Showing papers on "Siltation published in 2012"

Organic matter dynamics and stable isotope signature as tracers of the sources of suspended sediment

Abstract: . Suspended sediment (SS) and organic matter in rivers can harm brown trout Salmo trutta by affecting the health and fitness of free swimming fish and by causing siltation of the riverbed. The temporal and spatial dynamics of sediment, carbon (C), and nitrogen (N) during the brown trout spawning season in a small river of the Swiss Plateau were assessed and C isotopes as well as the C/N atomic ratio were used to distinguish autochthonous and allochthonous sources of organic matter in SS loads. The visual basic program IsoSource with 13Ctot and 15N as input isotopes was used to quantify the temporal and spatial sources of SS. Organic matter concentrations in the infiltrated and suspended sediment were highest during low flow periods with small sediment loads and lowest during high flow periods with high sediment loads. Peak values in nitrate and dissolved organic C were measured during high flow and high rainfall, probably due to leaching from pasture and arable land. The organic matter was of allochthonous sources as indicated by the C/N atomic ratio and δ13Corg. Organic matter in SS increased from up- to downstream due to an increase of pasture and arable land downstream of the river. The mean fraction of SS originating from upper watershed riverbed sediment decreased from up to downstream and increased during high flow at all measuring sites along the course of the river. During base flow conditions, the major sources of SS are pasture, forest and arable land. The latter increased during rainy and warmer winter periods, most likely because both triggered snow melt and thus erosion. The measured increase in DOC and nitrate concentrations during high flow support these modeling results. Enhanced soil erosion processes on pasture and arable land are expected with increasing heavy rain events and less snow during winter seasons due to climate change. Consequently, SS and organic matter in the river will increase, which will possibly affect brown trout negatively.

Reservoir siltation and sediment yield in the kruger national park, south africa: a first assessment

Abstract: Human-induced soil erosion is a widespread phenomenon in South Africa, and soil erosion rates reported are among the highest in the world. In addition to human disturbance, unfavourable environmental conditions are mentioned to explain the situation. But data on ‘natural’ erosion from undisturbed sites are rare. This paper presents the first assessment of sediment yield as an integrate measure of erosion, deposition and sediment transport from five catchments located entirely within Kruger National Park (KNP). KNP has been spared from agricultural development for a century and represents a near to natural geo-ecosystem in the semi-arid savanna biome. Sediment yield estimates are based on a survey of post-dam deposits in five reservoirs located in the south-eastern part of KNP. Reservoir lifetime ranges from 40 to 60 years and the size of the catchments from 8 to 100 km2. The results show distinct relations of long-term average sediment yield (SY) and area-specific sediment yield (SSY) with catchment size. Despite the unfavourable semi-arid environmental conditions, SY is comparatively low. SY varies from 130 ± 45 t y−1 for the 8 km2 catchment to 1130 ± 230 t y−1 for the 100 km2 catchment. SSY is 55 ± 15 t km−2 y−1 for catchments of 12 ± 3 km2 and 11 ± 2·4 t km−2 y−1 for the 100 km2 catchment. The latter finding suggests that decrease of SSY with increasing catchment size is not attributable to human disturbance only. However, further research is necessary to improve and enlarge the database and to verify first results and hypothetical conclusions. Copyright © 2012 John Wiley & Sons, Ltd.

