scholarly journals Unraveling the impacts of meteorological and anthropogenic changes on sediment fluxes along an estuary-sea continuum

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Florent Grasso ◽  
Eliott Bismuth ◽  
Romaric Verney
Keyword(s):  
Human Activities ◽  
River Discharge ◽  
Morphological Changes ◽  
Large River ◽  
Fine Sediment ◽  
Global Changes ◽  
Anthropogenic Pressures ◽  
Estuarine Ecosystem ◽  
Anthropogenic Changes ◽  
Sediment Fluxes

AbstractSediment fluxes at the estuary-sea interface strongly impact particle matter exchanges between marine and continental sources along the land-sea continuum. However, human activities drive pressures on estuary physical functioning, hence threatening estuarine habitats and their ecosystem services. This study explores a 22-year numerical hindcast of the macrotidal Seine Estuary (France), experiencing contrasted meteorological conditions and anthropogenic changes (i.e., estuary deepening and narrowing). The hindcast was thoroughly validated for both water column and sediment bed dynamics and showed good capacities to simulate annual sediment budgets observed from 1990 to 2015. We aim at disentangling the relative contributions of meteorological and human-induced morphological changes on net sediment fluxes between the estuary and its adjacent coastal sea. Our results highlight that intense wave events induce fine sediment (≤ 100 µm) export to the sea but coarser sediment (≥ 210 µm) import within the estuary. Although intense river discharges induce mud export to the sea, moderate to large river discharges prove to support mud import within the estuary. Wave and river discharge events were less intense in 2005–2015 than in 1990–2000, reducing fine sediment export to the sea. The estuary deepening and narrowing due to human activities increased fine sediment import within the estuary, shifting the estuary from an exporting to importing system. We propose a conceptualization of mud flux response to river discharge and wave forcing, as well as anthropogenic pressures. It provides valuable insights into particle transfers along the land-sea continuum, contributing to a better understanding of estuarine ecosystem trajectories under global changes.

scholarly journals Unraveling The Impacts of Meteorological and Anthropogenic Changes on Sediment Fluxes Along an Estuary-Sea Continuum

2021 ◽  
Author(s):  
Florent Grasso ◽  
Eliott Bismuth ◽  
Romaric Verney
Keyword(s):  
Human Activities ◽  
River Flow ◽  
Morphological Changes ◽  
Large River ◽  
Fine Sediment ◽  
Global Changes ◽  
Anthropogenic Pressures ◽  
Estuarine Ecosystem ◽  
Anthropogenic Changes ◽  
Sediment Fluxes

Abstract Sediment fluxes at the estuary-sea interface strongly impact particle matter exchanges between marine and continental sources along the land-sea continuum. However, human activities drive pressures on estuary physical functioning, hence threatening estuarine habitats and their ecosystem services. There is an increasing societal need to better predict the potential trajectories of estuarine sediment fluxes resulting from natural and anthropogenic pressures, but the concomitance of human-induced and meteorological-induced changes makes the responses ambiguous. Therefore, this study explores a 22-year numerical hindcast, experiencing contrasted meteorological conditions and human-induced morphological changes (i.e., estuary deepening and narrowing), in order to disentangle the relative contributions of meteorological and anthropogenic changes on net sediment fluxes between a macrotidal estuary and its adjacent coastal sea. Our results highlight that intense wave events induce fine sediment (≤100 µm) export to the sea but coarser sediment (≥210 µm) import within the estuary. Remarkably, moderate to large river flows support mud import within the estuary. Over 25 years, the reduction of intense wave and river flow events reduces fine sediment export to the sea. In addition, the estuary morphological changes due to human activities increase fine sediment import within the estuary, shifting the estuary from an exporting to importing system. We propose a conceptualization of mud flux response to river flow and wave forcing, as well as anthropogenic pressures. It provides valuable insights into particle transfers along the land-sea continuum, contributing to a better understanding of estuarine ecosystem trajectories under global changes.

