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L'étude a pour objectif l'identification des zones d'accès à l'eau des agro-pasteurs en saison sèche dans le bassin versant du Goudébo. La démarche utilisée est l'Analyse à Référence Spatiale (AMC-RS) basée sur le Système d'Information Géographique et l'analyse multicritère. Les points d'eau utilisés pour les différents besoins (cours d'eau, boulis, forages, mares, citernes, puisards, puits et barrages) ont été répertoriés avec les populations. Les documents cartographiques et les levés de terrain ont permis, grâce au SIG, de constituer une base de données cartographique de ces éléments. La prise en compte des temps de trajet a permis de spatialiser l'accessibilité aux points d'eau. Les AMC-RS ont été réalisées à partir des résultats du SIG, sur la base de critères de pondération proposés par les producteurs lors des séances d'interviews semi-structurées. Les résultats de l'analyse ont donné 7,4 % de zones présentant un bon niveau d'accès cumulé à différents types de point d'eau. Ces zones relativement limitées sont circonscrites autour de 20 % des villages. L'importance prise par les barrages, et particulièrement celui de Yakouta, pose le problème de la gestion de leur bassin d'alimentation dans l'avenir. The study aims to identify areas where agro-pastoralists access to water during the dry season in the drainage basin of the river Goudébo. The approach is the spatial reference analysis AMC-RS based on Geographic Information System and Multi-Criteria Analysis. Water points used for different needs (boulis, drillings, ponds, tanks, sumps, wells and dams) were identified with the people. Cartographic documents and field surveys have constitute, through the GIS, a map database of these elements. Taking into account the travel times allowed a spatial representation of the accessibility to water points. The AMC-RS were made from the results of GIS, on the basis of criteria proposed by the people during the interviewing sessions. The results of the analysis gave 7.4 % of areas with a high level of aggregate access to different types of water point. These relatively small areas are circumscribed around 40 % of the villages. The importance taken by dams, and particularly that of Yakouta, puts the problem of the management of their feed area in the future.geographic information system, multi-criteria analysis, access to water, Burkina Faso

Entre la Petite Kabylie, au nord, le Hodna, au sud, et les Aurès, au sud-est, s'étendent les Hautes Plaines sétifiennes, terroir céréalier réputé. Dans ces vastes plaines semi-arides, plusieurs massifs montagneux sont isolés. Le djebel Mégriss est l'un des massifs les plus importants de la partie nord de ces Hautes Plaines. Il joue le rôle d'une barrière géographique, en diminuant les influences du sud sur les massifs avoisinants, notamment les monts du Djurdjura et des Babors. Il peut aussi être à l'origine de phénomènes d'isolement biologique, qui ont conduit au maintien d'espèces relictuelles dans des biotopes très localisés, comme des mares temporaires.Il se caractérise par une grande diversité de milieux terrestres et aquatiques. Les milieux terrestres sont représentés, sur le plateau et ses talus, par des pelouses et des matorrals bas. Les milieux humides se composent de mares temporaires de superficie variable, de sources, de ruisseaux temporaires, de prairies inondées en hiver et de marécages à graminoïdes. Cette variété des milieux a joué un grand rôle dans la diversité de la flore où 500 espèces végétales (Phanérogames et Cryptogames vasculaires) et 22 sous-espèces ont été recensées appartenant à 276 genres et 72 familles.Parmi les espèces végétales vasculaires recensées, 40 % sont d'origine méditerranéenne, 24 % sont d'origine nordique, 19 % sont des espèces de transition entre l'élément méditerranéen et les autres éléments chorologiques, 10 % sont des endémiques, 5 % sont des cosmopolites et 2 % sont d'origine tropicale.Deux des particularités de la flore du massif sont, d'une part, sa richesse en orchidées, en particulier en Dactylorhiza, genre eurasiatique, monophylétique, présent principalement dans les zones boréales et tempérées du globe, et, d'autre part, la présence de nombreuses espèces rares appartenant à d'autres secteurs que le Constantinois auquel appartient le djebel Mégriss (Butomus umbellatus, Myosorus minimus, Brunella laciniata, etc.).Le site est menacé par de multiples formes d'anthropisation : surpâturage, captation d'eau, propagation d'espèces envahissantes, cueillette, pollution. Between the little Kabylia, in the North, the Hodna, in the South, and the Aurès, in the southeast, extends the High Plains within the Sétif Province. In these vast plains, semi-arid, several mounts are isolated. The djebel Megriss, represents one of the most important mounts of the north part of these High Plains. It plays the role of a geographical barrier, by decreasing the influences of the South on the neighbouring mounts, in particular the mounts of Djurdjura and Babors. It can also be at the origin of phenomena of biological isolation, which drove to the preservation of relics in very located biotopes (temporary ponds).Its ecosystem is extremely heterogeneous in terms of environment, with characteristic grassland, meadows, low shrubland consisting of Quercusilex and low shrubland consisting of Calicotome and Ampelodesmos ("diss grass"); a peculiarity is the presence of temporary ponds, sources, temporary streams, meadows flooded in winter and meadows dominate by Juncus and Carex.This variety of environment played a big role in the variety of the flora where 500 botanical species (Phanerogams and vascular Cryptogams) and 22 subspecies were listed belonging to 276 genres and 72 families.Among the botanical species vascular listed, 40 % are of Mediterranean origin, 24 % are septentrional, 19 % are species of transition between the Mediterranean element and the other elements, 10 % are endemic, 5 % are cosmopolitan and 2 % are tropical.Two of the peculiarities of the flora of the massif are, on one hand, its wealth in orchids, in particular in Dactylorhiza, present mainly in the boreal and temperate zones of the globe, and, on the other hand, the presence of numerous rare species and belonging to the other sectors than the Constantine region to which belongs djebel Megriss (Butomusumbellatus, Myosorusminima, Brunella laciniata, etc.).The ecosystem is affected by many menaces (cultivation, repeated passage, harnessing of the water, the picking, the distribution of intrusive species, pollution).

