Xiaolangdi Reservoir Research Articles

Study on multi-objective optimal operation of Xiaolangdi Reservoir based on NNIA algorithm

The contradiction between the reservoir and the target is becoming more and more prominent, and the current reservoir scheduling method is difficult to well support the regional social and economic development. This paper takes the Xiaolangdi Reservoir on the mainstream of the Yellow River as the research object, establishes a dual-objective and three-objective reservoir optimal operation model, uses NNIA, MOPSO and FSS-NNIA to solve the dual-objective reservoir optimal operation model, and validates FSS-NNIA through quantitative analysis for the rationality and effectiveness of the system, FSS-NNIA is used to solve the three-objective reservoir optimal operation model, and to explore the competitive game relationship between the three objectives. The results show that: (1) Compared with NNIA and MOPSO algorithms, FSS-NNIA has a wide range of non-inferior solution distribution, it has advantages in uniformity and stability, and higher-quality Pareto-Front curves can be obtained; (2) The different performance indexes showed the superiority of the FSS-NNIA compared to the other algorithms. For example, the hypervolume (HV) of FSS-NNIA is 0.116 and 0.0016 larger than MOPSO and NNIA; the non-dominated solutions of FSS-NNIA is 71 and 31 more than MOPSO and NNIA. Also, the computational time for the FSS-NNIA was 27 s and 5 s less than MOPSO and NNIA, respectively; (3) Solving the three-objective optimization scheduling model by FSS-NNIA verifies that there is a competitive relationship between the three objectives, and uses the three-dimensional projection method to obtain the transformation efficiency distribution law of any two objectives. The research results provide a new solution idea and method for reservoir multi-objective optimization scheduling, which has important theoretical significance for supplementing and improving the theory and method of the reservoir multi-objective scheduling, and has been important guiding significance and application value for the comprehensive utilization and scheduling operation of Xiaolangdi Reservoir.

Multi-objective water-sediment optimal operation of cascade reservoirs in the Yellow River Basin

Sediment deposition in sediment-laden rivers seriously restricts the normal operation of reservoirs and the socioeconomic development of the basin. Studying the water–sediment joint operation of cascade reservoirs is important for extending the life of reservoirs. The objective of this paper is to provide a sound scientific approach to optimize the water–sediment operation of cascade reservoirs considering multiple objectives. An innovative time-dependent objective function was proposed, in which the sediment release efficiency equations suitable for different sediment inflow scenarios were introduced for sediment flushing calculation. The Sanmenxia (SMX) and Xiaolangdi (XLD) Reservoirs on the Yellow River were selected as case studies to test the proposed method. First, two typical data sets, including high and low flow magnitudes, were taken as model input scenarios. Second, the multiple-objective joint optimal operation model was established. Discrete differential dynamic programming (DDDP) was used to solve the operation model. Finally, the operation results based on different weights were discussed. Results indicate that, for sediment-laden rivers, such as the Yellow River, the proposed model can achieve the maximization of the hydropower generation and sediment flushing benefits for the high flow and low flow series. And the proposed model can guarantee the flood control, ice flood control, water supply, and ecological objectives. For the SMX-XLD cascade reservoirs, when the water resources are abundant, the hydropower generation reservoirs increase significantly. And in flood season, the weight for sediment flushing can be increased appropriately to improve the comprehensive benefits of the reservoir in sediment-laden rivers. In addition, the time-dependent objective function can provide a reference for the multi-objective optimal operation of cascade reservoirs. The optimal operation model provides a model basis for the water–sediment-energy joint operation of large-scale reservoir group in the sediment-laden basins.

