Downstream Tributaries Research Articles

Exploring PCSWMM for Large Mixed Land Use Watershed by Establishing Monitoring Sites to Evaluate Stream Water Quality

Extensive hydrologic and water quality modeling within a watershed benefits from long-term flow and nutrient data sets for appropriate model calibration and validation. However, due to a lack of local water quality data, simpler water quality modeling techniques are generally adopted. In this study, the monitoring sites were established at two different locations to collect hydraulic data for the hydraulic calibration and validation of the model. In addition, water quality samples were collected at eight monitoring sites and analyzed in the lab for various parameters for calibration. This includes total suspended solids (TSS), soluble phosphorus, five-day biochemical oxygen demand (BOD5), and dissolved oxygen (DO). The Personal Computer Storm Water Management Model (PCSWMM) 7.6 software was used to simulate all the pollutant loads using event mean concentrations (EMCs). The performance of the model for streamflow calibration at the two USGS gauging stations was satisfactory, with Nash–Sutcliffe Efficiency (NSE) values ranging from 0.51 to 0.54 and coefficients of determination (R2) ranging from 0.71 to 0.72. The model was also validated with the help of historical flow data with NSE values ranging from 0.5 to 0.79, and R2 values ranging from 0.6 to 0.95. The hydraulic calibration also showed acceptable results with reasonable NSE and R2 values. The water quality data recorded at the monitoring stations were then compared with the simulated water quality modeling results. The model reasonably simulated the water quality, which was evaluated through visual inspection using a scatter plot. Our analysis showed that the upstream tributaries, particularly from agricultural areas, were contributing more pollutants than the downstream tributaries. Overall, this study demonstrates that the PCSWMM, which was typically used for modeling urban watersheds, could also be used for modeling larger mixed land use watersheds with reasonable accuracy.

Analysis of Spatiotemporal Variation and Driving Factors of Water Quality in the Xiangjiang River Basin from 1990 to 2016

In order to explore the spatiotemporal variation characteristics and driving mechanism of water quality in the Xiangjiang River Basin, the data of 16 water quality parameters at 113 stations over 26 years from 1990 to 2016 in the Xiangjiang River Basin were collected for synthetically assessing the water quality and identifying its main pollutants through the water quality index and other methods. The causal mechanism of water quality, especially the driving effect of water level and land use pattern, was analyzed. The results showed that： ① The overall water quality grade of the Xiangjiang River Basin during the study period was "good." However, the water quality deteriorated first （from 1990 to 2003） and then improved （from 2004 to 2016）. The season variation in water quality was not obvious, but the water quality fluctuation of the wet season was larger. The water pollution load of the main stream decreased successively from the middle reaches, downstream reaches, and upstream reaches. The upstream tributaries had the best water quality, whereas areas with poor water quality were mainly distributed at the mouth of the middle and downstream tributaries, especially in areas where multiple tributaries converged. ② Toxic heavy metals had the characteristics of toxicity, persistence, and bioaccumulation. If they exceeded a certain concentration in water, they were difficult to purify, posing great harm to the natural environment and human health. The toxic metal index （CI1） was the leading factor affecting water quality, in which Hg and Cd were the main parameters affecting the overall water quality of the Xiangjiang River Basin. ③ The water level had a positive impact on the water quality of the Xiangjiang River by diluting environmental parameters. Land type had little effect on heavy metal concentration, whereas forest land could improve water quality. Grassland had a negative correlation with permanganate index over a large scale range （≥ 5 km）. The increase in water bodies, arable land, and impermeable surface areas within the watershed increased the probability of high fecal coliform concentration in the water body. ④ With the increase in buffer distance, the water quality explained by the land use pattern increased. On the scale of 10 km buffer zone in the riparian zone, the explanation degree by land use pattern on water quality was the highest, which was an effective scale for water quality control of the Xiangjiang River. This research showed that the driving factors of heavy metal pollution and other pollution were different, but their regional differences were all obvious in the Xiangjiang River Basin. Therefore, pollution control should be classified and taken according to local conditions.

