will serve to encourage hydrocarbon (HC) exploration in the DKC Basin by adopting strategies where seismic stratigraphy combined with well datas will be the most likely means of providing drill targets to more independent operators. The results of this study will serve for the future prospector on the neighboring oil and gas fields of our study area. Significant advances has been made to ensure future exploration success.

COVID-19 on the riverbank.

She curled into the mound of tattered old blankets piled high against the frozen clay banks along Winnipeg’s Assiniboine River. A skiff of snow covered the ground beneath the elm trees that stood sentinel over this liminal ribbon of land between the river and the rest of the city. This was

Gharials (Gavialis gangeticus) in Bardiya National Park, Nepal: Population, habitat and threats

Abstract The Critically Endangered gharial (Gavialis gangeticus) residing within Bardiya National Park (BNP) in Nepal constitutes the sixth major sub‐population of this unique lineage; however, this population is not well studied. A 46 km protected stretch of the Babai River and a 60 km stretch of the Karnali River in and around BNP were surveyed for gharials in early 2017 and in 2019. Gharial counts in 2017 – 17 from the Babai and one from the Karnali rivers – consisted of 10 adults, five sub‐adults and three juveniles. In 2019, 19 gharials were counted – 18 for the Babai and one for the Karnali – comprising 11 adults, six sub‐adults and two juveniles. In the Babai River within BNP, four breeding groups were identified. Gharials in BNP prefer sandy vs. rocky banks for basking and completely avoid sand‐grass and clay banks. Habitat preference did not vary with size class. Protected stretches of both rivers inside BNP (76 km) have resident gharial, intact habitats and few human threats. In contrast, the unprotected stretch of the Karnali (30 km) is threatened by boulder quarrying, sand mining and unlicensed fishing, and is avoided by gharials despite the availability of habitat. This study established baseline data, including indices of population size, distribution and habitat preferences, and documented resident gharials that are breeding in the Babai River in BNP. The conservation of this Babai population is crucial for the species’ survival in BNP. Based on this study, we recommend the following conservation actions on the Babai stretch: (a) determine hatching success; (b) assess juvenile recruitment; (c) consider supplementation by releasing captives; (d) study riverine features important as baselines; (e) accommodate upstream movements on the protected Babai stretch; and (f) protect the downstream Babai outside the boundary of the BNP.

Recycling untreated sugarcane bagasse ash and industrial wastes for the preparation of resistant, lightweight and ecological fired bricks

In order to mitigate environmental damage and reduce the exploitation of clay banks caused by the production of fired brick, research on the effect of the partial replacement of clay (CLAY) by industrial waste is under development. It has been reported that in brickmaking the partial substitution of clay with sugarcane bagasse ash (SCBA) affects the physical and mechanical properties by increasing absorption and reducing compressive strength. SCBA is a waste material produced in large quantities by the sugar industry and is generally discarded in open dumps. This research evaluates the effect of the partial replacement of CLAY with agricultural and industrial waste on the strength and durability properties of fired bricks. In the first phase of this study, CLAY was partially replaced by untreated sugarcane bagasse ash (UtSCBA), and in the second phase by combinations of UtSCBA plus fly ash (FA) and UtSCBA plus silica fume (SF). Binary and ternary mixtures were elaborated and characterized. The plasticities of all mixtures were evaluated, and bricks were fabricated at 900 and 1000 °C for the binary mixtures and at 900, 1000 and 1100 °C for the ternary mixtures. The fired bricks were tested for linear shrinkage, apparent density, apparent porosity, water absorption, initial rate of absorption, compressive strength and flexural strength. It was found that the bricks made with 70CLAY + 20UtSCBA + 10SF mixture fired at 1100 °C are only 2.08% more resistant to compression, 84% more resistant to bending, and only 7.03% lighter than the control bricks; nevertheless, with this mixture the use of clay is reduced by up to 30%.