Scenario-based multi-objective optimization of reservoirs in silt-laden rivers: A case study in the Lower Yellow River

Severe sedimentation often takes place in the river channel of silt-laden rivers, which is often mitigated through water-sediment regulation of the reservoirs. However, watersediment regulation is often competitive with other objectives of reservoirs, like water supply and hydropower generation; on the other hand, the reduction of channel sedimentation is often achieved at the expense of reservoir sedimentation, which reduces the service life of reservoirs. The Yellow River used to be the river with largest sediment transport over the world, but has experienced significant declination of runoff and sediment in recent years. This study presents a scenario-based multi-objective optimization operation model for the Xiaolangdi reservoir considering hydropower generation, reservoir sedimentation and channel sedimentation, with a generalized linear model coupled to calculate channel sedimentation based on runoff and sediment time series. A stochastic model that can reproduce both spatial correlations and low frequency attributes of the data series is adopted to generate two different scenarios based on different periods of observation and the performance of the multi-objective operation model under different scenarios is tested. The results indicate that: (1) the proposed optimization model can generate different schemes of reservoir operation and enhance operation performance; (2) the generalized linear model can well fit the relationship between daily channel sedimentation and runoff-sediment factors, but tends to overestimate the erosion efficiency after 2005; (3) the reservoir sedimentation and channel sedimentation show linear competitive relation, i.e., an average increase of 1 ton in reservoir sedimentation would result in declination of channel sedimentation from 0.455 to 0.488 tons, while the competitive relationship between hydropower generation and reservoir sedimentation is non-linear and weak; (4) the increase in the proportion of non-flood sediment load to the total sediment load makes it more difficult to prevent the reservoir from silting up.

Predicting plant diversity in beach wetland downstream of Xiaolangdi reservoir with UAV and satellite multispectral images

Accurate and timely acquisition of plant diversity information downstream of the reservoir is helpful to understand the impact mechanism of reservoir operation on wetland plant diversity and formulate reasonable water and sediment regulation strategies. In this study, we conducted field surveys in two communities (Phragmites australis and Tamarix chinensis) at a typical wetland in the lower reaches of Xiaolangdi Reservoir on the Yellow River, and employed UAV and Gaofen 1B multispectral images to estimate the wetland plant diversity. Results showed that most diversity indexes had a higher correlation with the mean of spectral vegetation indexes (DVI, RVI, NDVI, SAVI, and MSAVI). The diversity indexes (C_SP and C_SW) constructed by relative coverage had a better overall correlation with spectral indexes. Interestingly, opposite correlations were found between Tamarix chinensis and Phragmites australis plots. We further gave a deep insight into the interspecific associations in Phragmites australis and Tamarix chinensis plots with the variance ratio (VR) method. It was found that plant species in Tamarix chinensis plot showed positive association (VR > 1), with a VR value of 1.095. Plant species in Phragmites australis plot had a negative association (VR < 1), with a VR value of 0.983. In Phragmites australis plot, C_SP and C_SW showed a significant decreasing trend (r2 of 0.36 and 0.33 respectively, and P values less than 0.001) with the increase of Phragmites australis coverage. Moreover, the effect of spatial resolution was not significant on plant diversity estimation. Correlations between remote sensing indexes and diversity indexes were improved with the quadrat size changing from 2 m × 2 m to 4 m × 4 m. These findings demonstrate promising approaches for remote sensing of wetland plant diversity and indicate that the type of wetland plant community determines the relationship between diversity index and spectral index.

The long-term spatial and temporal variations of sediment loads and their causes of the Yellow River Basin

The erosion, deposition and transport processes of sediment alter the basin surface environment, and affect the function and structure of ecosystems. The sediment loads showed a significant decreased trend under the impacts of climate changes and human activities in the Yellow River Basin (YRB). Understanding the sediment transport patterns and causes is a prerequisite of sediment management and ecological restoration of the river basins. This study explored the sediment long-term fluctuation characteristics and the influences of various driving factors on the sediment variations based on the sediment loads data from the source region to the delta of the YRB. We found that the sediment fluxes showed a significant decreasing trend in the mainstream and tributaries of the YRB. The average sediment loads of the upper basin decreased to 42.88 ± 26.14 Mt/yr in 2000–2019, which is less than 30% of the average value recorded before 1968. Compared with 1950–1968, the sediment loads in the middle and lower reaches decreased by approximately 88% and 89% from 2000 to 2019, respectively. In addition, the middle reaches of the Yellow River (YR) is in a persistent degradation state prior to 2000, the source-to-sink relationships of sediment downstream the Huayuankou station are changing frequently due to the operation of Sanmenxia and Xiaolangdi reservoirs. According to the sediment rating curves (SRCs), the sediment transport regimes have changed at time scale along the mainstream of the YR in recent three decades. Moreover, the human activities (reservoir constructions, water-soil conservation, etc.) are the dominant factors for explaining the progressively reduction trend of sediment loads, the contributions of human activities to sediment reduction was approximately 93% in recent two decades in the YRB. Precipitation and temperature are the predominant meteorological factors affecting sediment variations, and ENSO is the dominant teleconnection pattern for explaining the multiscale characteristics of sediment loads in the lower reaches of the YRB. The findings of this study could provide effective reference for the ecological restoration and sediment management of the YRB.