Reservoir Mud Releasing May Suboptimize Fluvial Sand Supply to Coastal Sediment Budget: Modeling the Impact of Shihmen Reservoir Case on Tamsui River Estuary

AbstractRegular release of sediment from reservoir has been increasingly adopted as a strategy for sustainable management. Here, we use a process‐based morphodynamic model to simulate the estuarine sediment dynamics impacted by turbidity current venting implemented by the Shihmen Reservoir during three typhoon events in 2008. Upon validation with the post‐event bathymetries, the model hindcasts reveal that mud releasing can be effective in mitigating reservoir siltation, yet may be a suboptimal strategy for alleviating coastal sediment deficit. A vast majority of the released muds were delivered through the estuary and exported to offshore by flood advection, wave dispersion, and tidal flushing. The flood‐driven sands, sourced mainly from downstream tributaries, were instead the major contributor to coastal sediment budget. However, mud mantling (covering and immobilizing sand deposits by the reservoir‐released muds) reduced sand availability and thus sand delivery to the coast. For the present case, 25% of the released muds were deposited along the way, presence of these mud covers reduced sand delivery by 15%, compared to a hypothetical scenario of clear‐water flood releases. The relative sand transport deficit is found to increase linearly with the degree of bed mud saturation, 1–D/R, with D/R the ratio of single‐event mud deposit to release. Given broad relevance to global reservoirs encountering the problems of siltation and coastal sediment deficit, our findings highlight that sustainable management needs to look beyond just a bulk amount of sediment, but it is critical to consider how different sediment fractions are interacting and impacted by human activities.

Prediction of Tail Water Level under the Influence of Backwater Effect Based on Deep Learning Models: A Case Study in the Xiangjiaba Hydropower Station

Accurate forecasting of the tail water level (TWL) is of great importance for the safe and economic operation of hydropower stations. The prediction accuracy is significantly influenced by the backwater effect of downstream tributaries and the operation of adjacent hydropower stations, but the explicit quantification method of the backwater effect is lacking. In this study, a deep-learning-model-based forecasting method for TWL predictions under the backwater effect is developed and applied in the Xiangjiaba (XJB) hydropower station, which is influenced by the backwater effect of downstream tributaries, including the Hengjiang River (HJR) and the Minjiang River (MJR). Firstly, the random forest algorithm was used to analyze the influence of HJR and MJR flows with different lag times on the TWL prediction error of the XJB hydropower station. The results show that the time lags of the backwater effect of HJR and MJR run offs on the TWL of the XJB are 5~7 h and 1~2 h, respectively. Then, the run off thresholds of the HJR and MJR for impacting the TWL of the XJB station are obtained through scenario comparison, and the results show that the run off thresholds of the HJR and the MJR are 700 m3/s and 7000 m3/s, respectively. Finally, based on the analysis of the time lag and the threshold of the backwater effect, a deep learning model (LSTM)-based TWL forecasting method is established and applied to predict the TWL of the XJB station. The results show that the forecasting model has a good predictive performance, with 98.22% of absolute errors less than 20 cm. The mean absolute error over the validation dataset is 5.27 cm, and the maximum absolute error is 63.35 cm. Compared with the LSTM-based prediction model without considering the backwater effect, the mean absolute error decreased by 31%, and the maximum absolute error decreased by 71%.

A hybrid deep learning model based on feature capture of water level influencing factors and prediction error correction for water level prediction of cascade hydropower stations under multiple time scales

The operating conditions of large cascade hydropower stations are complex. Improving the water level prediction accuracy of large cascade hydropower stations is significant for flood control, shipping, irrigation, etc. A new hybrid model based on a refined deep residual shrinkage network and an optimized gated recurrent unit – long term memory network (GRU-LSTM) model is proposed for water level prediction at different time scales. First, to make the input data in the form of a feature map so the model can capture the weight characteristics of each influencing factor when the water level changes, the water level, flow rate, and hydroelectric power plant output data are constructed as high-dimensional feature inputs. To reduce the prediction error caused by downstream tributary backwater jacking, downstream tributary flow is added to the input data. At the same time, a semisoft threshold function with an adjustable function is inserted into the model to improve feature recognition accuracy, reduce deviation, and eliminate the noise of the original hydrological data. Second, an error weight correction function is used to adjust the error between the predicted water level and the observed water level so that the model can automatically adjust the weights of each influencing factor according to the evaluation results of water level prediction. In this process, the parameters of LSTM are optimized using the Archimedes optimization algorithm, and the output results of the LSTM and GRU networks are weighted to obtain a more accurate water level prediction. The proposed model achieves good accuracy and efficiency in downstream water level prediction of the Xiangjiaba Hydropower Station, outperforms existing hydrodynamic and artificial intelligence methods, and has robust scalability in flood forecasting and urban rainwater forecasting.