Home Range of Yellow-Spotted Amazon River Turtles (Podocnemis unifilis) (Testudines: Podocnemididae) in the Trombetas River Biological Reserve, Pará, Brazil

Adult Podocnemis unifilis were monitored using VHF radio tracking from September 2013 to September 2014 in the Rio Trombetas Biological Reserve, Para, Brazil. Our aim was to analyze the use of space by this species near the nesting beach base by describing size and overlap of estimated home ranges. Transmitters were attached to 10 males and 10 females. The mean home range size calculated through the fixed-kernel (FK) method with 95% of the fixes was 79.28 ± 77.08 ha (0.56–215.07 ha; n = 13). The mean of overlapping areas was 14% with FK95% (0.02%–81%; n = 13) and 5% with FK50% (0.1%–23%; n = 9). There was a significant difference in the mean overlapping areas between females and males. The analysis of the overlap of activity centers estimated by FK50% is extremely important for the establishment of conservation strategies in the management plan for this species in the reserve. We were able to identify 2 critical areas for the maintenance of this population where there was a frequent overlap of activity centers: the first, identified during the dry season, was composed of small overlaps among 7 turtles and was near the nesting areas on the clay banks within the Lago Jacare; the second, identified during the rainy season, was composed of a concentration of overlap areas of larger size among 6 turtles and was an open area in the flooded forest. It is important not only to protect the nesting areas during the dry season but also to protect flooded forest areas with the major intensity of use along with the canals that link the flooded forests to the lakes in the rainy season. For conservation purposes, it is necessary to continue the protection of the nesting beaches throughout the savannas inside the lake where the species nests in the dry season. The flooded forest areas that are zones of intense use during the rainy season, and the canals where the turtles can move between lakes must be protected throughout the year.

SÍNTESIS DE UN GEOPOLÍMERO Y USO DE LA METODOLOGÍA DE SUPERFICIE DE RESPUESTA PARA OPTIMIZAR SU ADHERENCIA EN LADRILLO ROJO PARA SU USO COMO RECUBRIMIENTO INTERNO EN HORNOS LADRILLEROS

In Mexico, fixed kilns made of red brick are often used today. However, after several burn cycles at temperatures of up to 1000 °C, these kilns may expand, crack and open. In light of that, we worked to obtain a refractory geopolymer that attaches to red brick to use as an internal kiln coating to increase the useful life of the kiln. We studied the consolidation from refractory clays and a solution of commercial sodium silicate ( =1.38, SiO2/Na2O ratio =3.09). This process originates the synthesis of a geopolymer. The clays were previously selected for their refractory characteristics from different clay banks in the municipality of Comonfort, Guanajuato, Mexico; they have been identified as Caolin, Tepozan, and Bauwer. The clays were subjected to a process of grinding and sieving to a particle size of 60 Tyler mesh . Next, they were characterized using energy dispersive X-ray spectroscopy (EDS), which determined that they contained high percentages of SiO2 and Al2O3. The mineralogy of the raw clays was analyzed by powder X-ray diffraction (XRD), yielding high percentages of kaolinite, alunite, quartz and smectite. This composition validates the refractory potential of clays. A simplex-centroid design was used to formulate the geopolymer. The response surface methodology was used for optimization, keeping the commercial sodium silicate concentration constant. The adherence of the formulated geopolymer on red clay brick was taken as a response variable, yielding 50% for the consolidating material (commercial sodium silicate), 21% for Caolin, 23% for Tepozan, and 6% for Bauwer, where the curing time was 7 days and the burning cycle was 8 hours at 1000 °C. This property was measured in a universal testing machine. The best fit was a quadratic model with synergistic interactions between all factors, and the mean adherence of 28.11 kgf/cm2 (2.8 MPa) was obtained. Common potential applications of geopolymer coatings include protection against salt corrosion of marine concrete, reinforced concrete manufacturing, concrete infrastructure rehabilitation, fire inhibition, resistance to temperature and corrosion and as heat insulators. Geopolymers may also have promising use in construction due to their similar strength and durability properties as conventional concrete. The red brick joined to the obtained geopolymer can be used as an internal coating in fixed brick kilns to increase its useful life. In addition, it has potential use for bonding materials that may be exposed to temperatures below 1000 °C or for replacing concrete in ovens exposed to high temperatures.