Monitoring the spatiotemporal dynamics of surface water body of the Xiaolangdi Reservoir using Landsat-5/7/8 imagery and Google Earth Engine

Abstract Xiaolangdi Reservoir is a key control project to control the water and sediment in the lower Yellow River, and a timely and accurate grasp of the reservoir’s water storage status is essential for the function of the reservoir. This study used all available Landsat images (789 scenes) and adopted the modified normalized difference water index, enhanced vegetation index, and normalized difference vegetation index to map the surface water from 1999 to 2019 in Google Earth Engine (GEE) cloud platform. The spatiotemporal characteristics of the surface water body area changes in the Xiaolangdi Reservoir in the past 21 years are analyzed from the water body type division, area change, type conversion, and the driving force of the Xiaolangdi water body area changes was analyzed. The results showed that (1) the overall accuracy of the water body extraction method was 98.86%, and the kappa coefficient was 0.96; (2) the maximum water body area of the Xiaolangdi Reservoir varies greatly between inter-annual and intra-annual, and seasonal water body and permanent water body have uneven spatiotemporal distribution; (3) in the conversion of water body types, the increased seasonal water body area of the Xiaolangdi Reservoir from 1999 to 2019 was mainly formed by the conversion of permanent water body, and the reduced permanent water body area was mainly caused by non-water conversion; and (4) the change of the water body area of the Xiaolangdi Reservoir has a weak negative correlation with natural factors such as precipitation and temperature, and population. It is positively correlated with seven indicators such as runoff and regional gross domestic product (GDP). The findings of the research will provide necessary data support for the management and planning of soil and water resources in the Xiaolangdi Reservoir.

Full-stream erosion in the lower Yellow River: Feasibility, sustainability and opportunity

The issue of how to achieve removal of recently accumulated sediment is one of the largest unresolved puzzles in China's lower Yellow River. In this work, the feasibility and sustainability of achieving full-stream erosion in the lower Yellow River based on a water-sediment regulation scheme (WSRS) have been comprehensively investigated. The results indicate that the erosion–deposition state of the lower Yellow River is controlled by the incoming flow discharge level and the corresponding sediment concentration. The year 1987 is identified as an abrupt change point for streamflow in Xiaolangdi station. The relationships between channel erosion or deposition and the sediment concentration of the incoming discharge are constructed for the periods 1960–1987 and 1988–2017. Based on a constrained optimization approach, a sediment concentration lower than 19.96 kg/m3 in the discharge from Xiaolangdi Reservoir is determined to be the critical controlling condition for achieving full-stream erosion in the lower Yellow River under the average discharge level observed during 1960–1987; however, it is challenging to achieve full-stream erosion under the average discharge level of 1988–2017. Although this erosion status could potentially be achieved through continued implementation of the WSRS, its sustainability is restricted by the declining storage capacity of Xiaolangdi Reservoir, decreasing water discharge levels and riverbed coarsening in the Yellow River. It is necessary to design cross-basin collaboration measures for the upper, middle and lower Yellow River to achieve sustainable sediment reduction and healthy development of the Yellow River basin as a whole.