Assessment of Debris Flow Activity in Response to an Earthquake Using the Sediment Connectivity Index

Large earthquakes can trigger landslides and collapses, which not only increase the mass of loose solid materials but also change the topography of catchments. Debris flow activity in response to earthquakes is of widespread concern; however, most studies have focused on the material conditions and flow property variations prior to and after earthquakes. In this study, we investigate temporal variations in the debris flow activity in a typical catchment in the Wenchuan Earthquake area via the sediment connectivity index (IC), which reflects the sediment delivery efficiency in the catchment. The IC values in different tributaries and during different time periods were calculated to determine their spatial distribution and temporal variations. The results show that high IC values are distributed in downstream tributaries near the main fault. The IC values decreased significantly following a 2008 Wenchuan Earthquake, indicating a continuous decrease in the sediment transfer ability. The debris flow history and loose solid material amounts were also investigated via field surveys. The debris flow activity is closely related to variations in the solid material source amounts and the IC values in the catchment. This study provides a new insight into the assessment of debris flow activity with respect to its close relationship with the distribution of loose solid materials and the sediment connectivity.

Characterizing Molecular Weight Distribution and Optical Properties of Dissolved Organic Matter and Unraveling the Origins of Anthropogenic Fluorophores in Yangtze River and Its Tributaries

In this study, size exclusion chromatography (SEC) coupled with multiple detectors was used to characterize the composition, molecular weight (MW), and optical properties of dissolved organic matter (DOM) in the Yangtze River main stream and its 88 tributaries. The SEC chromatograms revealed that DOM in the investigated water samples mainly comprised nonhumic proteinaceous biopolymers with apparent MW > 20 kDa and humic substances with apparent MW ranging from ∼0.5 to ∼7 kDa. The SEC fluorescence chromatograms further unraveled that there was a kind of characteristic fulvic-acid-like fluorophore in downstream tributaries, which showed triple-excitation peaks at ∼250, 310, and 365 nm with an emission peak at ∼460 nm (designated as HS-Em460-Ex3 hereinafter). Via field investigation and parallel factor analysis, this characteristic HS-Em460-Ex3 fluorophore was identified to originate from the discharge of residual naphthol and naphthylamine moieties in biologically treated textile wastewater. The SEC fluorescence fingerprints also demonstrated the occurrence of the characteristic HS-Em460-Ex3 fluorophore in the Yangtze River main stream from Changzhou to Nantong, suggesting that the discharge of textile wastewater might have altered the optical properties of riverine DOM and advanced treatment processes should be applied to eliminate residual aromatic fluorophores in textile wastewater.

Geomorphic effects of a run-of-the-river dam in a multi-driver context: The case of the Upper Garonne (Central Pyrenees)