Uncertainty and sensitivity in a bank stability model: implications for estimating phosphorus loading

AbstractEutrophication of aquatic ecosystems is one of the most pressing water quality concerns in the United States and around the world. Bank erosion has been largely overlooked as a source of nutrient loading, despite field studies demonstrating that this source can account for the majority of the total phosphorus load in a watershed. Substantial effort has been made to develop mechanistic models to predict bank erosion and instability in stream systems; however, these models do not account for inherent natural variability in input values. To quantify the impacts of this omission, uncertainty and sensitivity analyses were performed on the Bank Stability and Toe Erosion Model (BSTEM), a mechanistic model developed by the US Department of Agriculture – Agricultural Research Service (USDA‐ARS) that simulates both mass wasting and fluvial erosion of streambanks. Generally, bank height, soil cohesion, and plant species were found to be most influential in determining stability of clay (cohesive) banks. In addition to these three inputs, groundwater elevation, stream stage, and bank angle were also identified as important in sand (non‐cohesive) banks. Slope and bank height are the dominant variables in fluvial erosion modeling, while erodibility and critical shear stress had low sensitivity indices; however, these indices do not reflect the importance of critical shear stress in determining the timing of erosion events. These results identify important variables that should be the focus of data collection efforts while also indicating which less influential variables may be set to assumed values. In addition, a probabilistic Monte‐Carlo modeling approach was applied to data from a watershed‐scale sediment and phosphorus loading study on the Missisquoi River, Vermont to quantify uncertainty associated with these published results. While our estimates aligned well with previous deterministic modeling results, the uncertainty associated with these predictions suggests that they should be considered order of magnitude estimates only. Copyright © 2016 John Wiley & Sons, Ltd.

Ecology and biogeography of the endemic scorpionEuscorpius carpathicus(Scorpiones: Euscorpiidae): a multiscale analysis

Abstract We present a first analysis of the ecology and potential distribution of Euscorpius carpathicus (Linnaeus, 1767), a scorpion species endemic to southern Romania, and report on the overwintering habitat selection of this species. Using field data, literature review, species distribution modelling, and habitat selection models, we document the broad scale distribution and ecology of E. carpathicus, as well as habitat selection in the foothills of the Curvature Carpathians, including exclusive microhabitat selection of riverine clay banks. In contrast with other species of the genus that inhabit cracks in cliffs or walls, E. carpathicus has adapted to cracks in clay.

Funnels, gas exchange and cliff jumping: natural history of the cliff dwelling ant Malagidris sofina

The Malagasy endemic ant Malagidris sofina (Bolton and Fisher 2014) nests on cliff faces in natural rock alcoves or clay banks. Colonies have single ergatoid queens and reproduce by fission. Each nest has a funnel-shaped entrance that projects horizontally from the cliff face. We examine three hypotheses for the function of the funnels—water exclusion, gas exchange and defense. Entrance funnels are relatively impermeable and divert water from nests, but simple tubes would achieve the same result. Consistent with the gas exchange hypothesis, projected funnel entrances likely increase gas exchange rates over sixfold compared to simple tubes and may increase air flow within the nest. Gas exchange may explain the recurrent evolution of funnel entrances in several ant lineages, especially among cliff dwelling species. We outline M. sofina defense responses to conspecifics and co-occurring ant species, and find no support for a defense role of entrance funnels. Workers display little aggression but respond to several species with an original form of nest defense––cliff jumping—in which workers drop off the cliff face while clinging to invaders and then return to their nest. M. sofina is a restricted range species under threat of extinction by habitat destruction. Its novel lifestyle underscores the urgency of exploration and conservation in a tropical biodiversity hotspot.

Invasive crayfish as drivers of fine sediment dynamics in rivers: field and laboratory evidence

ABSTRACTDespite increasing recognition of the potential of aquatic biota to act as ‘geomorphic agents’, key knowledge gaps exist in relation to biotic drivers of fine sediment dynamics at microscales and particularly the role of invasive species. This study explores the impacts of invasive signal crayfish on suspended sediment dynamics at the patch scale through laboratory and field study. Three hypotheses are presented and tested: (1) that signal crayfish generate pulses of fine sediment mobilisation through burrowing and movement that are detectable in the flow field; (2) that such pulses may be more frequent during nocturnal periods when signal crayfish are known to be most active; and (3) that cumulatively the pulses would be sufficient to drive an overall increase in turbidity. Laboratory mesocosm experiments were used to explore crayfish impacts on suspended sediment concentrations for two treatments: clay banks and clay bed substrate. For the field study, high frequency near‐bed and mid‐flow turbidity time series from a lowland river with known high densities of signal crayfish were examined. Laboratory data demonstrate the direct influence of signal crayfish on mobilisation of pulses of fine sediment through burrowing into banks and fine bed material, with evidence of enhanced activity levels around the mid‐point of the nocturnal period. Similar patterns of pulsed fine sediment mobilisation identified under field conditions follow a clear nocturnal trend and appear capable of driving an increase in ambient turbidity levels. The findings indicate that signal crayfish have the potential to influence suspended sediment yields, with implications for morphological change, physical habitat quality and the transfer of nutrients and contaminants. This is particularly important given the spread of signal crayfish across Europe and their presence in extremely high densities in many catchments. Further process‐based studies are required to develop a full understanding of impacts across a range of river styles. Copyright © 2013 John Wiley & Sons, Ltd.

