Showing papers on "Siltation published in 2014"

Morphometry and land cover based multi-criteria analysis for assessing the soil erosion susceptibility of the western Himalayan watershed

Abstract: Complex mountainous environments such as Himalayas are highly susceptibility to natural hazards particular those that are triggered by the action of water such as floods, soil erosion, mass movements and siltation of the hydro-electric power dams. Among all the natural hazards, soil erosion is the most implicit and the devastating hazard affecting the life and property of the millions of people living in these regions. Hence to review and devise strategies to reduce the adverse impacts of soil erosion is of utmost importance to the planners of watershed management programs in these regions. This paper demonstrates the use of satellite based remote sensing data coupled with the observational field data in a multi-criteria analytical (MCA) framework to estimate the soil erosion susceptibility of the sub-watersheds of the Rembiara basin falling in the western Himalaya, using geographical information system (GIS). In this paper, watershed morphometry and land cover are used as an inputs to the MCA framework to prioritize the sub-watersheds of this basin on the basis of their different susceptibilities to soil erosion. Methodology included the derivation of a set of drainage and land cover parameters that act as the indicators of erosion susceptibility. Further the output from the MCA resulted in the categorization of the sub-watersheds into low, medium, high and very high erosion susceptibility classes. A detailed prioritization map for the susceptible sub-watersheds based on the combined role of land cover and morphometry is finally presented. Besides, maps identifying the susceptible sub-watersheds based on morphometry and land cover only are also presented. The results of this study are part of the watershed management program in the study area and are directed to instigate appropriate measures to alleviate the soil erosion in the study area.

Impact of the Hoa Binh dam (Vietnam) on water and sediment budgets in the Red River basin and delta

Abstract: . The Hoa Binh dam (HBD), located on a tributary of the Red River in Vietnam, has a capacity of 9.45 × 109 m3 and was commissioned in December 1988. Although it is important for flood prevention, electricity production and irrigation in northern Vietnam, the Hoa Binh dam has also highly influenced the suspended sediment distribution in the lower Red River basin, in the delta and in the coastal zone. Its impact was analysed from a 50-year data set of water discharge and suspended sediment concentration (1960–2010), and the distribution of water and sediment across the nine mouths of the delta was simulated using the MIKE11 numerical model before and after the dam settlement. Although water discharge at the delta inlet decreased by only 9%, the yearly suspended sediment flux dropped, on average, by 61% at Son Tay near Hanoi (from 119 to 46 × 106 t yr−1). Along the coast, reduced sedimentation rates are coincident with the lower sediment delivery observed since the impoundment of the Hoa Binh dam. Water regulation has led to decreased water discharge in the wet season (−14% in the Red River at Son Tay) and increased water discharge in the dry season (+12% at the same station). The ratios of water and suspended sediment flows, as compared to the total flows in the nine mouths, increased in the northern and southern estuaries and decreased in the central, main Ba Lat mouth. The increasing volume of dredged sediments in the Haiphong harbour is evidence of the silting up of the northern estuary of Cam–Bach Dang. The effect of tidal pumping on enhanced flow occurring in the dry season and resulting from changed water regulation is discussed as a possible cause of the enhanced siltation of the estuary after Hoa Binh dam impoundment.

Impact of no-tillage agricultural systems on sediment yield in two large catchments in Southern Brazil

Abstract: Purpose The impact of agriculture on water resources has long been a problem associated with the formation of runoff, the siltation of lakes and reservoirs, and overall depletion of water quality. In Brazil, these problems are mainly related to soil degradation by water erosion. However, studies of catchment-scale erosion are still rare particularly in grain-producing regions which have adopted conservative tillage systems for soil protection. In order to contribute to a better understanding of the impact of conservation agriculture on water resources, this study determined the runoff coefficient and sediment yield for two agricultural catchments.

Temporal Variation of Streamflow, Sediment Load and Their Relationship in the Yellow River Basin, China

