Variations In Sediment Load Research Articles

Hydrological Changes and Sediment Dynamics in the Inner Mongolia Section of the Yellow River: Implications for Reservoir Management

The Inner Mongolia section of the Yellow River is a primary alluvial segment of the main channel. The variations in water and sediment not only alter the cross-sectional morphology and flow capacity of the river but also impact the scheduling of upstream cascade reservoirs. Based on runoff and sediment load data and topographic information from typical hydrological stations, the characteristics of runoff and sediment load variations and the evolutionary pattern of siltation in the Inner Mongolia River section were analyzed via trend analysis methods, Mann–Kendall test methods, the sediment load transport rate method, and the water level–flow relationship. The results showed that the water and sediment loads at the hydrological stations in the Inner Mongolia River section significantly changed from the 1960s to after 2000, with runoff decreasing by approximately 22% to 32% and the sediment load decreasing by approximately 65% to 73%. Sedimentation in the river section generally increased, and the average annual siltation amount reached 0.144 billion t. The joint utilization of the Longyangxia and Liujiaxia reservoirs in 1987 was the main reason for the rapid increase in siltation, and siltation in the Inner Mongolia River section was slightly reduced after 2005. In addition, the critical sediment load coefficients of the Bayangaole–Sanhuhekou and Sanhuhekou–Toudaoguai River sections were 0.0073 and 0.0051 kg·s/m6, respectively, from 1952 to 1968, and 0.0053 and 0.0037 kg·s/m6, respectively, from 1969 to 2020. This study could provide technical support for river flood control and reservoir water sediment regulation in Inner Mongolia.

Impact of Hydrographic Network Organization on the Morphology of the Kert Basin: Analysis of Consequences

This study investigates the intricate relationship between hydrographic network organization, geological faults, and regional dynamics within the Kert basin in the Eastern Rif region. Through GIS hydrographic analysis, we analyze the impact of the hydrographic network on landscape morphology and hydrological dynamics, emphasizing implications for sustainable water resource management. Results reveal the presence of dendritic and parallel hydrographic networks influenced by geological faults, which guide water flow and shape drainage patterns. Seasonal variations in sediment load show significant transport in September and May, indicating increased torrentiality in upstream areas. Fault structures play a crucial role in landscape formation and water quality, with tectonic movements contributing to the development of reliefs and valleys. Understanding these interactions is vital for developing effective strategies for flood mitigation, ecosystem conservation, and sustainable water supply in the Kert basin and similar regions worldwide.

Morphological change and its response to human activities in the estuary of Minjiang River, China, since last early century

AbstractThe evolution of subaqueous deltas in mountain rivers is highly sensitive to variations in sediment load and hydrodynamic conditions, and human activities can rapidly alter these parameters. To better understand the evolution of the subaqueous Minjiang River Delta (MRD) under human activities, we investigated the effects of construction of reservoirs, channel training walls, land reclamation activities, and sand mining from 1910 to 2010. Analysis of bathymetric and fluvial discharge data revealed that the MRD shoals generally experienced slight development during the study period, but with alternating stages of erosion and deposition that were related closely to sediment discharge and the role of human activities. The northern MRD was more strongly affected by decreasing sediment load, while the southern MRD was more influenced by land reclamation. Human activities in the MRD can be divided into five stages: Weak (before 1935), blockage (1935–1950), slight strong (1950–1970), strong (1970–2000), and stable (since 2000). Correspondingly, the geomorphic evolution of the MRD can also be divided into five stages: Natural evolution, channel blockage, southern channel erosion, divergence, and degradation. Furthermore, the morphodynamic response time of MRD to a decrease in riverine sediment was found to be less than 10 years, which is much faster than the morphodynamic changes observed in large‐scale estuaries and deltas. These results provide further insight into interpreting morphodynamic changes in typical small/medium‐sized estuaries and deltas under various human activities.

