Small-scale Rivers Research Articles

Effects of River Scale on the Aesthetic Quality of Urban On-Water Sightseeing

On-water sightseeing plays a key role in the tourism of traditional Chinese landscapes. The on-water landscape affects tourism potential and the quality of urban landscapes. Current research on river landscape is mainly based on remote sensing images or on-land approaches, while studies of on-water perspective landscapes at different river scales is lacking. In this paper, with Guilin city rivers taken as an example, we adopt image semantic segmentation technology to evaluate the visual landscape characteristics under different river scales, and subsequently employ automatic linear modeling to screen important factors affecting aesthetic quality. The results reveal the obvious differences between the on-water landscape characteristics of different scale rivers. The on-water landscape quality of large- and small-scale rivers is mainly affected by seven and four factors, respectively. The Karst landform of Guilin is observed to significantly improve the on-water landscape quality of large-scale rivers. By considering the impact mechanism of landscape composition on the aesthetic quality and the different scale rivers, we propose several aesthetic quality improvement strategies based on low-cost methods, including the planting of vegetation and the micro renewal of artificial constructions. This study contributes to the intelligent evaluation of urban on-water landscape and provides reference for on-water route selection and urban planning.

Spatial variability of microplastic pollution on surface of rivers in a mountain-plain transitional area: A case study in the Chin Ling-Wei River Plain, China

Inland lakes and rivers are large reservoirs of microplastics. But currently, not too much research was done on microplastics of mountain rivers. The protection of water sources from microplastics is extremely significant for the safety of human drinking water. We quantified the distribution and variation of microplastics in the surface water from tributary (upstream water-source regions) to main stream (human settlements) in the Chin Ling-Wei River Plain Rivers, and assessed the pollution risk. Rivers in the Chin Ling-Wei River Plain contained various levels of microplastics (2.30–21.05 items/L), and the main stream of the river contained higher concentrations most commonly of microplastics than tributaries. The microplastics were fragments and films; they constituted 82.3% of the total abundance of microplastics. Microplastics with a particle size < 500 µm accounted for 64.3% of all the samples. As rivers flow from the mountains to the plains, the land-use types along the rivers become more multifunctional. Thus, the risk of river microplastic pollution increases sharply with distance downstream. Our research explored the microplastics pollution in the Chin Ling mountains based on topography and land-use types and thus provides a reference for further studies exploring the spatial distribution characteristics of microplastics in small-scale rivers and for pollution risk assessments.

MRSE-Net: Multiscale Residuals and SE-Attention Network for Water Body Segmentation From Satellite Images

Automatic extraction of water bodies from various satellite images containing complex targets is a very important and challenging task in remote sensing and image interpretation. In recent years, convolutional neural networks (CNNs) have become an important choice in the field of semantic segmentation of remote sensing images. However, generic CNN models present many problems when performing water body segmentation, such as: (1) blurred water body boundaries; (2) difficulty in accommodating different scales of rivers, often losing information about many small-scale rivers; and (3) a large number of trainable parameters. This paper proposes an end-to-end CNN structure based on multi-scale residuals and SE-attention for water segmentation, called MRSE-Net. MRSE-Net consists of an encoder-decoder and a skip connection, which captures contextual information at different scales using the encoder, and then passes the encoder feature mapping through the improved skip connection, while localization is achieved by the decoder is implemented. With the multi-scale residual module, the number of parameters in our model can be significantly reduced and water pixels can be extracted accurately. The SE-attention module is used to enhance the prediction results, mitigate the blurring effect, and make the segmented water boundaries more continuous. Landsat-8 images are used to train our model and validate our proposed method&#x2019;s performance and effectiveness. In addition, we evaluate our method on Landsat-7 and Sentinel-2 images and obtain the best water segmentation results. Preliminary results on Sentinel-2 images show that the cross-sensor generalization capability of our model is beyond the range of the Landsat sensor family.