Abstract: Variation of streamflow and sediment load in the Yellow River basin has received considerable attention due to its drastic reduction during the past several decades. This paper presents a detailed investigation on the changes of streamflow and sediment load from 1952 to 2011 using monthly observations at four gauging stations along the Yellow River. The results show significant decreasing trends for both streamflow and sediment load at all four gauging stations over the past 60 years. The wavelet transform demonstrated discontinuous periodicities from 1969 to 1973 and after 1986 due to the construction of large reservoirs and implementation of numerous soil and water conservations practices. The sediment rating curves with the power-law function was applied to investigate the relationship between discharge and sediment load. The results indicate distinct variations of the relationship between streamflow and sediment and implied significant hydro-morphological changes within different periods. The reducing sediment supply from the source region and the increased erosive power of the river are detected at Lanzhou station, while the decrease of the transport capacity at Toudaoguai is caused by severe siltation. Significant changes in the relationship between streamflow and sediment load are found at Huayuankou and Gaocun stations, which are largely induced by evident sediment income and trapping effects of large reservoirs. It is estimated that numerous reservoirs have strongly altered the regime and magnitude of streamflow and trapped large amount of sediment, leading to severe siltation and evident reduction of their total volumes. A decrease in precipitation, incoming water from the upper reaches, soil and water conservation measures as well as water consumption contribute most to the significant reduction of streamflow. The decrease of sediment load mainly resulted from various soil and water conservation measures and trapping in reservoirs from 1986 to 2011.

Check dam sediments: an important indicator of the effects of environmental changes on soil erosion in the Loess Plateau in China.

Abstract: Check dam sediments document the process of soil erosion for a watershed. The main objectives of this research are as follows: first, to determine whether the sediments trapped in check dams can provide useful information about local erosion and the environment, and second, to obtain the extent to which they can be stratigraphically interpreted and correlated to the land use history of an area controlled by check dams. Particle size and the concentration of (137)Cs in sediments are the indicators used to study the effects of environmental changes on soil erosion in the Loess Plateau, China. A total of 216 soil samples were collected from four sediment profile cores at the Yangjuangou watershed check dam constructed in 1955 and fully silted with sediments by 1965. The results indicated that (137)Cs dating and sediment particle size can characterize the sediment deposition process. Silt makes up more than 50 % of the sediment; both the clay and silt sediment fractions decrease gradually in the upstream direction. The sediment profiles are characterized by three depositional layers. These layers suggest changes in the land use. The top layer showed tillage disturbance, with moderate sediments and new soil mixed from 0 to 20 cm. A transition stage from wetlands (characterized by vegetation such as bulrush) to cropland is inferred from sediments at depths of 20-85 cm. Below 85 cm, sedimentary layering is obvious and there is no tillage disturbance. At the downstream site, A0, the average rate of sediment deposition from 1958 to 1963 was approximately 6,125.4 t year(-1) km(-2). Because of their high time resolution, check dam sediments indicate the effects of environmental changes on soil erosion, and they can provide a multiyear record of the soil erosion evolution at the local scale in the middle reaches of the Yellow River.

Process-based modelling of erosion, sediment transport and reservoir siltation in mesoscale semi-arid catchments

Abstract: To support scientifically sound water management in dryland environments a modelling system has been developed for the quantitative assessment of water and sediment fluxes in catchments, transport in the river system, and retention in reservoirs. The spatial scale of interest is the mesoscale because this is the scale most relevant for management of water and land resources. This modelling system comprises process-oriented hydrological components tailored for dryland characteristics coupled with components comprising hillslope erosion, sediment transport and reservoir deposition processes. The spatial discretization is hierarchically designed according to a multi-scale concept to account for particular relevant process scales. The non-linear and partly intermittent run-off generation and sediment dynamics are dealt with by accounting for connectivity phenomena at the intersections of landscape compartments. The modelling system has been developed by means of data from nested research catchments in NE-Spain and in NE-Brazil. In the semi-arid NE of Brazil sediment retention along the topography is the main process for sediment retention at all scales, i.e. the sediment delivery is transport limited. This kind of deposition retains roughly 50 to 60 % of eroded sediment, maintaining a similar deposition proportion in all spatial scales investigated. On the other hand, the sediment retained in reservoirs is clearly related to the scale, increasing with catchment area. With increasing area, there are more reservoirs, increasing the possibility of deposition. Furthermore, the area increase also promotes an increase in flow volume, favouring the construction of larger reservoirs, which generally overflow less frequently and retain higher sediment fractions. The second example comprises a highly dynamic Mediterranean catchment in NE-Spain with nested sub-catchments and reveals the full dynamics of hydrological, erosion and deposition features. The run-off modelling performed well with only some overestimation during low-flow periods due to the neglect of water losses along the river. The simulated peaks in sediment flux are reproduced well, while low-flow sediment transport is less well captured, due to the disregard of sediment remobilization in the riverbed during low flow. This combined observation and modelling study deepened the understanding of hydro-sedimentological systems characterized by flashy run-off generation and by erosion and sediment transport pulses through the different landscape compartments. The connectivity between the different landscape compartments plays a very relevant role, regarding both the total mass of water and sediment transport and the transport time through the catchment.