In this paper, we evaluate morphological changes related to the Plan d'Arem dam (1970), a run-of-river (RoR) dam located on the Upper Garonne (central Pyrenees), and disentangle its morphological effects from other drivers (post-Little Ice Age [LIA] climate change, changes in agricultural practice, catchment afforestation, upstream damming, and bypassing). The work is based on a before-after-control-impact approach, a space-time framework that allowed the stating of four hypotheses distinguishing the effects of the considered dam from other pressures. We first examined the potential reduction to the flow regime (QL) and bedload transport (QS) from these pressures, then assessed planimetric changes (1942–2019), vertical evolution (1922–2014), and sediment size within the channel. The results show the river completed adjustments related to post-LIA climate change and catchment afforestation at the beginning of the study period, with channel narrowing affecting the whole study reach and ranging from 0.6% to 1.2% yr−1. Upstream dams and catchment afforestation reduced both the frequency and magnitude of peak flows and sediment supply, resulting in an increase in the channel narrowing rate on the upstream sub-reach (−1.2% yr−1). However, downstream tributaries buffered these changes, and no downstream propagation was found. The effects of the Plan d'Arem started around 15 yr after its construction, with channel narrowing at a rate of 0.9% yr−1 until the 2010s. The exceptional flood of June 2013 resulted in important channel widening followed by a new period of narrowing upstream of the Plan d'Arem dam, combined with channel stability downstream caused by a new dam management regime (flushing actions). We conclude that the before-after-control-impact approach is effective for isolating the effects of an RoR dam from those of other pressures, and that flushing actions mitigated the effects of the dam.

基于SWAT模型的汾河流域生态补水研究

PDF HTML阅读 XML下载 导出引用 引用提醒 基于SWAT模型的汾河流域生态补水研究 DOI: 10.5846/stxb202106291724 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家重点研发计划项目（2017YFA0605001） Study on ecological water supplement in Fenhe River Basin based on SWAT Model Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:随着人类对于河流的开发利用日益增强，显著改变了河流的天然径流过程，生态供水不足成为流域生态系统健康的重要制约因素。以山西省汾河流域为研究区，基于天然和实测径流数据，利用SWAT模型分别模拟了流域近30年天然径流和近10年跨流域调水情况下现状径流过程，并在此基础上对流域各河道生态流量及现状径流量进行时空量化，探讨了不同生态流量标准下生态缺水量在时间和空间上的变化情况。研究结果表明：（1）汾河流域各河道生态流量时空差异明显，汛期（0.50-18.80m3/s）河道生态流量需求显著高于非汛期（0.05-1.81m3/s），总体分布特征为中下游干流远高于上游支流；（2）在Tennant法的不同生态流量标准下，汾河流域非汛期生态流量保障情况整体优于汛期，高频缺水区主要分布在支流，呈上下游分散分布；（3）在中等级生态流量标准下，流域约84%的区域能保障基本生态流量需求，关键缺水区为岚河、潇河、浮山县及浍河地区；（4）建议流域生态补水在时间上侧重汛期补水，空间上侧重高频缺水地区，基于流域生态缺水量时空分布特征分配跨流域调水资源，提高水资源利用效率。研究从时空上量化了跨流域调水工程实施后流域生态流量满足程度，可以为未来流域水资源管理提供有效指导。 Abstract:Facing the increasingly serious water shortage problem, with the increasing demand for water resources, the development and utilization of rivers by human beings have been enhanced, which significantly changed the natural hydrological process of basins. The basic ecological water demand of rivers cannot be guaranteed, and the shortage of ecological water supply has become an important factor restricting the health of watershed ecosystem. In order to effectively guarantee the river ecological flow, the Soil and Water Assessment Tool (SWAT) model was used to simulate the natural runoff and the current runoff process with inter basin water transfer in Fenhe River Basin of Shanxi Province based on the natural and measured hydrological data. First, based on the SWAT model, the monthly natural runoff for about 30 years and the monthly current runoff after the implementation of inter basin water transfer projects in recent 10 years were simulated in the Fenhe River Basin. Second, based on the improved Tennant method, the ecological flow values under different ecological flow criteria were quantified in each river channel in flood season and non-flood season. Last, the temporal and spatial distribution characteristics of ecological flow and ecological water shortage were analyzed in the whole basin. The results showed that:(1) the ecological flow of each channel showed significantly temporal and spatial differences, with the values were 0.05-1.81 m3/s for non-flood season and 0.50-18.8 m3/s for flood season. The overall distribution characteristics were that the ecological flow in the middle and lower reaches was much higher than that in the upstream tributaries. (2) Under different ecological flow criteria of Tennant method, the satisfaction of ecological flow in non-flood season was better than that in flood season, and the areas with high-frequency of water shortage were mainly distributed in the upstream and downstream tributaries. (3) Under the medium-level environmental flow standards, about 84% of the basin could guarantee the basic ecological flow demand, and the key water shortage areas were Lanhe, Xiaohe, Fushan County and Huihe River basin. (4) The ecological water supplement of the basin should focus on flood season in time and areas with high frequency of water shortage in space, and the water resources of inter-basin water transfer projects should be allocated based on the spatial and temporal distribution characteristics of ecological water deficiency to improve the utilization efficiency of water. In conclusion, this study quantified the satisfaction degree of ecological flow after the implementation of inter basin water transfer projects in time and space, which can provide effective guidance for watershed water resources management. 参考文献 相似文献 引证文献