Microplastics in the sediments of small-scale Japanese rivers: Abundance and distribution, characterization, sources-to-sink, and ecological risks

Microplastic pollution in small-scale river sediments remains mostly unknown. This study explored microplastics in the sediments of four small-scale Japanese rivers in Yamaguchi Prefecture: the Awano, Ayaragi, Asa, and Majime. Sediment samples (n = 23) were collected from the selected stations. Density separation and wet peroxidation methods were applied to extract microplastics. Polymers were detected through attenuated total reflectance-Fourier transform infrared spectroscopy. Microplastic abundance indicated relatively moderate values in the small-scale Japanese rivers compared to other rivers around the world. Large microplastics (1–5 mm) in size, fragments in shape, and high-density particles of diverse polymers dominated. Polyvinyl chloride, polyethylene, and polypropylene were the major polymers. The polymers—polyvinyl chloride, polymethylmethacrylate, polyurethane, fluorinated ethylene propylene, and polybutylene in sediments were distinct from those detected in surface water, as were the predominance of large-size (1–5 mm) and fragment-shape microplastics. In contrast to surface water, sediments preserved both common and distinctive microplastics. Thus, the riverine sediment compartment acted as microplastic sink. Scanning electron microscopic (SEM) analysis suggested the presence of weathered microplastics in sediments. Energy dispersive X-ray spectroscopic analysis (EDX) revealed metal contaminants on the microplastic surfaces, indicating synergistic hazard potentials in the riverine ecosystems. Ecological risk assessment results suggested low to very high risks of microplastic pollution for the rivers. The higher abundances of microplastics and highly toxic polymers contributed to the elevated ecological risks. Polyvinyl chloride, acrylonitrile butadiene styrene, polyurethane, and polymethylmethacrylate were the detected highly toxic polymers. The urban and residential areas affected stations ranked high to very high ecological risks. The sites posing very high ecological risks were regarded as pollution hotspots. Overall, this study developed new insights into microplastic pollution in the small-scale rivers and ecological risks for riverine environments, as well as providing a baseline for more comprehensive risk assessments and developing pollution control and management strategies.

Assessing small-scale freshwater microplastics pollution, land-use, source-to-sink conduits, and pollution risks: Perspectives from Japanese rivers polluted with microplastics

Rivers are vital for understanding freshwater microplastics pollution, along with the conduits from land-sources to marine-sinks. In this study, we investigated microplastics in the small-scale Awano and Ayaragi rivers, which flow into the Sea of Japan (SJ), and the Asa and Majime rivers, which flow into the Seto Inland Sea (SIS) in Yamaguchi Prefecture, Japan. Surface water samples were collected from 29 stations. Filtration, wet peroxidation, and density separation methods were employed to extract microplastics. Polymers were identified via attenuated total reflectance-Fourier transform infrared spectroscopy. Microplastics abundances and comparisons among different rivers revealed that these small-scale rivers were highly polluted than others around the world. Characterization demonstrated that small microplastics (<1000 μm) in size, fibers and fragments in shape and the polymers—polyethylene, polypropylene, vinylon, polyethylene terephthalate, and polystyrene were dominant. These small-scale rivers emitted substantially higher quantities of Japan land-sourced microplastics (0.4–154.27 billions/day and 0.01–17.55 tons/day) into the SJ and SIS environments than larger rivers in other countries compared to basin areas. The pollution load index indicated that all the river stations were polluted with microplastics. An assessment of the polymeric and pollution risks revealed variably low to high risks. The higher were the abundances of microplastics and toxic polymers, the higher were the pollution level and risks. The sites at high risk of pollution were regarded as hotspots. Both point and non-point land-uses sources of pollution could release microplastics into the river freshwater environments, affected posing high risks and hotspots. Moreover, the pollution characteristics (shapes-sizes-polymers) indicated serious ecotoxicological threats to these rivers and their downstream environments. This study provided new insights into river microplastics pollution and revealed small-scale rivers to be prominent source-to-sink microplastics conduits. Risk assessments provided a baseline for future comprehensive assessments and developing practical approaches to wards setting water quality criteria, pollution control and management.