Identifying and quantifying the impact of non-climatic effects on the water cycle in a semi-arid environment 

2021 ◽  
Author(s):  
Julie Collignan ◽  
Jan Polcher ◽  
Pere Quintana Seguí
Keyword(s):  
Climate Change ◽  
Land Cover ◽  
Water Balance ◽  
Human Activities ◽  
River Discharge ◽  
Water Cycle ◽  
Land Cover Changes ◽  
Anthropogenic Changes ◽  
The Impact ◽  
Semi Arid

<p>In a context of climate change, the stakes surrounding water availability and use are getting higher, especially in semi-arid climates. Human activities such as irrigation and land cover changes impact the water cycle, raising questions around the effects it could have on regional atmospheric circulation and how to separate the impact of climate change from the impact of anthropogenic activities to better understand their role in the historical records. The ORCHIDEE Land Surface Model from Institut Pierre Simon Laplace (IPSL) simulates global carbon cycle and aims at quantifying terrestrial water and energy balance. It is being developed at regional scale but does not include satisfying hypothesis to account for human activities such as irrigation at such scale so far.</p><p>We <span>propose</span> a methodology to semi-empirically separate the effect of climate from the impact of the changing catchment characteristics on river discharge. <span>It is based on</span> the Budyko framework and <span>allows to characterise the</span> annual river discharge of over 363 river monitoring stations in Spain. The Budyko parameter is estimated for each basin and <span>represents</span> its hydrological characteristics. Precipitations and potential evapotranspiration are derived from the forcing dataset GSWP3 (Global Soil Wetness Project Phase 3) – from 1901 to 2010 –. Two methods are used to estimate evapotranspiration : the first uses evapotranspiration from the ORCHIDEE LSM outputs while the second deduced evapotranspiration from river discharge observations and the water balance equation. The first method only accounts for the effects of atmospheric forcing while the other combines, through the observations, <span>climatic and non-climatic processes</span> over the watersheds. We then study the evolution over the <span>Budyko</span> parameter fitted with these two <span>estimates of evaporation</span>. Studying the watershed parameter allows us to free ourselves from some of the climate interannual variability compared to directly looking at changes in the river discharge and better separate anthropogenic changes from the effect of climatic forcing.</p><p>Our results show that for most basins tested over Spain, there is an increasing trend in the <span>Budyko parameter representing increasing evaporation efficiency</span> of the watershed which <span>can not be</span> explained by the climate forcing. This trend is consistent with changes in irrigation equipment and land cover changes over the studied period. However changes of the basin characteristics can not be fully quantified by this variables. Other factors as glaciers melting which derails the water balance over our time of study.</p><p>The methodology needs to be extended to other areas such as Northern Europe to see if the differences in response of the catchments to anthropogenic changes quantified by our methodology corresponds to known contrasts. Balance between climatic and anthropogenic changes of basin characteristics are different in semi-arid climate than in northern more humid regions.</p>

scholarly journals An Alternative Statistical Model for Predicting Salinity Variations in Estuaries

2020 ◽  
Vol 12 (24) ◽  
pp. 10677
Author(s):  
Ronghui Ye ◽  
Jun Kong ◽  
Chengji Shen ◽  
Jinming Zhang ◽  
Weisheng Zhang
Keyword(s):  
Statistical Model ◽  
River Discharge ◽  
Numerical Models ◽  
Low Cost ◽  
River Estuary ◽  
Pearl River Estuary ◽  
Large River ◽  
Physical Models ◽  
Long Term Effects ◽  
Salinity Variations

Accurate salinity prediction can support the decision-making of water resources management to mitigate the threat of insufficient freshwater supply in densely populated estuaries. Statistical methods are low-cost and less time-consuming compared with numerical models and physical models for predicting estuarine salinity variations. This study proposes an alternative statistical model that can more accurately predict the salinity series in estuaries. The model incorporates an autoregressive model to characterize the memory effect of salinity and includes the changes in salinity driven by river discharge and tides. Furthermore, the Gamma distribution function was introduced to correct the hysteresis effects of river discharge, tides and salinity. Based on fixed corrections of long-term effects, dynamic corrections of short-term effects were added to weaken the hysteresis effects. Real-world model application to the Pearl River Estuary obtained satisfactory agreement between predicted and measured salinity peaks, indicating the accuracy of salinity forecasting. Cross-validation and weekly salinity prediction under small, medium and large river discharges were also conducted to further test the reliability of the model. The statistical model provides a good reference for predicting salinity variations in estuaries.