Microplastics in the Koshi River, a remote alpine river crossing the Himalayas from China to Nepal

Studies of microplastics (MPs) in remote, trans-boundary and alpine rivers are currently lacking. To understand the sinks and transport mechanisms of MPs, this study investigated the distributions and sources of MPs in the surface waters and sediments of five tributaries of the Koshi River (KR), a typical alpine river in the Himalayas between China and Nepal. Mean abundances of MPs in water and sediment were 202 ± 100 items/m3 and 58 ± 27 items/kg, dry weight, respectively. The upstream tributary, Pum Qu in China, had the smallest abundance of MPs, while the middle tributary, Sun Koshi in Nepal, had the greatest abundance. Compared to international values in rivers, contamination of the KR with MPs was low to moderate. Fibers represented 98% of all MP particles observed, which consisted of polyethylene, polyethyleneterephthalate, polyamide, polypropylene, and polystyrene. Blue and black MPs were prevalent, and small MPs (<1 mm) accounted for approximately 60% of all MPs. Atmospheric transmission and deposition were considered to be the principal sources of MPs in the upstream tributary. The results imply that point sources associated with mostly untreated sewage effluents and solid wastes from households, major settlements, towns, and cities were most important sources of MPs in the KR. Non-point sources from agricultural runoff and atmospheric transport and deposition in the middle stream tributaries also contribute a part of microplastics, while the least amount was from fishing in the downstream tributary. Urbanization, agriculture, traffic, and tourism contributed to pollution in the KR by MPs. Equations to predict abundances of MPs based on river altitudes revealed that different trends were affected by both natural and human factors within the KR basin. This study presents new insights into the magnitude of MP pollution of a remote alpine river and provides valuable data for developing MP monitoring and mitigation strategies in similar environments worldwide.

Characteristics of Volatile Organic Compounds Pollution and Risk Assessment of Nansi Lake in Huaihe River Basin

This study aimed to investigate the pollution characteristics of the volatile organic compounds in Nansi Lake and evaluate the ecological and health risks. In November 2017, water samples collected from 25 sampling points in Nansi Lake using the purge and trap technique and GC-MS detected 52 types of VOCs. The detection rate of ethylbenzene, m-/p-xylene, o-xylene, 1,2-dichlorobenzene, and naphthalene reached 100%, and cis-1,3-dichloropropene and toluene reached 96%. The detection rate of 1,2,4-trimethyl benzene was the lowest, at only 12%, the average concentration of 1,2-dichlorobenzene was the highest, reaching 3.49 μg·L-1, and 1,2,4-trimethyl benzene was only 0.02 μg·L-1. The concentration of 1,2-dichlorobenzene in Nansi Lake was generally higher than that of other VOCs. Meanwhile, the concentrations of m-/p-xylene and ethylbenzene at point NSH-24 far exceeded the other VOCs, but the median value of all VOCs did not exceed 4 μg·L-1. The spatial distribution of the VOCs concentrations in Nansi Lake presented high values in the northwest and southeast, and low in the middle. The leading cause of VOCs pollution in Nansi Lake may be the exhaust gas emitted by shipping vessels during navigation, and the secondary cause is the collection of VOCs in the upstream and downstream tributaries and the influence of human factors. The health risk assessment of Nansi Lake found that, overall, there was no carcinogenic or non-carcinogenic health risk, but the risk value of individual points was relatively high, even exceeding the risk threshold set by the US EPA. There were 12 points in Nansi Lake where the ecological risk quotient exceeded 1, indicating an ecological risk to aquatic organisms.

