scholarly journals Temperature signal in suspended sediment export from an Alpine catchment

2017 ◽  
Author(s):  
Anna Costa ◽  
Peter Molnar ◽  
Laura Stutenbecker ◽  
Maarten Bakker ◽  
Tiago A. Silva ◽  
...  
Keyword(s):  
Snow Cover ◽  
Suspended Sediment ◽  
Air Temperature ◽  
Suspended Sediment Concentration ◽  
Sediment Concentration ◽  
Sediment Supply ◽  
Free Surfaces ◽  
Ice Melt ◽  
Alpine Catchments ◽  
Sediment Export

Abstract. Suspended sediment export from large Alpine catchments (> 1000 km2) over decadal timescales is sensitive to a number of factors, including long–term variations in climate, the activation–deactivation of different sediment sources (proglacial areas, hillslopes, etc.), transport through the river system, and potential anthropogenic impacts on the sediment flux (e.g. through impoundments and flow regulation). Here, we report on a marked increase in suspended sediment concentrations observed close to the outlet of the upper Rhône River Basin in the mid–1980s. This increase coincides with a statistically significant step–like increase in basin–wide mean air temperature. We explore the potential explanations of the suspended sediment rise in terms of discharge (transport capacity) change, and the activation of different sources of fine sediment (sediment supply) in the catchment by hydroclimatic forcing. Time series of precipitation and temperature–driven snowmelt, snow cover and ice–melt simulated with a spatially distributed degree–day model, together with erosive rainfall on snow–free surfaces, are tested as possible reasons for the rise in suspended sediment concentration. We demonstrate that the abrupt change in air temperature reduced snow cover and the contribution of snowmelt, and enhanced ice–melt. The results of statistical tests showed that the onset of increased ice–melt was likely to play a dominant role in the suspended sediment concentration rise in the mid–1980s. Temperature–driven enhanced melting of glaciers, which cover about 10 % of the catchment surface, can increase suspended sediment yields through increased runoff from sediment–rich proglacial areas, increased contribution of sediment–rich meltwater, and increased sediment supply in proglacial areas due to glacier recession. The reduced extent and duration of snow cover in the catchment may also have partly contributed to the rise in suspended sediment concentration through hillslope erosion by rainfall on snow free surfaces, and by reducing snow cover on the surface of the glaciers and thereby increasing meltwater production. Despite the rise in air temperature, changes in mean discharge in the mid–1980s were statistically insignificant, and their interpretation is complicated by hydropower reservoir management and the flushing operations at intakes. Thus, the results show that to explain changes in suspended sediment transport from large Alpine catchments it is necessary to include an understanding of the multitude of sediment sources involved together with the hydroclimatic conditioning of their activation (e.g. changes in precipitation, runoff, air temperature). This is particularly relevant for quantifying climate change and hydropower impacts on streamflow and sediment budgets in high Alpine catchments.

scholarly journals Temperature signal in suspended sediment export from an Alpine catchment

2018 ◽  
Vol 22 (1) ◽  
pp. 509-528 ◽  
Author(s):  
Anna Costa ◽  
Peter Molnar ◽  
Laura Stutenbecker ◽  
Maarten Bakker ◽  
Tiago A. Silva ◽  
...  
Keyword(s):  
Snow Cover ◽  
Suspended Sediment ◽  
Air Temperature ◽  
Suspended Sediment Concentration ◽  
Sediment Concentration ◽  
Sediment Sources ◽  
Free Surfaces ◽  
Ice Melt ◽  
Alpine Catchments ◽  
Sediment Export