Quantitative study on influences of terraced field construction and check-dam siltation on soil erosion

Abstract: To study the influences of terraced field construction and check-dam siltation on soil erosion of a watershed, we built a simplified watershed model for the Loess Plateau hilly-gully region including terraced fields, slope farmlands, steep-slope grasslands, and dam farmlands, and defined three states of watershed (i.e., pioneer, intermediate, and climax stages, respectively). Then, the watershed soil erosion moduli at various stages were studied by using a revised universal soil loss equation. Our results show that the pioneer and climax stages are the extreme states of watershed soil-and-water conservation and control; in the pioneer stage, the soil erosion modulus was 299.56 t·ha−1·a−1 above the edge of gully, 136.64 t·ha−1·a−1 below the edge of gully, and 229.74 t·ha−1·a−1 on average; in the climax stage, the soil erosion modulus was 39.10 t·ha−1·a−1 above the edge of gully, 1.10 t·ha−1·a−1 below the edge of gully, and 22.81 t·ha−1·a−1 on average; in the intermediate stage, the soil erosion modulus above the edge of gully exhibited an exponential decline along with the increase in terraced field area percentage, while the soil erosion modulus below the edge of gully exhibited a linear decline along with the increase in siltation height.

Identifying Major Stressors: The Essential Precursor to Restoring Cultural Ecosystem Services in a Degraded Estuary

Abstract: Worldwide estuaries have been subject to multiple and escalating anthropogenic impacts which have resulted in the loss of many ecosystem goods and services including: commercial activities, navigation and marine transportation, recreational and landscape values, and flood control and biodiversity support. An example of these losses is provided in an urban-industrial region of an estuary in northern Tasmania, Australia, where excessive silt deposition has resulted in almost complete loss of the channel at low tide. The causes of siltation have long been attributed to poor watershed management and high concentrations of flocculated and suspended sediments transported upstream by asymmetrical tides. However, historical analysis of anthropogenic changes in estuarine and riverine processes revealed different stressors. These included the decrease in the tidal prism and hence regime equilibrium, brought about by channel infilling and draining of tidal wetlands to create dry land for urban and agricultural uses, and the reduction and redirection of freshwater inflows for the generation of hydroelectricity. Watershed sediment loads exerted a relatively minor role in the estuarine equilibrium, which is solely dependent on tidal flows and river discharges for maintenance of stable cross-sectional areas. Sustainable remediation measures include increasing the tidal prism through the restoration of dynamic river flows and reconnection and restoration of tidal wetlands. However, the former will not be achievable without changes in major provisioning services, particularly the use of water to generate hydroelectricity. This study emphasises the importance of identifying stressors as the basis for examining the potential to reduce the trade-offs between the multiple ecosystem services provided by an estuary and its tributaries, particularly between provisioning and cultural ecosystem services, within a rehabilitation context.

Recent sedimentation rates in Garaet El Ichkeul Lake, NW Tunisia, as affected by the construction of dams and a regulatory sluice

Abstract: Ichkeul National Park, NW Tunisia, is a UNESCO Biosphere Reserve. Garaet El Ichkeul Lake is known for its seasonal variability in water level and salinity. In recent decades, the waterbody has been affected by the construction of new hydraulic structures. To reduce the impacts of dams and to maintain the sustainability of the ecosystem, a sluice was built at the outlet of the lake, and it operated for the first time in 1996. This paper describes an investigation of recent sedimentation dynamics in Ichkeul Lake, determined by radiometric dating of sediment cores. A sediment core was collected with a UWITEC gravity corer at the deepest, central part of the lake in August 2009. Specific activities of unsupported lead-210 (210Pb) and caesium-137 (137Cs) were measured in the core, enabling calculation of recent sediment accumulation rates (SAR). Published radiometric data from nearby sediment cores, collected in 1997 and 1982, provide a comparison. The measured excess 210Pb inventory was 5300 ± 500 Bq m−2, leading to an estimation of constant flux of 165 ± 16 Bq m−2 yr−1, a value higher than the best estimate for local atmospheric fluxes (123 ± 12 Bq m−2 yr−1) and the flux estimated from the core collected in 1982 (48 Bq m−2 yr−1). The 137Cs inventory was 3550 ± 120 Bq m−2, two times higher than the historical 137Cs atmospheric deposition in the area. The 137Cs profile displayed a distinct peak, but the 137Cs depth-distribution did not follow the pattern expected from atmospheric deposition. Application of the constant rate of supply (CRS) model, with the reference point method, produced a chronology and SAR values comparable to those found in previous work. The whole 137Cs profile was quantitatively reconstructed from the historical records of atmospheric deposition, using the system-time-averaged (STA) model. The CRS and STA models provide consistent sediment accumulation results for the whole data set, considering the time resolution of the chronology (~6 years) and analytical uncertainties. Results from cores sampled in 1982, 1997 and 2009 reveal an increasing SAR trend, from ~0.25 g cm−2 yr−1 in the early 1940s to ~0.67 g cm−2 yr−1 at present. In the 13 years since installation of sluice gates at Tinja, SAR in the central Ichkeul Lake has not declined. Thus, if siltation continues at the present rate, shallowing of the lake will seriously affect the hydromorphology and ecology of this important lake.