Variation characteristics of rainfall erosivity in tropical China and its impact on river sediment load

Rainfall erosivity is one of the important factors leading to soil and water erosion, affecting the intensity of soil erosion and the variation of river sediment load. This work aimed to explore the distribution and variation characteristics of rainfall erosivity in the Nandu River Basin in tropical China and to clarify the effect of rainfall erosivity on sediment load variation. The daily rainfall data of 13 meteorological stations in the Nandu River Basin during 1971–2020 were used to calculate the rainfall erosivity of the river basin by using the rainfall erosivity model based on the daily rainfall. The analyses were conducted using the Mann-Kendall non-parametric trend/abrupt test, wavelet analysis, inverse distance weighted interpolation and other research methods to determine the temporal and spatial fluctuation patterns of rainfall erosivity and sediment load. The annual mean rainfall erosivity in the Nandu River Basin during 1971–2020 was 16,497.67 MJ mm·ha−1·h−1, which showed an upward trend. The distribution of rainfall erosivity was concentrated from July to September. Except spring, the variation of rainfall erosivity in summer, autumn and winter showed an upward trend. Spatially, rainfall erosivity showed a decreasing trend from south to north. The variation coefficient of each meteorological station ranged from 0.24 to 0.43, showing high regional variability. The correlation between rainfall erosivity and erosive rainfall in the basin was the highest, followed by altitude and latitude. From 1980 to 2020, the sediment load in the Nandu River Basin showed an overall upward trend, with obvious periodic changes. The main change period was 25 years, and the sediment load had a large inter-annual variation. Taking the period before the inflection point of the double accumulation curve of sediment load and rainfall erosivity as the base period, since 2009, the river sediment load increased by 46.36% compared with the base period. The influence of the variation of rainfall erosivity on sediment load is −22.23%, and that of human activities on sediment load is 122.23%. These findings can provide a scientific reference for soil erosion model prediction, soil and water conservation and environmental management in tropical basins of China.

Long-term variations in water discharge and sediment load of the Pearl River Estuary: Implications for sustainable development of the Greater Bay Area

The water discharge and sediment load have been increasingly altered by climate change and human activities in recent decades. For the Pearl River, however, long-term variations in the sediment regime, especially in the last decade, remain poorly known. Here we updated knowledge of the temporal trends in the sediment regime of the Pearl River at annual, seasonal and monthly time scales from the 1950s to 2020. Results show that the annual sediment load and suspended sediment concentration (SSC) exhibited drastically decreased, regardless of water discharge. Compared with previous studies, we also found that sediment load and SSC reached a conspicuous peak in the 1980s, and showed a significant decline starting in the 2000s and 1990s, respectively. In the last decade, however, water discharge and sediment load showed slightly increasing trends. At the seasonal scale, the wet-season water discharge displays a decreasing trend, while the dry-season water discharge is increasing. At the monthly scale, the flood seasons in the North and East Rivers typically occur one month earlier than that in the West River due to the different precipitation regimes. Precipitation was responsible for the long-term change of discharge, while human activities (e.g. dam construction and land use change) exerted different effects on the variations in sediment load among different periods. Changes in the sediment regime have exerted substantial influences on downstream channel morphology and saltwater intrusion in the Greater Bay Area. Our study proposes a watershed-based solution, and provides scientific guidelines for the sustainable development of the Greater Bay Area.

Study on the sediment and phosphorus flux processes under the effects of mega dams upstream of Yangtze River

The upper Yangtze River (UYR) plays an important role in water supply, hydropower generation, environmental and ecological protection. Constructions of Mega cascade reservoirs have significantly affected the transport of sediment and P, but the evolution of sediment and P in the mega cascade reservoirs of the UYR is unclear. This study investigated the variations in sediment load and total P (TP) flux based on the flow and sediment data from 1990 to 2019 and TP concentrations from 2005 to 2019. In addition, the proportion of sediment load and TP flux from tributaries, variations in the concentrations of particulate P (PP) and dissolved P, trapping effect of dams, and statistical uncertainties were analyzed and discussed. The main results are as follows: (1) the sediment load and TP flux evidently decreased after the impoundment of reservoirs in the UYR and Jinsha River, and the contribution rate of TP flux from main tributaries (except Wu River) to mainstream increased by 3.82–24 %; (2) the error of TP flux calculated by daily and monthly data is within 30 %, which shows that the uncertainty range is clear at some degree attributed to the different monitoring frequency, and the concentration of PP in flood season is greater than that in non-flood season; (3) the total retention rates of sediment and TP in the Three Gorges Reservoir and Gezhouba were 86.78 %, and 49.83 % (2009–2012), respectively, but decreased to 82.85 % and 15.26 % (2013–2019), and the values in Xiangjiaba and Xiluodu were 97.83 % and 60.27 % (2013–2019). The retention rates of newly built reservoirs (Wudongde and Baihetan) were predicted using an empirical method, and the results revealed that new dams would facilitate long-term reduction in sediment downstream.