Abstract. Suspended sediment export from large Alpine catchments (> 1000 km2) over decadal timescales is sensitive to a number of factors, including long-term variations in climate, the activation–deactivation of different sediment sources (proglacial areas, hillslopes, etc.), transport through the fluvial system, and potential anthropogenic impacts on the sediment flux (e.g. through impoundments and flow regulation). Here, we report on a marked increase in suspended sediment concentrations observed near the outlet of the upper Rhône River Basin in the mid-1980s. This increase coincides with a statistically significant step-like increase in basin-wide mean air temperature. We explore the possible explanations of the suspended sediment rise in terms of changes in water discharge (transport capacity), and the activation of different potential sources of fine sediment (sediment supply) in the catchment by hydroclimatic forcing. Time series of precipitation and temperature-driven snowmelt, snow cover, and ice melt simulated with a spatially distributed degree-day model, together with erosive rainfall on snow-free surfaces, are tested to explore possible reasons for the rise in suspended sediment concentration. We show that the abrupt change in air temperature reduced snow cover and the contribution of snowmelt, and enhanced ice melt. The results of statistical tests show that the onset of increased ice melt was likely to play a dominant role in the suspended sediment concentration rise in the mid-1980s. Temperature-driven enhanced melting of glaciers, which cover about 10 % of the catchment surface, can increase suspended sediment yields through an increased contribution of sediment-rich glacial meltwater, increased sediment availability due to glacier recession, and increased runoff from sediment-rich proglacial areas. The reduced extent and duration of snow cover in the catchment are also potential contributors to the rise in suspended sediment concentration through hillslope erosion by rainfall on snow-free surfaces, and increased meltwater production on snow-free glacier surfaces. Despite the rise in air temperature, changes in mean discharge in the mid-1980s were not statistically significant, and their interpretation is complicated by hydropower reservoir management and the flushing operations at intakes. Overall, the results show that to explain changes in suspended sediment transport from large Alpine catchments it is necessary to include an understanding of the multitude of sediment sources involved together with the hydroclimatic conditioning of their activation (e.g. changes in precipitation, runoff, air temperature). In addition, this study points out that climate signals in suspended sediment dynamics may be visible even in highly regulated and human-impacted systems. This is particularly relevant for quantifying climate change and hydropower impacts on streamflow and sediment budgets in Alpine catchments.

scholarly journals Hydroclimatic control on suspended sediment dynamics of a regulated Alpine catchment: a conceptual approach

2018 ◽  
Vol 22 (6) ◽  
pp. 3421-3434 ◽  
Author(s):  
Anna Costa ◽  
Daniela Anghileri ◽  
Peter Molnar
Keyword(s):  
Suspended Sediment ◽  
Sediment Concentration ◽  
Sediment Dynamics ◽  
Time Lags ◽  
Rating Curve ◽  
Conceptual Approach ◽  
Ice Melt ◽  
Alpine Catchments ◽  
Erosive Rainfall ◽  
Hydroclimatic Variables

Abstract. We analyse the control of hydroclimatic factors on suspended sediment concentration (SSC) in Alpine catchments by differentiating among the potential contributions of erosion and suspended sediment transport driven by erosive rainfall, defined as liquid precipitation over snow-free surfaces, ice melt from glacierized areas, and snowmelt on hillslopes. We account for the potential impact of hydropower by intercepting sediment fluxes originated in areas diverted to hydropower reservoirs, and by considering the contribution of hydropower releases to SSC. We obtain the hydroclimatic variables from daily gridded datasets of precipitation and temperature, implementing a degree-day model to simulate spatially distributed snow accumulation and snow–ice melt. We estimate hydropower releases by a conceptual approach with a unique virtual reservoir regulated on the basis of a target-volume function, representing normal reservoir operating conditions throughout a hydrological year. An Iterative Input Selection algorithm is used to identify the variables with the highest predictive power for SSC, their explained variance, and characteristic time lags. On this basis, we develop a hydroclimatic multivariate rating curve (HMRC) which accounts for the contributions of the most relevant hydroclimatic input variables mentioned above. We calibrate the HMRC with a gradient-based nonlinear optimization method and we compare its performance with a traditional discharge-based rating curve. We apply the approach in the upper Rhône Basin, a large Swiss Alpine catchment heavily regulated by hydropower. Our results show that the three hydroclimatic processes – erosive rainfall, ice melt, and snowmelt – are significant predictors of mean daily SSC, while hydropower release does not have a significant explanatory power for SSC. The characteristic time lags of the hydroclimatic variables correspond to the typical flow concentration times of the basin. Despite not including discharge, the HMRC performs better than the traditional rating curve in reproducing SSC seasonality, especially during validation at the daily scale. While erosive rainfall determines the daily variability of SSC and extremes, ice melt generates the highest SSC per unit of runoff and represents the largest contribution to total suspended sediment yield. Finally, we show that the HMRC is capable of simulating climate-driven changes in fine sediment dynamics in Alpine catchments. In fact, HMRC can reproduce the changes in SSC in the past 40 years in the Rhône Basin connected to air temperature rise, even though the simulated changes are more gradual than those observed. The approach presented in this paper, based on the analysis of the hydroclimatic control of suspended sediment concentration, allows the exploration of climate-driven changes in fine sediment dynamics in Alpine catchments. The approach can be applied to any Alpine catchment with a pluvio-glacio-nival hydrological regime and adequate hydroclimatic datasets.