Temporal variations of water discharge and sediment load of Huanghe River, China

Abstract: Based on the data from gauging stations, the changes in water discharge and sediment load of the Huanghe (Yellow) River were analyzed by using the empirical mode decomposition (EMD) method. The results show that the periodic oscillation of water discharge and sediment load of the Huanghe River occurs at the interannual, decadal, and multi-decadal scales, caused by the periodic oscillations of precipitation, and El Nino/Southern Oscillation (ENSO) af- fects water discharge by influencing precipitation distribution and contributes to periodic varations in precipitation and water discharge at interannual timescale. The water discharge and sediment load of the Huanghe River have decreased since the 1960s under the influence of precipitation and huamn activities, and human activities attribute more than precipitation to the reduction in the water discharge and sediment load, furthermore, water abstraction and water-soil conservation practices are the main causes of the decrease in water discharge and sediment load, respectively. The reduction in sediment load has directly impacted on the lower reaches of the Huanghe River and the river delta, causing considerable erosion of the river channel in the lower reaches since the 1970s along with River Delta changing siltation into erosion around 2000.

Challenging established narratives on soil erosion and shifting cultivation in Laos

Abstract: The official environmental discourse in Laos describes a “chain of degradation” stretching from upland shifting cultivation, increased runoff and soil erosion to the siltation of wetlands and reservoirs. This perspective has had wide-ranging impacts on rural development policy which, in the uplands, has long favoured forest conservation over agriculture. Integrating soil erosion and water sediment data with local perceptions of land degradation in an upland village of northern Laos, this study tests the validity of the official environmental discourse. Biophysical measurements made in a small agricultural catchment indicate a significant correlation between the spatial extent of cultivation and soil erosion rates. However, sediment yields recorded at the outlet of the catchment highlight relatively low levels of off-site sediment exportation. Furthermore, farmers' perceptions suggest that local land degradation issues and crop yield declines could be less related to soil erosion than to agricultural land shortage, increased weed competition, and fertility losses resulting from the intensification of shifting cultivation. The study concludes that a better understanding and management of land degradation issues can be achieved by developing more inclusive and scientifically-informed approaches to environmental perceptions and narratives. (Resume d'auteur)

Relative Sea Level Changes and Worsening Floods in the Western Pampanga Delta: Causes and Some Possible Mitigation Measures

Abstract: Despite declining rainfall, flooding continues to worsen around the northern end of Manila Bay. In Pampanga, flooding is enhanced by siltation of streams by sediments from the 1991 Mt. Pinatubo eruption, but the entire region has always been flood-prone, and Bulacan and Metro Manila, far from Pinatubo, also suffer worsening floods. Urbanization and deforestation are blamed, but have less impact than local sea level rise. Global warming causes the ocean surface to rise only 2 mm/yr; localized subsidence of the region from both natural and anthropogenic causes is an order of magnitude faster. Movements associated with faulting and the Pinatubo and Taal volcanoes probably are less important than the compaction of deltaic sediments under their own accumulating weights. All natural causes of subsidence are dwarfed by the contribution from excessive groundwater withdrawal, which greatly facilitates natural sediment dewatering and compaction. Several centimeters per year of documented subsidence at well sites have been corroborated by recent resurveys of elevation benchmarks established in the 1950s. In the short-term, flooding can be ameliorated by restoring original channel widths and by modifying current aquaculture practices. In the longer term, reforestation should also help by increasing infiltration and decreasing erosion and siltation. Flooding will inexorably continue in the coming century, however, both from natural compaction of delta sediments and from global sea level rise. Subsidence will continue to accelerate if the use of groundwater by the growing population is not regulated and reduced.