Quantitative assessment of safety, society and economy, sustainability benefits from the combined use of reservoirs

The joint operation of reservoirs is a major method of water resource development and management. To ensure the sustainable development of river basins and maintain the health of rivers, it is necessary to establish a comprehensive scheduling and operation method for reservoirs that is unified with the coordination of benefits, disaster reduction and ecology, and consider how to obtain the maximum benefit from different scheduling methods. Therefore, taking benefit as an effective way to evaluate the effect of reservoir combined operation. Based on the multi-disciplinary theories of emergy, economics, hydrology, and ecosystem service functions, this article propose a multidimensional benefits evaluation theory and quantitative method system under the joint application of reservoirs, covering safety (flood damage, sedimentation), socioeconomic (power generation, water supply), and sustainability (ecological environment) benefits. Taking the middle and lower reaches of the Yellow River controlled by the Sanmenxia and Xiaolangdi reservoirs as an example, a large historical flood in 1843 (hydrological frequency of 0.1%) was selected to analyze the multi-dimensional benefits of reservoirs under control and traditional schemes. The results showed that the flood in 1843 was extremely large, resulting in extensive flood damage (control scheme: −212.9 × 108 RMB; traditional scheme: −283.6 × 108 RMB) and the negative sedimentation benefits (control scheme: −268.5 × 108 RMB; traditional scheme: −194.2 × 108 RMB) were relatively large, leading to the comprehensive benefit of both schemes being negative. Although the comprehensive benefit of the control scheme was inferior to that of the traditional scheme, it can effectively mitigate downstream flood damage while satisfying the socio-economic and sustainability benefits; furthermore, the safety benefit has the highest priority in the multi-functional operation of the reservoir. The theory and method system proposed in this paper can quantify the benefits of reservoirs comprehensively, scientifically and effectively, and provide new theories and methods for evaluating the effect of joint operation of reservoirs. A benefit evaluation model covering safety, social economy, and sustainability is helpful for the establishment and implementation of sustainable development strategies for humans and nature.

Impact of water-sediment regulation on the concentration and transport of dissolved heavy metals in the middle and lower reaches of the Yellow River

Anthropogenic activities in river basins, especially large-scale water conservancy projects, have notably impacted the physical, chemical and ecological environments of estuaries and coastal areas. In this paper, the effects of water and sediment regulation (WSR) on the concentration and transport of heavy metals in the Yellow River were studied based on a continuous daily heavy metal survey in both the middle reaches (Xiaolangdi station) and lower reaches (Lijin station) of the Yellow River during the WSR period in 2019. The results indicated that the variation in the water oxidation-reduction environment of the Xiaolangdi reservoir during the WSR process exerted an important impact on the concentrations of dissolved Cu, Cd, Pb, Cr and As at the Xiaolangdi station but exerted almost no influence on the concentration of dissolved Ni. At Lijin station, the dissolved heavy metal content first increased and then decreased in the first stage, which mainly depended on the release of heavy metals from resuspended sediments. In the second stage, the heavy metal content gradually decreased due to adsorption onto fine particles discharged from the reservoir. The dissolved heavy metal flux during the water-sediment regulation scheme (WSRS) period accounted for 16.9–33.4% of the annual total dissolved heavy metal flux. WSRS changed transport of water and sediment. The dissolved heavy metal concentrations at the Xiaolangdi station were mainly controlled by the discharge of water and sediments from the Xiaolangdi reservoir, while the dissolved heavy metal concentration at the Lijin station was largely affected by the sediments resuspended from downstream riverbeds and the water and sediment scheduling mode of the Xiaolangdi reservoir. Dissolved heavy metal transportation was highly influenced by the WSR process within a short time. Human intervention, especially WSRS operation, apparently alters the natural states of both the mainstream and estuarine environments of the Yellow River.