Scale-specific variation in daily suspended sediment load in karst catchments

Temporal variation in sediment load is generally scale dependent and affected by many factors operating at different timescales. Due to the complexity of sediment transportation mechanisms and the nonlinear behavior of hydrological processes, identifying multi-timescale effects of variables on daily suspended sediment load (SSL) is challenging. Using multivariate empirical mode decomposition (MEMD), the aims of this study were to investigate scale-dependent relationships between daily SSL and associated variables and to predict daily SSL based on these relationships. Data on daily SSL in four typical karst catchments of southwest China and five potential variables affecting daily SSL (i.e., runoff, precipitation, air temperature, potential evapotranspiration, and Normalized Differential Vegetation Index) were collected during 2009–2012. The results indicated that MEMD decomposed temporal patterns of daily SSL and five potential variables affecting daily SSL into eight or nine intrinsic mode functions (IMFs) and a residue. Short timescale oscillations of IMF1 to IMF4 contributed more than 72 % of the total variance in daily SSL in the four catchments, indicating that temporal variation in SSL was dominated by short intervals of 4–23 days. Runoff was the dominant explanatory variable for the overall daily suspended sediment load prediction at the observation scale. The predictions of daily SSL based on the IMFs and their residuals greatly outperformed those based on the original time series data. This result implies that a single scale (e.g., observation scale) is not sufficient to capture the complex relationships that exist between daily SSL and associated variables at all timescales. The results demonstrate the superiority of MEMD in characterizing scale-specific relationships between daily SSL and associated variables and improving daily SSL predictions. Given the complexity, nonlinearity, and nonstationarity inherent in many hydrological and sediment transport processes, MEMD is recommended for identifying scale-specific variation in daily SSL in future studies.

Natural and anthropogenic effects on spatio-temporal variation in sediment load and yield in the Godavari basin, India

River sediment, the most crucial component of the land-ocean interaction, is enduring substantial changes worldwide because of anthropogenic alterations and climate change. Our study assesses the interaction of sediment load variability and yield to the rainfall, land-use, and dam constructions at both spatial and temporal scales in the Godavari and its major tributaries. The most important river basin in Peninsular India, the Godavari, has witnessed a dramatic decline (p-value <0.001) in sediment load over the past five decades, with average annual rates of 2 million tonnes (Mt) yr−1. Sediment load in the Godavari reduced from 150 Mt between 1970 and 1979, to 115 Mt in 1980–1989, 98 Mt in 1990–1999, 48 Mt in 2000–2009, and 47 Mt in 2010–2019, respectively. While sediment load in the Godavari and its major tributaries is declining significantly, the rainfall showed an overall insignificant increasing trend barring the Sabari sub-catchment, where the rainfall is increasing at a significant rate of 7 mm yr−1 (p-value = 0.001). Twenty-five sub-basins in the Godavari showed a large variation in sediment yield (28 to 3404 t km−2 yr−1). Our results revealed that spatial variability in sediment yield is primarily associated with both rainfall and land-use pattern. The temporal variation in sediment load in the Godavari and Pranhita is associated with intensified human activities during the most recent decades, while climate is the primary controlling factor in Indravati and Sabari sub-catchments. Sediment entrapment under a high rate of siltation by reservoirs in the Godavari has sharply reduced the sediment flux to the Bay of Bengal, causing aggravated delta erosion by wave actions. The findings of this study have significant implications for understanding the complex interrelationship between the management of reservoirs, land use, sediment loads, denudation, and coastal erosion in the Godavari catchment.