Sediment delivery from right bank valleys to mosul reservoir, iraq

Abstract: Mosul dam reservoir is the biggest reservoir on the River Tigris with 11.11 billion m3 storage capacity located at the northern part of Iraq. The dam is used for irrigation, hydropower generationand flood control. Siltation of the reservoir and sediment delivery from the valleys to the reservoir was not measured since the operation of the dam in 1988. Sediment accumulation in its reservoir can effect the dam operation (pumping station, hydropower plantsand bottom outlets) and it will defi- nitely shorten the life span of the dam. In this study, the Soil and Water Assessment Tool (SWAT) under Geographical Information System (GIS) was applied to simulate the yearly surface runoff and sediment load for the main three valleys on the right bank of Mosul Dam Reservoir for the period 1988-2008. The result- ant values of the average annual sediment load are 42.7*103, ton. This implies that significant sediment load enters the reservoir from these valleys. Sediment accumulation can effect the dam operation (pumping station, hydropower plantsand bottom outlets) and it will definitely

A GIS-based estimation of soil loss in the Densu basin in Ghana

Abstract: Distributed erosion simulation models are useful in evaluation of different strategies for land-use and soil management improvement in watersheds. The increased soil erosion in Densu basin of Ghana has led to siltation of the river channel that is causing flooding in some parts of Accra, Ghana. The most urbanized basin in Ghana, Densu, supplies water to 600,000 people, with agriculture employing about 40% of the active population. A PCRaster GIS soil loss risk maps have been developed for Densu basin using models of Universal Soil Equation (USLE) and Revised Universal Soil Equation (RUSLE). Soil loss factors such as rainfall erosivity, soil erodibilty, slope and slope length were also mapped for the basin. The model predicted average, minimum and maximum annual soil loss rates of 2.2, 0, and 63 t ha–1y–1 , respectively, indicating that some areas in the basin are above tolerance level of 5.0 t ha–1yr–1. The total soil loss was 756,507 tonnes per hectare per year. Among the soil types Lixisols experienced the highest soil loss of 402,080 t ha–1 yr–1 with Plinthosols experiencing the lowest soil loss of 64 t ha–1 yr–1. Among the administrative districts in the basin Suhum, Kraboa and Coaltar experienced the highest absolute soil loss of 216,957 t ha–1 yr–1 while Fanteakwa experienced the highest average soil loss of 4.5 t ha–1 yr–1. The results can serve as data and information to water resources managers and soil conservationists.

Reduction of the Storage Capacity of two Small Reservoirs in Jordan

Abstract: Scarcity of water resources in the Middle East represents a prime factor in the stability of the region and its economic development and prosperity. Accordingly, augmenting water is considered very important. Therefore, building of dams is an important mean to achieve such a goal. Despite the fact that number of dams had been built but maintenance operations and reduction of siltation rates are still not up the standards. Two small reservoirs, north West Jordan, were investigated. Sad Wadi Alarab reservoir constructed in 1986 (storage capacity of 20x10 6 m 3 ). The second, Alghadeer Alabyadh, was constructed 1966(storage capacity 7 x10 5 m 3 ). The actual storage capacities of these reservoirs were calculated using echo-sounding traverses. Data obtained were used in special computer software to construct the bathymetric maps and calculate the existing storage volume. The results showed that the reservoir storage capacities were reduced at an average annual rate of 0.3 x10 6 and 1.7 x10 4 m 3 respectively. This implies that Sad Wadi Alarab reservoir will be filled with sediment within 38 years, while Alghadeer Alabyadh reservoir is already filled with sediment now. Bottom sediments of the reservoirs were collected and analyzed. In all the cases, sand, silt and clay were the dominant sediment components.