Environmental magnetic properties of core sediments in the Yellow River subaqueous delta and their chronologicalapplications

The Yellow River has shifted frequently in the downstream region since 1885; it has flowed into the sea through the Qingshuigou channel from 1976 onward, thus forming the latest delta lobe (1976–present). During the past ~40 years, the sediment load of the Yellow River has been greatly reduced because of human and natural activities, such as reservoir construction, soil and water conservation, and river avulsion. Beginning in 2002, the water-sediment regulation scheme (WSRS) has also changed the sediment loading patterns of the Yellow River. Several studies have reported on the erosion and deposition characteristics of the latest lobe of the Yellow River Delta over the past several decades, based on remote sensing methods and water-depth measurements. However, continuous sedimentary records of delta erosion and deposition and their responses to natural and human activities in the watershed are lacking. Here, we obtained three sediments cores, YD01, YD02, and YD03, from the subaqueous delta of the latest lobe of the Yellow River Delta. These cores contain sediments deposited from 1976 to 2018. We analyzed the environmental magnetism and lithological characteristics of these cores, and investigated their responses to natural and human activities in the watershed of the Yellow River, as well as possible applications to sediment dating in the Yellow River Delta. The results show that frequency-dependent susceptibility ( χ fd%) and anhysteretic remanent magnetization susceptibility ( χ ARM) values were high in core sediments deposited from 1976 to 1996, indicating abundant contents of fine single-domain (SD) and superparamagnetic (SP) magnetic particles, and therefore a dominant sediment supply from the Chinese Loess Plateau. Small decreases in χ fd% and χ ARM in sediments deposited after 1986 revealed slight reduction of the sediment load from the Yellow River, which was likely caused by sediment retention related to the construction of the Longyangxia Reservoir. Rapid rises in χ fd% and χ ARM occurred in core YD01 sediments deposited during 2002 and ~2007, likely in response to the implementation of the WSRS, which resulted in an increase in sediment transportation. Increases in hard isothermal remanent magnetization (HIRM) values, an indicator of high-coercivity magnetic minerals such as goethite and hematite, in cores YD02 and YD03 from 2002 to ~2007 may also represent the start of the WSRS. This is because the downstream riverbed of the Xiaolangdi Reservoir underwent intense erosion during the implementation of the WSRS, leading to large-scale transportation of coarse sediments enriched in goethite and hematite, which were deposited on the riverbed before the implementation of the WSRS. The lack of increased contents of fine SD and SP magnetic minerals in cores YD02 and YD03 compared with YD01 in the interval deposited between 2002 and ~2007 was attributed to erosion and redeposition in the areas around cores YD02 and YD03. Large drops in SD and SP contents after ~2007 were detected in all three cores, revealing intense erosion near the river mouth likely caused by river channel shift and reduced capability of the WSRS to remove sediments. Contents of SD and SP particles increased again in sediments deposited after 2014 in cores YD02 and YD03, likely related to erosion of the present (after 1996) Yellow River mouth and transportation of fine particles to the region near cores YD02 and YD03. In summary, the magnetic parameters χ fd% and χ ARM and the lithological characteristics of cores YD01, YD02, and YD03 recorded sediment delivery changes caused by four events in the Yellow River watershed: The main river channel shift in 1976, construction of the Longyangxia Reservoir in 1986, the beginning of the WSRS in 2002, and weakened capability of the WSRS to remove sediments after ~2007. The notable changes of χ fd%, χ ARM, and lithology at the 1976, 1986, 2002, and ~2007 horizons may be used as dating points in future research of sediment cores from the Yellow River Mouth.

Characterizing and identifying bedforms in the wandering reach of the lower Yellow River

The lower Yellow River (LYR) is a fully alluvial system with a fine-grained bed that has a high proportion of silt. Bathymetric survey data collected with a Multi-Beam Echo Sounder (MBES) from the wandering reach of the LYR indicates that the bedforms are characterized by large aspect ratios (wavelength/height) and low lee-side angles. Since the Xiaolangdi Reservoir (XLD) has been operational in the middle reach of the Yellow River, bedforms have been dominated by two-scales of dunes, that is, a frame of compound dunes with first-order dunes superimposed on the stoss and lee sides, which disappear during high sediment concentration floods that occur during the annual sediment and water regulation. The bedform formation regime has changed with dune beds having more chances, and upper regime beds having less chances, to form. Longitudinal profile data measured using a sounding-rod before the XLD began filling demonstrate that the bedforms were mainly dunes during low flows (less than 1200 m3/s) or upper regime beds during high-flows (larger than 2000 m3/s). A discriminator is proposed to describe the conditions for bedform formation and to predict the alluvial resistance which gives better results than those from Manning approach. When a bedform system is almost at equilibrium, the changes in the sediment concentrations versus the discriminator can be defined into three segments in the LYR.