International audience; The study area is a geographical entity organized around the floodplain of the lower river valley of the Oued Loukkos and the historic cities of Lixus and Larache. Owing to the double heritage value of this area, natural and historical, the reconstruction of the recent history of its vegetation and its landscapes is particularly relevant. Besides his former occupation in prehistory and antiquity, the area of Larache has played an important role in the Middle Ages and modern times into the greater or lesser strained relations between Morocco and European Powers. In the history, the river Loukkos has always been a route of penetration inside the country and its mouth a strategic site. The port of Larache was also the main export outlet for productions of Gharb and great cities of the hinterland as Basra or Fez (cork, grains, wool ...), since the 16th century. Based on a pollen diagram obtained in the adjacent valley of Oued Sakh-Sokh, we propose here to reconstruct the outline of recent vegetation history (since 14th century), especially the wetlands of the floodplain and the cork oak forest, which constitutes the natural vegetation of the area. This information will then crossed with available historical sources for assessing the various factors of landscape dynamics identified since medieval times. The role of different waves of population and their kinds of exploitation and enhancement of the environment are examined. Degradation of the forest is old because it is on the territory of the cork oak forest that clearing activities took place, mainly for cereal cultivation and livestock. Other human activities such as logging, charcoal production, shipbuilding or fires there also contributed. Agro-silvo-pastoral Parklands are built at the same time. They are comparable to the Dehesa and Montado from the Iberian Peninsula. The history of these original landscapes is recognized for the first time in Morocco.; La reconstitution de l'histoire récente de la végétation et des paysages de la région du Bas-Loukkos, sur la côte atlantique de la péninsule tingitane, avec les villes historiques de Lixus et Larache, revêt un intérêt particulier en raison d'une double valeur patrimoniale : naturelle et historique. A partir d'un diagramme pollinique de l'Oued Sakh-Sokh, les grandes lignes de l'évolution récente de la végétation (depuis le 14ème siècle) sont retracées, en particulier celle de la dépression humide et de la forêt de chêne-liège, qui constitue la végétation naturelle de la zone. Ces informations sont ensuite croisées avec les sources historiques disponibles pour apprécier les différents facteurs des dynamiques paysagères identifiées, depuis l'époque médiévale. Le rôle des différentes vagues de peuplement et leurs formes d'exploitation et de mise en valeur de l'espace est examiné. La dégradation de la forêt est ancienne. Élevage, agriculture et autres activités humaines (exploitation du bois, charbonnage, chantiers navals, incendies) y contribuèrent. Parallèlement, se construisent des parcs arborés à finalité agro-sylvo-pastorale comparables à la Dehesa et au Montado de la Péninsule Ibérique. L'histoire de ces paysages originaux est reconnue pour la première fois au Maroc.

Sur les rives de la sebkha Essijoumi, à l'ouest du centre de Tunis, la croissance démographique est accompagnée d'une extension urbaine soutenue, qui fait des terres agricoles le bassin d'accueil d'une urbanisation le plus souvent non réglementée. L'extension des zones imperméables, l'accroissement de la population et le développement des activités sont à l'origine d'écoulements considérables d'eaux de ruissellement et d'eaux usées domestiques et industrielles, qui rejoignent la sebkha Essijoumi, en grande partie par l'intermédiaire de l'oued Guériana. Aujourd'hui, alors que les rives de la sebkha sont constamment marécageuses et que l'eau y persiste même pendant la période la plus chaude de l'année, la pollution du plan d'eau paraît complexe, tout à la fois organique, bactériologique et chimique.En fait, tout un contexte naturel, social et économique a subi une transformation rapide et profonde. La société occupe et exploite un milieu qui aurait dû rester à l'état naturel ou dont l'aménagement exigeait à tout le moins de nombreuses précautions et une connaissance profonde de sa dynamique.

Situé au Nord Ouest de l'Algérie, le bassin versant en amont du barrage Meffrouche, d'une superficie de 89 km2, a reçu des précipitations annuelles moyennes de 659 mm (à Meffrouche) sur une période de 68 années (1943-44 à 2010-11). Ce bassin, à l'instar de l'ensemble du Maghreb, subit depuis quelques décennies une sécheresse persistante. Différentes approches utilisant les données pluviométriques et hydrologiques sont utilisées dans cette étude afin de préciser le degré de sévérité de cette sécheresse. Les résultats obtenus montrent l'existence d'une cassure d'homogénéité vers le milieu des années 1970. La période avant cette date est qualifiée d'humide, celle qui suit de sèche. Le déficit de la seconde période par rapport à la première, est évalué à près de 30 % pour les précipitations et à plus de 60 % pour les écoulements. Si les années très humides ou extrêmement sèches ont été observées, les deux périodes mises en évidence montrent une humidité, pour l'une, et une sécheresse, pour l'autre, d'intensité légère. Une ou deux années déficitaires en pluviométrie au milieu d'années excédentaires, n'a pas d'effet direct sur l'alimentation en eau des barrages. Par contre, la succession de plusieurs années à pluviométrie moyenne peut générer une année aux écoulements abondants. Meffrouche watershed, located in North-West Algeria with a land area of 89 km2, collects a mean annual rainfall of 659 mm (Meffrouche), computed over a period of 68 years (1943­1944 to 2010-2011). This basin, like most of the Maghreb, has been undergoing a persistent drought for a few decades. Different approaches, using a dataset of precipitation and depth of runoff, are addressed in this study to highlight the severity of this drought. The results obtained show the existence of a break of homogeneity located in the mid-1970s. The previous period is classified as wet, the one after is dry. The deficit between the two periods, valued at nearly 30 % for precipitation caused a drop in flow of more than 60 %. Periods of wetness and dryness are highlighted with a mild tendency to drought. Although some years have been very wet or extremely dry, the appearance of one or two years deficient rainfall in the mid-year surplus has no direct effect on water supplies in dam. For cons, the succession of several years with medium rainfall can generate a strong flow of water year.

L'identification des différentes formations quaternaires de la vallée de l'Orbieu, puis la reconstitution de leur géométrie, permettent de mettre en évidence les principales déformations tectoniques qu'elles ont subies. La néotectonique de cette région des Corbières a été active jusqu'à l'accumulation de la nappe alluviale de la basse terrasse weichsélienne. La datation des travertins de Graffan permettrait de caler la chronologie relative pour le système des terrasses de l'Orbieu. A geomorphological and sedimentological analysis makes it possible to identify the different Quaternary formations in the Orbieu valley. Then, the reconstruction of the longitudinal and transversal profiles shows the evolution of tectonic deformations since the formation settling. Neotectonics have been active up to the accumulation of the alluvial deposits of the Weichselian lower terrace. The dating of the Graffan travertines would allow adjust the Orbieu terraces system chronology.

Les zones côtières sont le lieu d'activités nécessitant des eaux de bonne qualité physico-chimique : usages récréatifs, aquaculture et pêche. Ces zones sont sous l'influence directe des eaux d'oueds et des eaux usées, par où transitent les apports des bassins versants, rejets urbains et industriels. Ces rejets entraînent, lorsque le renouvellement des masses d'eau est faible par rapport aux quantités rejetées, des dégradations notables de la qualité des eaux et des écosystèmes marins.La présente étude porte sur une évaluation qualitative des eaux d'effluents urbains et industriels de deux pôles urbains du littoral oranais (Oran et Mostaganem), dans l'objectif d'évaluer l'état de la contamination par les métaux lourds (Cd, Pb et Zn), ainsi que l'évaluation de la qualité physico-chimique des eaux marines pour déterminer l'impact potentiel de la pollution métallique sur la côte ouest algérienne.La concentration moyenne du cadmium est maximale pour le rejet industriel de Mostaganem (0,88 mg/l – écart-type : 1,35 mg/l). Pour le zinc, la concentration moyenne la plus élevée (0,92 mg/l – écart-type : 1,35 mg/l) correspond au rejet urbain de Mostaganem. Le plomb présente des teneurs moyennes assez fortes au niveau des trois rejets étudiés : 0,23 mg/l pour le rejet urbain d'Oran (écart-type : 0,22 mg/l), 0,22 mg/l pour le rejet industriel de Mostaganem (écart-type : 0,21 mg/l) et 0,19 mg/l pour le rejet urbain de Mostaganem (écart-type : 0,20 mg/l). Si les concentrations en métaux lourds varient beaucoup d'un prélèvement à l'autre, comme le traduisent les écarts-types, aucune évolution durable ne ressort. Seules les teneurs moyennes du cadmium dépassent la limite normative. The coastal areas are the locus of activities requiring water of good physicochemical quality: recreational uses, aquaculture and fishing. These areas are under the direct influence of wadis and wastewaters which pass by the contributions of watersheds, urban and industrial discharge. These discharges result, when the renewal of water masses is small compared to release, significant degradation of water quality and marine ecosystem.This study focuses on an assessment of water quality of urban and industrial effluents from two coastal urban centers western (Oran and Mostaganem), with the aim of assessing the state of contamination by heavy metals (Cd, Pb and Zn), as well as the evaluation of the physico-chemical quality of marine waters to determine the potential impact of metal pollution on the west coast of Algeria.The average concentration of cadmium is maximal for the industrial effluent of Mostaganem (0.88 mg.l-1 – standard deviation: 1.35 mg.l-1). For zinc, the highest average concentration corresponds to the urban effluent of Mostaganem (0.92 mg.l-1 – standard deviation: 1.35 mg.l-1). Lead has average concentrations high enough at the three studied effluents: 0.23 mg.l-1 at the urban effluent of Oran (standard deviation: 0.22 mg.l-1), 0.22 mg.l-1 at the industrial effluent of Mostaganem (standard deviation: 0.21 mg.l-1) and 0.19 mg.l-1 at the urban effluent of Mostaganem (standard deviation: 0.20 mg.l-1). If heavy metal concentrations vary greatly from one sample to another, as reflected in the standard deviations, no lasting change is apparent. Only average levels of cadmium are exceeding the normative.