Analysis of sediment variation and influencing factors in the upper Yangtze River in the past 50 years, China

Abstract River sediment load has a profound impact on river geomorphology and river ecosystems. We selected sediment load data from 1965 to 2019 from three key hydrological stations in the upper reaches of the Yangtze River: Pingshan, Cuntan, and Yichang. We have used the Mann-Kendall method, t-test, and wavelet analysis to analyze the characteristics of sediment load variation, the Cumulative volume slope rate of change, and the River Impact method to quantitatively assess the degree of sediment variation and the influencing factors. The results show that (1) The annual sediment load at the upper reaches of the Yangtze River at the Pingshan, Cuntan, and Yichang stations all showed a significant decreasing trend, with mutations in 1997, 2003, and 2002, respectively, with the main period of 15 years, 24 years, and 10 years. (2) A series of human activities such as interception of dams, sand mining in river channels, and soil and water conservation measures are the main reasons for the significant reduction of sediment load in the upper reaches of the Yangtze River, with the contribution of human activities exceeding 80% in all cases after the 1990 s and 90% after the 21st century. (3) Under human activities, the annual sediment load at Cuntan station has been highly altered, while serious alterations have occurred at Pingshan and Yichang stations. The results of the study can provide a corresponding reference for ecological protection and restoration in the Yangtze River basin.

Effects of climate variability and anthropogenic factors on sediment load reduction in the Weihe River basin, China

AbstractSediment load of China's Yellow River has dramatically decreased due to the interplay of climate variability and human activities in the past decades. However, the contribution of individual driving factors and the detailed spatial distribution of sediment load at a catchment scale were not well understood. In the study, we quantitatively assessed the relative contributions of individual climatic (i.e. precipitation) and anthropogenic (i.e. vegetation restoration, terrace construction) driving factors to sediment load variations in the largest tributary of the Yellow River, Weihe River. The employed annual sediment load measurements and rainfall data for 1961–2015 were collected at 15 hydrological and 60 meteorological stations that were widely distributed in the basin. Changing trends, periodicity, and abrupt changes of hydro‐climatic variables were detected using the non‐parametric Mann–Kendall test, the empirical mode decomposition method, and Pettitt's test. Results showed that annual sediment load presented significantly decreasing trends at 12 hydrological stations. Annual rainfall erosivity showed a mixed tendency, with the changing trends varying among different regions. A 3‐year periodicity was identified in the annual sediment load at three main stream gauging stations. Abrupt changing points in sediment load primarily occurred in the 1990s and early 2000s at all of the 15 hydrological stations, which were largely attributed to human activities. The increase in vegetation cover was responsible for approximately 40.6%, 37.4%, and 54.7% of the sediment load reduction in the main stream of the Weihe River, the Jinghe River, and the Beiluohe River, respectively. Meanwhile, terrace construction accounted for 19.7%, 43.8%, and 9.9% of the sediment variation, respectively. Conversely, precipitation change accounted for 5.7%, 12.4%, and 8.3% of sediment load reduction, respectively. Overall, vegetation restoration and terrace construction were found to be the two dominating factors for sediment load reduction in the study area.

Sediment yields variation and response to the controlling factors in the Wei River Basin, China

Assessing regional sediment yield variation and their responses to the potential controlling factors are critical to develop specific strategies of soil conservation measures to adapt to future climate change. This study attempted to investigate the spatial–temporal variation of sediment load in the Wei River basin in the midstream of the Yellow River during 1961–2015 at 15 hydrological stations. The results indicated that annual sediment load in the past six decades decreased significantly (P < 0.01) with the changing trends of −6.43 × 104, −3.86 × 104, −4.6 × 104 t/a at Xianyang, Zhangjiashan, and Zhuangtou stations, respectively. Annual sediment load exhibited abrupt changes in the mid-1990s, which were largely attributed to the strong effects of soil conservation measures in the study area. The spatial pattern of soil erosion were characterized by high sediment yield in the north with sparse vegetation cover and well-developed gullies, and low sediment yield in the south with flat plain and good vegetation cover in the Wei River basin. The results of the partial least squares-structural equation model (PLS-SEM) showed that vegetation changes and rainfall variability explained 62.3%, 47.3%, and 40.1% of the variation in runoff at Xianyang, Zhuangtou, and Zhangjiashan stations, respectively, whereas 59.4%, 17.6% and 48% of the variation in sediment load were explained by the combining effects of rainfall variability, changes of vegetation and runoff. This study provides a deep insight for understanding the effects of driving forces on sediment yield changes, and can be useful to regional soil conservation planning in the region.