scholarly journals Hydroclimatic control on suspended sediment dynamics of a regulated Alpine catchment: a conceptual approach

2018 ◽  
Author(s):  
Anna Costa ◽  
Daniela Anghileri ◽  
Peter Molnar
Keyword(s):  
Suspended Sediment ◽  
Suspended Sediment Concentration ◽  
Sediment Concentration ◽  
Sediment Dynamics ◽  
Time Lags ◽  
Rating Curve ◽  
Conceptual Approach ◽  
Alpine Catchments ◽  
Erosive Rainfall ◽  
Hydroclimatic Variables

Abstract. We analyse the control of hydroclimatic factors on suspended sediment concentration (SSC) in Alpine catchments by differentiating among the potential contributions of erosion and suspended sediment transport driven by erosive rainfall, defined as liquid precipitation over snow free surfaces, icemelt from glacierized areas, and snowmelt on hillslopes. We account for the potential impact of hydropower by intercepting sediment fluxes originated in areas diverted to hydropower reservoirs, and by considering the contribution of hydropower releases to SSC. We obtain the hydroclimatic variables from daily gridded datasets of precipitation and temperature, implementing a degree–day model to simulate spatially distributed snow accumulation and snow–ice melt. We estimate hydropower releases by a conceptual approach with a unique virtual reservoir regulated on the basis of a target–volume function, representing normal reservoir operating conditions throughout a hydrological year. An Iterative Input Selection algorithm is used to identify the variables with the highest predictive power for SSC, their explained variance, and characteristic time lags. On this basis, we develop a hydroclimatic multivariate rating curve (HMRC) which accounts for the contributions of the most relevant hydroclimatic input variables mentioned above. We calibrate the HMRC with a gradient–based nonlinear optimization method and we compare its performance with a traditional discharge–based rating curve. We apply the approach in the upper Rhone Basin, a large Swiss Alpine catchment, heavily regulated by hydropower. Our results show that the three hydroclimatic processes – erosive rainfall, icemelt, and snowmelt – are significant predictors of mean daily SSC, while hydropower release does not have a significant explanatory power for SSC. The characteristic time lags of the hydroclimatic variables correspond to the typical flow concentration times of the basin. Despite not including discharge, the HMRC performs better than the traditional rating curve in reproducing SSC seasonality, especially during validation at the daily scale. While erosive rainfall determines the daily variability of SSC and extremes, icemelt generates the highest SSC per unit of runoff, and represents the largest contribution to total suspended sediment yield. Finally, we show that the HMRC is capable of simulating climate–driven changes in fine sediment dynamics in Alpine catchments. In fact, HMRC can reproduce the changes in SSC in the past 40 years in the Rhone Basin connected to air temperature rise, even though the simulated changes are more gradual than those observed. The approach presented is this paper, based on the analysis of the hydroclimatic control on suspended sediment concentration, allows the exploration of climate–driven changes in fine sediment dynamics in Alpine catchments. The approach can be applied to any Alpine catchment with a pluvio–glacio–nival hydrological regime and adequate hydroclimatic datasets.