The Effects of Topographic Map Scale and Costs of Land Surveying on Geometric Model and Flood Inundation Mapping

The quality of topographic datasets plays a key role in deriving terrain model and hydraulic simulation. In developing countries, data-sparse regions and most parts of the world, accessing to high-quality datasets is almost impossible and topographic maps with a specific scale should be used to derive the geometry of river bed and floodplains. For these areas, understanding the effects of map scale on the costs of land surveying/river projects and flood inundation mapping may lead to an appropriate flood modeling and reduce huge amounts of financial resources. This research addresses the effect of using topographic maps with different scales on the hydraulic properties and focuses on using the relationship between topographic map scale, the costs of land surveying and hydraulic properties. The results from the three river reaches (SojasRood and SafaRood rivers in Zanjan and Mazandaran provinces, respectively and Sarbaz river in Sistan-Baluchistan province, Iran) used in this study show that in small-scale rivers (SojasRood and SafaRood rivers), the effect of topographic map’s scale on water surface elevation (WSE) isn’t meaningful up to 1:4000 (4 K) map scale, while in the case of Sarbaz river WSE is approximately scale independent (even up to 1:10000 (10 K) map) and there is no considerable discrepancy between low and high-quality maps in predicting this important variable. For example, in SojasRood river the mean absolute error (MAE) in simulation of WSE for low-quality maps (5 K and 6 K maps) varies between 0.79 m and 1.78 m, while for high-quality maps (1 K, 2 K and 3 K) it restricts to only 0.25 m. Also, in the case of Sarbaz river, for maps with the scale of higher than 5 K (high resolution maps) the maximum values of MAE and RMSE statistics limit to 0.13 m and 0.16 m, respectively. Moreover, findings demonstrate that using the topographic maps with the scales of 2 K and 7 K instead of high quality maps (1 K and 2 K maps in small-scale rivers and Sarbaz river, respectively as base maps) lead to the same geometric model and the mean relative error (MRE) in simulating inundation extents is lower than 10%. These outcomes clearly indicate that by accepting some reasonable errors the low quality maps, that are cost-effective and not time-consuming, can be considered as alternative maps for flood simulation in low budget projects. Furthermore, assessing the costs of ground surveying shows that it highly depends on the scale of topographic maps and by using low quality instead of high quality maps the costs of topographic maps’ production significantly decreases. In addition, changes in hydraulic properties due to using these maps are not considerable when compared to the significant saved financial resources.

Complex geographic- and habitat-based niche partitioning of an East Asian habitat generalist mayflyIsonychia japonica(Ephemeroptera:Isonychiidae) with reference to differences in genetic structure

AbstractWe focused on the genetic structure and evolutionary divergence of a typical habitat generalist mayfly, Isonychia japonica, inhabiting rivers widely distributed across eastern Asia. In the Japanese Archipelago, they are distributed across a wide range of environments, including up- and downstream areas in 1 river basin. We analyzed DNA sequences of this mayfly from both the mitochondrial (cytochrome oxidase c subunit I [COI] and 16S ribosomal RNA) and nuclear genomes (Histone H3 and ITS2) of specimens from populations across the eastern Asian region, with emphasis on the Japanese Archipelago. Isonychia japonica is genetically differentiated into 2 major clades (C = continental clade, J = Japanese Archipelago clade). Furthermore, clade J is composed of 2 subclades (clades J-U and J-D). Clade J is separated by environment, with specimens constituting clade J-U occurring in small-scale rivers of the upstream regions and specimens constituting clade J-D occurring in large-scale rivers of downstream re...