In situ river experiments to explore variability in Microcoleus autumnalis mat expansion

Proliferations of benthic mats dominated by anatoxin-producing Microcoleus autumnalis (basionym Phormidium autumnale) pose an increasing health risk to human and animals worldwide. This study assessed M. autumnalis mats in two in situ experiments undertaken at three spatial scales: (1) reach-scale along a river; (2) reach-scale, focusing on two sites upstream and downstream of a tributary with substantial differences in naturally occurring M. autumnalis; and (3) patch-scale differences in light intensity. Most studies exploring drivers of proliferation have surveyed natural populations with correlative analyses; these in situ experiments aimed to validate previously hypothesised drivers. In experiment one, M. autumnalis mat area and expansion tended to increase downstream. This longitudinal variation was partially associated with increases in dissolved inorganic nitrogen, fine sediment and associated biologically available phosphorus. M. autumnalis mat area differed markedly at sites above and below the most downstream tributary. A second experiment with additional parameters (metals, grazing and light) was undertaken in this reach. None of the parameters conclusively explained differences in mat area, although numerous metals were identified for further investigation with a controlled experimental approach. These results posit that there are multiple non-linear drivers of M. autumnalis proliferation and their hierarchy of importance varies amongst sites.

Dynamics of Hg and MeHg in the Madeira River basin (Western Amazon) before and after impoundment of a run-of-river hydroelectric dam

The impact of a hydroelectric run-of-river (RoR) dam construction on the dynamics of total mercury (THg) and methylmercury (MeHg) is of interest to the environment and health of human and wild life. We monitored (May 2010 to October 2018) THg and MeHg in the waters and in the suspended particulate matter (SPM) of the Madeira River and its tributaries (before and after dam construction) to evaluate changes upstream and downstream from the Santo Antonio Hydroelectric Dam (SAHD). We collected 2826 samples of water and SPM at sampling stations upstream (UPMD-01, UPMD-02 and UPMD-03) and downstream the Madeira River (DWMD-04, DWMD-05 and DWMD-06), and Tributaries upstream (Branco River, Jaci-Parana River, Jatuarana-I Igarapé, Contra River, Caripunas Igarapé, Ceara Igarapé, and Teotonio Igarapé) and downstream (Jatuarana-II Igarapé and Belmont Igarapé) from the SAHD and monitored water and the total load of SPM. SPM was significantly higher in the Madeira River (median: 178.63 mg.L−1) than in upstream and downstream tributaries (median: 15.30 mg.L−1); however, the THg and MeHg concentrations were significantly higher in the tributaries (median: 161.14 ng g−1 and 9.03 ng g−1, respectively) than in the mainstream Madeira River (median = 57.06 ng g−1 and 1.63 ng g−1, respectively). THg concentration in the water was significantly higher in the mainstream Madeira River (median = 6.51 ng.L−1) than in the tributaries (median = 2.57 ng.L−1). However, the percentage of methylation in the tributaries (median = 4.9%) was 4-times higher than in the Madeira River (median: 1.3%). The significantly higher MeHg percentages in the tributaries may indicate natural (hydro-bio-geochemical factors) still predominant in this changing landscape of the Western Amazon. So far, the data suggest that this RoR has not yet impacted the THg and MeHg concentrations.

Dam reverse flow events influence limnological variables and fish assemblages of a downstream tributary in a Neotropical floodplain

AbstractWe used a dam‐free tributary (the Baía River) in the upper Paraná River floodplain downstream of a major dam in the Paraná River, Brazil to investigate the effects of dam‐regulated reverse flow on limnological variables and fish. We tested the hypotheses that limnological variables in tributaries change based on flow direction and that fish assemblages respond to this variation. Sampling sites were determined considering flow direction (normal or reverse) and position (near or far from the river mouth). Limnological variables showed higher values for transparency, oxygen, pH, and electrical conductivity at sites near the mouth of the Baía River during reverse flow. Species richness and evenness differed significantly in relation to position, with higher values closer to the Paraná River. The average standard length of fish species was higher near the mouth of the Baía River and during the reverse flow period. No significant differences in species abundance were found. Reverse flow into the Baía River brought nutrient‐poor water from the dammed Paraná River, thereby altering the limnological variables. This flow condition impelled the entry of species with higher average standard lengths. However, increased species richness and low evenness were due to the increase in species dispersal rates under all flow conditions. Our results emphasize that the effects of dams can extend several kilometres into the floodplain, provide basic knowledge on the effects of major dams on downstream pristine tributaries, and highlight the need for further studies to understand the wider influences.

