A Bidimensional Model of the Tagliamento River

The propagation of a flood wave is a very challenging topic, crucial in managing the flood risk. In the literature, several numerical models have been proposed to deal with this issue; most of them need the roughness coefficients to be assigned by the operator. The bottom roughness calibration of floodplains and channels represents a key point for flood studies, because it can heavily influence the results of any kind of numerical simulation. In this study, a numerical model is applied to the Tagliamento River, in North-East Italy. One of the main characteristics of this river is its natural environment, which changes from a very wide braided channel in the middle course to a narrow meandering river moving towards the sea. This makes the bed roughness extremely variable along the river, with different kind of vegetation, braiding, different grain size, meandering, etc. In this regard, particular care should be devoted to the roughness coefficient attribution and calibration. In the present paper, we present the detailed step of calibration and validation of a bidimensional numerical model on the Tagliamento River. A novel method to assign and calibrate roughness coefficient is introduced. Finally, the model is validated against two main flood events occurred in 1966 and 1996.

Sandstone body character, river styles, and geomorphology of the lower Eocene Willwood Formation, Bighorn Basin, Wyoming, USA

The lower Eocene Willwood Formation of the intermontane Bighorn Basin, Wyoming, USA, is an alluvial red bed succession with a sand content of ca. 20%-25%. The formation has been studied intensively for paleontology, paleoclimate, and sedimentary reconstruction. However, alluvial sandstone bodies and their corresponding river styles remain little characterized and documented. Here, efforts are made to study the characteristics and river styles of sandstone bodies through ca. 300 m of alluvial stratigraphy in the McCullough Peaks outcrop area based on the field data and a georeferenced 3-D photogrammetric model. Four channel facies associations are recognized, and they are ascribed to four river planform styles: distributary channel, massive trunk-shaped channel, braided channel, and sinuous channel, with the latter two styles being the more abundant. The channel sandstone bodies that show the character of sinuous rivers and those of braided rivers differ significantly in average thickness (6.1 m versus 9.0 m) and insignificantly in average width (on average 231 m) and paleoflow directions (on average N003). Braided-character dominated and sinuous-character dominated river styles are seen to alternate in the outcrop, while they show no spatial dependency in the 10 km2 study area. Bighorn Basin margins varied in the early Eocene, with differing tectonic, geological, and topographic characteristics. The observed mixture of river styles may be attributed to differential influences of axial and transverse river systems and/or climate change that controls water discharge and sediment load. An early Eocene geomorphologic reconstruction is constructed summarizing these new and earlier results.

Hydrodynamics of braiding river

Braided river reaches and alluvial systems are characterized by their multi-threaded planform and agents of sediment transport due to eroding and deposing to form the bars and riffles. In braided river, frequent sediment transport and the quick shifting of the positions about the river channel induce many attentions discussion and relating a complicated consideration of the combinations of disciplines. In this article we introduce its fundamental characteristics and further the complicated mechanism in the literature and methodologies. The braided channel ecology and the management of braided river are mentioned and discussed, especially, the secondary currents, in this paper we explain in detail, the combinations on multiplying of 2-D flow of the velocity fluctuations. The interdisciplinary approach on linking engineers, earth scientists and social scientists concerned with environmental economics, planning, and societal and political strategies in order to fully evaluate the validity and reliability of different selections to various timescales is really sensitive. Furthermore, the requirements of public education on reinforcing about the mechanism of braided river formation will be obviously important and necessary.

Dendrogeomorphic reconstruction of debris-flow activity in Mazeri Valley, Greater Caucasus, Georgia

