scholarly journals Anthropogenic Reservoirs of Various Sizes Trap Most of the Sediment in the Mediterranean Maghreb Basin

Water ◽  
2018 ◽  
Vol 10 (7) ◽  
pp. 927 ◽  
Author(s):  
Mahrez Sadaoui ◽  
Wolfgang Ludwig ◽  
François Bourrin ◽  
Yves Bissonnais ◽  
Estela Romero
Keyword(s):  
Arid Zones ◽  
Anthropogenic Pressure ◽  
Sediment Retention ◽  
Natural Sediment ◽  
Sediment Yields ◽  
Sediment Fluxes ◽  
Erosion Rates ◽  
Riverine Sediment ◽  
The Mediterranean ◽  
The Impact

The purpose of this study is to obtain a spatially explicit assessment of the impact of reservoirs on natural river sediment fluxes to the sea in the Mediterranean Maghreb Basin (MMB), a region where both mechanical erosion rates and the anthropogenic pressure on surface water resources are high. We combined modeling of riverine sediment yields (sediment fluxes divided by the drainage basin area) and water drainage intensities in a 5’ × 5’ grid point resolution (~10 km × 10 km) with a compilation of existing reservoirs in the area, and calculated sediment trapping based on average water residence time in these reservoirs. A total number of 670 reservoirs could be assembled from various sources (including digitization from Google maps), comprising large-scale, small-scale and hillside reservoirs. 450 of them could be implemented in our modeling approach. Our results confirm that natural sediment yields are clearly above the world average, with the greatest values for Morocco (506 t km−2 year−1), followed by Algeria (328 t km−2 year−1) and by Tunisia (250 t km−2 year−1). Including dams in the downstream routing of suspended sediments to the sea reduces the natural sediment flux in the entire MMB to the sea from 96 to 36 Mt km−1 year−1, which corresponds to an average sediment retention of 62%. Trapping rates are highest in the Tunisian basin part, with about 72%, followed by the Algerian (63%) and the Moroccan basin parts (55%). Small reservoirs and hillside reservoirs are quantitatively important in the interception of these sediments compared to large reservoirs. If we only considered the dams included in the widely used Global Reservoir and Dam (GRanD) database which comprises mainly large reservoirs sediment retention behind dams would account for 36% of the natural suspended particulate matter (SPM) flux to the Mediterranean Sea. Our data reveal negative correlation between sediment retention and natural erosion rates among the three Maghreb countries, which can be explained by the greater difficulties to build dams in steep terrains where natural sediment yields are high. Although the lowest sediment retention rates are found in the Moroccan part of the MMB, it is probably here where riverine sediment starvation has the greatest impacts on coastline dynamics. Understanding the impact of dams and related water infrastructures on riverine sediment dynamics is key in arid zones such as the MMB, where global warming is predicted to cause important changes in the climatic conditions and the water availability.

Comparing the hydrological response of regulated vs. not regulated mountain torrents in the Mediterranean semi-arid environment: a case study in Southern Italy

2021 ◽  
Author(s):  
Giuseppe Bombino ◽  
Daniela D'Agostino ◽  
Pietro Denisi ◽  
Antonino Labate ◽  
Pedro Perez Cutillas ◽  
...  
Keyword(s):  
Agricultural Land ◽  
Southern Italy ◽  
Arid Environment ◽  
Hydrological Response ◽  
Sediment Yields ◽  
Erosion Rates ◽  
Check Dams ◽  
The Mediterranean ◽  
The Impact ◽  
Semi Arid

