Showing papers on "Siltation published in 2017"

The potential impact of new Andean dams on Amazon fluvial ecosystems.

Abstract: Increased energy demand has led to plans for building many new dams in the western Amazon, mostly in the Andean region. Historical data and mechanistic scenarios are used to examine potential impacts above and below six of the largest dams planned for the region, including reductions in downstream sediment and nutrient supplies, changes in downstream flood pulse, changes in upstream and downstream fish yields, reservoir siltation, greenhouse gas emissions and mercury contamination. Together, these six dams are predicted to reduce the supply of sediments, phosphorus and nitrogen from the Andean region by 69, 67 and 57% and to the entire Amazon basin by 64, 51 and 23%, respectively. These large reductions in sediment and nutrient supplies will have major impacts on channel geomorphology, floodplain fertility and aquatic productivity. These effects will be greatest near the dams and extend to the lowland floodplains. Attenuation of the downstream flood pulse is expected to alter the survival, phenology and growth of floodplain vegetation and reduce fish yields below the dams. Reservoir filling times due to siltation are predicted to vary from 106-6240 years, affecting the storage performance of some dams. Total CO2 equivalent carbon emission from 4 Andean dams was expected to average 10 Tg y-1 during the first 30 years of operation, resulting in a MegaWatt weighted Carbon Emission Factor of 0.139 tons C MWhr-1. Mercury contamination in fish and local human populations is expected to increase both above and below the dams creating significant health risks. Reservoir fish yields will compensate some downstream losses, but increased mercury contamination could offset these benefits.

A GIS-based soil erosion prediction using the Revised Universal Soil Loss Equation (RUSLE) (Lebna watershed, Cap Bon, Tunisia)

Abstract: Soil erosion is a natural process causing grave land degradation problems. In Tunisia, soil erosion represents a serious environmental problem. Both man-made and natural phenomenon is reducing acres of agricultural land. The problem of soil erosion by water is very critical in Lebna watershed. In fact, Lebna is a town in the northeast of Tunisia and it seems high time to protect water and ground resources and to prevent the Lebna dam situated in the downstream from silting. In this context, the application of geographic RUSLE model using the techniques of geographic information system (GIS) and remote sensing has made it possible to assess the estimation of the soil erosion risk at the targeted watershed. This model is composed of several factors associated with climate, topography, soil and vegetation. The spatial distribution of annual average rate of soil loss resulting of this methodology shows an average of 24 ton/ha/year. Consequently, this method based on a combination of RUSLE as erosion model gave very similar results with bathymetric measures performed by Institute of Research for Development. It was about 29 ton/ha/year. Accordingly, Lebna watershed belongs to a zone of rather a steep erosive potential knowing that the maximum acceptable limit value of the erosive potential estimated is 12 ton/ha/year (Roose in Introduction a la gestion conservatoire de l’eau, de la biomasse et de la fertilite des sols (GCES). FAORome, 1994). The results have shown that Lebna watershed has a serious risk on soil erosion on sloping land. The highest values are mainly associated with the steep slopes, poor conservation practices, low vegetation cover and high rainfall. The final soil loss map can be thus a base to plan appropriate strategies for decision-makers to avoid soil erosion risks and consequently to lengthen dam life.

The pernicious problem of streambed colmation: a multi-disciplinary reflection on the mechanisms, causes, impacts, and management challenges.

Abstract: The accumulation of fine sediments in rivers is a pernicious problem with wide-ranging consequences for the healthy functioning of rivers throughout the world. It is linked to a range of landuse changes and human activities that have increased sediment inputs leading to elevated fine sediment loads that exceed the sediment transport capacities of rivers. Surficial deposits of fine material can also create the conditions for fine sediment to move into and accumulate within the coarser bed substrate, a process known as colmation and the focus of this review. Colmation, also referred to as clogging, fine sediment infiltration, fine sediment deposition, ingress, infilling, intrusion of fines, siltation, and the surface–subsurface exchange of particles, is particularly damaging to river habitats and ecosystems. It causes degradation through the physical effects of reduced porosity and flow connectivity and the biogeochemical changes arising from the hydraulic and hydrological impacts and the effects of sediment-bound contaminants, all of which can impact on river ecology. Different aspects of the phenomenon of colmation have been studied across a number of disciplines and over several decades and this paper synthesizes this wide literature to provide a multidisciplinary perspective on the mechanisms, causes, and impacts of colmation and discusses some key management challenges. For further resources related to this article, please visit the WIREs website.