Les résultats du projet ESEDSEN (Étude sédimentaire du Sénégal) constituent une contribution à la connaissance de l'évolution spatio-temporelle récente de la brèche artificiellement ouverte en 2003 sur la Langue de Barbarie et de ses conséquences. Les profils topographiques réalisés entre octobre 2010 et décembre 2011, indiquent que la rive nord a progressé de 550 m vers le sud entre le 1er mars et le 31 décembre 2011. Dans le même temps, cette rive s'est élargie de près de 100 m. La rive nord fonctionne comme un pôle d'accumulation et/ou de redistribution de débits solides qui alimentent la formation de bancs de sable à l'intérieur et/ou à proximité de l'embouchure du fleuve Sénégal. Sur la même période, la rive sud a régressé de 830 m. La largeur de la brèche fluctue au gré des saisons et des facteurs hydrodynamiques, mais dans une dynamique générale d'élargissement (28 m/mois en moyenne sur la période d'observation). En octobre 2012, la Langue de Barbarie a subi une rupture naturelle importante un peu plus au sud. Cette dynamique de la brèche expose la rive gauche de la lagune de Mboumbaye (falaise du Gandiolais) à une érosion rapide, le recul du rivage dépassant 15 m/an dans les secteurs les plus touchés. Les potentialités économiques et environnementales du littoral du Gandiolais se trouvent ainsi menacées par la migration méridionale de l'embouchure du fleuve Sénégal. The results of ESEDSEN (Étude sédimentaire du Sénégal – Sedimentary Study of Senegal) project are a contribution to the knowledge of the recent space-temporal evolution of the breach artificially opened in 2003 on the Langue de Barbarie and its consequences. Topographic profiles carried out between October 2010 and December 2011 indicate that the north bank rose 550 m to the south between March and December 2011. Meanwhile, the same bank has expanded nearly 100 m. The northern shore functions as a storage and/or redistribution center of sediment discharge fueling the formation of sandbars in and/or near the mouth of the Senegal River. During the same period, the south bank fell by 830 m. The width of the gap fluctuates because of the seasons and hydrodynamic factors, but in a general expansion dynamics (28 m/month on average over the period of observation.) In October 2012, the Langue de Barbarie went through a major natural break a little further in the South. This dynamics of the breach exposes the left bank of the lagoon of Mboumbaye (Gandiolais cliff) to rapid erosion, shoreline retreat being greater than 15 m/year in the most affected sectors. The economic and environmental potential of the Gandiolais coastline are then threatened by the southern migration of the mouth of the Senegal River.

Strong wind events frequently result in creating large areas of windthrow, which causes abrupt environmental changes. Bare soil surfaces within pits and root plates potentially expose soil to erosion. Absence of forest may alter the dynamics of water circulation. In this study we attempt to answer the question of whether extensive windthrows influence the magnitude of geomorphic processes in 6 small second- to third-order catchments with area ranging from 0.09 km2 to 0.8 km2. Three of the catchments were significantly affected by a windthrow which occurred in December 2013 in the Polish part of the Tatra Mountains, and the other three catchments were mostly forested and served as control catchments. We mapped the pits created by the windthrow and the linear scars created by salvage logging operations in search of any signs of erosion within them. We also mapped all post-windthrow landslides created in the windthrow-affected catchments. The impact of the windthrow on the fluvial system was investigated by measuring a set of channel characteristics and determining bedload transport intensity using painted tracers in all the windthrow-affected and control catchments. Both pits and linear scars created by harvesting tend to become overgrown by vegetation in the first several years after the windthrow. The only signs of erosion were observed in 10% of the pits located on convergent slopes. During the period from the windthrow event in 2013 until 2019, 5 very small (total area 2) shallow landslides were created. The mean distance of bedload transport was similar (t-test, p=0.05) in most of the windthrow-affected and control catchments. The mapping of channels revealed many cases of root plates fallen into a channel and pits created near a channel. A significant amount of woody debris delivered into the channels influenced the activity of fluvial processes by creating alternating zones of erosion and accumulation.

Wood accumulations are important morphological agents forming the character of high-gradient streams in the Moravskoslezske Beskydy Mts. The aim of the research is to define both the extent and character of the impact of wood accumulations on the streams. A total of 126 accumulations have been identified of the total wood volume of 503 m3 that is unevenly distributed within the studied streambeds. The wood volume in the studied streambeds is particularly dependent on the age and species composition of vegetation, channel morphology, and the geological bedrock resistance to the action of the stream, especially in forced alluvial reaches. The research revealed the deposition of fine-grained material immediately upstream of the wood accumulations, creating gravel bars and capturing fine organic debris. On the other hand, immediately downstream of the accumulations fine-grained fractions are carried away and coarser material is deposited, creating pools and plunge pools, evorsion potholes and bank scours. The research further showed a low intensity of the transport of woody material through the streambeds. The accumulations usually occur in the place where the stream has been dammed by a fallen tree member or in structurally predisposed streambed segments. As a result, discontinuities in energy and material flow occur that help to increase the streambed heterogeneity.

The impacts of channel morphology on the residues and ecological risks of 14 polychlorinated biphenyl (PCB) congeners in water and sediment were investigated in summer (July) and autumn (September) in the Chahe River, in Nanjing, China. The residual concentrations of tri-chlorobiphenyls (tri-CBs, PCB 18) and tetra-CBs (PCB 52) in water were significantly higher than those of penta-CBs to deca-CBs, and the average residual concentration of ∑PCBs (sum of 14 PCB congeners) in summer was about six times higher than in autumn. However, the residues in sediment did not change significantly. Redundancy analysis (RDA) indicated that channel morphology and the corresponding environmental indices had significant impacts on PCB residues and their composition profiles in water and sediment. The overflow weir and lake-type watercourse may remarkably reduce the residual concentration and ecological risks of PCBs in water. The highest reduction percentages of the residual concentration and ecological risks of ∑PCBs induced by an overflow weir were 78% and 67%, respectively, and those induced by a lake-type watercourse were 36% and 70%, respectively. The watercourses with different channel morphologies were ranked by residual ∑PCBs concentrations in the following descending order: the natural ecological watercourse, vertical concrete watercourse, and vegetation-type riprap watercourse. However, they were ranked by residual ∑PCBs concentrations in sediment in the following descending order: the vertical concrete watercourse, vegetation-type riprap watercourse, and natural ecological watercourse.