The impact of gaza fishing harbour on the mediterranean coast of gaza

Abstract: The Mediterranean coast of Gaza strip, which is covered about 40 km in length, is rich by coastal resources. The development that occurred along the coastal lines has led to the host of problems such as increased erosion, siltation, loss of coastal resources and the destruction of the fragile marine habitats. In order to conserve the depleting coastal resources, the changes due to development and associated activities must be monitored. Studying the temporal pattern of shoreline change is considered one of the most effective means of monitoring the cumulative effects of different activities. An attempt was made to study the impact of Gaza harbour on shoreline displacement along 6 km. This paper was intended to detect changes of coastal area in Gaza city to provide future database in coastal management studies. The analysis was carried out using image processing technique (ERDAS) and Geographical Information System platform. The variation during 38 years in the shoreline along the Gaza coast was determined by analyzing MSS, TM and ETM Landsat images from 1972 to 2010. The analyses identified the erosion and accretion patterns along the coast. The shoreline was advanced south of the Gaza fishing harbor, where the wave-induced littoral transport was halted by southern breakwater and the annual beach growth rate was 15,900 m2. On the downdrift side of the harbor, the shoreline was retreating and beaches erode at an annual rate of -14,000 m2. This study was emphasized that the coastal band is considered as a critical area, it is therefore necessary to monitor coastal zone changes because of the importance of environmental parameter and human disturbance. In particular, the projections of future shoreline erosion and accretion rates are considered important for long-term planning and environmental assessment for a variety of projects, including the construction and tourism facilities

Short-term macroinvertebrate recruitment and sediment accumulation: A novel field chamber approach

Abstract: Stream-deposited sediment is one of the major stressors affecting stream biota. Several methods exist to quantify stream sediment embeddedness, but they are relatively qualitative and operationally defined. The authors developed a short-term in situ embeddedness chamber method to measure aquatic insect recruitment and associated sediment accumulation in a more quantitative, better replicated manner. With sediment accumulation and aquatic insect recruitment as endpoints, three exposure periods were evaluated (4, 7, and 14 d) on a low-order stream (Honey Creek, New Carlisle, Ohio, USA) and a medium-order stream (Stillwater River, Covington, Ohio, USA). Chamber results show significant positive correlations between newly deposited fine sediment and insect recruitment. Embeddedness was also measured using the more conventional techniques of the Burns method and the U.S. Geological Survey National Water Quality Assessment Program method. This in situ chamber method allows for increased experimental options for assessing the stress of embeddedness and siltation on benthic communities and may prove useful for investigating the resilience of benthic communities after disturbances. Environ. Toxicol. Chem. 2012;31:1098-1106. # 2012 SETAC Keywords—Artificial substrate Benthic macroinvertebrates In situ Recruitment Embeddedness

Quantitative study on influences of terraced field construction and check-dam siltation on soil erosion

Abstract: 为了学习 terraced 的影响，在一个分水岭的土壤侵蚀上回答建设和检查水坝 siltation ，我们包括 terraced 领域，斜坡农田，陡峭斜坡的草地，和水坝农田为黄土高原多山溪谷的区域造了一个简化分水岭模型，并且定义分水岭的三个状态(即，先驱，中介，和高潮阶段，分别地)。然后，在各种各样的阶段的分水岭土壤侵蚀 moduli 被使用一个修订通用土壤损失方程学习。我们的结果证明先驱和高潮阶段是分水岭 soil-and-water 保存和控制的极端状态；在先驱阶段，土壤侵蚀模量是 299.56 t 牵 ? 畢湲 ? 潦敲瑳 ? 潦 ? 敲汣浡瑡潩 ? 氠慥楤杮琠? 桴 ? 敤牣慥敳漠 ? 牡潢 ? 潰汬湥愠 ? ‵慫?? 湩挠牯 ? 牡慥? 景琠敨夠湡獧慨 ? 畣瑬牵吗？

