Majority Of Rivers Research Articles

A high-resolution perspective of extreme rainfall and river flow under extreme climate change in Southeast Asia

Abstract. This article provides high-resolution information on the projected changes in annual extreme rainfall and high- and low-streamflow events over Southeast Asia under extreme climate change. The analysis was performed using the bias-corrected result of the High-Resolution Model Intercomparison Project (HighResMIP) multi-model experiment for the period 1971–2050. Eleven rainfall indices were calculated, along with streamflow simulation using the PCR-GLOBWB hydrological model. The historical period 1981–2010 and the near-future period 2021–2050 were considered for this analysis. Results indicate that, over former mainland Southeast Asia, Myanmar will face more challenges in the near future. The east coast of Myanmar will experience more extreme high-rainfall conditions, while northern Myanmar will have longer dry spells. Over the Indonesian maritime continent, Sumatra and Java will suffer from an increase in dry-spell length of up to 40 %, while the increase in extreme high rainfall will occur over Borneo and mountainous areas in Papua. Based on the streamflow analysis, the impact of climate change is more prominent in a low-flow event than in a high-flow event. The majority of rivers in the central Mekong catchment, Sumatra, Peninsular Malaysia, Borneo, and Java will experience more extreme low-flow events. More extreme dry conditions in the near future are also seen from the increasing probability of future low-flow occurrences, which reaches 101 % and 90 %, on average, over Sumatra and Java, respectively. In addition, based on our results over Java and Sumatra, we found that the changes in extreme high- and low-streamflow events are more pronounced in rivers with steep hydrographs (rivers where flash floods are easily triggered), while rivers with flat hydrographs have a higher risk in terms of the probability of low-flow change.

Vegetation of natural and stabilized riverbanks and early effects of removal of bank fixation

AbstractThe majority of rivers in Europe has been dramatically altered in terms of their morphology and hydrology with severe consequences for the diversity and ecological functioning of the rivers and their floodplains. Consequently, an increasing number of river reaches has been restored over the past decades, often including the removal of bank fixation to reinitiate bank erosion and allowing for a rewidening of the rivers' cross‐section. However, monitoring in detail the effect of such a measure on riverine vegetation is scarce. Using a Before‐After‐Control‐Impact (BACI) design, we analysed the early changes of the vegetation 2 years after the removal of bank fixation at the Mulde River (central Germany). The results were compared with two types of control sites, representing a nonrestored as well as a natural riverbank that has never been fixed. We analysed differences in taxonomic and functional composition of the vegetation between bank types as well as community turnover after restoration. Two years after restoration, the vegetation differed clearly from the nonrestored sites. A substantial proportion of the community, especially the newly established species, became more similar to the natural bank community. Most importantly, spatiotemporal heterogeneity of the vegetation increased after removal of bank fixation, being an indicator for re‐established dynamic processes similar to the natural site. The presented data serve as a baseline for a long‐term monitoring and quantitative meta‐analysis of restoration effects.

A quantitative approach to investigate natal philopatry in Hickory Shad (Alosa mediocris) using otolith chemistry

The goal of this study was to understand if Hickory Shad exhibit natal homing. Hickory Shad were captured in eighteen major rivers along the known spawning range. LA-ICP-MS was used to quantify seven elements (Mg, Mn, Cu, Zn, Sr, Ba, and Pb), along a continuous transect that ran from the ventral edge of the otolith through the core to the dorsal edge of each otolith, resulting in a time resolved model of the environmental exposure history of each fish. Hidden Markov models were used to estimate a natal river element signature for each Hickory Shad. The true number of natal rivers present in the dataset were unknown, so a Gaussian mixture model was used to estimate the number of mixture distributions and classify hickory shad based on natal river signatures. Five clusters were identified; Hickory Shad captured in the majority of rivers were assigned to one of three or more clusters, while those captured in a few rivers had unique element profiles and were assigned the same cluster at high rates (70%–90% of samples per river). A Chi-Square test confirmed that there was a significant relationship (p < 0.01) between capture location and cluster assignment. Overall, the results of this study suggest a high rate of straying from natal rivers through most of the Hickory Shad spawning range, and that some localized populations may return to natal rivers at a higher rate. This study provides the first piece of quantitative information about the rate at which Hickory Shad exhibit natal homing, and provides an important inferential baseline for future studies to understand their life history strategies and population dynamics.