Understanding large wood (LW, ≥ 1 m long and ≥ 10 cm in diameter) dynamics in rivers is critical for many disciplines including those assessing flood hazard and risk. However, our understanding of wood entrainment and deposition is still limited, mainly because of the lack of long‐term monitoring of wood related processes. The dataset presented here was obtained from more than 8 years of monitoring of 1264‐tagged wood pieces placed in four low‐order streams of the Chilean mountain ranges, and is used to further our understanding of key factors controlling LW dynamics. We show that LW displacement lengths were longer during periods when peak‐flow water depths (Hmax) exceeded the bankfull stage (HBk) than in periods with Hmax ≤ HBk, and that these differences were significantly higher for smaller wood pieces. LW length and length relative to channel dimensions were the main factors governing LW entrainment; LW displacement lengths were inversely related to the ratio of piece length to H15% (i.e. the level above which the flow remains for 15% of the time) and to the ratio of H15% to bankfull width. Unrooted logs and LW pieces located at the bankfull stage travelled significantly longer distances than logs with attached rootwads and those located in other positions within the bankfull channel. A few large logjams were broken during the period of observation, and in all occasions, LW from these broken logjams did not travel over longer distances than other pieces of LW moved in the same periods and in the same stream segments. Most importantly, our work reveals that LW dynamics tend to be concentrated within a few reaches in each stream and that reaches exhibiting high wood dynamics (extensive entrainment, deposition or repositioning of LW) are significantly wider and less steep than less dynamic reaches.

Understanding and modelling the dynamics of large wood (LW) in rivers during flood events has spurred a great deal of research in recent years. However, few studies have documented the effect of high-magnitude flash floods on LW recruitment, transport and deposition. On 25 October 2011, the Magra river basin (north-western Italy) was hit by an intense rainstorm, with hourly rainfall rates up to 130 mm h−1 and event rain accumulations up to 540 mm in 8 h. Such large rainfall intensities originated flash floods in the main river channels and in several tributaries, causing severe damages and loss of lives. Numerous bridges were partly or fully clogged by LW jams. A post-flood survey was carried out along the channels of two catchments that were severely and similarly affected by this event, the Gravegnola (34.3 km2) and Pogliaschina (25.1 km2). The analysis highlighted a very relevant channel widening in many channel reaches, which was more marked in the Gravegnola basin due to highly erodible material forming the slopes adjacent to the fluvial corridor. Large wood recruitment rates were very high, up to 1270 m3 km−1, and most of it (70–80 %) was eroded from the floodplains as a consequence of channel-widening processes, while the rest came from hillslopes processes. Overall, drainage area and channel slope are the most relevant controlling variables in explaining the reach-scale variability of LW recruitment, whereas LW deposition appears to be more complex, as correlation analysis did not evidence any statistically significant relationship with the tested controlling variables. Indeed, in-channel LW displacement during the flood has been mostly limited by the presence of bridges, given the relatively large width attained by channels after the event.

Rivers change through time in response to upstream and downstream controls and may change over very short time periods (i.e., few years), in particular when human impact affects fluvial systems. In the Lighvan River catchment, a semi-arid mountainous area in northwestern Iran, remarkable changes in the fluvial environment and channel morphology have taken place over the last few years. The aim of this paper is to explain driving factors of channel changes along the Lighvan River, in a 16-km-long reach, over the period 2000–2012. Data and methods used include maps and field survey to quantify channel changes; analysis of hydrological data (precipitation and discharges); Landsat images for land-use classification and then evaluation of possible changes in flood peak discharge by SCS method; and calculation of unit stream power changes. In general, the channel underwent incision (up to 1 m) and narrowing (up to 18 m), although aggradation occurred in few cross sections in the upstream part of the study reach and widening in few cross sections in the downstream part. Investigation of causes of these changes showed that magnitude of annual peak discharges increased over the period 1991–2012, and it can be suggested that such increase is related to natural causes (i.e., increase of precipitation) and human impact so that both human and natural factors had a role in the recent evolution of the Lighvan River. Channelization and increase of peak discharges (due to an increase of precipitation and land-use changes) have been the main drivers of channel evolution.

The catchments in the western Rift Valley escarpment of northern Ethiopia are highly responsive in terms of hydro-geomorphic changes. With deforestation, dense gully and scar networks had developed by the 1980s on the escarpment between the towns of Alamata and Korem, transporting huge amounts of runoff and sediment down to the fertile and densely populated Raya Valley. To reverse this problem, catchment-scale rehabilitation activities were initiated in the mid-1980s. In this study, we examine the major hydro-geomorphic response of streams after catchment rehabilitation. Scar networks in 20 adjacent catchments were mapped on Google Earth imagery of 2005, and their density was explained in terms of its corresponding Normalized Difference Vegetation Index and slope gradient. Soil and water conservation measures and vegetation recovery have reduced discharge and sediment flow which in turn resulted in various hydro-geomorphic changes. In a multiple regression analysis, scar density was negatively related with Normalized Difference Vegetation Index and positively with average gradient of very steep slopes (r2 = 0·53, p