Hydro-meteorological Correlations of Himalayan Glaciers: A Review

2021 ◽  
Vol 7 (3) ◽  
pp. 45-55
Author(s):  
Virendra Bahadur Singh ◽  
AL. Ramanathan ◽  
Pramod Kumar
Keyword(s):  
Suspended Sediment ◽  
Air Temperature ◽  
Meteorological Parameters ◽  
Suspended Sediment Concentration ◽  
Strong Relationship ◽  
Sediment Concentration ◽  
Chhota Shigri Glacier ◽  
Meltwater Runoff ◽  
Himalayan Glaciers ◽  
Fast Decline

This review manuscript addresses hydro-meteorological correlations of various glaciers situated in the Himalayan region. Meteorological parameters influence the discharge pattern of the glacier. A strong correlation has been observed between discharge and air temperature of the studied Himalayan glaciers. Whereas, other meteorological parameters such as wind speed and wind direction etc. were not significantly correlated with the meltwater runoff of different glaciers in this region. In general, variability (Cv) in discharge from the various Himalayan glaciers such as Chhota Shigri and Gangotri glaciers follow the variability (Cv) in the temperature of these glaciers. Maximum variability (Cv) in meltwater runoff from the Chhota Shigri glacier has been reported in the month of September, which might be due to the fast decline in stream runoff and air temperature of the study area during the month of September. A strong relationship has been observed between suspended sediment concentration and temperature of the majority of studied Himalayan glaciers. Such type of result shows that the suspended sediment concentration in the glacial meltwater has increased with rising air temperature in this region.

scholarly journals Suspended sediment concentration – discharge relationships in the (sub) humid Ethiopian highlands

2012 ◽  
Vol 9 (7) ◽  
pp. 9011-9041 ◽  
Author(s):  
C. D. Guzman ◽  
S. A. Tilahun ◽  
A. D. Zegeye ◽  
T. S. Steenhuis
Keyword(s):  
Suspended Sediment ◽  
Rainy Season ◽  
Suspended Sediment Concentration ◽  
Sediment Concentration ◽  
Base Flow ◽  
Sediment Supply ◽  
Discharge Data ◽  
Low Concentrations ◽  
Rating Curves ◽  
In The Beginning

Abstract. Loss of top soil and subsequent filling up of reservoirs in much of the lands with variable relief in developing countries degrades environmental resources necessary for subsistence. In the Ethiopia highlands, sediment mobilization from rain-fed agricultural fields is one of the leading factors causing land degradation. Sediment rating curves, produced from long-term sediment concentration and discharge data, attempt to predict suspended sediment concentration variations that exhibit a distinct shift with the progression of the rainy season. In this paper, we calculate sediment rating curves and examine this shift in concentration for three watersheds in which rain-fed agriculture is practiced to differing extents. High sediment concentrations with low flows are found in the beginning of the rainy season of the semi-monsoonal climate, while high flows and low sediment concentrations occur at the end of the rainy season. Results show that a reasonable unique set of rating curves were obtained by separating biweekly data into early, mid, and late rainfall periods and by making adjustments for the ratio of plowed cropland. The shift from high to low concentrations suggests that diminishing sediment supply and dilution from greater base flow during the end of the rainfall period play important roles in characterizing changing sediment concentrations during the rainy season.

scholarly journals Suspended sediment concentration–discharge relationships in the (sub-) humid Ethiopian highlands