<p>The Mazeri Valley in the Greater Caucasus (Georgia) is characterized by a highly dynamic landscape with several active mass-wasting processes. The spatial and temporal dynamics of these geomorphic processes have, over time, resulted in the formation of large cones and fans. In this context, the coupling between the hillslope and the channel plays a fundamental role in controlling the catchment sediment dynamics. The sediment produced at higher altitudes on hillslopes may occasionally reach the debris-flow channel network, and downstream propagation may have significant effects on the fluvial environment and create potential hazards for the resident population, tourists and infrastructures. In this study, we aim to better understand sediment fluxes in the mountain headwater stream in the Mazeri Valley. In this regard, a tree-ring-based chronology of the debris-flow activity on a large cone was created, to shed light on sediment connectivity and better understand the coupling between the main debris-flow channel and the bedload of Dolra river. The 161 disturbed trees sampled allowed to reconstruct a minimum of 12 significant debris-flow events over the last 65 years, with all of these events involving possible sediment input into the stream system of the Dolra river. These successional events, with a return interval of 5.4 years, have partially destabilized the fluvial system and locally induced a switch in the channel style to a braided channel. Although the cone studied is not directly located in a proglacial environment, its geomorphological dynamics remain highly dependent on water and sediment inputs from upstream, giving the presence of retreating glaciers and then paraglacial conditions at high altitude. The ongoing glacial retreat and increased climate variability will certainly lead to a massive output of sediments at high altitude, favoring an increase in geomorphic activity in the area. Many other fan and cone complexes are present in the Mazeri Valley, as well as in other adjacent valleys, and there are no documentations regarding their dynamics (e.g., typology, nature and source areas of hillslope processes, their coupling with channelized sediment-water flows, frequency–magnitude relationships). In this regard, we expect that the present pioneering study in this area will encourage more researches to investigate sediment fluxes for a better land use and preservation of water in Georgia under climate change.</p><p><em>Cette étude représente une contribution pour le projet « Impact du changement climatique sur les glaciers et les risques associés dans le Caucase Géorgien - IMPCLIM », financé par l’Agence Universitaire de la Francophonie (AUF) et le Ministère pour la Recherche et l'Innovation de Roumanie (MRI) à travers l'Institut Roumain de Physique Atomique (IFA).</em></p>

Application of Spectral Decomposition and RGB Blending for Delineation of “S” Channel At Asri Basin

Gita member is part of Talang Akar Formation is known as hydrocarbon reservoir at Asri Basin, eastern part of South Sumatra. This formation consists of several depositional systems such as braided channel, meandering channel, fluvial-deltaic, and estuarine system. A channel system was an interesting system developed in the Asri Basin, however, to get the channel distribution in Asri Basin is quite challenging because the thickness of the channels caused its appearance is generally close or under seismic resolution, the existence of coal below our target also affects the impression of “S” sand on seismic data. In this study, spectral decomposition and RGB Blending have been successful to identify “S” sand. RGB Blending map is extracted from 15 Hz as low frequency, 45 Hz as middle frequency, and 75 Hz as high frequency. Our interpretation was applied at RGB Blending map and reveal the “S” sand is classified as a meandering channel depositional system with the main direction of the channel is Northeast – Southwest.

Braided rivers networks dynamics: analyzing topographic data from a large flume experiment

<p>Braided rivers are highly dynamical systems characterized by varying network-like structures even under quasi-steady conditions. Understanding their dynamics is crucial in geomorphology and river engineering (e.g., river restoration in Alpine and piedmond streams). Open questions about these dynamics include the definition and quantitative description of bed equilibrium. Here we propose to tackle this problem using a new method based on graph theory. This algorithm, called low-path allows one to extract the network structure of a braided river from its Digital Elevation Model (DEM). It is then possible to quantify and analyse the dynamics of the braided system, and not just the bed evolution, as has been done in earlier studies. To assess the dynamics and equilibrium of a braided river, we study two runs representing two distinct phases of the same braided river: the transition from a single channel to a braided river (run 1) and the equilibrium state of this river (run 2). A set of control parameters was used to characterise both runs and supplement the low-path method. We find that although a clear distinction can be made between straight channel and braided channel for both methods, it is more difficult to distinguish between transitional braided and equilibrium braided rivers. Finally we propose a set of dimensionless numbers that specify the braided network and can be used with numerical or stochastic simulations of a braided network. To illustrate their utility, we apply the Low Path method to a real Alpine braided river (the River Navisence, Wallis, Switzerland) and compare the results to our experimental data.</p>

The Khuray deep-water fan: a beautifully complex lacustrine depositional system of Lake Baikal