La haute vallée de l'oued Sébaou a une vocation agricole. Située dans la région de Tizi-Ouzou, au nord de l'Algérie, elle connaît un climat méditerranéen. Les réserves en eau y sont considérables, grâce à une nappe dont la réalimentation et la qualité sont directement liées aux transferts d'eau et de solutés depuis la surface du sol. L'étude de ces transferts nécessite, en premier lieu, de connaître les paramètres hydrodynamiques de la zone non saturée proche de la surface du sol et d'établir les courbes caractéristiques K(h) et θ(h) traduisant l'évolution de la conductivité hydraulique (K) et celle de la rétention en eau (θ) en fonction du potentiel de pression (h). Des mesures d'infiltration ont été effectuées in situ, sur cinq sites dont les sols présentent des textures différentes, au moyen d'un infiltromètre à disque, selon la méthode multipotentiel d'ANKENY et al., en appliquant successivement les succions -10, -6, -3, -1 et -0,5 cm. L'infiltration cumulative [I(t)] ainsi mesurée, associée aux humidités initiale et finale, a servi comme donnée dans l'inversion numérique réalisée au moyen du logiciel Hydrus-2D. Cela a permis d'estimer les paramètres du modèle de MUALEM et VAN GENUCHTEN (MVG) choisi pour la présente étude. En complément de l'inversion numérique, des courbes K(h) et θ(h) ont également été tracées selon les méthodes analytiques (de WOODING et d'ANKENY et al.) et à partir des mesures au laboratoire sur un bac à sable. L'effet de la variabilité spatiale de l'humidité initiale a été examiné en prenant en considération, pour chaque essai, les humidités minimale, moyenne et maximale mesurées. Les résultats ainsi obtenus montrent une parfaite corrélation entre les infiltrations cumulatives mesurées et optimisées, avec un coefficient de corrélation très proche de 1 (R² > 0,993) et des intervalles de variation des paramètres optimisés très réduits. Les courbes θ(h) issues de la simulation et du laboratoire sont presque identiques ; cependant, en ce qui concerne les courbes K(h), une différence est constatée, au voisinage de la saturation, entre les résultats de la simulation et ceux des méthodes analytiques. L'hétérogénéité spatiale de l'humidité initiale a en outre un impact sur les paramètres optimisés du modèle MVG, notamment sur la conductivité hydraulique à la saturation (Ks), qui présente des coefficients de variation très élevés, d'une valeur maximale de l'ordre de 60 %. Agricultural valley of High Sebaou is located in the region of Tizi-Ouzou in northern Algeria, it is Mediterranean climate. She has considerable reserves of groundwater in the form of an unconfined aquifer whose recharge and water quality are directly related to transfers of water and solutes from the soil surface. The study of these transfers requires, first, knowledge of hydrodynamic parameters of the unsaturated zone near the soil surface and the establishment of the characteristic curves K(h) et θ(h) reflecting the evolution of the hydraulic conductivity (K) and the water retention (θ) in terms of pressure heads (h). Measurements of infiltration, in situ, on five sites with different textures were made using a disc infilltrometer, using the multipotential method of ANKENY et al., by applying the suctions: -10, -6, -3, -1 and -0.5 cm successively. The measured cumulative infiltration [I(t)] associated with initial and final humidity has served as data in the numerical inversion with Hydrus-2D software to estimate the parameters of the MUALEM-VAN GENUCHTEN model (MVG) used in this study. In addition to the numerical inversion, curves K(h) and θ(h) were also established with the analytical methods (of WOODING and of ANKENY et al.) and from laboratory measurements on the sandbox. The effect of spatial variability of the initial moisture was examined by considering, for each test, the minimum, maximum and average measured values of the humidity. The results thus obtained show a perfect correlation between the measured and optimized cumulative infiltration with correlation coefficient very close to 1 (R2 > 0.993) and with variations intervals very small of the optimized parameters. The curves θ(h) obtained from the simulation and the laboratory are almost identical. However, as regards the curves K(h), a difference is found in the vicinities of saturation between the simulated and analytical methods. Besides, the spatial heterogeneity of the initial moisture has an impact on the optimized parameters of the MVG model, especially on hydraulic conductivity at saturation (Ks), which has very high coefficients of variation, with a maximum of the order of 60 %.

L'étude géomorphologique du petit bassin versant de la Goutte de l'étang de Saloup, en forêt de Tronçais, permet de montrer et d'expliquer la variété des formes des lits fluviaux en milieu forestier et non forestier. L'abondance du bois mort explique, pour une large part, la topographie très irrégulière du lit majeur, façonnée par des chenaux secondaires, qui présente des formes en relief et en creux d'une amplitude verticale de 1 à 1,5 m. La variété spatiale des formes résulte aussi de la lithologie et de la longue histoire du massif forestier qui a subi divers types d'exploitation. Ainsi la destruction par le feu de la forêt associée au développement de clairières cultivées, aux alentours du VIIème siècle AD, a-t-elle pu provoquer une crise érosive aboutissant à une importante accumulation sableuse transformée localement en terrasse. Depuis sa réalisation en 1817, le barrage de Saloup favorise l'accumulation de sables près de l'exutoire des cours d'eau qui l'alimentent. A geomorphological and sedimentological analysis of the Goutte de l'étang de Saloup watershed, in the Tronçais forest, makes it possible to show and explain the different channel morphologies in forested and non forested areas. Large woody debris have morphologic impacts that cause unequal topographies in the flood plain shaped by secondary channels, the level difference between relief and hole forms reaching 1­1,5 m. But the lithology and the forest long history, with forest clearing episodes, also explain the spatial morphologic variety. Thus, forest fires and clearings could have caused sandy accumulation at 1365±30 BP, date obtained from charcoal finded in the alluvial deposits. Since 1817, the Saloup dam also favoured sandy accumulation in the downstream river reaches.

I - Introduction Caulerpa racemosa est une macrophyte originaire du sud-ouest de l'Australie et dont l'aire de répartition actuelle est préoccupante, vue sa présence dans les mers tropicales et tempérées chaudes. Elle est décrite dans la littérature avec de nombreuses variétés et formes différentes qui pourraient en fait masquer plusieurs espèces distinctes (M. VERLAQUE et al., 2000). La forme Caulerpa racemosa, considérée comme envahissante par de nombreux auteurs (M. VERLAQUE et al., 2003, ...

La Macta est un complexe de marais littoraux alimenté par un réseau hydrographique temporaire et dense. Cette zone humide abrite des biotopes et des biocénoses très riches. Elle représente de ce fait un pôle de biodiversité à l'échelle de l'Algérie et même du bassin méditerranéen. L'accentuation de la pression anthropique n'a pas cessé de modifier le fonctionnement et les caractéristiques de cet écosystème fragile. Le classement de la Macta, en 2001, comme zone humide à protéger dans le cadre de la convention de Ramsar, ainsi que la promulgation plus récente d'une loi littorale, devraient normalement permettre de jeter les bases d'une protection durable de cet espace. Cependant nos investigations de terrain et les entretiens que nous avons menés avec les différents acteurs impliqués dans la gestion des marais de la Macta, ont montré la persistance de grosses difficultés dans la mise en œuvre des actions de sauvegarde préconisées. Macta is a complex of coastal marshes fed by a dense and temporary river network. This wetland hosts rich biotopes and biocenoses, and represent therefore an important biodiversity spot for Algeria and even for the Mediterranean Basin. Increasing anthropogenic pressure resulted in a constant environmental perturbation of this fragile ecosystem. The registration of La Macta, in 2002, as a wetland to be protected in the frame of Ramsar Convention, together with the promulgation of a national littoral protection act, will eventually ensure integrated and sustainable protection of this area. However, our field investigations as well as interviews with actors involved in the management of Macta marshes, highlighted continuous serious difficulties for the implementation of recommended measures of protection.