Nineteenth-century collapse of a benthic marine ecosystem on the open continental shelf.

Abstract: The soft-sediment seafloor of the open continental shelf is among the least-known biomes on Earth, despite its high diversity and importance to fisheries and biogeochemical cycling. Abundant dead shells of epifaunal suspension-feeding terebratulid brachiopods ( Laqueus ) and scallops on the now-muddy mainland continental shelf of southern California reveal the recent, previously unsuspected extirpation of an extensive offshore shell-gravel ecosystem, evidently driven by anthropogenic siltation. Living populations of attached epifauna, which formerly existed in a middle- and outer-shelf mosaic with patches of trophically diverse muds, are restricted today to rocky seafloor along the shelf edge and to the sandier shelves of offshore islands. Geological age-dating of 190 dead brachiopod shells shows that (i) no shells have been produced on the mainland shelf within the last 100 years, (ii) their shell production declined steeply during the nineteenth century, and (iii) they had formerly been present continuously for at least 4 kyr. This loss, sufficiently rapid (less than or equal to 100 years) and thorough to represent an ecosystem collapse, coincides with intensification of alluvial-plain land use in the nineteenth century, particularly livestock grazing. Extirpation was complete by the start of twentieth-century urbanization, warming, bottom fishing and scientific surveys. The loss of this filter-feeding fauna and the new spatial homogeneity and dominance of deposit- and detritus-feeders would have altered ecosystem functioning by reducing habitat heterogeneity and seawater filtering. This discovery, attesting to the power of this geological approach to recent ecological transitions, also strongly increases the spatial scope attributable to the negative effects of siltation, and suggests that it has been under-recognized on continental shelves elsewhere as a legacy of coastal land use.

Assessing the influence of watershed characteristics on soil erosion susceptibility of Jhelum basin in Kashmir Himalayas

Abstract: Soil erosion, a serious environmental problem, is a global challenge. Once a portion of a fertile soil is lost, it is very difficult to replace it, and this leads to decrease in crop production, damage to drainage networks, and siltation of dams and reservoirs. Human practices like intensive agriculture, overgrazing, and deforestation have intensified the rate of soil erosion all over the world. The Jhelum basin which forms the north-western part of the complex mountain system Himalayas is not only highly vulnerable to natural hazards like earthquakes, landslides, and floods but is also highly susceptible to soil erosion. There is an immediate need to device strategies to reduce adverse impacts of soil erosion and to conserve natural resources like soil, water, and forests by means of proper watershed management programs in the Himalayan region. The present study is carried out for eight upper watersheds of Jhelum basin, an area which are facing serious issues like boulder extraction, deforestation, and unplanned urbanization. The present work demonstrates the use of morphometry, land use, and slope coupled with the multicriteria analytical (MCA) framework to estimate the soil erosion susceptibility of these watersheds using Remote Sensing and Geographical Information System techniques. The present study revealed that out of eight upper watersheds, Arapal, Lidder, and Bringi fall in high priority and need immediate attention and measures to reduce soil erosion in the area. Sandran, Rembiara, and Romshii fall in medium priority. Kuthar and Vishav fall in the low-priority category and are least susceptible to soil erosion.

