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In this paper, by using GNSS technologies, some features of the distribution and some morphometric parameters of dams and ponds created by the Eurasian beaver (Castor fiber L.) along ten rivers of the Volga-Kama region of European Russia were identified. Detected features depend on the geomorphological, lithological, and landscape features of these rivers and their basins. The significant role of river slopes, as well as landscape zoning, in the distribution of beaver dams and ponds along small rivers in the study region is shown. In the rivers under study, almost all beaver constructions are located on riverbed slopes of less than 3% (most often, less than 2%). In the south of the forest zone (the southern taiga of the Vyatka River basin), the majority of dams and ponds (about 90%) are located on slopes of less than 1%, while, within the uplands of the forest-steppe zone, this location varies depending on the length of the rivers. In general, the greater the average slope of the river (the greater the average elevation of the river basin), the lower, other things being equal, the degree of beaver transformation of such rivers. This feature is better expressed in the rivers of the forest landscape zone and less expressed in the rivers flowing in the forest-steppe zone. Analysis of the morphometric parameters of beaver dams shows statistically significant trends towards an increase in their average height, as the channel slopes increase. Statistically significant trends were also identified towards a decrease in the length of dams and the length of associated ponds, with an increase in channel slopes. It is noteworthy that the critical values of the slope for a statistically significant and relatively sharp change in these parameters are 1.45%, 1.07 (or 0.54)%, and 0.65 (or 0.47)%, respectively. The greatest average heights of beaver dams are confined to those rivers where their basins are composed of loamy rocks/soils (especially those that are poorly plowed), compared with "sandy" river basins. This may be due to the peculiarities of the ratio of surface and underground water runoff in these basins and, as a consequence, different intensities of snowmelt- and rainfall-induced flood flow. We assume that the above-mentioned features reflect the early stages of beaver expansion (population growth) in the studied rivers. [ABSTRACT FROM AUTHOR]

Studies on beta diversity across different spatial scales can yield insight into the ecological factors that shape communities and the mechanisms of maintenance and loss of diversity. The coastal rivers in southeast Brazil have different lengths and salinity gradients because of variation in coastal plain width and slope. These differences in environmental characteristics promote natural gradients and patterns of macrophyte assemblage variation within and among rivers. To investigate the drivers of macrophyte beta diversity, we recorded the occurrence of species and life forms and collected limnological variables at 100 sampling sites over 8 unconnected rivers that run directly to the sea. We estimated macrophyte beta diversity, and its nestedness and turnover components, within (local scale) and among (regional scale) coastal rivers using traditional metrics (Jaccard dissimilarity matrix) and a metric that accounts for sampling effect (permutational analysis of multivariate dispersions). At each sampling site, we collected variables from water (nutrients, dissolved oxygen, and pH), sediment (nutrients, salinity, and grain type), and channel (width, littoral declivity, distance from river's mouth, and coastline). For assessment of regional-scale drivers of macrophyte beta diversity, we measured river length and calculated salinity gradient. We evaluated the potential of environmental variables to explain local and regional beta diversity using distance-based redundancy analysis and multiple linear regression. As expected, at the local scale, high species turnover and life-form nestedness were predominantly explained by the rivers' longitudinal gradients (mainly salinity, P, and channel width). At the regional scale, we found that river length explained life-form nestedness among rivers (small rivers are subsets of the largest rivers); however, neither river length nor salinity gradient explained the high species turnover among rivers. We suggest that dispersal limitation among rivers and historical colonization shaped the species pool in each river resulting in almost completely distinct assemblage compositions. This high turnover at the regional scale suggests that conservation strategies for macrophytes must consider multiple rivers and not only the largest ones. Overall, our results suggest that environmental variation strongly influences macrophyte beta diversity within and among coastal tropical rivers. [ABSTRACT FROM AUTHOR]