En s'appuyant sur des documents scientifiques originaux, l'inventaire des lahars historiques aux Antilles françaises a été réalisé dans l'objectif de constituer une base de données géoréférencées : la BDFAHL (French Antilles Historical Lahar). Cette base de données recense à la fois la localisation des coulées, leurs caractéristiques et leurs impacts éventuels. Avec plus de 170 lahars ou laves torrentielles recensés, cet inventaire a permis, d'une part, d'appréhender la diversité des processus lahariques et, d'autre part, de proposer une typologie des coulées selon trois critères : le contexte, l'origine et la concentration sédimentaire. En outre, malgré des lacunes durant les éruptions de la Montagne Pelée, cette base de données apporte également des éléments concernant l'occurrence et la menace que représente cet aléa. Enfin, l'inventaire met en évidence les cours d'eau identifiés comme étant "volcaniques majeurs ou principaux", qui concentrent la majorité de l'activité laharique, leur bassin de réception torrentiel se situant sous le sommet du volcan, par opposition aux cours d'eau "volcaniques secondaires", moins dangereux car drainant essentiellement la base du cône volcanique et les glacis d'accumulation. Avec une méthodologie similaire, cet inventaire devrait être étendu au reste de l'archipel, afin de constituer la BDLAHL (Lesser Antilles Historical Lahar). Ce serait l'occasion d'identifier les cours d'eau "volcaniques majeurs" de la région et d'éventuelles particularités ne se produisant pas sur les deux volcans français étudiés. Substantiated by original scientific reports, the inventory of historic lahars in the French West Indies was conducted in order to constitute a geo-referenced database: the BDFAHL (French Antilles Historical Lahar). This database lists the localization of flows, their characteristics and their possible impact. With more than 170 identified debris flows or lahars, this inventory takes into account the diversity of laharic processes and proposes a typology of flows according to three criteria: the context, the origin and the sediment concentration. Moreover, despite gaps in the continuity of magmatic eruptions of the Montagne Pelée, the database also provides evidence of the occurrence and the threat of this hazard. Finally, the inventory distinguishes the "major or principal volcanic" streams, in which concentrates the majority of the laharic activity occurs because their torrential catchment area is below the top of the volcano, from the "secondary volcanic" streams that are less dangerous because they essentially drain the base of the volcanic cone and the accumulation glacis. Following a similar methodology, this inventory should be extended to the rest of the archipelago to form the BDLAHL (Lesser Antilles Historical Lahar). This would provide an opportunity to identify the major volcanic streams of the region and to identify other possible features which do not occur on any of the other French volcanoes previously studied.

International audience; The Karakash river watershed is situated in an arid zone, in the southern part of Xinjiang. In this watershed, floods occur during summer, almost each year, and destroy crops that are the main income of the population. Flooding cause damages that hinder socio-economical development. Flood prevention must be integrated at the gobal water management. Our work demonstrates the applicability of hydrogeomorphological method in the Karakash watershed. Hydrogeomorphological mapping provides informations that are able to permit a spatial planning to prevent and reduce flood risks.; Le bassin versant du Karakash est situé au Sud du Xinjiang, dans une zone aride. Les inondations qui se produisent l'été, presque tous les ans, détruisent les récoltes, principales sources de revenus pour la population, et entravent le développement socio-économique. La prévention des inondations doit donc y être intégrée à la gestion globale de l'eau. Notre travail a pour objectif de démontrer l'applicabilité de la méthode hydrogéomorphologique, mise au point en France méditerranéenne, dans le bassin versant du Karakash. La cartographie hydrogéomorphologique fournit des informations suffisantes pour permettre aux aménageurs de réaliser une planification spatiale susceptible de prévenir et de réduire les risques d'inondation.

Dunes are present in nearly all fluvial channels and are vital in understanding sediment transport, deposition, and flow conditions during floods of rivers and estuaries. This information is pertinent for helping developing management practices to reduce risks in river transportation and engineering. Although a few recent studies have investigated the micromorphology of a portion of the Yangtze River estuary in China, our understanding of dune development in this large estuary is incomplete. It is also poorly understood how the development and characteristics of these dunes have been associated with human activities in the upper reach of the Yangtze River and two large-scale engineering projects in the estuarine zone. This study analyzed the feature in micromorphology of the entire Yangtze River estuary bed over the past three years and assessed the morphological response of the dunes to recent human activities. In 2012, 2014, and 2015, multi-beam bathymetric measurements were conducted on the channel surface of the Yangtze River estuary. The images were analyzed to characterize the subaqueous dunes and detect their changes over time. Bottom sediment samples were collected for grain size analysis to assess the physical properties of the dunes. We found that dunes in the Yangtze River estuary can be classified in four major classes: very large dunes, large dunes, medium dunes, and small dunes. Large dunes were predominant, amounting to 51.5%. There was a large area of dunes developed in the middle and upper reaches of the Yangtze River estuary and in the Hengsha Passage. A small area of dunes was observed for the first time in the turbidity maximum zone of the Yangtze River estuary. These dunes varied from 0.12 to 3.12 m in height with a wide range of wavelength from 2.83 to 127.89 m, yielding a range in height to wavelength of 0.003–0.136. Sharp leeside slope angles suggest that the steep slopes of asymmetrical dunes in the middle and upper reaches, and the turbidity maximum zone of the Yangtze River estuary face predominantly towards tides because of the ebb-dominated currents. Sharp windward slope angles in the lower reach of the North Passage show the influence of flood-dominated currents on dunes. It is likely that the scale of dunes will increase in the future in the South Channel because of a sharp decline of sediment discharge caused by recent human activities.

Topographic information is fundamental to geomorphic inquiry, and spatial prediction of bed elevation from irregular survey data is an important component of many reach-scale studies. Kriging is a geostatistical technique for obtaining these predictions along with measures of their reliability, and this paper outlines a specialized framework intended for application to river channels. Our modular approach includes an algorithm for transforming the coordinates of data and prediction locations to a channel-centered coordinate system, several different methods of representing the trend component of topographic variation and search strategies that incorporate geomorphic information to determine which survey data are used to make a prediction at a specific location. For example, a relationship between curvature and the lateral position of maximum depth can be used to include cross-sectional asymmetry in a two-dimensional trend surface model, and topographic breaklines can be used to restrict which data are retained in a local neighborhood around each prediction location. Using survey data from a restored gravel-bed river, we demonstrate how transformation to the channel-centered coordinate system facilitates interpretation of the variogram, a statistical model of reach-scale spatial structure used in kriging, and how the choice of a trend model affects the variogram of the residuals from that trend. Similarly, we show how decomposing kriging predictions into their trend and residual components can yield useful information on channel morphology. Cross-validation analyses involving different data configurations and kriging variants indicate that kriging is quite robust and that survey density is the primary control on the accuracy of bed elevation predictions. The root mean-square error of these predictions is directly proportional to the spacing between surveyed cross-sections, even in a reconfigured channel with a relatively simple morphology; sophisticated methods of spatial prediction are no substitute for field data. Copyright © 2007 John Wiley & Sons, Ltd.

Catchment-scale land-use changes and erosion-control works have geomorphic consequences as can be seen in the morphological evolution of river channels. An analysis of the consequences of check dams and reforestation works that took place in the 1970s on the channel morphology in the Rogativa catchment (53 km2) in SE Spain is conducted. A land-use change detection analysis of the catchment between 1956, 1981, and 1997 was performed. River channel changes were mapped between 1956 and 1997. Furthermore, morphological field mapping of river reaches, location of all check dams, and characterization of the areas upstream and downstream of them were carried out. Sediment sampling along 10.5 km of the channel and analysis of time series precipitation data were performed. A slight decreasing tendency of the annual precipitation and erosivity of rainfall since the 1940s has been detected. In addition, vegetation cover has increased enormously in the catchment since the 1950s. The dense forest has increased fivefold and the dryland farming areas have been reduced by a 57%. Of all 58 check dams, 72% are silted and 81% of them show erosion features downstream. The active channel has narrowed and many of the lateral bars have been colonized by vegetation. A lateral displacement of the active channel is also observed. Sediment supply has decreased because of the reduction of non-point sources of sediment (i.e., decrease in dryland farming areas and pasture land) and sediment retention behind check dams. Water flow with an increased transport capacity started erosion locally downstream of check dams. The decrease of sediment supply has caused a general armoring of channels. Currently, most of the check dams have lost much of their trap efficiency, erosion of the alluvial wedges upstream of dams is starting, degrading their structure and mobilizing the sediments retained during the past 30 years. Although seemingly clear that land-use changes, reforestation, and correction works affect the channel responses and sediment dynamics, the relative importance of each of these factors with respect to the morphological channel dynamics remains unclear, which is proposed for further research., This work has been financially supported by the project “Respuesta Hidrológica y Geomorfológica de los Sistemas Fluvio-Torrenciales afectados por proyectos de Restauración Hidrológico-Forestal en cuencas semiáridas del Sureste Peninsular” of the Fundación Instituto Euromediterráneo de Hidrotecnia (CE). The first author was financially supported by an I3P postdoc contract CSIC-CE and a “Ramón y Cajal” contract from the Education and Science Ministry (Spain). Gonzalo G. Barberá also was supported by I3P postdoc contract.