Using GeoWEPP model, high-resolution 3D models and ground-based survey to detect sedimentation changes and morphological adjustments in an ephemeral stream

2021 ◽  
Author(s):  
Carmelo Conesa-García ◽  
Alberto Martínez-Salvador ◽  
Francisco Martínez-Capel ◽  
Carlos Puig-Mengual ◽  
Pedro Pérez-Cutillas ◽  
...  
Keyword(s):  
High Resolution ◽  
Morphological Changes ◽  
Methodological Approach ◽  
Point Clouds ◽  
Global Changes ◽  
Ephemeral Stream ◽  
Event Scale ◽  
Sediment Yields ◽  
Calibration And Validation ◽  
Sediment Budgets

<p>The ephemeral streams, which drain steep and metamorphic catchments, experience rapid and torrential runoff with high sediment loads. These processes cause important morphological changes in the channels. This work proposes a methodological approach to verify the change patterns in the magnitude and frequency of the hydrological events that geomorphologically model this type of channels. A gravel-bed ephemeral stream, the Rambla de la Azohía, located in the coastal area of the Betic Mountains (southeastern Spain), has been chosen as a study case for the method validation. This approach focuses first on relationships between peak discharges and sediment budgets measured at checkpoints for specific events from 2018 to 2020 and then runoff data and sediment yields obtained using the GeoWEPP model for the same cases after calibration/validation. Water depths and concentrations of suspended sediment recorded during the events of 2018 and 2019 were used for model calibration and validation, respectively. For the calibration stage, a sensitivity analysis was carried out in order to detect the parameters that most influence the model output and are, therefore, suitable for calibration. Finally, the results obtained in the calibration and validation periods were evaluated using the Nash-Sutcliffe efficiency (NS) and percent bias (PBIAS). Values of NS and PBIAS equal to 0.86 and  7.81%, respectively, were found in the calibration period, while these indices were  0.81 and  -4.1% in the validation period. All these values confirm the model’s capacity to simulate peak flow and erosion in the experimental conditions. Topographical variations and sediment budgets, verified combining high-resolution digital terrain models (HRDTMs) with ortophotographs and point clouds dated in 2018, 2019 and 2020, and ground-based surveys, were analyzed in relation to changes in discharge in order to determine geomorphic flow thresholds. According to these thresholds, three classes of morphological adjustments were defined: 1. global changes caused by  discharges over the bankfull depth; 2. large alterations at the bankfull stage driven by a noticeable vertical bed accretion and lateral erosion; 3. moderate adjustments during sub-bankfull flows that are able to modify alluvial bars; and 4. minor events, in which the accretion of these bars ceases and shallow scouring and washing actions prevail. These geomorphic thresholds were then applied to the complete series of discharges simulated using GeoWEPP at the event scale during the period 1997-2019. The results revealed a significant increase in the number of events that are capable to produce bed aggradation and bank erosion. This research was funded by FEDER / Spanish Ministry of Science, Innovation and Universities - State Research Agency (AEI) / Projects CGL2017-84625- C2-1-R and CGL2017-84625-C2-2-R; State Program for Research, Development and Innovation Focused on the Challenges of Society.</p>

Fluvial sediment fluxes response to modern climate change and human activities in the Tibetan Plateau and its margins

2021 ◽  
Author(s):  
Dongfeng Li ◽  
Xixi Lu ◽  
Ting Zhang
Keyword(s):  
Climate Change ◽  
Water Resources ◽  
Tibetan Plateau ◽  
Air Temperature ◽  
Human Activities ◽  
Sediment Flux ◽  
The Tibetan Plateau ◽  
Fluvial Sediment ◽  
Sediment Fluxes ◽  
Cold Environments