Dam effects on bedload transport on the upper Santa Ana River, California, and implications for native fish habitat

AbstractDams disrupt the flow of water and sediment and thus have the potential to affect the downstream geomorphic characteristics of a river. Though there are some well‐known and common geomorphic responses to dams, such as bed armouring, the response downstream from any particular dam is dependent on local conditions. Herein, we investigate the response of the upper Santa Ana River in southern California, USA, to the construction of a large dam at the transition from mountains to valley, using calculations of bedload transport capacity on the mainstem below the dam and for major tributaries. Approximate sediment budgets were constructed for downstream reaches to estimate deposition and erosion rates for sand, gravel, and cobble particle sizes. Our results indicate that the classical response of bed armouring and erosion is likely limited to a short reach immediately below the dam. Farther downstream, though transport capacity is reduced by flow regulation by the dam, the channel reaches are likely to remain depositional but with reduced deposition rates. Persistent deposition, as opposed to erosion, is the result of the replenishment of flow and sediment supply by large downstream tributaries. In addition, the calculations indicate that the composition of the bed is unlikely to change substantially in downstream reaches. A Monte Carlo approach was employed to estimate the uncertainty in the sediment budget predictions. The impacts of the dam on the geomorphic character of the river downstream could have implications for native fish that rely on coarse substrate that supports their food base.

A mayfly’s rapid transition toward unisexual populations

AbstractSexual reproduction is overwhelmingly the most common reproductive mode among Metazoans, although it has been secondarily lost in some organisms. Ephoron shigae is a geographically parthenogenetic mayfly. Here, we provide details of the frequency of bisexual and parthenogenetic strains of E. shigae together with data on their sex ratios in the Abukuma-gawa River and one of its downstream tributaries, the Surikami-gawa River, in Japan. In a previous study in the 1990s, bisexual populations were observed in both rivers. The present study clearly shows that sex ratios have since changed to be almost entirely unisexual within the downstream area of the Abukuma-gawa River and the Surikami-gawa River. Our genetic analyses also show that these females are of a parthenogenetic strain, and that the original bisexual strains were overwhelmed within a period of &lt;20 years. However, it was recently observed that many males and females of the bisexual strains continue to inhabit upstream areas of the Abukuma-gawa River. Therefore, we suggest that the parthenogenetic strains have increased in abundance primarily downstream. We show that a drastic change has occurred over a short period, involving the replacement of one strain and a corresponding change in reproductive mode along a riverine environment.

Experiment and simulation of supersaturated total dissolved gas dissipation: Focus on the effect of confluence types

Total dissolved gas supersaturation (TDGS) downstream caused by spill discharge from high dams can easily cause fish to suffer from gas bubble disease (GBD). One potential approach to mitigate the impact of TDGS is at the confluence of a downstream tributary, where the introduction of low-TDG water might provide refuge space for fish. In this study, we carried out a series of flume experimental cases and established a three-dimensional TDGS model at confluences. The formula of the dissipation coefficient of TDGS had been obtained by parts of experiment cases. The other parts of experimental cases were carried out to validate the established TDGS model. The biggest relative error of TDG concentration between the experiment and simulation was −5.7%. The results show that the convergence of tributary water (TDG = 100%) can affect the mainstream water (TDG = 140% ∼ 150%) significantly. The two most obvious features are the presence of the separation zone and secondary flow which become more significant as the flow rate increases. The separation zone area at the bottom is smaller than that at the surface. There are two secondary circulations on transversal planes which decrease as the longitudinal distance increases. In addition, the area below 110% and 120% of TDGS in different planes of different cases were compared in detail. This study can provide scientific basis for the utilization of the low-TDG-saturation region to protect fish from the damage of TDGS at confluences during high dam discharge.