Analysis of potential impacts on coastal areas due to changes in wave conditions

Abstract: This study examines the main physical processes related to coastal and port engineering that could be altered by future changes in wave parameters as a consequence of climate change. To estimate the order of magnitude of the potential changes in these processes, several assumptions and simplifications are made and, in most cases, they are assessed by using simple, empirical state-of-the-art expressions. The studied processes are grouped in three categories according to whether they affect beaches, harbors or coastal structures in general. The changes in these processes are estimated as a function of the deepwater variations of the main wave parameters: wave height (H 0), wave period (T) and wave direction (θ 0). A moderate range of variation is assumed for these parameters at deep water (±10 or ±20 % in H 0 and its square root in T, and ±10o in θ 0), taking into account recent studies of future wave projections. The results indicate that potential changes in wave height will strongly affect overtopping discharge, stability and scouring of rubble-mound structures and, to a lesser extent, siltation, wave transmission and longshore sediment transport. Changes in wave direction will affect longshore sediment transport in particular and, at a lower magnitude, processes related to port operability (agitation and siltation). Siltation is the only process affected significantly by changes in T alone.

Green Water Credits – exploring its potential to enhance ecosystem services by reducing soil erosion in the Upper Tana basin, Kenya

Abstract: Food production, water availability and energy production are important ecosystem services of the Upper Tana basin (Kenya) and they decline due to upstream erosion affecting downstream water users. The effect of 11 soil conservation measures on soil erosion and the three ecosystem services was estimated by a modelling approach to assess agro-ecological processes and benefit/cost relations. Soil water available for evaporation and transpiration (‘green water’) functioned as a unifying concept to express the effects of erosion and the impacts of soil and water conservation measures that result in: (1) increased water availability for crops; (2) increased fluxes towards aquifers, thereby increasing water supply and regulating streamflow, and (3) a reduction of erosion and siltation of reservoirs used for hydroelectricity. Modelling indicated that the three ecosystem services could be improved, as compared with the base level, by up to 20% by introducing appropriate conservation measures with benefit/cost relations of around 7. However, farmers were unable to make the necessary investments and much effort and many institutional studies were needed to achieve progress towards implementation by initiating the Green Water Credits (GWC) programme intended to arrange payments by downstream businesses to upstream farmers. A timeline analysis is presented to illustrate the slow, but persistent, development of transdisciplinary activities as a function of time using connected value development as a guiding principle.

Hydrogeomorphic variability due to dam constructions and emerging problems: a case study of Damodar River, West Bengal, India

Abstract: In the first multipurpose river valley planning of India, the vast resources of Damodar River Basin (DRB) (eastern India) are not only to be envisioned in their entirety but also to be developed in a unified manner where the water, land, and people are simultaneously bounded in a seamless web. Four large dams (Konar, Tilaiya, Maithon, and Panchet), Durgapur barrage, and Tenughat reservoir are built to tamp the flood-prone Damodar River using water resource in an integrated method. The functionality of Damodar fluvial system is controlled by dams, barrage, weirs, sluices, embankments, and canals, maintaining a dynamic equilibrium between fluvial processes and anthropogenic processes. Carrying more than 50 years of legacy, the existing drainage and flood control system of Damodar Valley Corporation has aggravated a number of hydrogeomorphic problems especially in lower DRB, viz. siltation of river bed and reservoirs, uncontrolled monsoonal stream flow, declining carrying capacity of lower course, drainage congestion, low-magnitude annual floods, channel shifting, de-functioned canals, decay of paleochannels, decline of ground water level, and less replenishing of soils with fresh silts. The present paper is mainly tried to investigate the pre-dam and post-dam hydrogeomorphic variability in relation to flood risk and drawbacks of Damodar Valley Multipurpose Project. Specifically, the annual peak flow of Damodar shifts from August to September due to dam construction and reservoir storage. Applying the annual flood series of log Pearson type III distribution, we have estimated post-dam 5-year peak discharge of above 5,300 m3 s−1 and 100-year flood of above 11,000 m3 s−1. Due to siltation, the bankfull discharges of sample segments are gradually declined up to 4,011 m3 s−1, 2,366 m3 s−1, and 1,542 m3 s−1, respectively, having recurrence interval of 1.18–3.18 years only. With the regulation of monsoon flow, the standard sinuosity index is gradually increased downstream, having high dominance of hydraulic factors in respect of topographic factors. The upstream section of study area (Rhondia to Paikpara) now shows the dominance of aggradational landforms, braiding, avulsion, high width–depth ratio, breaching of right bank, and valley widening, but downstream of Barsul the phenomena of bank erosion, confined sinuosity, low width–depth ratio, and narrowness are more pronounced.