2013 ◽  
Vol 17 (3) ◽  
pp. 1067-1077 ◽  
Author(s):  
C. D. Guzman ◽  
S. A. Tilahun ◽  
A. D. Zegeye ◽  
T. S. Steenhuis
Keyword(s):  
Suspended Sediment ◽  
Rainy Season ◽  
Suspended Sediment Concentration ◽  
Sediment Concentration ◽  
Base Flow ◽  
Sediment Supply ◽  
Discharge Data ◽  
Low Concentrations ◽  
Top Soil ◽  
Rating Curves

Abstract. Loss of top soil and subsequent filling up of reservoirs in much of the lands with variable relief in developing countries degrades environmental resources necessary for subsistence. In the Ethiopia highlands, sediment mobilization from rain-fed agricultural fields is one of the leading factors causing land degradation. Sediment rating curves, produced from long-term sediment concentration and discharge data, attempt to predict suspended sediment concentration variations, which exhibit a distinct shift with the progression of the rainy season. In this paper, we calculate sediment rating curves and examine this shift in concentration for three watersheds in which rain-fed agriculture is practiced to differing extents. High sediment concentrations with low flows are found at the beginning of the rainy season of the semi-monsoonal climate, while high flows and low sediment concentrations occur at the end of the rainy season. Results show that a reasonably unique set of rating curves were obtained by separating biweekly data into early, mid, and late rainfall periods and by making adjustments for the ratio of plowed cropland. The shift from high to low concentrations suggests that diminishing sediment supply and dilution from greater base flow during the end of the rainfall period play important roles in characterizing changing sediment concentrations during the rainy season.

Sediment Transport from the Glacier Zone, Central Asia

1981 ◽  
Vol 2 ◽  
pp. 103-108 ◽  
Author(s):  
O. P. Shcheglova ◽  
O. P. Chizhov
Keyword(s):  
Suspended Sediment ◽  
Air Temperature ◽  
Suspended Sediment Concentration ◽  
Sediment Concentration ◽  
Tien Shan ◽  
Sediment Discharge ◽  
Exponential Relationship ◽  
Run Off ◽  
Central Asian ◽  
Glacial Streams

All available data on suspended sediment concentration and sediment discharge for Central Asian rivers have been used to estimate the small-grained sediment discharge from glaciated areas. Glacial streams discharge the bulk of suspended material during the period of intensive melting (July to September). There is a good exponential relationship between the suspended sediment concentration (or sediment discharge) and air temperature over glaciers. The area of the largest glacier in the watershed is another factor influencing the silt content and sediment run-off. Its contribution is smaller than that of air temperature. Yearly sediment run-off for glacial rivers in the Pamir and Tien Shan has been computed. Highest values are from the Pamir with many rivers yielding 3000 tonnes km–2 (11 200 tonnes km–2 for the Vukhsh river). The highest run-off in Tien Shan is 2 000 tonnes km–2 for the Chatkal river.

Neural networks approached for modelling river suspended sediment concentration due to tropical storms

2013 ◽  
Vol 11 (4) ◽  
pp. 457-466
Keyword(s):  
Neural Network ◽  
Neural Networks ◽  
Suspended Sediment ◽  
Suspended Sediment Concentration ◽  
Time Series Data ◽  
Water Discharge ◽  
Sediment Concentration ◽  
Series Data ◽  
Generalized Regression Neural Network ◽  
Event Based

Artificial neural networks are one of the advanced technologies employed in hydrology modelling. This paper investigates the potential of two algorithm networks, the feed forward backpropagation (BP) and generalized regression neural network (GRNN) in comparison with the classical regression for modelling the event-based suspended sediment concentration at Jiasian diversion weir in Southern Taiwan. For this study, the hourly time series data comprised of water discharge, turbidity and suspended sediment concentration during the storm events in the year of 2002 are taken into account in the models. The statistical performances comparison showed that both BP and GRNN are superior to the classical regression in the weir sediment modelling. Additionally, the turbidity was found to be a dominant input variable over the water discharge for suspended sediment concentration estimation. Statistically, both neural network models can be successfully applied for the event-based suspended sediment concentration modelling in the weir studied herein when few data are available.

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