The Volga River in the Russian Federation has been regulated by a cascade of reservoir dams since the 1950–1960s. This chapter presents an overview of the main hydrological and morphological responses of the Volga River downstream of the Volgograd reservoir dam. Regulation caused a decrease in magnitude of the spring peak flow, an earlier start and peak of the flood and a considerably steeper rise and fall of the flood. Morphological responses include a considerable channel incision in the river stretch downstream of the Volgograd dam. Furthermore, the reduction in peak flow magnitude results in a general tendency of silting up of secondary channels, and promotes vegetation colonisation along the active parts of the floodplain. Restoring the natural flow regime and morphodynamics will be problematic, particularly in view of the potential hydrological impacts of climate change.

On October 25th 2011, the Magra river basin (North-western Italy) was hit by an extreme meteorological event, with hourly rainfall rates up to 130 mm h−1 and event rain accumulations up to 540 mm. Such large rainfall intensities originated flash floods in the main river channels and in some of the tributaries, causing severe damages and loss of lives. Numerous bridges were partly or fully clogged by large wood (LW) jams. A post-flood survey was carried out along the channels of two catchments that were severely and similarly affected by this event: Gravegnola (34.3 km2) and Pogliaschina (25.1 km2). The results obtained show an important change in the morphology of the channels, which width increased on average 10 and 3 times respectively in the two catchments. Large wood recruitment rates are very high, up to 1,270 m3/km, and most of it (70–80 %) is eroded from the floodplains, while the rest come from the slopes. Despite the variability observed, large wood dynamics seems to be related to the channel morphology. The lessons learned from this event may be useful for a management of mountain catchments which should explicitly take into account the crucial role of LW during extreme events, especially for its interaction with bridges.

An integrated investigation based on field surveys and GIS modeling is being carried out in the Rienz basin (630 km2, Eastern Italian Alps), to predict large wood (LW) recruitment and transport during large flood events. Mobility and transport distance of LW elements of different size is being monitored through repeated surveys of tagged logs in different reaches of the main Rienz River and in one of its tributaries, the Brunst Creek (11.3 km2). Preliminary results show both mobility and displacement length seem to be highly influence by channel morphology characteristics rather than by hydraulic variables. Potential LW deriving from unstable slopes connected to the channel network is predicted using the SHALSTAB model coupled to a GIS-based connectivity index. Connected LW volumes from the slopes, summed to LW erodible within the river corridors, are then routed through the stream network applying simple Boolean transport conditions.

L'analyse des anciennes formes de terrain subaériennes a souvent été mise à contribution, s'agissant de terrasses d'abrasion marines ou de terrasses récifales, afin de rechercher les indices de terrain des anciennes lignes de rivage de haut niveau, et de mettre ainsi en évidence des variations globales du niveau de la mer qui se sont produites au cours du Quaternaire.S'agissant des terrasses marines construites de sédiments détritiques meubles, cet usage d'une analyse géomorphologique se heurte à plusieurs obstacles, allant de l'aménagement de terrasses de culture à l'érosion qui s'est exercée aux dépens de ces sédiments, parfois même avant la mise en place d'un dépôt de pente, faisant suite à la transgression.Mais, dans ce contexte, une autre démarche géomorphologique visant le même objectif final est envisageable. Elle consiste à identifier les anciennes formes de terrain fossiles, qui, sur une plaque continentale en cours de soulèvement, constituent immanquablement, en raison d'une érosion continentale ou marine, la surface de transgression sur laquelle reposent les sédiments de chaque dépôt de terrasse, ainsi distingué de celui qui le précède et de celui qui lui fait suite. La création de ces anciennes formes de terrain, et leur fossilisation, résultent du jeu de divers processus de morphogenèse et de sédimentation, qui témoignent d'une succession de régressions et de transgressions marines, voire des modalités du déroulement des transgressions, où les changements de la vitesse d'élévation du niveau de la mer, d'où dépendent celles de la profondeur d'eau, influent sur l'exercice du processus d'abrasion et sur les caractères des sédiments mis en place après son interruption, intervenant au cours de la transgression.Cette différenciation vaut aussi pour des oscillations glacio-eustatiques de fortes fréquences, qui se sont produites, notamment, pendant le Dernier Interglaciaire et l'avant-dernière déglaciation (Termination II), à l'échelle du millénaire. Ainsi, en Calabre méridionale, un taux de soulèvement élevé, de l'ordre de 1,3 m/ka, autorise la mise en évidence sur le terrain des preuves géomorphologiques profondes de variations du niveau de la mer, après que sa position ait dépassé son niveau actuel, confirmant et même complétant en cela les données enregistrées sur la courbe eustatique, dérivée de la courbe isotopique planctonique KL11 à haute résolution, en corrélation avec des décharges d'icebergs et les fluctuations de la température de l'air. Former subaerial landforms are the most commonly used marker for locating the paleo-shorelines, in order to detect global sea-level change.However, such a geomorphological survey presents some difficulties because of agricultural arrangements or natural erosion affecting loose marine siliciclastic sediments, even before the setting of slope deposits.But other geomorphological approach is possible. It consists to identify the former buried landforms, which are carved by terrestrial or marine erosion into an uplifting tectonic continental plate, and support the transgressive sediments package of each successive marine terrace deposit.The creation of these landforms, and their fossilization, are the result of a succession of sea-level fallings and sea-level rises, even if at a millenial-scale, where the rate of sea-level change and the resulting water-depth, control marine erosion and wave-induced shape-sorting processes.This approach also has somewhat to say about Last Interglacial and Termination II millenial-scale sea level variability.

article i nfo This study examines channel-reach morphology and bedload yield dynamics in relation to landscape structure and snowmelt hydrology in headwater streams of the Columbia Mountains, Canada. Data collection relies on field surveys and geographic information systems analysis in conjunction with a nested monitoring network of water discharge and bedload transfer. The landscape is characterized by subdued, formerly- glaciated upland topography in which the geomorphic significance of landslides and debris flows is negligible and fluvial processes prevail. While the spatial organization of channel morphology is chiefly controlled by glacially imposed local slope in conjunction with wood abundance and availability of glacigenic deposits, downstream patterns of the coarse grain-size fraction, bankfull width, bankfull depth, and stream power are all insensitive to systematic changes of local slope along the typically stepped long profiles. This is an indication that these alluvial systems have adjusted to the contemporary snowmelt-driven water and sediment transport regimes, and as such are able to compensate for the glacially-imposed boundary conditions. Bedload specific yield increases with drainage area suggesting that fluvial re-mobilization of glacial and paraglacial deposits dominate the sedimentary dynamics of basins as small as 2 km 2 . Stepwise multiple regression analysis shows that annual rates of sediment transfer are mainly controlled by the number of peak events over threshold discharge. During such events, repeated destabilization of channel bed armoring and re-mobilization of sedi- ment temporarily stored behind LWD structures can generate bedload transport across the entire snowmelt season. In particular, channel morphology controls the variability of bedload response to hydrologic forcing. In the present case studies, we show that the observed spatial variability in annual bedload yield appears to be modulated by inter-basin differences in morphometric characteristics, among which slope aspect plays a critical part.