Longshore Sediment Movement and Supply along the U.S. Shoreline of Lake Erie

To establish existing conditions for dredge material beneficial use projects and to help implement principles of Regional Sediment Management (RSM) into projects and studies, this paper is an assessment of sediment sources and sinks, physical processes, and longshore sediment transport along the west and south shore of Lake Erie. This summary compiles information from a widely scattered technical literature and synthesizes the results in preparation for development of a sediment budget. The U.S. shore of Lake Erie has 28 river or harbor mouths protected with jetties and structures, of which 16 are Federal navigation projects. Much of the sediment management since the mid-1800s has revolved around providing safe navigation, maintaining depth in navigation channels, and disposing of the dredged material. Sediment sources include material brought down the rivers (often fine-grained); industrial dumping and runoff from sewers, gravel, sand, and clay eroded from glacial till bluffs and clay banks; sediment created in situ from bedrock bluff weathering (primarily from shale); and limited supply from lake bed lowering and offshore outcrops. Losses include wave- and ice-induced transport to deep water, sediment trapped in fillets at harbor jetties, sediment dredged from harbor entrance channel and placed in confined disposal facilities (CDFs) or placed offshore, bluff armoring, and (formerly) beach mining. Today, the south shore of Lake Erie is severely sand-starved compared with conditions that existed 200 years ago. The lack of available sediment is largely due to man-made causes. As the shore developed and became urbanized after the mid-1800s, residents, industries, and municipalities attempted to arrest bluff erosion with the use of structures and vegetation. Now the U.S. shoreline of Lake Erie is almost 83% protected, a larger percentage than any ocean coast except in urban areas. It means that little sediment exchange occurs compared with predeveloped conditions, which, in turn, means that managers must recycle and reuse existing sediment to maintain recreation beaches. Managing sediment to benefit a region sustainably potentially will save money, allow use of natural processes to solve engineering problems, and improve recreation resources and natural habitat. Cet article est une évaluation des sources et puits de sédiments, des phénomènes physiques et du transport de sédiment le long des côtes ouest et sud du lac Érié. L'objectif est de décrire les conditions environnantes actuelles pour les projets de mise en valeur des matériaux de dragage et ainsi faciliter l'implémentation des principes de Gestion Régional des Sédiments (RSM) lors de projets et études. Information et données provenant d'une multitude d'articles scientifiques et de littératures techniques sont synthétisées et présentées en vue de la préparation d'un budget sédimentaire. La berge américaine du lac Érié possède 28 embouchures de rivières et ports protégés par des brise-lames ou autre structures. Seize d'entre eux sont des projets de navigation sous le gouvernement fédéral. Depuis la deuxième moitié du 19e siècle, la gestion des sédiments marin a surtout constitué à rendre les voies navigables sécuritaires, à maintenir la profondeur des canaux de navigation et à disposer des matériaux de dragage. Les sédiments côtier proviennent de plusieurs sources, notamment des rivières (particules fines surtout), de rejet industriel (cendre et débris), des drains fluviaux, de l'érosion des escarpements de till (gravier, sable, argile) et des bancs d'argile, de l'altération des affleurements rocheux (surtout du shale), et finalement, en moindre importance, de l'érosion des sédiments et des affleurements rocheux situé au fond du lac. Les pertes de sédiments surviennent lors de leur transport en eaux profonde par les vagues ou les glaces, par accumulation sur les flans des brise-lames, lorsque les sédiments de dragage sont placés dans des installations confinées ou déposés en

The nymph of Tortopus harrisi Traver (Ephemeroptera: Polymitarcyidae)

Polymitarcyidae is a family of burrowing mayflies (Ephemeroptera: Ephemeroidea) distributed throughout the world but with highest diversity in the Neotropics. Tortopus Needham & Murphy, with a Panamerican distribution, is known from twelve species described in the adult stage. Nymphs are only known for three species: T. puella (Pictet), T. obscuripennis Domínguez and T. sarae Domínguez, and present a rather homogeneous morphology (Molineri 2008). They were firstly described for T. puella by Scott et al. (1959) and later Molineri (2008) described the other two. Both studies reported that these species burrow U-shaped tunnels in clay banks of rivers and streams, thus preventing them from being sampled in most limnological studies (that use surbers, drags, or drift nets).