<p>In the Mediterranean semi-arid environment (e.g., in Southern Italy and Spain), headwaters are characterized by local factors, such as steep slopes, low drainage areas and heavy and short-duration rainstorms, which make the torrents prone to flash floods, soil erosion and landslides. The construction of check dams has contributed to mitigate the runoff and erosion rates, but the effectiveness of these structures has been rarely assessed. In these contexts, the availability of studies monitoring the mitigation effect of check dams on the hydrological response of torrents at the watershed scale over a long time could help developing new management strategies. To this aim, this study proposes an assessment of the multi-decadal runoff and erosion rates in two headwaters of torrents in Southern Italy, using a modeling approach. The first torrent (Vacale, 12.5 sq. km) is regulated by check dams built in ‘1950-1960, while the second torrent (Serra, 13.7 sq. km) is not regulated. Both catchments experienced an increase in forest cover up to the 70%, while the agricultural land decreased by about 30% of the total area after the construction of the control works until now. The hydrological response of the two headwaters has been simulated using the widely applied Hydrologic Modeling System (HEC-HMS) model for runoff and peak flow, coupled with the Modified Universal Soil Loss Equation (MUSLE) to model sediment yield. To this purpose, 10 heavy rainfall-runoff events occurred between 1956 and 1971 were modeled. The peak flows and sediment yields of the regulated watershed were compared with the corresponding simulations at the undisturbed torrent. To summarize the results of this modeling experience, the changes in land cover resulted in a noticeable decrease in flood peak discharge (on average -53%) in both torrents, while the torrent with check dams showed a significant reduction of eroded sediment for each event (on average -9%) compared to the unregulated headwater. These findings help supporting a better understanding on the impact of control works and land use changes on the hydrological responses of Mediterranean torrents, indicating the most effective strategy to mitigate flash flood hazards and heavy erosion risks in similar environmental contexts.</p><p>Acknowledgement: This research was funded by ERDF/Spanish Ministry of Science, Innovation and Universities-State Research Agency (AEI) /Project CGL2017-84625-C2-1-R; State Program for Research, Development and Innovation Focused on the Challenges of Society.</p>

The impact of reservoir construction on riverine sediment and carbon fluxes to the Mediterranean Sea

2018 ◽  
Vol 163 ◽  
pp. 94-111 ◽  
Author(s):  
Mahrez Sadaoui ◽  
Wolfgang Ludwig ◽  
François Bourrin ◽  
Estela Romero
Keyword(s):  
Mediterranean Sea ◽  
Carbon Fluxes ◽  
Riverine Sediment ◽  
Reservoir Construction ◽  
The Mediterranean ◽  
The Impact

Sediment fluxes and sinks for Magela Creek, Northern Territory, Australia

2018 ◽  
Vol 69 (7) ◽  
pp. 1018 ◽  
Author(s):  
Wayne D. Erskine ◽  
M. J. Saynor ◽  
J. M. Boyden ◽  
K. G. Evans
Keyword(s):  
Suspended Sediment ◽  
Sediment Load ◽  
Northern Territory ◽  
Bed Load ◽  
Sediment Yields ◽  
Sediment Fluxes ◽  
Erosion Rates ◽  
Dry Tropics ◽  
The World ◽  
Total Sediment

Sediment fluxes and sinks based on total sediment load for Magela Creek in the Australian wet–dry tropics have been constructed from detailed measurements of stream suspended sediment (turbidity and suspended sand) and bed load for the 10-year period, 2001–2002 to 2010–2011. This work shows that the sediment trap efficiency of the vegetated wetlands on lower Magela is high at ~89.5%. Sediment fluxes are the lowest in the world because of low soil erosion rates and because upstream floodplains and downstream wetlands trap and store sediment. Bedload yields are less than suspended sediment yields, but the amount of silt and clay is much less than the amount of sand (suspended sand and bedload). All sand is stored upstream of the East Alligator River. Downstream connectivity of sediment movement does not occur. Therefore, sediment moves discontinuously from the upper to the lower catchment.

New insights into nutrients dynamics and the carbonate system using a neural network approach in the Mediterranean Sea

2020 ◽  
Author(s):  
Marine Fourrier ◽  
Laurent Coppola ◽  
Fabrizio D'Ortenzio
Keyword(s):  
Neural Network ◽  
Mediterranean Sea ◽  
Dissolved Inorganic Carbon ◽  
In Situ Measurements ◽  
Total Alkalinity ◽  
Anthropogenic Pressure ◽  
Carbonate System ◽  
The Mediterranean ◽  
The Impact