International audience; Significant climate changes affect a large part of our planet. The various models show an increase in rainfall and temperatures in many parts of the world. This research work analyzes the evolution of temperatures and rainfall recorded on the Algerian coast during more than forty years. The evolution of these two parameters reflects the recent climate upheaval experienced in recent years in North Africa and the Great Maghreb.; Des changements climatiques importants affectent une grande partie de notre planète. Les différents modèles prévoient ainsi une hausse probable des précipitations et des températures dans plusieurs régions du monde. Le présent travail analyse l'évolution des températures et des pluies enregistrées sur le littoral algérien pendant plus de quarante années. Les évolutions de ces deux paramètres témoignent des bouleversements climatiques subis ces dernières années par l'Afrique du Nord et le Grand Maghreb.

Throughout the world before the 1970s, in-channel large wood (hereafter LW), was generally considered a nuisance or a hazard to be avoided because of the hydraulic effects and consequential associated risks that it could produce. LW was systematically removed from channels for a perceived benefit to human activities. Over the last four decades, LW has received an increasing interest among scientists who recognise it as a significant structural and functional component of aquatic ecosystems. Research in geomorphology has addressed LW characters and its effects on flow hydraulics, on channel and valley forms and their evolution, on the storage and transfer of sediment and organic matter, as well as on associated habitats for aquatic communities. After considering the space-time framework within which the wood dynamics can be studied, we highlight the LW effects on channel morphology and fluvial processes, the ecological and societal consequences of wood in rivers and implications in terms of river management and restoration. After centuries of wood removal, LW is now introduced in rivers for ecological improvement in some areas of North America, Europe, Australia, and Japan.

High-resolution topographic data expand the potential of quantitative analysis of the earth surface, improving the interpretation of geomorphic processes. In particular, the morphologies of the channel beds of mountain streams, which are characterised by strong spatial variability, can be analysed much more effectively with this type of data. In the present study, we analysed the aerial LiDAR topographic data of a headwater stream, the Rio Cordon (watershed area: 5 km2), located in the Dolomites (north-eastern Italy). The morphology of the channel bed of Rio Cordon is characterised by alternating step pools, cascades, and rapids with steps. We analysed the streambed morphology by means of ad hoc developed morphometric indices, capable of highlighting morphological features at a high level of spatial resolution. To perform the analysis and the data interpolation, we carried out a channel-oriented coordinate transformation. In the new coordinate system, the calculation of morphometric indices in directions along and transverse to the flow direction is straightforward. Three geomorphometric indices were developed and applied as follows: a slope index computed along the whole width of the channel bed, directional variograms computed along the flow direction and perpendicular to it, and local anomalies, calculated as the difference between directional variograms at different spatial scales. Directional variograms in the flow direction and local anomalies have proven to be effective at recognising morphologic units, such as steps, pools and clusters of large boulders. At the spatial scale of channel reaches, these indices have demonstrated a satisfactory capability to outline patterns associated with boulder cascades and rapids with steps, whereas they did not clearly differentiate between morphologies with less marked morphological differences, such as step pools and cascades.

No Abstract. Journal of Aquatic Sciences Vol. 20(2) 2005: 89-95

This research quantifies amounts and characteristics of woody debris in mountain channels of the Alps. All pieces of woody debris greater than 5 cm diameter and 0.3 m length have been surveyed along five channels of the Dolomites (Italian Alps) with channel slopes ranging from 0.04 to 0.26 (basin area 2.2–51 km2). During the survey, channels were divided into uniform reaches and the mean gradient, bankfull width and depth of flow were measured. Overall, 4900 woody debris pieces, single and jam-forming, were measured and classified with respect to several qualitative attributes, such as presence/absence of rootwads, orientation to flow, and position in the channel. Results show that very large variations in the volume of woody debris per unit area of the streambed occur even within single streams, and that inputs mainly result from slope instabilities adjacent to the channels. Amounts of woody debris are low compared to most previous data published from different world regions, but match with other mountain rivers of the Alps. Debris transport seems to be of minor importance compared to local inputs from the slopes, because reach characteristics are poorly correlated with the volume of woody debris in a reach. A strong negative correlation is, however, observed between basin area and average density of woody debris in the five channels, but debris removal in the larger channels likely affects such a trend. Finally, the frequency of log steps is inversely correlated to drainage area, and positively related to the density of debris.

A recent study reported considerable sediment trapping by three large channel bars downstream 18–28 km of the Mississippi–Atchafalaya River diversion (commonly known as the Old River Control Structure, ORCS) during the 2011 Mississippi River flood. In this study, we analyzed 3-decadal morphological changes of the 10-km river channel and the three bars to elucidate the long-term effects of river engineering including diversion, revetment and dike constructions. Satellite images captured between 1985 and 2015 in approximate 5-year intervals were selected to estimate the change of channel morphology and bar surface area. The images were chosen based on river stage heights at the time when they were captured to exclude the temporal water height effect on channel and bar morphology. Using a set of the satellite images captured during the period of 1984–1986 and of 2013–2014, we developed rating curves of emerged bar surface area with the corresponding river stage height for determining the change in bar volume from 1985 to 2013. Two of the three bars have grown substantially in the past 30 years, while one bar has become braided and its surface area has shrunken. As a whole, there were a net gain of 4,107,000 m2 in surface area and a net gain of 30,271,000 m3 in volume, an equivalent of approximately 36 million metric tons of sediment assuming a bulk density of 1.2 t/m3. Sediment trapping on the bars was prevalent during the spring floods, especially during the period of 1990–1995 and of 2007–2011 when large floods occurred. The results suggest that although revetments and dikes have largely changed the morphology of the channel and the bars, they seem to have a limited impact on the overwhelming trend of sediment deposition caused by the river diversion.

The distribution and abundance of macrophytes, land-use beyond the riparian zone, characteristics of the riparian zone and selected channel properties have been studied in 9 streams flowing through an agricultural landscape in the north-eastern part of Slovenia. The streams studied supported a rich macrophyte community. Altogether, 53 plant taxa were observed on 93 km of the streams. Canonical correspondence analysis indicated that 10 out of the 11 parameters examined significantly influenced macrophyte distribution. Of these, substrate characteristics and riparian vegetation type were the most influential. Species composition analysis revealed that the majority of species indicated moderate nutrient load while, in the more strongly modified reaches, species indicating eutrophic conditions, i.e. Myriophyllum spicatum and different species of genus Potamogeton , were more abundant.