The role of terrestrial sediment on turbidity near Singapore's coral reefs

Abstract: In past decades, the turbidity in Singapore's coastal waters has been increased. This has led to reduced visibility and increased siltation rates, detrimental for the coral reefs and other sensitive ecosystems around Singapore. The reasons for this increased turbidity are poorly known because little quantitative information exists on sediment dynamics around Singapore, on changes in sediment sources, and on the physical environment. Therefore we set out to quantify the effect of fluvial contributions on changes in sediment dynamics, using a combination of numerical models, satellite images, and hydrodynamic and sedimentary data. Results indicate that the main fluvial source enters an ebb-dominant estuary, with sediment export primarily balanced by settling/scour lags rather than estuarine circulation. A large part of the sediment load enters the Singapore Strait, where the large-scale marine currents effectively transport most sediment towards the coral reefs. However, mixing with marine water masses in both the estuary and the adjacent Singapore Strait sufficiently dilutes this fluvial sediment source to have a negligible impact on Singapore's coral reefs.

Coastal Zone Mapping through Geospatial Technology for Resource Management of Indian Sundarban, West Bengal, India

Abstract: The West Bengal part of the Ganges-Brahmaputra delta, popularly known as the Sundarban delta, is a system where intricate estuarine and coastal processes are influenced by adjacent marine, terrestrial and meteorological systems and the dynamic interface amongst the three. Being the center of population growth, coastal sea, ponds/wetlands, estuarine islands in this area are to sustain the negative impact caused by society’s commercial, recreational, and residential activities. Additionally, natural forcing like sea level rise or climate change is a prime issue of concern for this vulnerable tract. Presently, this deltaic system is facing degradation due to natural and anthropogenic causes. Degradation of this littoral tract is manifested in terms of frequent embankment failures, submergence & flooding, beach erosion, siltation within embankment, saline water intrusion in the agricultural field etc. In the above perspective, viable coastal zone management options are to be adopted based on scientific approach retaining socio-economic use of the coastal zone complying with preservation of resources and nature values. Knowledge and understanding of coastal morph dynamic behavior as well as middle to long-term developments therein is essential in this respect. Lack of data pertaining to this coast makes the task all the more difficult than expected and restricts proper estimation of impacts to be caused by the different coastal variables. The present study is aimed at predicting evolution of Sundarbans estuary located at the mouth of Bay of Bengal by a set of physical mathematical model through extrapolation of observed morphological behavior of erosion-accretion. The long term goal of this study is to identify the coupling amongst the coastal processes and mainly two dimensional evolutions (shoreline change) of the form of deltaic island system of West Bengal with special reference to sea level rise which in turn is guided by climate change. This study is carried out so that a greater degree of certainty can be achieved while applying the output as a blue print for the coastal managers and planners for this vulnerable niche. The coastal zone is under heavy pressure from land-based activities located in the catchment of rivers. Traditionally, both scientific research and framework have treated catchments and coasts as separate entities. However, it is increasingly recognized that they should in fact be treated as an integrated whole, encompassing both environmental and socio economic and political systems.

Effect of soil properties on peat erosion and suspended sediment delivery in drained peatlands

Abstract: Erosion from peat extraction areas is known to cause siltation of water courses and poor water quality. However, the main soil parameters affecting peat erosion and suspended sediment (SS) yields from different catchments are not well understood. This paper used peat properties (degree of humification, peat type, ash content, porosity, moisture content, bulk density, and shear strength) and novel erosion threshold measurements from intact soil cores to explain peat erodibility and spatial variations in SS concentrations (SSCs) and SS loads (SSLs) at 20 Finnish peat extraction sites. The erosion threshold measurements suggested that critical shear stresses for particle entrainment decrease with increasing degree of humification (von Post scale) and are significantly lower in well-decomposed peat than in slightly or moderately decomposed peat. Two critical shear stresses were obtained from moderately decomposed peat samples, indicating a degree of surface armoring by coarse peat fibers. Monitored long-term average SSC was highest at study sites with well-decomposed peat, while very fine-grained mineral subsoil explained some of the highest long-term SSC in areas where drainage ditches penetrated below the upper peat layer. Average SSL (kg d−1) at the study sites was best explained (R2 = 0.89) by average discharge and surface peat decomposition level. Overall, this study provides new knowledge on peat erosion and critical shear stresses that can be used in water conservation and sediment management practices for cutover peatlands and other similar land uses.