<p>Lake Baikal (Russia) is the World’s oldest and deepest lake, which has been formed within a recently active rift zone at the edge of Siberian platform. Active tectonics influences all subaqueous geological processes in the Lake area with sedimentation, in particular. Selenga River is the largest river flowing into Lake Baikal. The river carries a large amount of terrigenous material sourced from Siberian-Mongolian drainage basin. Selenga River forms a large delta and several deep-water fans in the Central and South Baikal basins. Large amount of supplied terrigenous material, high sedimentation rates, steep slopes of the Baikal basins and active tectonic are favorable factors for the development of gravity-driven sediment transport processes.</p><p>A new large depositional system, named the Khuray deep-water fan, was discovered and studied since 2014 in the deep part of Lake Baikal during six Class@Baikal Project expeditions. It is located at the south-west of the Central basin of Lake Baikal, where it occupies a narrow, SW-NE extended area of about 1500 square km. Several 2D seismic surveys and bottom sampling campaigns were run during the expeditions in this area ranging in water depth from 800 to 1580 meters. A comprehensive set of collected geophysical and geological data provided important insights on the architecture of the Khuray lacustrine deep-water depositional system.</p><p>The system is fed by the Kukuy canyon, which is incised into the north part of the Selenga delta-front. In its upper reaches, immediately beyond the mouth of the Kukuy canyon, the Khuray system is represented by a set of meandering channels forming typical deep-water channel-levee complexes, which are well-expressed in bottom topography. The central part of the system develops over a large uplifted fault block, which is separated from of the rest of the Central basin by a well-expressed tectonic escarpment up to 80 m high. Within the block the system of the meandering channels is gradually replaced by a system of less distinct channels, which form a large braided channel complex less commonly observed in deep-water fan systems. At the distal part of the system, the channels become better expressed in bottom relief again and begin merging with each other forming, eventually, a single main channel. Another very interesting feature, a secondary canyon, is also observed at the distal part of the Khuray system. Once the small channels converge into the single one, it reaches a tectonic escarpment and forms a distinct erosional incision named the Khuray canyon. Several depositional lobes forming the lower reaches of the Khuray fan are found beyond the mouth of this secondary canyon, which is associated with a base of an active tectonic fault.</p><p>Active tectonic processes are believed to be the key factors responsible for the development of such complex architecture of the Khuray lacustrine deep-water depositional system comprising typical slope meandering channels, braided channel complex and several cascading canyons.</p><p>The reported study was funded by RFBR according to the research project № 18-35-00363.</p>

FORMATION AND EVOLUTION OF PARALLEL-BRAIDED CHANNEL REACHES

The paper provides a comprehensive assessment of channel formation conditions and hydrological-morphological characteristics, and also considers the features of the channel changes regime of parallel-braided channel reaches, being the most complex and diverse in morphodynamics. The general condition for their development is a large width of channels (respectively, the maximum value of the criterion of the flow quasi-uniformity suggested by I.F. Karasev). In such channels, the flow is divided into two branches, between which, in the middle of the channel, occurs accumulation of sediments and formation of mid-channel bars and islands. At the same time, parallel-braided channels are the result of other channel types (non-meandering) development due to certain changes in determining factors: increased water content and sediment runoff, overgrowth of channel bars, as a result of which mid-channel bars turn into islands, and anthropogenic impacts on rivers. On sandy floodplain rivers, parallel-braided reaches are typical for low-stable and unstable channels in the absence of the directed influence from bedrock banks on the flow and when effective water discharge passes over the floodplain edge. The islands in such braided reaches are mostly small. On rivers with incised channels, they are either similar in morphology and the channel changes regime to wide floodplain unstable channels, differing from the latter in large islands with elongated shape, or form sculptural islands and are very stable. In any variety, parallel-braided channels are very individual in their channel changes regime and there are no universal channel control schemes for them.

Vestige of The Ancient Estuarine of Cisaar Valley, Sumedang as One of the Pleistocene Fossil Bearing Site in West Jawa

Cisaar Valley is located on the east part of Sumedang Regency, West Jawa Province. It’s close to the boundary of Sumedang-Majalengka Regency. In this location the sandy and clay dominated sedimentary rocks are well exposed along the outcrops in the Cisaar Valley. These sedimentary rocks is inferred from Pliocene-Pleistocene deposits from Kaliwangu and Citalang Formation. Foraminifera microfossil that commonly used for interpretation of depositional environment is rarely found, whereas freshwater mollusk and vertebrate fossils often found in the sediment rocks of this area. This condition raises a question, what is the environment of this valley in the past? Data obtained from measured stratigraphic sections along Cisaar river and its tributary rivers in Cibengkung and Cirendang hamlets, Jembarwangi village. There are at least three depositional paleoenvironments which from old to young are: shallow marine, estuarine and fluviatil braided channel depositional paleoenvironment. Characteristics of the lower, middle and upper of the estuarine environment were found in this Cisaar Valley as the evidences of the oceanic regression processes was happened in the past in this area.