River health assessment of the Yellow River source region, Qinghai-Tibetan Plateau, China, based on tolerance values of macroinvertebrates

For decades, the river health of the Yellow River source region (YRSR) on the Qinghai-Tibetan Plateau has been a focal issue owing to its unique geographic location and ecological functions. This study investigated the ecological status of the headwater streams, the main stem, and the tributaries of the Yellow River in the YRSR using the tolerance values of macroinvertebrates and those related to biotic indices. The macroinvertebrate assemblages of the headwater streams were characterized by lower biodiversity than the tributaries downstream, based on comparisons of taxonomical composition, functional feeding group composition, and the pollution-tolerant capacity of taxa. The headwater streams had a lower ratio (16%) of pollution-sensitive macroinvertebrate taxa than that of the tributaries downstream (30%). The biotic indices (family- and genus-level biotic indices) indicated that the ecological health of the headwater streams was comparably poorer than that of the downstream tributaries. The combined effect of vulnerable natural conditions and increasing human disturbance is likely the main cause of eco-environmental degradation in the Yellow River headwater streams.

Impoundment Impact of the Three Gorge Reservoir on the Hydrological Regime in the Lower Han River, China

Reservoir regulation has been playing an increasingly important role in water resources development and its influence on the hydrological processes of downstream tributaries has attracted much attention. The lower Han River is selected as a case study to examine the hydrological and hydraulic influence of the upstream flow regulation of the Three Gorges Reservoir (TGR) in the middle Yangtze River, China. Based on a hydrodynamic model and the observed data, the hydrological processes in the lower Han River were simulated and their changes were analyzed under the impoundment influences of the TGR. The results indicated that there were obviously hydrological changes in the lower Han River after the TGR operation. The decreased stage downstream the TGR during the impounding periods of the TGR resulted in an increase in the stage difference, current speed, hydraulic gradient and the discharge ratio. In addition, the stage difference between the two rivers was decreased during the periods of water compensation from the TGR, which led to the outflow congestion in the lower Han River. The hydrological changes in the lower Han River were the response to the flow regulation of the TGR and the inflow of the two rivers. The variation in the rating curve in the lower Han River mainly resulted from the stage difference between the two rivers during the dispatching periods of the TGR. These results help to explain the hydrological variability under the impounding influence of the TGR for the lower Han River and they can be extended to other river tributaries downstream to the reservoirs.

Response of the Downstream Braided Channel to Zhikong Reservoir on Lhasa River

Lhasa River basin is situated in the southern part of the Qinghai-Tibet Plateau, which is the most important region of economic and social development in Tibet. In order to efficiently utilize water resources in the basin and ease the shortage of regional electric power supply, Zhikong Reservoir was built in the upstream reach of the Lhasa River in 2006. Impoundment of this reservoir evidently affected the morphology and stability of the downstream braided channel below the dam. Yet, little is known about the complex responses of the downstream braided channel to the Zhikong Dam. Landsat images in the 2000–2016 period, together with daily discharges and field observations in the 2017–2018 period, were used to investigate the morphological response of the braided channel to the Zhikong Dam. The downstream Lhasa River below the Zhikong Dam was divided into four reaches (i.e., RS1, RS2, RS3 and RS4) based on the confluence of three downstream tributaries. Results showed that the number and area of central bars in the braided reach closest to Zhikong Dam (RS1) were increased because of main channel incision and water level drop. This increasing trend attenuated along the downstream channel of this reach. Braiding number index of multithread channels in RS1 obviously increased by 3 in one section and reduced by 2 in two sections, while changed in all sections randomly with no pronounced trend along the RS2 to RS3 and RS4 reaches. The average bar area in two focus reaches, RS1_B1 and RS2_B2, 6.0 km and 36.8 km far away to the Zhikong Dam, respectively, followed opposite trends with the former increasing and the later reducing. Furthermore, the mean dissection, landscape dissection and fragmentation shape indices in RS1, showed an increasing trend from 2001 to 2016, indicating the shape of irregular central bars varied greatly because clean water release of Zhikong Dam eroded the downstream braided channel.