Coastal Embayment Long-Term Erosion/Siltation Associated with P-A Relationships: A Case Study from Jiaozhou Bay, China

Abstract: Liu, Y.; Wang, Y.P.; Li, Y.; Gao, J.; Jia, J.; Xia, X., and Gao, S., 2012. Coastal embayment long-term erosion/siltation associated with P-A relationships: A case study from Jiaozhou Bay, China. Journal of Coastal Research, 28(5), 1236– 1246. Coconut Creek (Florida), ISSN 0749-0208. The sedimentary environment of a large coastal embayment, Jiaozhou Bay, eastern China, in terms of erosion/siltation, has been assessed on the basis of seabed bathymetry and coastline data sets from sea charts (1936–2002) and Landsat-5 TM images (1986–2011). Nine types of sedimentary environment are identified according to the sedimentation rate. The results indicate that slow siltation was generally present from 1936 to 1963, with exceptions of some patchy, slightly eroding areas within the embayment. Transformation to a slow erosion pattern occurred in the main channels over the central embayment in 1963, and such a situation continued until 1982. Subsequently, since 1986, most of the coastlines extended toward the sea at a rate of 10 1 –10 2 my 21 ; this was mainly attributable to human activities, including reclamation over the NW tidal-flat and harbour construction along the east and south coastlines. Using the same data set, patterns of changes in tidal prism and deposition rate within the entrance channel were established. An equivalent friction coefficient (K) is proposed to evaluate the P-A relationship of the large tidal inlets in Jiaozhou Bay. The K value increases gradually over time, indicating a trend toward stable equilibrium in Jiaozhou Bay. This coefficient can be used to examine the status of morphological stability and equilibrium of coastal embayments.

Coastline change detection of the Yellow River Delta by satellite remote sensing

Abstract: We used remote sensing and geographic information system to extracted coastlines of the Yellow River Delta from muti-temporal Landsat TM/ETM+ images(1989~2009),and analyzed the length and area variations of the Yellow River DeltaThe shape and length of the coastline in the Yellow River Delta had significantly changed since 1989Coastal erosion occurred in the Diaokou Estuary area where the shoreline was not protected by damThe whole coastline in Qingshuigou area extended seaward because some parts of it suffered from erosionCoastline in Shenxiangou area changed little because most parts of it were protected by damThe area of the Yellow River Delta increased from 1989 to 2009,though it decreased from 2006 to 2009The annual average of area that erosion occurred or siltation changed from small to largeThe Yellow River Delta was in expansion in the last 20 yearsBut from 2006 to 2009,the area of the Yellow River Delta was decreased and more area had been in erosion or siltation statusDischarge and sediment concentration of the Yellow River,precipitation and water diversion were main factors that influenced the area change of the Yellow River DeltaArtificial dams were able to resist the invasion of sea wave and to maintain the stability of coastlineThe result of this work is contributed to the management and reservation of coastal environment

Four terrestrialization characteristics of Baiyangdian Lake, China

Abstract: Terrestrialization is the process by which a water body changes from a wetland to a terrestrial ecosystem. Many factors contribute to the process, including climate change and macrophyte expansion. Among such factors, water level and eutrophication result in quantitative and qualitative changes on macrophyte communities, while expansion of macrophytes can accelerate the rate of terrestrialization by bioaccumulation. The siltation of sand also greatly contributes to terrestrialization. Here, the water quality, water level, siltation of sand, and vegetation of Baiyangdian Lake were analyzed to assess the terrestrialization characteristics of this lake and understand its terrestrialization process.