Variability of heavy metal transport during the water–sediment regulation period of the Yellow River in 2018

To understand the impacts of the human-induced flood event on heavy metal (HM) transport, spatiotemporal variations in contents and fluxes of metals (Cr, Ni, Cu, Zn, As, Pb, Cd), Pb stable isotopes and characteristics of water and sediment transport into the sea during Water-Sediment Regulation Scheme (WSRS) in Yellow River (YR) were studied based on field investigation at Xiaolangdi Reservoir (XLD), Lijin Station and Yellow River estuary (YRE). The HM transport was significantly controlled by hydrological process and dominated by particulate form with strong associations with particle size and suspended sediment concentration (SSC). In first stage, dissolved heavy metal (DHM) and particulate heavy metal (PHM) contents both increased significantly as coarser sediment with a mixed source of downstream river channel and XLD, while that maintained higher value for stable source of fine-grained XLD sediment in second stage. The HMs into the sea were mainly originated from upper and middle reaches but also contributed by human emissions from downstream area. As the source of HMs into the sea, the downstream area also acted as an important sink, especially in first stage, playing a role of buffering and filtration. During WSRS, the YR discharged 49%–60% of annual HM flux into the sea, and the second stage is the main transport period, leading to a great alternation in geochemical composition of the YRE sediment.

A framework for evaluating the impacts of reservoirs on seasonal ecohydrological conditions based on new eco‐flows

AbstractThe eco‐flow metrics (ecosurplus [ES] and ecodeficit [ED]) based on flow duration curves (FDCs) are currently less popular than other metrics used to assess the ecohydrological conditions of rivers. To fully utilize their application potential, the seasonal ES and ED are redefined based on discharge hydrographs (DHs) rather than their FDCs. The annual ES and ED are redefined as the sum of the four seasonal ES and ED values, respectively. The impact of reservoirs can be measured by the rate of increase of the cumulative seasonal eco‐flows. Taking the seasonal EDs calculated by the 10% DH and 20% DH as the two threshold values, a risk evaluation method is proposed that classifies the seasonal ecohydrological conditions into four risk levels: no risk, low risk, moderate risk, and high risk. A daily discharge time series ranging from 1956 to 2015 in the Yellow River is used to perform a case study. The results showed that the Shannon diversity index (H) had a strong relevance to the annual ED. Riverine biodiversity was more sensitive to summer and autumn droughts than to floods. The Xiaolangdi Reservoir affected the seasonal eco‐flows much more than the Sanmenxia Reservoir. The winter season is currently classified as having a high risk and should be given more attention by river managers in the future. After the ecological regulation measures are implemented in the future to improve the winter conditions, their effects can be re‐evaluated by the above framework.

Optimisation of reservoir operation mode to improve sediment transport capacity of silt-laden rivers

The inverse relationship between water and sediment is hindering the regulation of sediment in silt-laden rivers. Under natural conditions and insufficient water flow, sediment deposits along river channels, resulting in the accumulation of suspended river sediments above the ground level on both sides of the river. Then, during flooding, dam collapse and overflow can easily occur, threatening the life of residents in floodplain. The operation of upstream reservoirs to maximise the sediment transport capacity of downstream rivers into the sea is deemed the best strategy for the management of silt-laden rivers. However, as incoming water and sediment form a dynamic system, optimising the operation mode of reservoirs has become the most severe challenge in the field. This study proposes a method to remodel the water–sediment relationship of natural rivers by optimising the reservoir operation. First, data were collected and analysed to investigate sediment transport in the downstream river channel and the response relationship between erosion–deposition. Then, an empirical equation for calculating the desired incoming sediment was derived, and the threshold for sedimentary transport balance in the lower reach of silt-laden rivers was determined through mathematical modelling. Finally, the reservoir operation mode was optimised within the threshold range to study the discharge process of the reservoir with the highest sediment transport efficiency downstream. The Yellow River in China exhibits the highest sediment concentration worldwide and was used as a case study to verify the practicability of the proposed method. The critical threshold for sediment transport balance in the lower Yellow River was determined to be 250 million tons. The results demonstrate that the proposed method improved the sediment transport capacity of the lower reaches of the Yellow River. Moreover, it reduced the siltation of the XiaoLangDi Reservoir and the lower reaches of the Yellow River. The XiaoLangDi Reservoir can be jointly operated with the Guxian Reservoir, which is under construction and is expected to maintain the bankfull discharge of the lower reaches of the Yellow River at 4000 m3 for a long time. The optimisation process described in this study can be used to improve the management of silt-laden rivers.