<p>Sediment flux in cold environments is a crucial proxy to link glacial, periglacial, and fluvial systems and highly relevant to hydropower operation, water quality, and the riverine carbon cycle. However, the long-term impacts of climate change and multiple human activities on sediment flux changes in cold environments remain insufficiently investigated due to the lack of monitoring and the complexity of the sediment cascade. Here we examine the multi-decadal changes in the in-situ observed fluvial sediment fluxes from two types of basins, namely, pristine basins and disturbed basins, in the Tibetan Plateau and its margins. The results show that the fluvial sediment fluxes in the pristine Tuotuohe headwater have substantially increased over the past three decades (i.e., a net increase of 135% from 1985–1997 to 1998–2017) due to the warming and wetting climate. We also quantify the relative impacts of air temperature and precipitation on the increases in the sediment fluxes with a novel attribution approach and finds that climate warming and intensified glacier-snow-permafrost melting is the primary cause of the increased sediment fluxes in the pristine cold environment (Tuotuohe headwater), with precipitation increase and its associated pluvial processes being the secondary driver. By contrast, the sediment fluxes in the downstream disturbed Jinsha River (southeastern margin of the Tibetan Plateau) exhibit a net increase of 42% from 1966-1984 to 1985-2010 mainly due to human activities such as deforestation and mineral extraction (contribution of 82%) and secondly because of climate change (contribution of 18%). Then the sediment fluxes dropped by 76% during the period of 2011-2015 because of the operations of six cascade reservoirs since 2010. In an expected warming and wetting climate for the region, we predict that the sediment fluxes in the pristine headwaters of the Tibetan Plateau will continue to increase throughout the 21st century, but the rising sediment fluxes from the Tibetan Plateau would be mostly trapped in its marginal reservoirs.</p><p>Overall, this work has provided the sedimentary evidence of modern climate change through robust observational sediment flux data over multiple decades. It demonstrates that sediment fluxes in pristine cold environments are more sensitive to air temperature and thermal-driven geomorphic processes than to precipitation and pluvial-driven processes. It also provides a guide to assess the relative impacts of human activities and climate change on fluvial sediment flux changes and has significant implications for water resources stakeholders to better design and manage the hydropower dams in a changing climate. Such findings may also have implications for other cold environments such as the Arctic, Antarctic, and other high mountainous basins.</p><p>Furthermore, this research is under the project of "Water and Sediment Fluxes Response to Climate Change in the Headwater Rivers of Asian Highlands" (supported by the IPCC and the Cuomo Foundation) and the project of "Sediment Load Responses to Climate Change in High Mountain Asia" (supported by the Ministry of Education of Singapore). Part of the results are also published in Li et al., 2018 Geomorphology, Li et al., 2020 Geophysical Research Letters, and Li et al., 2021 Water Resources Research.</p>

scholarly journals River Discharge Estimation based on Satellite Water Extent and Topography: An Application over the Amazon

2019 ◽  
Vol 20 (9) ◽  
pp. 1851-1866 ◽  
Author(s):  
Dinh Thi Lan Anh ◽  
Filipe Aires
Keyword(s):  
River Discharge ◽  
Amazon Basin ◽  
Water Cycle ◽  
Large River ◽  
Water Volume ◽  
Discharge Estimation ◽  
Three Rivers ◽  
Storage Change

Abstract River discharge (RD) estimates are necessary for many applications, including water management, flood risk, and water cycle studies. Satellite-derived long-term GIEMS-D3 surface water extent (SWE) maps and HydroSHEDS data, at 90-m resolution, are here used to estimate several hydrological quantities at a monthly time scale over a few selected locations within the Amazon basin. Two methods are first presented to derive the water level (WL): the “hypsometric curve” and the “histogram cutoff” approaches at an 18 km × 18 km resolution. The obtained WL values are interpolated over the whole water mask using a bilinear interpolation. The two methods give similar results and validation with altimetry is satisfactory, with a correlation ranging from 0.72 to 0.89 in the seven considered stations over three rivers (i.e., Wingu, Negro, and Solimoes Rivers). River width (RW) and water volume change (WVC) are also estimated. WVC is evaluated with GRACE total water storage change, and correlations range from 0.77 to 0.88. A neural network (NN) statistical model is then used to estimate the RD based on four predictors (SWE, WL, WVC, and RW) and on in situ RD measurements. Results compare well to in situ measurements with a correlation of about 0.97 for the raw data (and 0.84 for the anomalies). The presented methodologies show the potential of historical satellite data (the combination of SWE with topography) to help estimate RD. Our study focuses here on a large river in the Amazon basin at a monthly scale; additional analyses would be required for other rivers, including smaller ones, in different environments, and at higher temporal scale.

scholarly journals Time Evolution of Estuarine Turbidity Maxima in Well-Mixed, Tidally Dominated Estuaries: The Role of Availability- and Erosion-Limited Conditions

2018 ◽  
Vol 48 (8) ◽  
pp. 1629-1650 ◽  
Author(s):  
Ronald L. Brouwer ◽  
George P. Schramkowski ◽  
Yoeri M. Dijkstra ◽  
Henk M. Schuttelaars
Keyword(s):  
River Discharge ◽  
Suspended Sediment Concentration ◽  
Time Lag ◽  
Sediment Concentration ◽  
Fine Sediment ◽  
Time Varying ◽  
Hydrodynamic Conditions ◽  
Good Qualitative Agreement ◽  
Estuarine Turbidity Maxima