Assessment of spatial habitat heterogeneity by coupling data-driven habitat suitability models with a 2D hydrodynamic model in small-scale streams

Habitat assessment considering habitat quality and quantity is a key approach in conservation and restoration works for biodiversity and ecosystems. In this regard, application of hydrodynamic model for modeling instream habitat conditions and machine learning (ML) methods for modeling habitat suitability of a target species can contribute to better modeling practices in ecohydraulics. Despite the importance of small streams for aquatic ecosystems, previous studies in ecohydraulics have been conducted mainly in medium to large rivers, often disregarding small-scale streams such as agricultural canals. The aim of this study is to demonstrate the applicability of a coupled use of ML and a two-dimensional (2D) hydrodynamic model for assessing spatial habitat heterogeneity in small-scale agricultural canals in Japan. Using abundance data of Japanese medaka (Oryzias latipes), four ML methods, namely artificial neural networks (ANNs), classification and regression trees (CARTs), random forests (RF) and support vector machines (SVMs), were applied to develop habitat suitability models considering water depth and flow velocity. A 2D hydrodynamic model was developed based on field surveys in two types of agricultural canals, namely earthen and concrete-lined canals. Information entropy was used for assessing the spatial heterogeneity of instream habitat conditions. As a result, the hydrodynamic models could model instream habitat conditions in a reasonable accuracy. Despite the differences in accuracies in habitat modeling, the four ML methods illustrated similar habitat suitability information for Japanese medaka. The coupled ecohydraulics modeling approach could quantify habitat quality and its spatial heterogeneity, based on which the differences between the earthen and concrete-lined canals were quantitatively assessed. This study demonstrated the applicability of ML-based habitat suitability evaluation and a 2D hydrodynamic model for modeling the spatial distribution of habitat suitability and assessing its spatial heterogeneity. Further study, assessing the spatial heterogeneity in various types of flows including natural/artificial and small/large streams, can contribute to establish quantitative criteria for an ecologically sound habitat and improved ecofriendly construction works in small-scale rivers and streams.

谷底平野を流下する河川の大洪水時の河幅の研究

Flood disasters caused by torrential rainfalls have recently been increasing in Japan. Representative examples are Tochigi Prefecture's Yosasa River disaster in 1998. Far exceeding capacity of flow made river widths and channel shape change because of bank erosion. But, there are few observation data such as discharge or the water level in the middle and small-scale rivers. So, we could not have discussed about appropriate river width and depth required for large flood flows. In this study, at first, we applied two-dimensional flood flow analysis for the 1998 flood occurred in Yosasa River and examine an evaluation method of the water width from the analysis and inundation situation in the floodplain areas. Then, we clarified a decision method of appropriate river width for large floods in rivers flowing valley bottom plain.

Land-sea interface features of four estuaries on the South America Atlantic coast

The Brazilian coastal zone extends from 4º N to 34º S latitude and because of its long extension, the interface zone from continent to ocean includes a high diversity of geomorphologic and oceanographic characteristics. The rivers from the Northeast and East regions are marked by a typical unimodal seasonal flux patterns but with different amplitudes. As the climate indicates, the rivers from the Northeast are subject to an accentuated seasonal variability with an elevated input and flood pulses during the rainy season and low to negligible fluxes during the dry season. Small-scale rivers usually present typical torrential behaviour. In the humid eastern region, the unimodal seasonal cycle is dampened with a more constant input supply. Recently, some studies have shown that the material supply from rivers along the Northeast and Eastern coasts is diluted by surface tropical waters of oceanic currents and that the estuarine plume dispersal is restricted to a narrow coastal belt. However, human impacts of course mask or even override both natural hydrological cycles and CO2 emissions from terrestrial biomes, or depending on the nature of the human impact, can even increase extreme events. Henceforth this contribution addresses the typological, hydrological and biome diversity of the four estuarine systems fed and affected by the respective Amazon, São Francisco, Paraíba do Sul and Plata watersheds.

河川の水質形成と集水域の土地利用形態との関係

The relationship between the formation of river water quality and the land use of river watershed at Lake Kasumigaura (Ls. Nishiura and Kitaura) was investigated in this study using measured in situ data and data calculated using a geographic information system (GIS). NO3-N concentrations in river water were high, particularly in L. Kitaura watershed. The NO3-N concentrations increased at a low-water-temperature period and decreased with dilution after rainfall. The relationship between river water quality and land use characteristics in river watershed was examined by principal component analysis. The nitrogen concentrations in river water were correlated with the number of livestock, upland field and forest area in their watershed at ordinary flow. A high correlation was confirmed particularly between the number of pigs and NO3-N concentration. Paddy field and urban area were correlated with phosphorus, organic matter and particulate matter concentrations. During flood due to rainfall, the nitrogen concentrations in small-scale rivers showed a high correlation with only the number of pigs.