Deposition development in post-flood seasons between 1999-2015 at the entrance of typical tributaries of Xiaolangdi Reservoir, Yellow River&lt;sup&gt;*&lt;/sup&gt;

Deposition development in post-flood seasons between 1999-2015 at the entrance of typical tributaries of Xiaolangdi Reservoir, Yellow River&lt;sup&gt;*&lt;/sup&gt;

Rapid and long-distance channel incision in the Lower Yellow River owing to upstream damming

The operation of the Xiaolangdi Reservoir has significantly altered the flow and sediment regime of the Yellow River, which has led to rapid and long-distance channel incision in the Lower Yellow River. Variations in the channel incision depth and stage-discharge relationships were identified in the braided, transitional and meandering reaches based on the cross-sectional profiles at 91 sedimentation sections and hydrological data at hydrometric stations. The results show that the cumulative reach-scale channel incision depths in the braided, transitional and meandering reaches in response to upstream damming were 3.0 m, 2.5 m and 2.3 m, respectively. In addition, water levels at given discharges dramatically decreased at three hydrometric stations in the different reaches. The previous 5-year average incoming sediment coefficients are the key fluvial factor influencing the cumulative channel incision depth in the Lower Yellow River. The cumulative bank retreat width increased with the cumulative channel incision depth in the braided reach, and a linear function between these parameters was established. However, bank retreat occurred when the channel incision depths reached critical values in the transitional and meandering reaches. Empirical equations were established between the cumulative channel incision depth and the relative bed roughness in the braided and transitional reaches, and they indicate that the riverbed coarsening process can mitigate channel incision to some extent.

The changes in physicochemical and stable isotope compositions in the lower Yellow River of China due to artificial flooding

Increasingly, modern hydrological technologies are dynamically altering river water flow and drastically affecting river hydrogeochemical cycle regimes globally. The present study focused on the reservoir discharges of artificial floodwaters that influence spatiotemporal variations in the physicochemical and stable isotope compositions in the lower Yellow River (LYR) of China. The surface water samples were collected at the nine sites along the LYR during the pre-, inter-and post-flood periods. Then, the collected samples were analysed with the following standard method. The δD and δ18O slopes of the waterline clearly indicated that the prolonged reservoir water and different water flows impacted the hydrological cycle in the LYR regions compared to GMWL (global meteoric water line) and LMWL (local meteoric water line). The thermal stratification processes of the water in the largest reservoir slightly enriched the heavy isotopes, and physicochemical alteration was neglected. Statistical analysis of two-way ANOVA revealed that the p-values (p < 0.01, p < 0.05) were very strong for most of the variables between the periods, and the linear regression exhibited weak values (R2 = 0.253, R2 = 0.150) at the surface water temperature variations and suggested no significant influence of isotope composition. Overall, the Xiaolangdi reservoir water prolonged time rates, and artificial floodwater flow had a very small effect on the isotope composition; in particular, a large high turbidity concentration in the discharged artificial floodwaters was the only considerable ecological risk condition in the LYR. This kind of proper monitoring work is immensely important and prevents reservoirs from causing hydrological cycle impacts in the LYR and the adjacent coastal ecosystems.