Modeling sediment sources and yields in a Pyrenean catchment draining to a large reservoir (Ésera River, Ebro Basin)

Abstract: The study aimed to use the Soil and Water Assessment Tool (SWAT) model to simulate erosion processes in an alpine–prealpine catchment in order to provide data and information that may be relevant for managers so as to minimize reservoir siltation and water quality degradation. The main objective was to assess sediment production across the catchment and sediment supply to the main reservoir. The Barasona reservoir catchment (1,509 km2) is located in the Central Spanish Pyrenees, in the Ebro Basin. This catchment was selected for the case study given the regional significance of the Barasona reservoir and its siltation problems. The catchment has a mountain climate, with strong altitudinal and north–south gradients. The catchment is characterized by heterogeneous topography and lithology, resulting in a varied mosaic of slopes, soil types, and land covers. The Jueu karst system and two small headwater reservoirs were parameterized and calibrated in the model. The SWAT model sediment calibration for the catchment was based on a prior monthly hydrologic calibration, and the model validation was based on the sediment depositional history of the Barasona reservoir. The simulation period (2003–2006) and the validation period (1993–2002) produced average sediment yields to the reservoir of 643,000 and 575,000 t year−1, respectively. Large variations in sediment production were found between the subcatchments in the Barasona catchment due to differences in rock outcrops, land cover, and slope gradient. Sediment loss in the Jueu karst system was 15,500 t and the two small headwater reservoirs retained 31,200 and 50,300 t. Sediment production in relation to precipitation showed high temporal variability, with specific sediment yields to the Barasona reservoir ranging from 2.74 to 8.25 t ha−1 year−1. Strong lithological control was observed for sediment production in the subcatchments. The main sediment sources were located in the badlands developed on marls in the middle part of the catchment (internal depressions). The proposed model has proved useful for identifying areas where significant erosion processes take place in large alpine–prealpine catchments at a regional level and also for assessing discharge losses by the karst system and the sedimentary role of the small reservoirs. The information obtained through this research will be of interest in assessing the spatial distribution of sediment sources and areas of high sediment yield, which will be useful to establish criteria for remediation strategies.

Comprehensive analysis on the sediment siltation in the upper reach of the deepwater navigation channel in the Yangtze Estuary

Abstract: The results from both the field measurements and numerical simulation were reported to comprehensively analyze the sediment siltation in the upper reach of the Deepwater Navigation Channel Project in the Yangtze Estuary after the project has been implemented. In this research, firstly some basic information about the river evolution in the Yangtze Estuary is analyzed, including the variations of water depths in the Hengsha Passage and the inlet cross-sections of the North Passage and the South Passage, and changes of diversion ratios of ebb flow and sediment flux in the North Passage and the South Passage. Then the Delft3D-FLOW model is applied to simulate the hydrodynamics and sediment transport in the Yangtze Estuary. This model has been calibrated and the simulated results agree well with the measured data of the tidal levels, flow velocities and suspended sediment concentration (SSC), indicating that the model can well simulate the hydrodynamics and sediment transport of the Yangtze Estuary caused by the Deepwater Navigation Channel Project. The research results show that the development of the Hengsha Passage and decrease of diversion ratio of ebb flow and sediment flux in the North Passage are the main reasons of sediment siltation in the upper reach of the Deepwater Navigation Channel in the Yangtze Estuary.

Chronology of recent sedimentation and geochemical characteristics of sediments in Alvarado Lagoon, Veracruz (southwestern gulf of Mexico) Cronología de la sedimentación reciente y caracterización geoquímica de los sedimentos de la laguna de Alvarado, Veracruz (suroeste del golfo de México)

Abstract: Coastal lagoons are very sensitive to anthropogenic impacts and sedimentary records may provide valuable temporal reconstructions of the environmental changes in the lagoon, the coastal zone, and the catchment area. The Alvarado Lagoon (Veracruz, southwestern gulf of Mexico) belongs to an extensive complex of wetlands recognized as a Ramsar site. However, its catchment basin has one of the highest deforestation rates in Mexico due to the transformation of lowlands for agriculture and grazing, thus causing siltation of the surrounding aquatic bodies. To evaluate the impact of land use change on Alvarado Lagoon, sediment fluxes and provenance were reconstructed by studying the elemental composition (determined by X-ray fluorescence spectrometry) of a sediment core dated radiometrically ( 210 Pb, 137 Cs, 239,240 Pu). The sedimentary record showed an acceleration of the sediment accumulation rate during more than 134 ± 17 years; however, the changes in elemental composition during the past 40 years (i.e., 1972-2011) indicated the incorporation of continental weathered sediments and an increment of sediment accumulation of circa 470%, in coincidence with the period of higher deforestation and siltation. The recent increase in sediment accumulation rates and changes in geochemical features are attributed to erosion caused by land use changes in the Alvarado Lagoon drainage basin.