From shifting cultivation to teak plantation: effect on overland flow and sediment yield in a montane tropical catchment

Abstract: Soil erosion supplies large quantities of sediments to rivers of Southeastern Asia. It reduces soil fertility of agro-ecosystems located on hillslopes, and it degrades, downstream, water resource quality and leads to the siltation of reservoirs. An increase in the surface area covered with commercial perennial monocultures such as teak plantations is currently observed at the expanse of traditional slash-and-burn cultivation systems in steep montane environments of these regions. The impacts of land-use change on the hydrological response and sediment yields have been investigated in a representative catchment of Laos monitored for 13 years. After the gradual conversion of rice-based shifting cultivation to teak plantation-based systems, overland flow contribution to stream flow increased from 16 to 31% and sediment yield raised from 98 to 609 Mg km−2. This result is explained by the higher kinetic energy of raindrops falling from the canopy, the virtual absence of understorey vegetation cover to dissipate drop energy and the formation of an impermeable surface crust accelerating the formation and concentration of overland flow. The 25-to-50% lower 137Cs activities measured in soils collected under mature teak plantations compared to soils under other land uses illustrate the severity of soil erosion processes occurring in teak plantations.

Spatial estimation of soil erosion risk using RUSLE/GIS techniques and practices conservation suggested for reducing soil erosion in Wadi Mina watershed (northwest, Algeria)

Abstract: The Wadi Mina Watershed, western area of Algeria is characterized by rare and irregular rains and a fragile and weak vegetable cover. The sediments resulting from erosion are transported and contributed to silting dam Sidi Mhamed Benaouda. The combination of the thematical maps of the various erosive factors according to the Revised Universal Soil Loss Equation (RUSLE) in SIG by ArcGIS 10.2 software provided a reliable forecast of the annual rates of soil loss by delimiting the areas prone to erosive risk in the catchment above mentioned. The estimated potential average annual soil loss is 11.2 t/ha/yr., and the potential erosion rates from recognized erosion classes ranged from 0.0 to plus 100 t/ha/yr. About 50% of the catchment area was predicted to have very low to low erosion risk, with soil loss between 0 and 7.4 t/ha/yr. Erosion risk is moderate over 13.9% of the catchment, where calculated soil loss is between 7.4 and 12 t/ha/yr. Erosion risk is high to dangerous over 36.1% of the catchment, where calculated soil loss is more than 12 t/ha/yr. According to this study, it appeared clearly that we must intervene quickly by using reliable and effective conservation techniques.

Parameterization of the Effect of Bench Terraces on Runoff and Sediment Yield by Swat Modelling in a Small Semi-Arid Watershed in Northern Tunisia

Abstract: In Tunisia, Soil and Water Conservation (SWC) interventions are among the most practicable strategies to prevent and mitigate rainwater losses through surface runoff and consequential erosion of fertile soils. In this study, a small and terraced agricultural catchment (Sbaihia) was used as an experimental site to analyze and parameterize the effects of bench terraces on water and sediment yield using the Soil and Water Assessment Tool (SWAT). Model calibration and validation was performed taking advantage from high-quality daily runoff data from 1994 to 2000 and a high resolution bathymetric survey of the hill lake at the watershed outlet. SWAT indicated that the local terraces, established on approximately 50% of the watershed area, reduced surface runoff by around 19% and sediment yield by around 22%, decelerating the siltation of the hill lake. Targeted model calibration delivered concise parameter set describing bench terrace impacts on runoff (SCS Curve Number method) and sediment yield (MUSLE) crucial for outscaling of SWC impacts and suitable watershed management.

Assessing and mapping the severity of soil erosion using the 30-m Landsat multispectral satellite data in the former South African homelands of Transkei

Abstract: Soil erosion is increasingly recognised as the principal cause of land degradation, loss of agricultural land area and siltation of surrounding water waterbodies. Accurate and up-to-date soil erosion mapping is key in understanding its severity if these negative impacts are to be minimised and affected areas rehabilitated. The aim of this work was to map the severity of soil erosion, based on the 30-m Landsat series multispectral satellite data in the former South African homelands of Transkei between the year 1994 and 2010. Further, the study assessed if the observed soil erosion trends and morphology that existed in this area could be explained by biophysical factors (i.e. slope, stream erosivity, topographic wetness index) retrieved from the 30-m ASTER Digital Elevation Model (DEM). The results of this study indicate that the Transkei region experiences varying erosion levels from moderate to very severe. The large portion of the land area under the former homelands was largely affected by rill erosion with approximately 74% occurring in the year 1984 and 54% in 2010. The results also revealed specific thresholds of soil erosion drivers. These include steeper areas (≥30°), high stream power index greater than 2.0 (stream erosivity), relatively lower vegetation cover (≤15%) and low topographic wetness index (≤5%). The results of this work demonstrate the severity of soil erosion in the Southern African former homelands of Transkei for the year 1984 and 2010. Additionally, this work has demonstrated the significance of the 30-m Landsat multispectral sensor in examining soil erosion occurrence at a regional scale where in-depth field work still remains a challenging task.