Effect of water-sediment regulation operation on sediment grain size and nutrient content in the lower Yellow River

The Yellow River (YR) is famous for its high sediment concentration. The Xiaolangdi dam (XLD), the most downstream dam on the mainstream of the YR, plays an integral role in siltation mitigation, flood defence, agriculture, and hydropower generation. To alleviate siltation of the Xiaolangdi Reservoir (XLDR) and riverbed uplift of the lower reaches of the YR and strengthen flood control safety downstream, the XLDR began to implement water-sediment regulation in 2002. Water-sediment regulation (WSR) has significantly changed the hydrological processes, erosion and deposition, and sediment transport in the downstream channel, and the downstream water environmental conditions have also changed. In this study, 10 sections in the Lower Yellow River (LYR, from the XLDR to the Lijin section) and 4 sections in the soft floodplain area were sampled in the field to analyse their surface sediment grain size composition and nutrient content. At the same time, data on the average annual median particle sizes (D50) of channel sediments and suspended particles in 7 typical sections in the LYR from 2004 to 2015 were statistically analysed. The results show that the channel sediment grain size in the LYR decreased along the river course, and the D50 ranged from 0.20 mm in the HYK section to 0.08 mm in the LJ section. Moreover the D50 of the suspended sediment was less than 0.05 mm. The D50 of the channel and suspended sediment were both ranked as follows: non-flood season > flood season > WSR period. After WSR, fine silt particles with diameters of 0.01–0.05 mm were deposited on the soft floodplain. The channel sediment size was mainly coarse particles with diameters of 0.05–0.20 mm due to channel erosion. The suspension of fine silt particles due to flood scouring led to the total organic carbon (TOC) and total nitrogen (TN) absorbed in the particles to also be resuspended in the water. As a result, the TOC and TN contents in the channel sediments decreased by approximately 40% after WSR.

Analysis on the Variation Trend of Evaporation and Precipitation in Xiaolangdi Reservoir

Based on the monthly evaporation and precipitation data from 1982 to 2013 of 13 meteorological stations in and around the Xiaolangdi Reservoir, the linear tendency estimation method, cumulative anomaly, M-K mutation detection method and ARIMA model are used to study and predict the changing characteristics of evaporation and precipitation. The results show that the annual evaporation and precipitation in the reservoir area both show a downward trend. The evaporation has an abrupt decline in 2001, and the precipitation decreases suddenly in 2003 and 2011. After impoundment, the annual evaporation volume changed from the upward trend to a weak downward trend, and the downward trend of annual precipitation is weakened. The impact of impoundment on evaporation and precipitation is limited, and the impact intensity decreases with increasing distance from the reservoir. The reservoir area’s evaporation and precipitation have significant seasonal variation characteristics, and the future evaporation will show a slight downward trend, while the precipitation will show a slight upward trend.

Monitoring of surface deformation in a low coherence area using distributed scatterers InSAR: case study in the Xiaolangdi Basin of the Yellow River, China

The Xiaolangdi Basin of the Yellow River, located between Mengjin County and Jiyuan City in Henan Province, is composed of a reservoir, a barrage dam, flood discharge buildings, and a water diversion and power generation system, among which, the Xiaolangdi project is the only control project in the lower reaches of the Yellow River that has a large storage capacity. In this study, distributed scatterers InSAR (DS-InSAR) deformation analysis was used to process 27 images of ESA Sentinel-1A data for the period between September 10, 2018, and July 19, 2019. Using the generalized likelihood ratio test (GLRT) to select the statistical homogeneous pixels (SHP) and the eigenvalue decomposition method to optimize the interference phase, the time series surface deformation of the study area was obtained. The results showed that the maximum deformation rate in the study area was − 40.71 mm/year, the maximum deformation rate of the Xiaolangdi project was − 10.09 mm/year, and the larger deformation rates in the area around the Xiaolangdi Reservoir were mostly within the range − 35 to − 20 mm/year. Furthermore, small baseline subset (SBAS) InSAR and DS-InSAR are used for verification and analysis, and the monitoring results have high consistency. Therefore, to sum up, the time series deformation of low coherence areas may be monitored using DS-InSAR.