The response of the suspended sediment load of the headwaters of the Brahmaputra River to climate change: Quantitative attribution to the effects of hydrological, cryospheric and vegetation controls

The response of suspended sediment load to climate change has important implications for downstream ecosystems and biogeochemical cycles. Glaciers, permafrost, vegetation and hydrological processes are rapidly changing in high-altitude regions. However, there is currently no consensus about how and to what extent these factors will affect interannual changes of fluvial sediment export. Here, we investigate the increasing trend of suspended sediment load in the headwaters of the Brahmaputra River from 1972 to 2008. The key influencing factors, including the hydrodynamic flux and erosivity of glacier runoff, precipitation, vegetation cover, and soil erodibility were quantified, and their changing trends were analyzed. Two methods were used to attribute the variation of sediment load; Partial Least Squares Path Modeling (PLS-PM) based on statistical regression and Sediment Identity (SI) based on algebraic equations. The results obtained by these two relatively independent methods were broadly consistent, and the error of the SI model was less than 8%. The sediment load showed a significant increasing trend at an average changing rate of 18.9%/10a, without any abrupt fluctuations. The increase in fluvial sediment load was primarily due to increases in both the amount (43%) and erosivity (55%) of precipitation, combined with minor influences from increased sediment supply due to earlier thawing (16%) and intensified glacier melting (14%). The increases in fluvial sediment load were partially buffered by a decrease in water yield capacity due to denser vegetation cover (−29%). This study provides valuable insights into the natural response of fluvial sediment loads to climatic and environmental change, and the findings are critical for soil and water conservation planning in cold and high-altitude regions.

Quantifying the impact of climate change and anthropogenic activities on runoff and sediment load reduction in a typical Loess Plateau watershed

Study regionThe Huangfuchuan Basin on the Loess Plateau, China. Study focusRunoff and the sediment load of the Yellow River in China have received substantial attention owing to their marked declines over recent decades. Climate change and intensive anthropogenic activities—soil and water conservation measures on the Loess Plateau—are regarded as the main factors responsible for the dramatic declines. Thus, attribution analysis on the roles of such influencing factors is important for the sustainable management. In this study, annual-scale variations of runoff and sediment load of a typical watershed undergoing intensive change were simulated using three regression algorithms. The impacts of climate change, namely precipitation and temperature, and anthropogenic activities, namely channel measures (check dam construction) and slope measures (terracing, afforestation, grass planting, and closures), on runoff and sediment load variations were quantified continuously for the period 1954–2015. New hydrological insights for the regionResults indicated that the main climate change factor was precipitation reduction, which was attributed to 35% and 34% of runoff reduction and sediment load reduction, respectively. Channel measures caused 32% and 39% of runoff reduction and sediment load reduction, respectively, whereas slope measures caused 33% and 27% of runoff reduction and sediment load reduction, respectively. We recommend that further implications of soil and water conservation measures be studied carefully on the Loess Plateau.

Spatio-Temporal Variations of Discharge and Sediment in Rivers Flowing into the Anzali Lagoon

In the last few years, trend identification has become an important issue in hydrological time-series analyses; it is also a difficult task, due to the variety of models and the impact of climate change on the river flow regime. Due to the vital importance of the Anzali Lagoon to the environment of the region, and the threat to its health caused by the volume or amount of inlet sediments, we decided to study the changes in flow and sediment in the rivers flowing into the Anzali Lagoon. For the present study, the long-term monthly, seasonal, and annual sediment and discharge data of seven stations were obtained during the period 1985–2019. According to the available information, the trend of sediment load variation was investigated at different time scales. In this study, the Mann–Kendall statistical test, the double-mass curve, and performance fitting were used to assess the seasonal and annual trends in sediment and river flow. The results showed that at Aghamahale station, the low relationship between discharge and sediment compared with that at other stations was due to the low slope and constant water of the Behmbar River, which caused the sediments to settle and decreased their carrying rate. Moreover, Nokhaleh station had the largest share of sediment transfer to the lagoon during 2002–2012. Sediment details also show that the highest amount of sediment in all stations occurred in non-crop seasons—i.e., from October to January—and was directly dependent on the amount of rainfall in these areas. The results of the sediment analysis also indicate that the discharge and the subsequent sediment loads from upstream to downstream were high over the summer. Furthermore, the rivers downstream demonstrated springtime peaks in the sediment loads and discharge, probably owing to snow melting.