Interacting effects of multiple factors on the morphological evolution of the meandering reaches downstream the Three Gorges Dam

Abstract: Elucidating the influence of dams on fluvial processes can inform river protection and basin management. However, relatively few studies have focused on how multiple factors interact to affect the morphological evolution of meandering reaches. Using hydrological and topographical data, we analyzed the factors that influence and regulate the meandering reaches downstream the Three Gorges Dam (TGD). Our conclusions are as follows. (1) The meandering reaches can be classified into two types based on their evolution during the pre-dam period: G1 reaches, characterized by convex point bar erosion and concave channel deposition (CECD), and G2 reaches, characterized by convex point bar deposition and concave channel erosion (CDCE). Both reach types exhibited CECD features during the post-dam period. (2) Flow processes and sediment transport are the factors that caused serious erosion of the low beaches located in the convex point bars. However, changes in the river regime, river boundaries and jacking of Dongting Lake do not act as primary controls on the morphological evolution of the meandering reaches. (3) Flood discharges ranging from 20,000 to 25,000 m3/s result in greater erosion of convex point bars. The point bars become scoured if the durations of these flows, which are close to bankfull discharge, exceed 20 days. In addition, the reduction in bedload causes the decreasing of point bar siltation in the water-falling period. (4) During the post-dam period, flood abatement, the increased duration of discharges ranging from 20,000 to 25,000 m3/s, and a significant reduction in sediment transport are the main factors that caused meandering reaches to show CECD features. Our results are relevant to other meandering reaches, where they can inform estimates of riverbed change, river management strategies and river protection.

Hydro-sedimentary processes of a shallow tropical estuary under Amazon influence. The Mahury Estuary, French Guiana

Abstract: Along the Guianas coast, coastal dynamic is characterized by the migration of mud banks originating from the Amazon. This singular feature affects the dynamic and the morphology of local estuaries and can induce rapid bathymetric evolution in lower estuaries. Since 2012, the navigation channel of the Mahury Estuary (French Guiana) is enduring a severe siltation whose origin comes from a mud bank crossing the estuary mouth. This study aims to determine how the migration of a mud bank through an estuary mouth could influence the transport and fluxes in the estuary. Field measurements were performed over a year with the monitoring of the salt intrusion length, mooring surveys during spring-neap cycles and shipboard profiling surveys during semi-diurnal cycles. Salt intrusion lengths underline a significant seasonal variation characterized by the transition from a steady-state length during high river discharge and a wide range of lengths with the tidal range during low to moderate river discharge. During the rainy season, measurements indicate a fluvial-dominated condition with low suspended-sediment concentrations most of the semi-diurnal cycle. Residual sediment fluxes are usually seaward excepted when river discharge is below seasonal average. During the dry season, maximum suspended-sediment concentrations are higher in the middle part of the estuary. Residual sediment fluxes are landward along the estuary and stronger during neap tides in the estuary mouth and few kilometers upstream. In this area, a persistent density stratification traps sediments in the bottom layer and generates a gravitational circulation during neap tides, which enhances landward transports up to 2.56 t m−1 over a semi-diurnal cycle. In the middle estuary, landward fluxes are most significant during the dry season and also during the rainy season when the river discharge is below the seasonal average. Although this study includes temporal and spatial limitations, it underlines significant mud inflows in the middle part of the estuary during low to moderate river discharges. Comparison with old data suggests higher sediment loads in the estuary during the migration of a mud bank but must be confirmed by further studies during the interbank period.