AbstractUsing an idealized width-averaged process-based model, the role of a mud pool on the bed and time-varying river discharge on the trapping of fine sediment is systematically investigated. For this purpose, a dynamically and physically motivated description of erodibility is presented, which relates the amount of sediment on the bed to the suspended sediment concentration (SSC). We can distinguish between two states: in the availability-limited state, the SSC is limited by the amount of erodible sediment at the bed. Over time, under constant forcing conditions, the estuary evolves to morphodynamic equilibrium. In the erosion-limited state, there is an abundant amount of sediment at the bed so that sediment pickup occurs at the maximum possible rate. The SSC is then limited by the local hydrodynamic conditions. In this state, the estuary keeps importing sediment, forming an erodible bottom pool that grows in time. These two states can be used to explain the response of an estuary to changing river discharge. Under availability-limited conditions, periods of high river discharge push estuarine turbidity maxima (ETMs) downstream, while drier periods allow ETMs to move upstream. However, when the estuary is in an erosion-limited state during low river discharge, a bottom pool is formed. When the discharge then increases, it takes time to deplete this pool, so that an ETM located over a bottom pool moves with a significant time lag relative to changes in the river discharge. Good qualitative agreement is found between model results and observations in the Scheldt Estuary of surface SSC using a representative year of discharge conditions.

Hydrological Cycles Change in the Yellow River Basin during the Last Half of the Twentieth Century

2008 ◽  
Vol 21 (8) ◽  
pp. 1790-1806 ◽  
Author(s):  
Qiuhong Tang ◽  
Taikan Oki ◽  
Shinjiro Kanae ◽  
Heping Hu
Keyword(s):  
Climate Change ◽  
River Basin ◽  
Human Activities ◽  
River Discharge ◽  
Yellow River ◽  
Yellow River Basin ◽  
The Yellow River ◽  
Linear Component ◽  
Annual Streamflow ◽  
The Yellow River Basin

Abstract A distributed biosphere hydrological (DBH) model system was used to explore the internal relations among the climate system, human society, and the hydrological system in the Yellow River basin, and to interpret possible mechanisms for observed changes in Yellow River streamflow from 1960 to 2000. Several scenarios were evaluated to elucidate the hydrological response to climate system, land cover, and irrigation. The results show that climate change is the dominant cause of annual streamflow changes in the upper and middle reaches, but human activities dominate annual streamflow changes in the lower reaches of the Yellow River basin. The annual river discharge at the mouth is affected by climate change and by human activities in nearly equal proportion. The linear component of climate change contributes to the observed annual streamflow decrease, but changes in the climate temporal pattern have a larger impact on annual river discharge than does the linear component of climate change. Low flow is more significantly affected by irrigation withdrawals than by climate change. Reservoirs induce more diversions for irrigation, while at the same time the results demonstrate that the reservoirs may help to maintain environmental flows and counter what otherwise would be more serious reductions in low flows.

Morphodynamic Process of Dachan Bay in Pearl River Estuary Affected by Human Activities

2014 ◽  
Vol 638-640 ◽  
pp. 1257-1260
Author(s):  
Rong Yao Ji ◽  
Qun Xu ◽  
Si Ping Mo
Keyword(s):  
Tidal Flat ◽  
Human Activities ◽  
Large Scale ◽  
Morphological Changes ◽  
River Estuary ◽  
Pearl River Estuary ◽  
Pearl River ◽  
Landsat Images ◽  
Change Analysis ◽  
Factors Affecting

The surrounding area of the Dachan Bay in the Pearl River Estuary has one of the highest economic development rates of China. Rapid industrialization and urbanization has resulted in extensive changes in land use, including the tidal flat reclamation and harbor construction. For the analysis of the morphological changes of the Dachan Bay, multi-temporal Landsat images have been digitized by using the integrated RS and GIS technique, and the digital elevation modes in different years were set up in combination with topographical and nautical data. From the change analysis, it can be concluded that the sea area of the Dachan Bay decreases to 6.0 km2, by 87.6% between 1907a and 2011a due to the large-scale tidal flat reclamation, and the maximum downcutting depth of the seabed in the entrance area is over 10m mainly caused by extensive harbor construction. Based on the research of the morphological change in recent decades, it is suggested that the human activities have become one of the major factors affecting the morphological processes of the Dachan Bay.

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