PERÍODO DE DESOVA E SUCESSO REPRODUTIVO DO TRACAJÁ Podocnemis unifilis TROSCHEL 1848 (TESTUDINES: PODOCNEMIDIDAE) NA VÁRZEA DA RDSM – MÉDIO SOLIMÕES, BRASIL

In this study the nesting biology of Podocnem is unifilis was investigated from July to November 1998 at the Mamirauá Sustainable Development Reserve, located in the Solimões river, near Tefé, Amazonas, Brazil. Podocnemis unifilis nested in August and September, with the hatching event occurring in October and November. Nests were excavated in clay soils (67.5%), sand (25%), and leaf litter (7.5%). Hatching success was highest in the sand beach nests and lowest in the clay banks nests. Humans and the tegu lizard (Tupinambis) were the main egg predators. This turtle population can recover only by the protection of nesting beaches, educational programs for the in habitants of the Reserve, participation of the community in the conservation and management program , and permanent guarding of the nesting beaches by Instituto Brasileiro do Meio Ambiente e Dos Recursos Naturais Renováveis-IBAMA authorities.

Relative Survival of Lake Trout Stocked at Different Sizes and Quality in Lake Michigan

Beginning in 1995, the size of yearling lake trout ( Salvelinus namaycush) stocked into the upper Great Lakes was increased based on the assumption that these fish would be healthier and survive better since natural mortality is thought to be inversely proportional to body size. We compared the postrelease, relative survival of paired stockings of lake trout reared to 44 fish/kg (standard size) with larger fish reared to 22–26 fish/kg (enhanced size) in Lake Michigan. About 60,000 lake trout each of the standard and enhanced sizes for the 1994–1997 year classes were released as yearlings in spring near Clay Banks Reef, Wisconsin, and identified with coded-wire tags and an adipose fin-clip. Recaptures were made from 1997 to 2003 in four gill net surveys conducted in spring and fall near the release location. Comparisons of catch-per-unit of effort corrected for numbers stocked generally indicated no significant differences in relative survival of standard and enhanced lake trout. An autopsy-based assessment of overall fish health and condition indicated few measures where significantly different between standard and enhanced lake trout prior to stocking. Size differences between standard and enhanced fish remained statistically significant at all observed ages at recapture; however growth rates were the same for the two groups. Stocking numbers at certain sites on Lake Michigan were reduced concurrent with the change to larger yearlings with the expectation of increased survival, which did not occur; hence recruitment was essentially reduced in these areas for the restoration program.

Taking In the Welcome Mat

ECOLOGY/EVOLUTION Ants are ubiquitous in tropical forests, and they exhibit a wide variety of nesting and foraging behaviors that have fascinated naturalists and ecologists ever since the pioneering of scientific exploration in the tropics. Despite many decades of intense study and the high visibility of ants, Longino has managed to unearth previously unreported nesting habits in two endemic Costa Rican ant species in the genus Stenamma . These ants build nests in the vertical clay banks of streams, and the entrance to the nest is formed by a tunnel through the center of a shallow dish sitting atop a pedestal of clay or through a similarly shaped disk of soil lying on a mound of small stones. In both types of dwelling, a spherical pebble near the entrance can be retrieved and used to plug the doorway in times of danger. Each ant colony maintains several such nests, but occupies only one at a time. Because of their colonial habit, ants attract predators, and much of their nesting repertoire revolves around defense. Hence, it appears that the elaborate constructions of Stenamma may minimize the chances of attack by marauding hordes of army ants, which are one of the dominant forces shaping tropical forest ecosystems. — AMS Biotropica 37 , 670 (2005).

Studies of protonemal morphogenesis in mosses. IX. Discelium nudum: exquisite pioneer of unstable clay banks

The protonemal system of Discelium nudum produces a sward of unicellular, colourless, starch-filled rhizoidal tubers ca 1 cm below the surface of unstable clay banks. These short-lived and desiccation-intolerant diaspores are exposed on new clay surfaces following winter exfoliation of the original substratum. Their abundance and rapid germination appears to be a reproductive strategy giving Discelium a competitive advantage in this highly unstable habitat. The rounded, thin-walled, non-gemmiferous chloronemal filaments and colourless rhizoids of Discelium suggest affinities with the Funariaceae and the Gigaspermaceae. An early report of multicellular tubers in Discelium is most probably due to misinterpretion of the large starch grains, up to 20 μm in diameter, as cells within the unicellular tubers.