Torrential flood prevention in the Kolubara river basin

Abstract: One of the most vulnerable parts to natural hazards in Serbia is Kolubara river basin. In the past, during the period from 1929 to 2013, 121 torrential flood events in the Kolubara river basin were recorded which show that this territory is extremely vulnerable to the torrential floods. The extreme event which occurred in May 2014 causing the catastrophic material damages and casualties was the latest and historical flood. The analysis of natural conditions in the Kolubara basin uniformly showed that this area is predisposed to a greater number of torrential floods due to its geomorphological, hydrological and land use properties. Torrential floods are closely related to the intensity and spatial distribution of erosive processes in the upper part of the Kolubara basin. The estimation of soil erosion potential is generally achieved by Erosion Potential Model (EPM). For the purposes of determining the degree of torrential properties in various water streams in the Kolubara basin, the calculation of susceptibility to torrential floods was assessed by Flash Flood Potential Index (FFPI). More than half of the basin area (57.2%) is located within the category of very weak and weak erosion (Zsr = 0.35), but the category of medium erosion is geospatially very common. Such a distribution of medium erosion category provides conditions for generating, i.e. production of sediment which would boost torrential properties of water streams. After the classification of the obtained FFPI values it was determined that 25% of the Kolubara basin is very susceptible to torrents and this data should be seriously taken into consideration. Based on the analyses, the best and most successful manner of defence is prevention which consists of the integrated river basin management system (integrated torrent control system) so that technical works in hydrographic networks of torrents and biological and biotechnical works on the slope of the basin would be the best solution. Permanent control of erosive and torrential processes in the river basin will be not only important for flood control but it can also protect the existing and future water reservoirs and retentions from siltation with erosion sediment which is of great significance to the water management, agriculture, energy sector, and the entire society.

Effects of Small-Scale Gold Mining Tailings on the Underwater Light Field in the Tapajós River Basin, Brazilian Amazon

Abstract: Artisanal and Small-scale Gold Mining (ASGM) within the Amazon region has created several environmental impacts, such as mercury contamination and changes in water quality due to increased siltation. This paper describes the effects of water siltation on the underwater light environment of rivers under different levels of gold mining activities in the Tapajos River Basin. Furthermore, it investigates possible impacts on the phytoplankton community. Two field campaigns were conducted in the Tapajos River Basin, during high water level and during low water level seasons, to measure Inherent and Apparent Optical Properties (IOPs, AOPs), including scattering (b) and absorption (a) coefficients and biogeochemical data (sediment content, pigments, and phytoplankton quantification). The biogeochemical data was separated into five classes according to the concentration of total suspended solids (TSS) ranging from 1.8 mg·L−1 to 113.6 mg·L−1. The in-water light environment varied among those classes due to a wide range of concentrations of inorganic TSS originated from different levels of mining activities. For tributaries with low or no influence of mining tailings (TSS up to 6.8 mg·L−1), waters are relatively more absorbent with b:a ratio of 0.8 at 440 nm and b660 magnitude of 2.1 m−1. With increased TSS loadings from mining operations (TSS over 100 mg·L−1), the scattering process prevails over absorption (b:a ratio of 10.0 at 440 nm), and b660 increases to 20.8 m−1. Non-impacted tributaries presented a critical depth for phytoplankton productivity of up to 6.0 m with available light evenly distributed throughout the spectra. Whereas for greatly impacted waters, attenuation of light was faster, reducing the critical depth to about 1.7 m, with most of the available light comprising of red wavelengths. Overall, a dominance of diatoms was observed for the upstream rivers, whereas cyanobacteria prevailed in the low section of the Tapajos River. The results suggest that the spatial and temporal distribution of phytoplankton in the Tapajos River Basin is not only a function of light availability, but rather depends on the interplay of factors, including flood pulse, water velocity, nutrient availability, and seasonal variation of incoming irradiance. Ongoing research indicates that the effects of mining tailings on the aquatic environment, described here, are occurring in several rivers within the Amazon River Basin.