Reconstructing environmental signals across the Permian-Triassic boundary in the SE Germanic basin: Paleodrainage modelling and quantification of sediment flux

Reconstructing sediment load in deep-time is one of the greatest challenges in the reconstruction of ancient sediment routing systems, particularly because solid statistical models are absent and paleo-climatic, paleo-tectonic, and sedimentary constraints are lacking. This study proposes a reliable workflow for the estimation of paleo-sediment fluxes (Qs) applying the BQART model to a case study from the SE Germanic Basin across the Middle Permian – Early Triassic interval. The input parameters of the simulations derive from: integrated plate modelling and structural kinematics; paleodrainage and paleogeographic reconstructions; global circulation models; and sandstone compositional signatures. We apply Monte Carlo simulation to overcome the input uncertainties for eight different scenarios obtained from the combination of two area estimates, two climate models, and two time resolutions. All the models are in general agreement and show changes in sediment flux (i) being steady or declining slightly through the Middle Permian, (ii) an increase of 31% at the beginning of the Late Permian (3.6–4.6 Mt yr−1), (iii) and a nearly 100% rise at the onset of the Early Triassic (7.4 Mt yr−1). The variation of sediment load across the PTB is coeval to the transition from meandering/sabkha to perennial braided depositional settings recorded from the well data of Obernsees-1 and Lindau-1; it results from both increased tectonism and seasonal precipitation. The Qs estimates agree with those of modern drainages under analogous environmental conditions, highlighting the reliability of the workflow included in this study for the quantification of sediment flux in deep time. Furthermore, the results of this study provide new insights on the highly debated evolution of the continental sequences across the PTB with strong implications for both past and future paleo-environmental reconstructions.

Ephemeral gully erosion in concentrated flow channels induced by rainfall and upslope inflow on steep loessial slopes

AbstractEphemeral gullies (EGs) play a crucial role in hydrological connectivity, soil erosion, and land degradation. However, little research has focused on flow hydraulics in concentrated flow channels and their effects on EG erosion on steep loessial slopes. A simulated experiment of rainfall (60–120 mm hr−1) and upslope inflow (0.45–2.25 m2 hr−1) were conducted on concentrated flow channels with loess at 15°–25° slope gradients. The concentrated flow was turbulent and subcritical in most cases. The flow shear stress, stream power, and unit stream power in the concentrated flow channels varied from 32.65 to 109.40 N m−2, 10.85 to 38.66 N m−1 s−1, and 0.08 to 0.16 m s−1, respectively. The EG depth, width, and width‐depth ratio varied within 14.8–24.6 cm, 18.5–33.8 cm, and 1.13–1.83, respectively. Moreover, the EG depth and width increased in a power function with the runoff rate (R2 = 0.82–0.83; p &lt; 0.01). The sediment yield rate (Ys) varied within 15.94–94.44 g m−2 s−1 under the different treatments and had a good linear relationship with the runoff rate (R2 = 0.78; p &lt; 0.01). Furthermore, the flow shear stress and stream power can be used to predict Ys by linear functions. The critical runoff rate and shear stress to initiate EG erosion were determined to be 0.09 m3 hr−1 and 2.66 N m−2. However, the coefficient of determination for the linear relationship between Ys and shear stress was low (0.58). The results indicate that the flow shear stress mechanism might not be enough to explain sediment load variation for EG erosion, and headcut erosion mechanism should be taken into account.