Ge/Si Ratio of River Water in the Yarlung Tsangpo: Implications for Hydrothermal Input and Chemical Weathering

Germanium/Silicon (Ge/Si) ratio is a common proxy for primary mineral dissolution and secondary clay formation yet could be affected by hydrothermal and anthropogenic activities. To decipher the main controls of riverine Ge/Si ratios and evaluate the validity of the Ge/Si ratio as a weathering proxy in the Tibetan Plateau, a detailed study was presented on Ge/Si ratios in the Yarlung Tsangpo River, southern Tibetan Plateau. River water and hydrothermal water were collected across different climatic and tectonic zones, with altitudes ranging from 800 m to 5000 m. The correlations between TDS (total dissolved solids) and the Ge/Si ratio and Si and Ge concentrations of river water, combined with the spatial and temporal variations of the Ge/Si ratio, indicate that the contribution of hydrothermal water significantly affects the Ge/Si ratio of the Yarlung Tsangpo River water, especially in the upper and middle reaches. Based on the mass balance calculation, a significant amount of Ge (11–88%) has been lost during its transportation from hydrothermal water to the river system; these could result from the incorporation of Ge on/into clays, iron hydroxide, and sulfate mineral. In comparison, due to the hydrothermal input, the average Ge/Si ratio in the Yarlung Tsangpo River is a magnitude order higher than the majority of rivers over the world. Therefore, evaluation of the contribution of hydrothermal sources should be considered when using the Ge/Si ratio to trace silicate weathering in rivers around the Tibetan Plateau.

Contemporary and Scenario Changes in River Runoff in the Don Basin

The results presented in the study characterize variations of river runoff in the Don Basin in the period of instrumental observations and under scenario conditions of global anthropogenic warming, which are likely in the early current century. Integral-difference curves are used to identify long-term phases of higher/lower annual and seasonal runoff of the Don and its major tributaries over the period 1870–2010. The length of the phases varies from 10 years to many decades (for Don runoff of the dry seasons). The identified contrast phases show statistically significant difference in the seasonal runoff and, in the majority of rivers, annual runoff as well; it varies from 10 to >100%. A model of monthly water balance and ensemble-averaged model scenarios of changes in air temperature, precipitation, and evaporation under anthropogenic climate warming, developed under IPCC CMIP3 and CMIP5, are used to assess the possible changes in Don runoff at Razdorskaya in the first three decades of the current century. Scenario changes in the mean long-term river runoff are far less than its differences typical of the long-term phases of its higher/lower values and its changes caused by anthropogenic impact on drainage basins and in river channels.

Methane Levels of a River Network in Wuxi City, China and Response to Water Governance

The majority of rivers are a CH4 source that accounts for an important proportion of annual global emissions. However, CH4 evasion from urban river networks has received disproportionately less attention than their contribution. The effect of water governance on water quality and CH4 emission in urban areas remains unclear. Water quality, CH4 concentrations, and fluxes from a river network in Binhu District, Wuxi City, and their response to water governance were analyzed in this study. CH4 concentrations in the investigated rivers ranged from 0.05 μmol L−1 to 16.37 μmol L−1 (2.47 ± 4.5 μmol L−1, medium 0.23 μmol L−1), and CH4 diffusive fluxes were 75.55 ± 171.78 μmol m−2 h−1 with a medium of 6.50 μmol m−2 h−1. CH4 concentration showed a significant correlation with water quality parameters, especially for NH3–N (r = 0.84, p &lt; 0.001). Significant differences in water quality and CH4 levels were found between sites that had conducted water management and those that continued to exhibit poor water quality. Our analysis showed that rivers under water governance have a positive tendency toward water ecological restoration, and a significant decrease in CH4 efflux to the air can be achieved after extensive and intensified water governance.

Distribution, source identification, and ecological risk assessment of heavy metals in wetland soils of a river-reservoir system.

The majority of rivers in the world have been dammed, and over 45,000 large reservoirs have been constructed for multiple purposes. Riparian and reservoir shorelines are the two most important wetland types in a dammed river. To date, few studies have concerned the heavy metal pollution in wetland soils of these river-reservoir systems. In this study, we measured the concentrations of ten heavy metals (Ba, Cd, Co, Cr, Cu, Mn, Ni, Pb, Sr, and Zn) in surface soils collected from riparian and reservoir shorelines along the Han River in different seasons. Our results found that the Co, Cu, and Ni concentrations in riparian wetlands were significantly lower than those in reservoir shorelines. In riparian wetlands, only soil Sr concentration significantly increased after summer and autumn submergence. Multivariate statistical analyses demonstrated that Ba and Cd might originate from industrial and mining sources, whereas Sr and Mn predominantly originated from natural rock weathering. The ecological risk assessment analysis indicated that both riparian and reservoir shorelines along the Han River in China exhibited a moderate ecological risk in soil heavy metals. The upper Han River basin is the water resource area of China's Middle Route of the South-to-North Water Transfer Project. Therefore, to control the contamination of heavy metals in wetland soils, more efforts should be focused on reducing the discharge of mining and industrial pollutants into the riparian and reservoir shorelines.