Bathymetry and siltation rate for Dokan Reservoir, Iraq

Abstract: The Dokan Reservoir dam is a concrete cylindrical arch with gravity abutments, located on the Lesser Zab River about 60 km from the city of Sulaimani in north-eastern Iraq. A bathymetric survey was conducted in November 2014 for a period of 10 days, using an echo sounder of 200-kHz single beam. The survey results indicated an annual average sediment deposition of 3.8 million m3. Thirty-two sediment samples were collected from the reservoir bed. The ratio of gravel, sand, silt and clay was 15:14:48:23, respectively. The reservoir bed is covered mainly with silt. The sediments are composed of silty clay (77.6%), silty sandy clay (10%), sandy gravely silty clay (1.2%) and gravely sandy silty clay (1%).

Variation of River Islands around a Large City along the Yangtze River from Satellite Remote Sensing Images

Abstract: River islands are sandbars formed by scouring and silting. Their evolution is affected by several factors, among which are runoff and sediment discharge. The spatial-temporal evolution of seven river islands in the Nanjing Section of the Yangtze River of China was examined using TM (Thematic Mapper) and ETM (Enhanced Thematic Mapper)+ images from 1985 to 2015 at five year intervals. The following approaches were applied in this study: the threshold value method, binarization model, image registration, image cropping, convolution and cluster analysis. Annual runoff and sediment discharge data as measured at the Datong hydrological station upstream of Nanjing section were also used to determine the roles and impacts of various factors. The results indicated that: (1) TM/ETM+ images met the criteria of information extraction of river islands; (2) generally, the total area of these islands in this section and their changing rate decreased over time; (3) sediment and river discharge were the most significant factors in island evolution. They directly affect river islands through silting or erosion. Additionally, anthropocentric influences could play increasingly important roles.

Effects of Land Deals on Peak Discharge and Sediment Transport in the Catchments Around the Grand Ethiopian Renaissance Dam

Abstract: Land degradation poses a threat to reservoirs because of siltation; hence, sustainable hydropower development necessitates the conservation of upstream catchments Ethiopia is currently constructing Africa's largest hydropower dam, the Grand Ethiopian Renaissance Dam (GERD), on the Blue Nile Given the commercialization of large tracts of land in the closer catchments, there is a need to explore the effects on peak discharge and suspended sediment concentration A field survey was conducted on 20 ephemeral streams to compare annual maximum peak discharges between catchments (0·4 – 15·5 km2), eight of which drain commercial farms and twelve others, land under traditional management We measured channel characteristics, observed flood marks and applied the empirical Manning equation to calculate peak discharges SSC samples were taken during each runoff event from a stream in each of the two dominant land management categories Results indicated that commercial farms contributed for the 51% increase in peak runoff compared to traditionally managed lands Catchments dominated by commercial farms also have a significantly higher SSC (mean = 6·44 ± 2·23 g l−1) compared to catchments without commercial farms (mean = 2·77 ± 2·31 g l−1) Forests and woodlands have a strong buffering effect upon flood generation while higher peak discharges and sediment transport have generated from crop lands However, leasing forests and woodland to agricultural companies has resulted in deforestation Consequently, the increased runoff response may lead to downstream bank erosion and affect downstream communities; the increased sediment transport poses a threat to the multibillion dollar hydropower reservoir of the GERD Copyright © 2016 John Wiley & Sons, Ltd

Factors Controlling Sediment Load in The Central Anatolia Region of Turkey: Ankara River Basin

Abstract: Better understanding of the factors controlling sediment load at a catchment scale can facilitate estimation of soil erosion and sediment transport rates. The research summarized here enhances understanding of correlations between potential control variables on suspended sediment loads. The Soil and Water Assessment Tool was used to simulate flow and sediment at the Ankara River basin. Multivariable regression analysis and principal component analysis were then performed between sediment load and controlling variables. The physical variables were either directly derived from a Digital Elevation Model or from field maps or computed using established equations. Mean observed sediment rate is 6697 ton/year and mean sediment yield is 21 ton/y/km² from the gage. Soil and Water Assessment Tool satisfactorily simulated observed sediment load with Nash-Sutcliffe efficiency, relative error, and coefficient of determination (R²) values of 0.81, −1.55, and 0.93, respectively in the catchment. Therefore, parameter values from the physically based model were applied to the multivariable regression analysis as well as principal component analysis. The results indicate that stream flow, drainage area, and channel width explain most of the variability in sediment load among the catchments. The implications of the results, efficient siltation management practices in the catchment should be performed to stream flow, drainage area, and channel width.