Effects of Dam Construction in the Wang River on Sediment Regimes in the Chao Phraya River Basin

The Wang River is one of the major tributaries of the Chao Phraya River (CPR) system in Thailand as the key riverine sediment source supplying the Chao Phraya Delta that has experienced severe shoreline retreat in the past six decades. Historical and observed river flow and sediment data measured during 1929–2019 were used to assess the variation in total sediment load along the Wang River and evaluate the effects of three major dam constructions on sediment supplied from the Wang River to the CPR. Results indicated that sediment loads increased toward downstream. Variation in long-term total sediment load (TSL) along the river suggested that construction of the Kiew Lom Dam in 1972 did not cause a reduction in sediment yield in the Wang River Basin because it impounded less than 20% of the average annual runoff, while the Mae Chang and Kiew Koh Ma Dams caused downstream sediment reduction. These three dams are located in the upper and middle river basins, and their effects on sediment load in the Wang River are ameliorated by additional sediment supplied from the lower basin. Results confirmed that construction of these three major dams in the Wang River did not greatly impact sediment supply from the Wang River to the CPR system. The dam site and sediment load variation along the river are the primary factors controlling the impact of the dam construction.

Quantifying delta channel network changes with Landsat time-series data

Delta channel networks (DCNs) are highly complex and dynamic systems that are governed by natural and anthropogenic perturbations. Challenges remain in quickly quantifying the length, width, migration, and pattern changes of deltaic channels accurately and with a high frequency. Here, we develop a quantitative framework, which introduces a water occurrence algorithm based on Landsat time-series data and spatial morphological delineation methods, in order to measure DCN structures and associated changes. In examining the Pearl River Delta (PRD) and Irrawaddy River Delta (IRD) as case studies, we analyze their conditions and trends between 1986 and 2018 at ten-year intervals. Both study areas have undergone various human interventions, including dam construction, sand mining, and land use change driven by urbanization. Our results show the following: (1) the use of a 0.5 water occurrence extraction based on Landsat time-series data, morphological delineation, and spatial change analysis methods can quantify the morphodynamics of DCNs effectively with a root-mean-square error of 15.1 m; (2) there was no evident channel migration in either PRD or IRD with average channel widths of 387.6 and 300.9 m, respectively. Most channels in the PRD underwent remarkable shrinkage, with average rates of 0.4–6.4 m/year, while there were only slight changes in the IRD, which is consistent with observed trends in sediment load variation. The results of this research have the potential to contribute to sustainable river management in terms of flood prevention, riparian tideland reclamation, and water and sediment regulation. Moreover, the proposed framework can be used to develop a new global delta channel network dataset and can be generalized to remotely sensed water discharge and river depth estimation.

Agriculture Land Use Change and Demographic Change in Response to Decline Suspended Sediment in Južna Morava River Basin (Serbia)

This study expounds the dynamic relationships among agricultural land-use change, rural population migration, and sediment transport. The variability of suspended sediment load was detected by Mann–Kendall and Pettitt tests. From 1961 to 2007, the annual trend in suspended sediment concentration and sediment load demonstrated significant reduction (α = 0.001), with decreasing rates of 0.0144 g/L/y and 84.7 t/y, respectively. An abrupt change-point was detected in 1984 for the sediment load (p = 0.0001). The double-mass curve method and regression analysis of sediment load versus precipitation were used to quantify the effects of climate change and human activities on sediment load variations. The changes in sediment load were predominantly impacted by human activities (89%), while precipitation explained 11% of the reduction in suspended sediment. An important land-use change recorded in the Južna Morava river basin comprised the abandonment of agricultural lands due to depopulation processes, as well as economic and social changes, which was followed by significant impacts on soil erosion and sediment transport. Land abandonment was most pronounced in marginal mountain or semi-mountainous areas, where agriculture was until recent decades traditional or semi-traditional. The results of the correlation matrix were significant at the p &lt; 0.05 level, demonstrating that the decrease of rural population, agricultural land, and arable land were directly related to the decline of suspended sediment. High correlation coefficients were found between anthropogenic indicators and sediment parameters, ranging from 0.94 to 0.97.