A unified framework for stability of channel bifurcations in gravel and sand fluvial systems

AbstractBifurcating rivers shape natural landscapes by distributing water and sediments on fluvial plains and in deltas. Symmetrical bifurcations were often found to be unstable so that one branch downstream of the bifurcation enlarged while the other dwindled. A unified theory able to predict bifurcation stability in both gravel bed and sand bed rivers is still lacking. Here we develop a new theory for the stability of bifurcations for the entire range of gravel bed to sand bed rivers. The theory indicates opposite behavior of gravel bed and sand bed rivers: we predict that symmetrical bifurcations are inherently stable for intermediate Shields stresses but are inherently unstable for the low and high Shields stresses found in the majority of rivers on Earth. In the latter conditions asymmetrical bifurcations are stable. These predictions are corroborated by observations and have ramifications for many environmental problems in fluviodeltaic settings.

Identifying priorities for nutrient mitigation using river concentration–flow relationships: The Thames basin, UK

Summary The introduction of tertiary treatment to many of the sewage treatment works (STW) across the Thames basin in southern England has resulted in major reductions in river phosphorus (P) concentrations. Despite this, excessive phytoplankton growth is still a problem in the River Thames and many of its tributaries. There is an urgent need to determine if future resources should focus on P removal from the remaining STW, or on reducing agricultural inputs, to improve ecological status. Nutrient concentration–flow relationships for monitoring sites along the River Thames and 15 of its major tributaries were used to estimate the relative inputs of phosphorus and nitrogen from continuous (sewage point sources) and rain-related (diffuse and within-channel) sources, using the Load Apportionment Model (LAM). The model showed that diffuse sources and remobilisation of within-channel phosphorus contributed the majority of the annual P load at all monitoring sites. However, the majority of rivers in the Thames basin are still dominated by STW P inputs during the ecologically-sensitive spring-autumn growing season. Therefore, further STW improvements would be the most effective way of improving water quality and ecological status along the length of the River Thames, and 12 of the 15 tributaries. The LAM outputs were in agreement with other indicators of sewage input, such as sewered population density, phosphorus speciation and boron concentration. The majority of N inputs were from diffuse sources, and LAM suggests that introducing mitigation measures to reduce inputs from agriculture and groundwater would be most appropriate for all but one monitoring site in this study. The utilisation of nutrient concentration–flow data and LAM provide a simple, rapid and effective screening tool for determining nutrient sources and most effective mitigation options.

Climate change effects on winter river runoff in Transbaikalia

Considered are interannual variations of the river runoff in Transbaikalia during the freeze-up and their dependence on the climate change. The air temperature in winter has increased since the middle of the 20th century that results in the ice thickness decrease on the majority of rivers on the territory under study. The runoff volume in winter depends significantly on the preliminary moistening of catchments. Warming effect is manifested in the increase in the fraction of the winter runoff in the annual runoff volume during the long-term period.

Interstate river conflicts: lessons from India and the US

In both India and the US, the majority of rivers are interstate and the states retain substantial legal power over water resources. In the US, negotiation of river compacts has not eliminated controversy, due to their inflexibility over time. In India, court-appointed tribunals, employed for major interstate river conflicts, have frequently relied on a vague principle of just and equitable apportionment in resolving interstate disputes. The experiences of the two countries show that conflict resolution must involve positive rewards for all the parties involved. This involves imaginative application of the principle of benefit sharing and the expansion of water markets to cover the entire river basin.

Fish passage experience at small-scale hydro-electric power plants in France

There are more than 1,700 small-scale hydro-electric power stations in France today, which can be found on the majority of rivers with migratory species in them. This article gives an overview of the different types of fish facilities in use at these small-scale hydro plants. The relative advantages and drawbacks of each type of fish pass are discussed, with reference to the requirements of migratory species and the site-specific constraints. Emphasis is placed on the problems of attraction and maintenance. The article also mentions the various techniques used to evaluate existing or recently constructed fish passes. Experience in using bypass facilities combined with trashracks for downstream juvenile salmonids and eels are related. The author points out the severe cumulative impact which may occur due to the existence of several small-scale hydro projects on the same river. He presents his view on the priorities for research on fish passage facilities, especially on “fish friendly” small-scale hydropower intakes.