River morphology is the science of knowing the river system in terms of general shape, dimensions and characteristics of hydraulic geometry, the direction and longitudinal profile of the bed, as well as the mechanism of its changes. Morphological study is needed to understand the current conditions and the potential for future river changes in the future, and perhaps it is only that it is possible to predict the natural behavior of the river in relation to natural changes or actions arising from the implementation of various river engineering projects. Most of the water structures such as dams, bridges and pumping stations are located in the margins of rivers that can be affected by changes in river morphology. Application of remote sensing images and Geographical Information Systems (GIS) can be effective to achieve a more accurate analysis. Today, land use change, vegetation cover and morphological changes of rivers in River Engineering Sciences are of great importance using remote sensing and GIS techniques. Yamani and Sharafi (2012) showed that morphological changes and erosion of the Herrud River from the upstream downstream has decreased. Also, the geological and lithological structures of the bed and river bank are the most important factors in the stability of the bed. Yousefi et al. (2013). In order to investigate the changes of some Meander parameters in the Karun River using Landsat satellite images, morphological parameters of 20 Meanders were determined in an interval of 128 km length of Karun River after the preparation of a land use map for each period. Rashidi et al. (2016) studied geomorphologic changes of the Karoon River bed and its causes from 1334 to 1391. The results indicate significant changes in river morphology including latitudes, meanders, and sedimentary islands due to the decrease in the discharge, the construction of multiple bridges along the path, geological factors and vegetation. The study of past research shows that the study of river morphology in other countries has also been of great importance. Clerici et al. (2015) examined the morphological changes of the Taro River in Italy over the last two centuries and showed that human beings have made the most of the changes for agricultural and industrial purposes, the construction of multiple bridges and casualization. According to the research, the main issue of this research is to investigate the changes in the Gamasiab River, which in recent years has threatened the communication paths, landscapes and, in summary, human structures along the river banks. Therefore, the objective is to study the variation of the morphology of the Gamasiab river from the point of view of the central radius and angle, and the number of archs during the 1990-2013 period, and the extent of the development of the piers.

One of the most important problems in mountain and foothill territories is to ensure antitorrential safety of settlements and economic facilities. The problem acquires the increasing relevance and significance in connection with the large-scale technogenic development of new natural landscapes that is followed by destructive torrential flows, including on the Krasnaya Polyana Olympic mountain cluster. At the same time, reliable basic data on hydrological and geophysical characteristics of torrential pools are extremely necessary for the development of reliable protective hydraulic engineering structures. However, in the last decade, a number of published studies on torrential subject do not conform to the specified requirements, that can lead to an incorrect assessment of the current situation on torrential danger and threats to human life. In the light of the above, critical remarks on some studies on torrents science are given, and their unsuitability for both theoretical and practical use is proved. [ABSTRACT FROM AUTHOR]

When looking for the area and length of the Yellow River, it was difficult to find theeigenvalue such as area and length of the Yellow River during more than 2,000 years since the Yellow River was recorded in history. By consulting relevant information of more than one hundred years since the late Qing Dynasty, we found that the latest characteristics concept and data such as length of the Yellow River began to appear in the recent period of the republic of China because of the frequent change of Yellow River water system and basin boundary , combined with the limitation of measurement technology. The paper introduced the history of the eigenvalue such as watershed area and the length of the Yellow River in detail. The latest river and lake survey results show that the catchment area and the length of the Yellow Riv-er are about 813,122 km2 and 5,687 km respectively. There are 4,157 rivers with an area of more than 50 km2 and 146 lakes with an area of more than 1 km2 in the Yellow River basin. [ABSTRACT FROM AUTHOR]

Abstract: Aim: To identify the contributions of geomorphological and hydrological/climatic factors to differences in total and endemic freshwater fish species richness between Atlantic and Pacific drainages. Location: Glaciated and unglaciated catchments draining to the Atlantic and Pacific Oceans in North (NA) and South America (SA). Taxon: Fish. Methods: A database of native freshwater fish species richnesses in drainage basins was compiled from published information, and the contributions of temperature, rainfall, catchment area, river length, channel gradient, discharge and geographic location in accounting for variation in total and endemic species richness were assessed using boosted regression trees. Results: Atlantic drainages have larger catchments, with longer rivers, lower channel gradients, greater discharges and lower flow variability than Pacific ones of the same size. Unglaciated Atlantic drainages in both NA and SA have more species than Pacific drainages, but glaciated Pacific NA had significantly more species than the other Pacific areas. Geographic location had the greatest influence on total richness, but catchment area, river length and temperature were more important for endemic species. Pacific drainages had proportionally more endemics than Atlantic drainages. Main conclusions: Tectonically driven topographic change, by altering relief, affects catchment size, slopes and connectivity, with the latter also affected by climatic changes in ice cover and aridity. These geomorphic and long‐term climatic changes, by influencing speciation, extinction and dispersal, govern freshwater fish species richness in Atlantic and Pacific catchments. [ABSTRACT FROM AUTHOR]