The Lake Manzala of Egypt: an ambiguous future

Abstract: The Lake Manzala of Egypt has a relatively short history and its future, however, is uncertain. The lake which was the biggest coastal wetland along the Mediterranean Coast is moving toward its disappearance by two opposite forces, one of them is the shrinking of the water body by siltation of sediments coming from agricultural lands and the abundance of weeds and swamp vegetation as well as the drying practices for agriculture, whereas the other force incorporates the removal of the coastal sand bar separating the lake from the Mediterranean Sea by erosion, which should eventually lead to the conversion of the lake into a coastal embayment instead of being a closed coastal lagoon. The study provided a spatiotemporal change analysis of the lake using remotely sensed data.

Morphodynamic processes of the Elbe River estuary, Germany: the Coriolis effect, tidal asymmetry and human dredging

Abstract: The Digital Elevation Model (DEM) based on the historical sea-charts and on-site hydrological records were used to examine the morphological change of the Elbe River estuary. The results show that siltation predominated in the tidal flat in the northern estuary, with a net siltation rate of 1.8 cm·a−1 during 1927–2006. In contrast, a continuous erosion prevailed in the main river channel, south of the estuary, with a net erosion rate of 2.5 cm·a−1 in the same time. In addition, a seaward shift of the estuarine island has happened with the old island coalescing to the northern tidal flat and new one emerging through siltation process. The tidal asymmetry via ebbing flow (maximum at 140 cm·s−1, and average at 76 cm·s−1) prevailed in the tidal flat, meaning continuous aggradation northwestward, while flooding flow (maximum at 100 cm ·s−1, and average at 67 cm·s−1) dominated in the main river channel with deepening thaweg at south, showing a landward sedimentation via the tidal pumping processes. This dextral extension of the estuarine morphology is due to the Coriolis force, leading to the inconsistent directions of in-out flows, which enables to facilitate the estuarine siltation. Human dredging prevailing in the estuary has dramatically altered the nature of the silted river channel to erosional since the last century. This is characterized by a net erosion rate of 3.2 cm·a−1 derived from the DEMs mapping, but only partially accounting for the dredging amount of 1994–2006, when the total dredging volume was 67 × 106 m3, equal to 5.9 cm·a−1.

Anthropogenic effect on deposition dynamics of lake sediments based on 137Cs and 210Pbex techniques in Jiuzhaigou National Nature Reserve, China

Abstract: Radionuclide dating techniques characterized by 137Cs and 210Pbex have recently been applied in the study of lake sediments around the world. In this study, a chronological series of sediment cores was established based on 137Cs and 210Pbex analyses along with the evaluation of sediment properties, such as particle size distribution, total organic carbon (TOC), carbonate content, and acid-insoluble residue, to study sediment accumulation rates, sediment sources, and responses to human activities in the Jiuzhaigou National Nature Reserve in southwestern China. In terms of the particle size distribution of sediments, silt content was the highest, and clay and sand contents were relatively low. The sediments displayed high TOC contents because of the significant amounts of vegetation grown in the lakes. The carbonate content was also high due to the overall geological background of carbonates in Jiuzhaigou. Carbonate content tended to decline from top to bottom in the sediment cores, whereas the acid-insoluble residue tended to increase. These results suggested that the depth variation of the environmental parameters of the sediments in two lakes in Jiuzhaigou would correspond to each other. The results indicated that the sediment rate of Jiuzhaigou was generally high with strong siltation, indicating that serious soil loss was induced by intensive human activities in the basin over the past decades. The increases in the mass accumulation rate, contents of acid-insoluble residue, and mean particle size during the periods of 1840–1900s, late 1930s-early 1950s, 1966–1978, and 2003–2006 revealed the occurrence of severe soil and water loss as a result of extensive agricultural expansion, large-scale deforestation, and road construction in Jiuzhaigou. The deposition rate and the properties of lacustrine sediments could reflect the significant impact of human activities on lake sedimentation during Jiuzhaigou’s history.

Bottom topography, recent sedimentation and water volume of the Cerro Prieto Dam, NE Mexico

Abstract: The Cerro Prieto dam, a relatively small water reservoir in NE Mexico, is one of the main resources of potable water for Monterrey, a city with a population of about four million inhabitants. A high resolution seismic study using non-linear parametric sub-bottom echo-sounder SES-2000 was carried out in this water reservoir. High resolution acoustic data interpretation shows that the thickness of recent sediments due to siltation of the reservoir reaches 3.5-4.0 m. It shows a high recent sedimentation rate (1-2 up to 14 cm/ year). Based on the echo-sounder data, the first bathymetric map and a digital model of recent sediment thickness were designed. A significant (5-12%) difference between the volume capacity value used by National Commission of Water (CNA) and acoustic survey results was revealed. Differences between the CNA and acoustic data indicate storage losses from 12-17 up to 30 million cubic meters. The results obtained through study such as this one, could be useful to improve a water resources management.