Erosion of undisturbed clay samples from the banks of the St. Lawrence River

In some regions the clay banks of the St. Lawrence River along the Montréal to Lac St. Pierre reach have recession rates of up to 1–3 m/year. The banks are formed of structured marine clays of the Champlain Sea (Leda clay). In this laboratory study, undisturbed samples of this high-plasticity inorganic clay taken at Îles de Verchères were subjected to a unidirectional current and a constant wave climate to investigate the mechanisms of erosion and the factors influencing erosion rates. Initially, surface erosion resulted in the formation and enlargement of cracks and the smoothing of competent surfaces. The dominant erosion process was a mass erosion of the blocks of clay delineated by the cracks. Desiccation or weathering significantly increased erosion rates, as tension cracks formed due to drying, and upon rewetting, the formation of microfissures resulted in disintegration into small, easily erodable flakes. The estimated critical shear stress of the samples was 6–20 Pa. For the St. Lawrence River, these results suggest that waves are the dominant erosion mechanism, with shipping contributing significantly to the erosion of banks close to the navigation channel. Weathering caused by wetting and drying from changing water levels or wave runup greatly increases erosion rates.Key words: erosion, Leda clay, undisturbed clay, natural clay structure, St. Lawrence River, waves, weathering, desiccation, vegetation.

Dynamique fluviale et évolution des berges du cours inférieur des rivières Nottaway, Broadback et de Rupert, en Jamésie (Québec

La dynamique fluviale et l'évolution des berges des rivières Nottaway, Broadback et de Rupert sont examinées en regard des phénomènes d'érosion et des caractéristiques morpho-sédimentologiques. Parmi les nombreux agents d'érosion fluviale, ce sont les vagues et les courants qui sont les plus efficaces. Les berges constituées de matériaux limono-argileux et sableux, dont les pentes sont abruptes (< 25°), sont particulièrement sensibles à l'activité fluviale. Les phénomènes et les formes d'érosion les plus fréquemment observés dans la portion aval des rivières étudiées sont les glissements et les éboulements. Ces mouvements de masse entraînent le long des pentes une perte importante de matériaux qui sont directement livrés aux cours d'eau. Les sédiments les plus fins sont transportés en aval et une grande quantité est déversée dans la baie de Rupert. On évalue à près de 883 000 tonnes par année la quantité de sédiments en suspension transportés par les rivières Nottaway, Broadback et de Rupert. Ces apports sédimentaires ont pour conséquence de combler progressivement la baie de Rupert qui est déjà peu profonde (3 à 6 m en moyenne). Ce comblement progressif risque de modifier les conditions hydrologiques et sédimentologiques, notamment en ce qui à trait à l'écoulement et à la circulation des eaux de la baie de Rupert et de la baie de James. Le relèvement isostatique résiduel constitue un autre facteur contribuant à la modification des conditions biophysiques de la baie de Rupert.

Distribution and status of the smooth-coated otter Lutra perspicillata in National Chambal Sanctuary, India

The distribution and relative density of smooth-coated otters Lutra perspicillata Geoffroy were studied along a 425 km stretch of Chambal river within the National Chambal Sanctuary, Central India, between 1988 and 1992. Sample sites of 1 km were surveyed every 5 km. The study revealed that the distribution of otters along the river is patchy and largely restricted to the upper reaches. During the 1988 survey, 36% of sites were found with otter signs but only 24% in 1992. Recent increases in disturbance along the river due to construction of road bridges and mining activities might have put pressure on the population. Most of the positive sites (66%) were found on rocky banks, followed by clay banks (19%), banks with shoreline vegetation and marsh (11%) and sandy banks (3%). During intensive monitoring of four radio-implanted otters, c. 78% locations were made on rocky banks, 19% on banks with shoreline vegetation and marsh, with < 3% on sandy banks and <1% on clay banks, indicating greater preference for rocky banks owing to the greater availability of den sites. As a conservation measure, monitoring of the otter population should be done regularly and restrictions on cultivation, grazing and mining along the banks should be imposed within the Sanctuary limits, especially in the identified stretches.