<p>The semi-enclosed nature of the Mediterranean Sea, together with its small inertia which is due to the relatively short residence time of its water masses, make it highly reactive to external forcings and anthropogenic pressure. In this context, several rapid changes have been observed in physical and biogeochemical processes in recent decades, partly masked by episodic events and high regional variability. To better understand the underlying processes driving the Mediterranean evolution and, anticipate changes, the measurement, and integration of many biogeochemical variables are mandatory.</p><p>The development of new BGC sensors implemented on <em>in situ</em> autonomous platforms allows to increase the acquisition of essential biogeochemical variables. However, the measurements carried out by<em> in situ</em> autonomous platforms (e.g. profiling floats, gliders, moorings) are not exhaustive.</p><p>Recently, deep learning techniques and in particular neural networks have been developed. The CANYON-MED (for Carbonate system and Nutrients concentration from hYdrological properties and Oxygen using a Neural-network in the MEDiterranean Sea) neural network-based method provides estimations of nutrients (i.e. nitrates, phosphates, and silicates) and carbonate system variables (i.e. total alkalinity, dissolved inorganic carbon, pH<sub>T</sub>) from systematically measured oceanographic variables such as in situ measurements of pressure, temperature, salinity, and oxygen together with geolocation and date of sampling.</p><p>This regional approach, therefore, using quality-controlled in situ measurements from more than 35 cruises. CANYON-MED obtains satisfactory results: accuracies of 0.73, 0.045, and 0.70 µmol.kg<sup>-1</sup> for the nitrates, phosphates and silicates concentrations respectively, and 0.016, 11 µmol.kg<sup>-1</sup> and 10 µmol.kg<sup>-1</sup> for pH<sub>T</sub>, total alkalinity and dissolved organic carbon respectively. CANYON-MED thus generates “virtual” data of parameters not yet measured by autonomous platforms, while ably reproducing the data already sampled, emphasizing its ability to fill the gaps in time-series.</p><p>Hence, by applying it to the large and growing network of autonomous platforms in the Mediterranean Sea, this method allows us to gain new insights into nutrients and carbonate system dynamics in targeted areas. In particular, in the northwestern Mediterranean Sea, the impact of deep convection on biogeochemistry (e.g., nutrient replenishment and pH<sub>T</sub> variability) is highly variable over time and poorly covered by observing networks. In this case, CANYON-MED would improve our observations and understanding of the dynamic and coupled system.</p>

scholarly journals Assessing the Impact of Man–Made Ponds on Soil Erosion and Sediment Transport in Limnological Basins

2019 ◽  
Author(s):  
Mario J. Al Sayah ◽  
Rachid Nedjai ◽  
Konstantinos Kaffas ◽  
Chadi Abdallah ◽  
Michel Khouri
Keyword(s):  
Sediment Transport ◽  
Soil Erosion ◽  
Swat Model ◽  
Erosion Risk ◽  
Sediment Yields ◽  
Erosion Rates ◽  
Risk Zones ◽  
Transport Patterns ◽  
Scientific Attention ◽  
The Impact

The impact of ponds on basins has recently started to receive its well–deserved scientific attention. In this study, pond–induced impacts on soil erosion and sediment transport were investigated at the scale of the French Claise basin. In order to determine erosion and sediment transport patterns under current conditions, the CORINE erosion and SWAT models were used. The impact of ponds on the studied processes was revealed by means of land cover change scenarios, using ponded versus pondless inputs. Results show that under current conditions (pond presence), 12.48% of the basin corresponds to no–erosion risk zones (attributed to the dense pond network), while 65.66% corresponds to low–erosion risk, 21.68% to moderate–erosion risk and only 0.18% to high–erosion risk zones. The SWAT model revealed that ponded sub–basins correspond to low sediment yields areas, in contrast to the pondless sub–basins, which yield appreciably higher erosion rates. Under the alternative scenario, erosion risks shifted to 1.12%, 0.52%, 76.8% and 21.56% for no, low, moderate and high–erosion risks, respectively, while the sediment transport pattern of the Claise completely shifted to higher sediment yield zones. This approach solidifies ponds as powerful man–induced modifications to hydro/sedimentary processes.