Siltation of the reservoir of vea irrigation dam in the bongo district of the upper east region, ghana

Abstract: The Vea Irrigation Dam was constructed in 1980 to promote the production of food crops in the dry harmattan season. Thirty three years after construction, this study was conducted to assess the level of siltation in the reservoir and farming practices that impacts siltation within the catchment. Ten soil profiles, five on either banks of the reservoir and each of surface dimensions 1.2 m x 1.2 m were dug in the reservoir 30 m away from the water to ascertain the depth of soil sediments. Average depth of sediments was multiplied by the area of reservoir to obtain the volume of deposited sediments, from which annual depositions were estimated. Eighty (80) farmers in the four fringe communities within the catchment (Vea, Gowrie, Kunkua, and Kuyelingo) were purposively sampled and interviewed. At an average depth of 1.1 m, total deposit of about 140000 m 3 of sediments into the reservoir should be a cause for concern. Conventional tillage and continuous grazing, practiced by majority of farmers along the steep slope of the dam’s upstream have direct influence on erosion and hence siltation of the reservoir. High intensity rainfall with high kinetic energies, recorded in the months of June, July, August and September results in considerable level of detachment of the already erodible soil aggregates, which contributes to erosion and subsequent siltation of the reservoir. Whilst vegetative cover reduces direct impact of rain drops, these are scanty and scattered: exposing the bare soil to erosion. In order to save the dam and its reservoir from short lifespan as a result of massive siltation, soil conservation measures, and Best Agricultural Management Practices on watersheds are recommended to local farmers within the catchment area.

Integrated Evaluation of Soil Erosion Hazard and Risk Management in the Oued Beht Watershed Using Remote Sensing and GIS Techniques: Impacts on El Kansra Dam Siltation (Morocco)

Abstract: The initial state of the Oued Beht watershed (430,728 ha) is characterized by a socio-ecological vulnerability associated to the water erosion risk. Especially, the consequences are chained and the soil loss alters its hydrological behavior and its ability to protect functional and structural challenges (good land, El Kansra dam, agricultural activities). In this perspective, this study suggests a methodology, reproducible and generalizable, to assess the natural water erosion risk (R). The approach used is based on spatial processing technology of information to develop a spatial database and geographic information system (GIS) concerning biophysical and topoclimatic parameters in the Oued Beht watershed. Thus, the risk analysis is obtained by combining thematic maps of Susceptibility (S) and potential Consequences (C). Although, the spatial analysis of maps obtained reveals the extent of susceptibility involving land degradation, with the potential risks, which generated a decrease in the storage capacity of El Kansra dam (?3.03 Mm3/year). The results show that erosion is active on more than three quarters (3/4) of the watershed, and a considerable loss of land with 8.36 Million tonnes per year. In this way, flood analysis and study of hydrometeorological events identified the vulnerability of flood sites (hot-spot) contributing at 77% of El Kansra siltation dam. Therefore, the consequence assessment is obtained by identifying risk elements and estimating potential damage coefficient, which represents the financial gap flow affecting the socio-economic context due to the erosion impacts.

Impact of suspended sediment load on the silting of SMBA reservoir (Algeria)

Abstract: The phenomenon of suspended sediment load is very complex in Mina River basin because of its important soil heterogeneity, vegetation deficiency and rainfall variability in time and space. The methodological approach adopted in this paper consists of finding a regressive power model, which may explain better the suspended sediment discharge as a function of the flow discharge collected at Wadi El-Abtal and Sidi AEK Djilali hydrometric stations by studying this relation at various temporal scales: daily, annual, monthly and seasonal. The obtained monthly power relations, explaining the greatest part of the variance, lead to interpolate, extrapolate and analyse suspended and bed loads deposited on Sidi M’hamed Ben Aouda (SMBA) reservoir since being in service in 1977/1978. These allow authors to find relations between specific erosion and effective rainfall and propose some solutions for river basin managers and policy makers to reduce the silting of SMBA reservoir.