A DRIFT WOOD HAZARD AND ITS COUNTERMEASURES IN STEEP SMALL-SCALE RIVERS

In 2004, a sever drift wood hazard caused by fallen trees drifting in muddy flows and overflowing at river bridges happened in many steep small-scale rivers of Ehime Prefecture. In this paper, a countermeasure in which the rail on the bridge girder is removed and some of flowing flood water overflows on the bridge girder like a sinking bridge is proposed and the effect of the countermeasure is examined through runoff experiments in hydraulic steep channels. As a result, it was made clear that the countermeasure removing the rails is a very effective one which reduces a destructive power of overflooding water to one third.

Modeled Dynamics of a Small-scale River Plume under Different Forcing Conditions

Abstract Freshwater plumes in continental and shelf seas are common, relevant features of the coastal environment and its management. In order to analyze and predict the overall shape and scale of freshwater plumes, the well-known hydrodynamic model COHERENS was used to perform several simulations of river-plume evolution. The area considered in this study has an idealized straight coastline with longitudinally uniform bathymetry and a constant bottom slope. In this domain, constant river discharge is assumed with an outflow rate ranging from that of typical mean conditions for small-scale Mediterranean rivers (e.g., Jucar) to that of larger-scale ones (e.g., Ebro). A simplified version of the underlying mesoscale circulation is considered and the effects of wind-forcing on the evolution of the freshwater plume are taken into account by considering different wind scenarios. This study describes the physical characteristics and associated dynamics of a river plume as a function of the river-flow magnitude ...

Distribution characteristics of polychlorinated biphenyls in crucian carp ( Carassius auratus) from major rivers in Korea

Polychlorinated biphenyls (PCBs) levels in crucian carp were determined at 20 locations along four major river systems, several small-scale rivers and a wetland in Korea. Twenty-eight congeners, ranging from tri- to hepta-CBs were detected. A gas chromatograph with a mass selective detector was used to quantify the individual PCB congeners. The objectives of this study were to investigate the levels of contamination of PCBs in freshwater fish and to observe the pattern of their distribution. The sampling locations were chosen among 31 sampling sites that are currently used as environmental residue checkpoints by the Korean Ministry of Environment. Concentrations of individual congeners ranged from not detectable (n.d.) to 0.75 ng g −1 on a wet weight basis. The total concentrations of PCBs at each site ranged from n.d. to 5.41 ng g −1 of wet weight. The most heavily contaminated site was the Nakdong estuary located near the Shinpyung-Janglim factory district. The PCB 153 and 138 were the principal congeners and penta- and hexa-chlorinated biphenyls comprised the main congener groups.

B115 曲がり開水路の断面流れに関するPIV実験

Turbulent flow in a curved open channel has been investigated by PIV experiments. The curved channel model retains some geometrical features of a small curved river in Nara prefecture and is conceived for modeling the accumulation of contamination in canals or small-scale rivers. The PIV experiments are focused on the cross sectional flows in stream-wise and transverse directions which, respectively, give rise to primary and secondary vortex motions under the influence of the centrifugal force.

A mechanism determining river mouth location of medium and small scale rivers flowing into a pocket beach and river mouth improvement

Pocket beach width, length of headlands on both sides of pocket beach, relative location of river mouth, basin area of 24 rivers pouring into the pocket beach were investigated through the case study in Tottori and Hyogo Prefectures facing the Sea of Japan. It is found that rivers flow into the sea in the adjacent area of headlands independent of the scale of rivers because of wave dissipation effect due to the headlands. Relative berm height formed by wave run-up at the center and end of the pocket beach is given by Zs1 / Zs2= (Hb1/Hb2) 5/8. This shows that parallel jetty method is not enough and is required to dissipate wave energy at the river mouth using some device such as artificial reef in the river mouth improvement of small rivers.