Long-term soil and water conservation in red soil region of southern China significantly reduced riverine sediment load: A case study of Pingjiang River in the upper reaches of Ganjiang River, Lake Poyang Basin

长时间序列水沙数据分析有助于科学评价流域尺度水土保持减流减沙效应，为科学开展区域水土保持成效评估提供实现路径.本文选取南方红壤区水土保持工程最为集中、持续时间最长的典型流域——平江流域，基于1975—2014年的逐日降水量、流量、含沙量数据，综合应用预置白M-K检验法、Theil-Sen趋势度估计法、Pettitt检验法与累积量斜率变化率比较法，开展河流水沙变化特征及归因分析，揭示长期水土流失治理对河流水沙的影响.结果表明：（1）1975—2014年平江年输沙量、汛期输沙量和非汛期输沙量均存在显著减少趋势，年均减少率分别为2.38×10⁴、1.75×10⁴和0.44×10⁴ t/a，汛期输沙量在流域开始实施系统水土流失治理时即发生突变，而年输沙量和非汛期输沙量在系列国家水土保持重点工程实施一段时间后方开始突变；（2）流域长期水土保持显著减少平江输沙，但对径流无显著影响，重点治理期、治理后期以水土保持为主的生态保护工程对输沙量减少的贡献均在94.0%以上，且生态保护工程对汛期输沙量减少的贡献较非汛期的更为突出；（3）以水土保持为主的长期生态保护工程导致平江全年、汛期、非汛期输沙量分别减少59.3%、60.7%和55.7%；（4）在剔除大型水利工程（尤其是大中型水库）建设影响后，南方红壤区可以基于长时间序列水沙数据分析科学评价流域尺度水土保持减流减沙效应.研究结果可以为南方红壤区流域尺度水土保持减流减沙效应评价提供参考，并有望为区域系列国家生态保护与建设工程的布局和管理提供科学依据.;The analysis of water and sediment data with long time series is helpful for the scientific evaluation of flow and sediment reduction effect of watershed-scale soil and water conservation, and provides an effective method for the scientific evaluation of regional soil and water conservation effectiveness. The Pingjiang River Watershed in the upper reaches of Lake Poyang Basin, which is the typical watershed with the most concentrated and longest ecological protection engineering construction in the red soil region of southern China, was selected as the study area. Based on the daily rainfall, flow, and sediment concentration data of 1975-2014, pre-whitening Mann-Kendall test, Theil-Sen trend analysis, Pettitt's test, and comparative method of the slope changing ratio of cumulative quantity were conducted. Variation characteristics of flow discharge and sediment load were analysed, major influencing factors were identified, their contribution rates to flow discharge and sediment load variation were quantified, and effects of long-term soil and water conservation on flow discharge and sediment load were revealed. The results showed that: (1) From 1975 to 2014, sediment load of the whole year, flood season, and non-flood season all decreased significantly, with the yearly decreasing rate of 2.38×10⁴, 1.75×10⁴, and 0.44×10⁴ t/a, respectively, and the mutation of flood sediment load occurred once the soil and water conservation project began, while the mutation of the whole year and non-flood sediment load didn't happen until most of soil and water conservation projects accomplished. (2) Long-term soil and water conservation in the watershed significantly reduced the sediment load in Pingjiang River, yet had no significant effect on runoff discharge. During both the key control period and post-control period, the contributions of ecological protection projects, which mainly focused on soil and water conservation, contribution rate to the reduction of sediment load were more than 94.0%, while the contribution of ecological protection projects to the reduction of sediment transport in flood season was more than that in non-flood season.(3) Long-term ecological protection projects based on soil and water conservation resulted in a decrease of 59.3%, 60.7%, and 55.7% for sediment load of Pingjiang River during annual, flood, and non-flood period, respectively. (4) After excluding the impact of large-scale hydraulic engineering construction projects, especially large and medium-sized reservoirs construction, the effect on flow and sediment reduction in the watershed scale of soil and water conservation could be scientifically evaluated based on the analysis of long-term flow discharge and sediment load data in the red soil region of southern China. The results can be used as reference for the evaluation of the effect on soil and water conservation in the watershed scale of soil and water conservation in the red soil region of southern China, and are expected to provide scientific basis for the layout and management of national ecological protection and construction projects.