Sedimentation assessment in a multipurpose reservoir in Central Kerala, India

Abstract: Dams and their reservoirs, constructed to manage the water scarcity problems of a region, sometimes lose whole or part of their functionality due to sedimentation. This issue, seen as a negative impact as far as reservoir life and its purpose is concerned, can be a boon to the construction industry, by providing a highly demanding construction material in the form of sand dredged from the reservoirs. Malampuzha reservoir, a multipurpose reservoir in the South Indian state of Kerala, is also losing considerable part of its storage due to siltation. This paper assesses the rate of sedimentation in Malampuzha reservoir, through bathymetric survey and suggests measures for utilization of the removable sediment. Our analysis has shown that the reservoir capacity is reduced from 226 to 205.19 Mm3; a reduction in capacity of 20.81 Mm3 in 55 years. The rate of sedimentation of the reservoir is estimated as 16.95 mm/year. The dead storage capacity of the reservoir has reduced to 47.5 % from the original at present. The composition of deposited sediments is also identified, based on which its productive use is recommended.

Sources and trace element geochemical characteristics of the coarse sediment in the Ningxia-Inner Mongolia reaches of the Yellow River

Abstract: Siltation of coarse sediment in the river channel is the main cause of flooding and dike burst on China’s Yellow River, and the loess are thought as the coarse sediment sources of the lower reach of the Yellow River. The Ningxia-Inner Mongolia reaches of the Yellow River flow through an extensive area of aeolian desert, with flood events occurring frequently in this region. In this paper, we investigate the trace element contents of the coarse sediment in the Ningxia-Inner Mongolia reaches of the Yellow River. The main chemical components of the coarse sediments consist of 28 trace elements. Correlation analysis and factor analysis of 21 of these trace elements indicates that Ti and Zr are stable indicators of the coarse sediment sources. Comparing the spatial distribution of some of the main trace elements to major sources and riverbed sediment of the main reaches of the Yellow River suggests that the coarse sediments deposited in the Ningxia-Inner Mongolia reaches are mostly controlled by the local sediment sources. The results of R-factor analysis further proved that desert sand, riverbank material, and the Ten Tributaries are the primary sources of the coarse sediment in the Ningxia-Inner Mongolia reaches of the Yellow River.

Impact of water and sediment discharges on subaqueous delta evolution in Yangtze Estuary from 1950 to 2010

Abstract: In order to determine how the subaqueous delta evolution depends on the water and sediment processes in the Yangtze Estuary, the amounts of water and sediment discharged into the estuary were studied. The results show that, during the period from 1950 to 2010, there was no significant change in the annual water discharge, and the multi-annual mean water discharge increased in dry seasons and decreased in flood seasons. However, the annual sediment discharge and the multi-annual mean sediment discharge in flood and dry seasons took on a decreasing trend, and the intra-annual distribution of water and sediment discharges tended to be uniform. The evolution process from deposition to erosion occurred at the −10 m and −20 m isobaths of the subaqueous delta. The enhanced annual water and sediment discharges had a silting-up effect on the delta, and the effect of sediment was greater than that of water. Based on data analysis, empirical curves were built to present the relationships between the water and sediment discharges over a year or in dry and flood seasons and the erosion/deposition rates in typical regions of the subaqueous delta, whose evolution followed the pattern of silting in flood seasons and scouring in dry seasons. Notably, the Three Gorges Dam has changed the distribution processes of water and sediment discharges, and the dam's regulating and reserving functions can benefit the subaqueous delta deposition when the annual water and sediment discharges are not affected.

Pollution and Siltation of Rivers in the Western Highlands of Cameroon: a Consequence of Farmland Erosion by Runoff

Abstract: . Water is one of the most important natural resources in maintaining the balance of global ecosystems. Water is the engine of life but she can also devastate. Subject of controversy, lusts, strategic issues, water is currently raising awareness of the need to preserve this precious commodity which directly affects food security, socioeconomic development and health. Sustainable management and protection of water resources must then involve all social strata. In one community, water is the source of life, source of peace, source of development, but it can also be a main source of conflict and instability. The western highlands of Cameroon are an agro-ecological zone of high population density and rapid population growth. In this area where land tenure is quite complex, farmers cultivate steep slopes (> 25%) for the production of vegetable crops. In order to facilitate the turning of the land, these farmers prepare seedbeds flat or forming ridges along the steepest slope, two methods of land preparation that do not include any measure of water conservation. With these methods of land preparation favouring runoff, pesticides and fertilizers applied in cultivated plots are transported by runoff or transfer of sediments to rivers; this transfer negatively affects an agricultural function which is environmental protection therefore water. To establish liability of agricultural practices in pollution and siltation of rivers, we studied a section of the main river of MA©loh watershed whose width varies between 2 and 3.5m on a twisty length of 300m. This study showed that tied ridging reduced siltation of rivers by 72%; so this is an effective technique to fight against water pollution in mountain agriculture.