The length of the main trunk in a river basin is an important morphometric parameter and it depends on the size of the drainage basin. The Ganga River Basin is one of the largest basins in the world with the Ganga River considered to be the main stem. Variable lengths of this river in the literature motivated us to study its exact length and also to test whether geomorphically it is the longest river in the basin. The results show that the maximum river length of 2758 km is attained when source is considered at the headstream of the Tons River. This length is more than any of the traditional lengths of the Ganga River in the literature. We propose to call the longest segment of the river in Ganga Basin as the Himalayan Foreland River. [ABSTRACT FROM AUTHOR]

Flooding river valleys following construction of dams restrict fluvial environments to reaches that were formerly headwaters. Whether remaining habitat is suitable for all life stages of fluvial species is poorly understood. A fluvial species, Arctic grayling Thymallus arcticus, showed a dramatic decline following flooding of the Upper Peace River and the formation of the Williston Reservoir. We related landscape and field site-specific features with occurrence of juvenile Arctic grayling using an information theoretic approach. For the landscape model, an association was identified between stream order and Arctic grayling occurrence although stream order alone was a poor predictor. A positive association between juvenile Arctic grayling occurrence and distance from the Williston reservoir and stream order, as well as a negative association with water temperature and temperature variance, was deemed important for the field site model. Both modelling approaches indicated size of stream system to be an important influence on occurrence of juvenile grayling in the Williston watershed. River length required for suitable river habitat for salmonids has not previously been identified, but should be factored into future management plans when evaluating the impact of proposed hydroelectric dams and subsequent flooding of river systems. [ABSTRACT FROM AUTHOR]

Abstract: Length of river reaches is one of the most important characteristics of stream networks when applying hydrological or environmental simulation models. A common method of obtaining estimates of river lengths is based on deriving flow directions, accumulated area and drainage lines from raster digital elevation models (DEM). This method leads to length estimates with variable accuracy, which depends on DEM horizontal resolution, flatness of terrain, DEM vertical accuracy, the algorithm used to obtain flow directions and the way by which distances are calculated over raster structures. We applied an automatic river length extraction method for eight river reaches in the River Uruguay Basin (206000km2), in Southern Brazil, and compared its results to the lengths obtained from drainage vector lines digitalized over satellite images. Our results show that relative errors can be higher than 30% in flat regions with relatively low DEM resolution. Preprocessing of DEM by the method known as stream burning greatly improves results, reducing errors to the range 1.9–7.4%. Further improved estimates were obtained by applying optimized values for the length of orthogonal and diagonal steps called distance transforms, reducing the errors to the range −2.0–3.3%. [Copyright &y& Elsevier]

Summary: Application of regular grid-based distributed hydrological models requires information related to river drainage networks, such as flow directions, flow accumulated areas, basin delineation, and length and slope of river reaches for every grid cell. Most of those data may be extracted automatically from Digital Elevation Models (DEM). However, when dealing with large basins, available DEMs are usually in higher spatial resolution than the model grid. Upscaling procedures have therefore been developed to extract low-resolution flow directions and flow accumulated areas from relatively high-resolution DEMs. This paper presents a new methodology, which extends the upscaling method, to automatically extract length and slope of river reaches for large-scale grid-based hydrological models. The proposed method is new and is believed to be the first attempt to produce such information automatically from DEMs. The methodology was applied to parts of the Uruguay river basin in South-America, using the globally-wide available DEM produced by the Shuttle Radar Topography Mission (SRTM-90m). Quality of results was assessed by comparing calculated river lengths with distances measured over vectorized river networks, which were assumed to be correct. It was shown that the proposed methodology adequately assigns river lengths to every model cell, while ensuring that the whole length of the streams is considered. The effect of DEM resolution on calculated river length errors was analyzed by resampling the SRTM DEM to three different cell sizes, with best results obtained for the higher resolution DEM. The modification of the original high-resolution DEM through the process known as stream burning was also tested, largely improving the quality of the results. Finally, optimal distance transforms were used for the calculation of distance increments, instead of Euclidean local distances, giving results that were generally better. The quality of results for calculated slope values could not be assessed because no reliable data were available for comparison. [Copyright &y& Elsevier]