INTEGRAL ASSESSMENT OF ANTHROPOGENIC PRESSURE ON WATER BODIES IN THE LAKE BAIKAL BASIN

2020 ◽  
Author(s):  
Irina Ulzetueva ◽  
Bair Gomboev ◽  
Daba Zhamyanov ◽  
Valentin Batomunkuev ◽  
Zorikto Banzaraktsaev
Keyword(s):  
Lake Baikal ◽  
River Basins ◽  
Anthropogenic Load ◽  
Anthropogenic Pressure ◽  
Linear Network ◽  
Baikal Basin ◽  
Discharge Water ◽  
Lake Baikal Basin ◽  
Integral Assessment ◽  
The Impact

The integrated assessment of the ecological state of the main rivers of the lake Baikal basin - Verkhnyaya Angara, Tyya, Barguzin, Selenga, Snezhnaya, Bolshaya Rechka, Khilok, Chikoy is based on the assessment of the variability of the basin system under the influence of two groups of indicators: 1) Direct (immediate) impact - the volume of water intake and wastewater discharge, water use and sequential water supply. Assessment of the impact on the state of the above-listed rivers basins from wastewater was performed using the algorithm proposed by A. Korolev et al. (2007). 2) Indirect (mediate) impact - indicators of areal and linear-network impacts on the catchment area. Based on the calculation of the integral anthropogenic pressure on the territory of the above-listed river basins, only the Selenga river experiences an “average” anthropogenic load. On the territory of most river basins, the anthropogenic load is “lowered” and “low”.

scholarly journals Impact of air–sea coupling on the climate change signal over the Iberian Peninsula

2021 ◽  
Author(s):  
Alba de la Vara ◽  
William Cabos ◽  
Dmitry V. Sein ◽  
Claas Teichmann ◽  
Daniela Jacob
Keyword(s):  
Climate Change ◽  
Iberian Peninsula ◽  
Mediterranean Sea ◽  
Large Scale ◽  
Regional Distribution ◽  
Coupled Model ◽  
Climate Change Signal ◽  
The North ◽  
The Mediterranean ◽  
The Impact

AbstractIn this work we use a regional atmosphere–ocean coupled model (RAOCM) and its stand-alone atmospheric component to gain insight into the impact of atmosphere–ocean coupling on the climate change signal over the Iberian Peninsula (IP). The IP climate is influenced by both the Atlantic Ocean and the Mediterranean sea. Complex interactions with the orography take place there and high-resolution models are required to realistically reproduce its current and future climate. We find that under the RCP8.5 scenario, the generalized 2-m air temperature (T2M) increase by the end of the twenty-first century (2070–2099) in the atmospheric-only simulation is tempered by the coupling. The impact of coupling is specially seen in summer, when the warming is stronger. Precipitation shows regionally-dependent changes in winter, whilst a drier climate is found in summer. The coupling generally reduces the magnitude of the changes. Differences in T2M and precipitation between the coupled and uncoupled simulations are caused by changes in the Atlantic large-scale circulation and in the Mediterranean Sea. Additionally, the differences in projected changes of T2M and precipitation with the RAOCM under the RCP8.5 and RCP4.5 scenarios are tackled. Results show that in winter and summer T2M increases less and precipitation changes are of a smaller magnitude with the RCP4.5. Whilst in summer changes present a similar regional distribution in both runs, in winter there are some differences in the NW of the IP due to differences in the North Atlantic circulation. The differences in the climate change signal from the RAOCM and the driving Global Coupled Model show that regionalization has an effect in terms of higher resolution over the land and ocean.

scholarly journals A process-based method for predicting lateral erosion rates

2021 ◽  
Author(s):  
Myron van Damme
Keyword(s):  
Soil Mechanics ◽  
High Surface ◽  
Shear Stresses ◽  
Empirical Equations ◽  
Predictive Capability ◽  
Surface Shear ◽  
Erosion Rates ◽  
Material Texture ◽  
Empirical Coefficients ◽  
The Impact

AbstractAn accurate means of predicting erosion rates is essential to improve the predictive capability of breach models. During breach growth, erosion rates are often determined with empirical equations. The predictive capability of empirical equations is governed by the range for which they have been validated and the accuracy with which empirical coefficients can be established. Most empirical equations thereby do not account for the impact of material texture, moisture content, and compaction energy on the erosion rates. The method presented in this paper acknowledges the impact of these parameters by accounting for the process of dilation during erosion. The paper shows how, given high surface shear stresses, the erosion rate can be quantified by applying the principles of soil mechanics. Key is thereby to identify that stress balance situation for which the dilatency induced inflow gives a maximum averaged shear resistance. The effectiveness of the model in predicting erosion rates is indicated by means of three validation test cases. A sensitivity analysis of the method is also provided to show that the predictions lie within the range of inaccuracy of the input parameters.

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