Hydrological changes and ecological impacts associated with water resource development in large floodplain rivers in the Australian tropics

AbstractThe majority of rivers in the Australian tropics possess near‐natural flow regimes and are an ecological asset of global significance. We examined flow variability in large floodplain rivers in the Gulf of Carpentaria, northern Australia, and the potential ecological impacts of future water resource development (WRD). Flow metrics based on long‐term records were used to classify flow regimes and predict hydrological drivers of ecological function. Flow regimes of selected rivers were then compared with those simulated for pre‐ and post‐WRD flows in the Darling River, a highly modified river in Australia's south‐east. Generally, rivers were classified as typically ‘tropical’ (more permanent, regular flows) or ‘dryland’ (more ephemeral, with greater flow variability). In addition, all rivers displayed wet–dry seasonality associated with changes in flow magnitude or number of zero‐flow days. We propose that these features (flow permanence and regularity; flow variability and absence; wet–dry seasonality) are the key hydrological drivers of biodiversity and ecological function in the floodplain rivers of Australia's north. In terms of WRD, inter‐annual flow variability was predicted to increase or decrease depending on rivers' natural flow regimes, specifically their tendency toward lower or higher flow magnitudes. Either outcome is expected to have adverse effects on the biodiversity and ecological function of these relatively pristine rivers and floodplain habitats. In particular, reduced and homogenized habitat, loss of life‐history cues, inhibited dispersal and shifts in community composition, as a result of WRD, threaten the ecological integrity of rivers adapted to the three hydrological drivers above. These findings serve as a caution for careful consideration of WRD options for rivers in the Australian tropics and for those with similar flow regimes the world over. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Defining chemical status of a temporary Mediterranean River

Although the majority of rivers and streams in the Mediterranean area are temporary, no particular attention is being paid for such systems in the Water Framework Directive (WFD). A typical temporal Mediterranean river, draining an intensively cultivated basin, was assessed for its chemical status. Elevated concentrations of nitrates and salts in river water as well as nutrients and heavy metals in river sediments have been attributed to agricultural land uses and practices and point sources of organic pollution. A scheme for the classification of the river's chemical status (within the ecological quality classification procedure) was applied by combining pollution parameters in groups according to related pressures. In light of the temporal hydrological regime and anthropogenic impacts, sediment chemical quality elements were considered, in addition to hydrochemical ones. Despite the extensive agricultural activities in the basin, the majority of the sites examined showed a good quality and only three of them were classified as moderate. For the classification of the chemical quality of temporary water bodies, there is a need to develop ecologically relevant salinity and sediment quality standards.

Hydrogeochemistry of Hodgson Creek catchment, Queensland Murray-Darling Basin

The majority of rivers in the Murray Darling Basin (MDB) export more salt than they receive via rainfall or inflow. This is generally ascribed to the change in water balance following clearing and agricultural development. The transfer of salts is generally treated as a hydrological problem, with electrical conductivity (EC) assumed to represent salt load. We use the Hodgson Creek, a 3 rd order catchment in the Queensland MDB, to evaluate the efficacy of this assumption and make comment on the simplified notion of EC as a proxy for salinity in surface and groundwaters. Hodgson Creek exports 9000t/a, or 16t/km 2 /a; comparable to some of the higher exporting catchments of the southern MDB. Unlike most rivers in the southern MDB, EC in Hodgson Creek groundwaters is dominated by non-chloride salts (mostly sodium bicarbonate). Magnesium is also high, from weathering of the regional basalts. Salt export is dominated by infrequent, large flood events of low salinity, raising the issue of the significance of salt load when describing salinity impacts and end of valley targets. The hydrogeology of the area can be represented as three groundwater flow systems. Flat-lying, Jurassic coal measures and sandstones are overlain by layered Tertiary basalts, with unconsolidated alluvium filling valley floors. Of more than 1400 bores sunk in the area, only 21 are used for routine monitoring. About 500 have geochemical data and 200 are pumped for irrigation. We use chemistry and isotopes to help define the groundwater flow systems and the groundwater attributes required for modelling groundwater and salt movement through this catchment using reactive transport modelling. We compare groundwater chemistry with stream base-flow and examine the significance of this for salinity studies and end-of-valley salinity determinations. We quantify the groundwater component and use equilibrium mass balance reactions to estimate the evolution of waters through the regolith.