Modeling the sedimentary response of a large Pyrenean basin to global change

Abstract: Erosion processes at the catchment scale control a basin’s morphology and sediment patterns in the river network. Eroded sediments are transported and deposited downstream and may cause environmental problems and relevant effects on water storage and hydropower infrastructures. Quantification of water and sediment yield is complex due to the physical processes involved and their temporal and spatial variability, especially at the light of current global change. Numerical models that use spatially distributed information constitute a useful tool for these estimates, when sufficient input data are available. In this study, we applied the hydrological and sedimentological TETIS model to determine the patterns of water and sediment yield in a large mountain catchment. Flow discharge data obtained from two gauged stations were used for calibration and validation of the hydrological sub-model. Data from two reservoir bathymetries at the outlet of the study area were used for calibration of the sedimentological sub-model. After model calibration, several scenarios of climate and land use change were simulated. Climate scenarios show a general decrease in average annual precipitation and an increase in temperature, associated with an increase in extreme rainfall events. Global change scenarios lead to a counteracting effect between the increase in sediment transport during extreme events and the decrease in sediment erosion associated with afforestation following the abandonment of agricultural land. In the case of the most extreme climate scenario combined with total catchment deforestation, the model indicates a complete siltation of the reservoir by 2050. Model performance emphasizes its potential as a tool for evaluating water and sediment yield for large catchments, as well as of its usefulness for water and sediment management in light of future climate and land use change scenarios.

Water and sediment fluxes in Mediterranean mountainous regions: comprehensive dataset for hydro-sedimentological analyses and modelling in a mesoscale catchment (River Isábena, NE Spain)

Abstract: . A comprehensive hydro-sedimentological dataset for the Isabena catchment, northeastern (NE) Spain, for the period 2010–2018 is presented to analyse water and sediment fluxes in a Mediterranean mesoscale catchment. The dataset includes rainfall data from 12 rain gauges distributed within the study area complemented by meteorological data of 12 official meteo-stations. It comprises discharge data derived from water stage measurements as well as suspended sediment concentrations (SSCs) at six gauging stations of the River Isabena and its sub-catchments. Soil spectroscopic data from 351 suspended sediment samples and 152 soil samples were collected to characterize sediment source regions and sediment properties via fingerprinting analyses. The Isabena catchment (445 km 2 ) is located in the southern central Pyrenees ranging from 450 m to 2720 m a.s.l.; together with a pronounced topography, this leads to distinct temperature and precipitation gradients. The River Isabena shows marked discharge variations and high sediment yields causing severe siltation problems in the downstream Barasona Reservoir. The main sediment source is badland areas located on Eocene marls that are well connected to the river network. The dataset features a comprehensive set of variables in a high spatial and temporal resolution suitable for the advanced process understanding of water and sediment fluxes, their origin and connectivity and sediment budgeting and for the evaluation and further development of hydro-sedimentological models in Mediterranean mesoscale mountainous catchments. The dataset is available at http://doi.org/10.5880/fidgeo.2018.011 .

A new management approach of dams siltation

Abstract: The present article examines in a first phase the current situation of the silting of Algerian dams based on the collection and analysis of data from about a hundred bathymetric surveys carried out by the National Agency of Dams and Transfers. A second phase proposes a methodology for managing the siltation of dams. The results show that, after 160 years of operation, siltation reached 1.7 billion m 3 in the 74 dams with a capacity of 8.5 billion m 3 of water. Either a loss of capacity of 20%. The siltation rate reached 65 million m 3 /year. Dams located in the Chellif Zahrez watershed are the most threatened by siltation. In this study, we established a ranking of dams on the basis of the annual filling rate. Thus, we have identified 20 dams with a total capacity of 2370 million m 3 are seriously threatened by mud deposits. Eight new dams of up to 14 years old are vulnerable to siltation. Twelve dams with a total capacity of 830 million m 3 are moderately silted and 24 dams are slightly silted. In 2017, the volume of mud deposited in the 74 dams is estimated at 1.9 billion m 3 .