Trends in the Maximum, Mean, and Low Flows of Turkish Rivers

Abstract In this study the existence of trend in maximum, mean, and low flows of Turkish rivers has been investigated. The data consisted of the daily mean flows of nearly 100 flow stations in 24 hydrological regions of Turkey. Trend analysis has been carried out using the parametric t test and nonparametric τ (Mann–Kendall) test. Both tests have been applied to annual maximum, mean, 1-day, and 7-day low flows. Trend existence was detected in the majority of rivers in western and southern Turkey and in some parts of central and eastern Turkey. Trends in mean and low flows were more common compared with maximum flows. Except at a few stations, flows showed a decreasing trend. In the time period of the last 30–60 yr, statistically significant decrease was found especially in the mean and low flows (and in some of the maximum flows) in western, central, and southern parts of Turkey. Such trends were not observed in other regions. These results are in agreement with those of the precipitation trend studies in Turkey.

Mechanism of wetting and river runoff in the east european plain

The general picture of wetting the East European Plain in 1966–1985 is established by studying the trajectories of more than 5000 cyclones in the Northern Hemisphere. The role of the Arctic High as a regulator of the paths of the Atlantic cyclones is established. It is shown that the majority of rivers of the East European Plain feature higher rate of streamflow in the years with the El Nino effect.

Salinity-Induced Density Stratification in Near-Laminar Open-Channel Flows

Salt tracer experiments are a cost-effective tool widely used in studies of flow and transport in free surface flows. Whereas in a large majority of rivers and streams, fully turbulent conditions achieve rapid vertical mixing of injected tracers, this is not necessarily the case with very low Reynolds number flows as encountered e.g., in wetland ponds. There, often laminar to near-laminar transitional flow regimes prevail, and the fact that solutions of elevated salinity are distinctly heavier than water may result in the development of stable density layers, trapping part of the salt tracer and distorting the breakthrough curve recorded at the outlet. In this study, the conditions under which density stratification develops due to salt injection are analyzed, and a criterion is presented which permits an intended salt tracer experiment to be judged at the planning stage already.

Analysis of the El Niño Effect on the Discharge of Selected Rivers in the Asia-Pacific Region

Discharge records originating from 78 rivers within the Asia-Pacific region are used to assess a possible relationship between a temporal El Niño-Southern Oscillation (ENSO) Index and regional discharges of rivers. The rivers selected have long monthly discharge series and are geographically distributed throughout the whole region. Analyses of variance are used to identify the sub-regions most teleconnected to the ENSO signal. Composite analyses show the temporal patterns of the relationships between river discharge and the ENSO signal and the possible presence of a time lagged relationship. The analyses show that the rivers of the Oceania-Pacific region are the most affected and that a majority of rivers show a similar temporal pattern, thus allowing the construction of a regional composite streamflow index. The temporal patterns of the identified relationships demonstrate the possibility of forecasting the occurrence of abnormally high or low flows (floods/droughts) months ahead of time.

Phenotypic variance of bilateral characters as an indicator of genetic and environmental conditions in bream Abramis brama (L.) (Pisces, Cyprinidae) populations

The expressions of factorial (s̀2s) and stochastic (s̀2s) components of henotypic variance of bilateral characters are given, regarding simple connection of the latter to the fluctuating asymmetry indicator, being traditionally used for assessment of developmental stability. The values of both components were calculated for 5 meristic characters in 172 samples of bream collected over most of its geographic range. The s̀2s values were to indicate possible effects of genetic disbalance and to measure environmental stress, while s̀2s was regarded as a rough estimate of the genetical heterogeneity. It was found that s̀2s values tended to grow in following situations: a) zones of interpopulational contacts or in populations with unusual morphology; b) zones of increased anthropogeneous pollution, in particular In the lower parts of the artificial reservoirs as compared to the upper arts and the majority of rivers and lakes. On the other hand, s̀2f values in lakes appeared to be lower than in rivers, probably due to comparatively low genetic heterogeneity of the lake populations. The whole set of samples exhibits another clear trend: negative correlation between s̀2s and s̀2f, which seems to illustrate a well-known connection between developmental homeostasis and heterozygosity. A conclusion may be made that the phenotypic variance components are useful in ecological and genetical monitoring of large population systems, although the data are often difficult to interpret properly for separate populations.