Grain size distribution and transportation trends of bottom sediments in the sand ridge field of the south yellow sea,china

Abstract: Grain size distribution and end-member-modeling algorithm analysis(EMMA) were conducted for the 117 bottom sediments taken from the radial sand ridge field(RSRF) of the South Yellow SeaSediment sources,transportation pattern and topography changes as well as the shifting of boundaries of the Yellow and Changjiang Rivers and their sediments diffusion pattern were studied for revealing the evolutionary trend of the radial sand ridge field and the siltation potential of the tidal flatsThe RSRF region is dominated by silt and sand,though there is distinguished lateral variationThere occur silty materials in the subaqueous delta of the abandoned Yellow River,sandy silts in the northern RSRF,silty sands in the central RSRF,fine sands in the radial sand ridges,and more silty materials in the southern RSRFThe results of EMMA reveal that coarse silts from the Abandoned Yellow River Subaqueous Delta(AYRSD) and the Changjiang River have a significant effect on the bottom sediments of the RSRFThe fine materials from the AYRSD have been transported southwards and northeastwards,and the fine materials from the Changjiang River delta transported northwards,whereas the fine sands in the central RSRF have been transported southwards up to the foreshore areaCompared with the samples recovered from the RSRF during the surveys in 1980s and 1990s,fine materials in the whole study area are reduced and the sediments getting coarser as the result,showing an obvious trend of erosion

Siltation and erosion processes on a tributary of lake itaipu due a dam reservoir

Abstract: It is known that sediments in the river have their origin from different sources. Therefore, the proportion that each source contributes to the mix varies over time and space, as a result of erosion processes that are ongoing in the basin of contribution. Within this context, both in human actions in urban and rural watersheds generate different rates of sediment production, but mainly with different characteristics or quality. Thus, the fluvial sedimentology should have a broad character within the study area and check all the possible influences of land use and soil. Hydrosedimentological processes are complex and include a disaggregation ("erosion" in the strict definition), transport, sedimentation, consolidation of sediments. Therefore, it is necessary more detailed studies of sediments and their interactions with the environment, considering it as a topic of interest to economic, social and ecological needs of a sustainable management, where they articulate an understanding of the physical and chemical properties of sediments with ecological and hydrological information of the water bodies receiver on a regional scale and thus evaluate the possible scenarios of pollution of water resources. This information will support in decision-making processes for managing the watershed and its water resources. Therefore, this project aims to determine the interference that a hydroelectric plant, together with the lack of proper management of the basin, can cause to the river morphology. The research is conducting a survey of sensitive areas to erode and the influence of a newly installed hydropower in a tributary of Lake Itaipu. Could notice that the removal of riparian vegetation is accelerating the erosion processes at various points of the river, but the agriculture system used in the rural area, without revolving of soil, has reduced the sediment load produced by this source. However, the retention of much of the coarse sediments by the new dam is creating an imbalance between the small amount of sediment transported after the hydroelectric and flow transport capacity. There are two cases occurring in a dam: 1) the dam upstream has a reduction of velocity and it start a process of sedimentation that will accelerate its siltation and reducing its useful life, 2) dam downstream has water velocity again and then initiate erosion process due the lack of sediments in the liquid mass. It can be concluded that changes of use and occupation of land in the watershed generate

Statistical modelling of suspended sediment transport in the Cherf drainage basin, Algeria

Abstract: This work deals with the main topic of the assessment of the Cherf drainage basin sediment yield based on available water discharge and suspended sediment concentration observations, and on the application of general and multivariate models. This study is also part of a broader effort aiming to predict reservoir siltation and future reliability. The 19 years of available sediment concentration data (1975/1976-1993/1994) is used to predict suspended sediment loads. From 1994, this drainage basin has shown a construction of a reservoir at its outlet (Cherf dam) for civil and industrial use. From that date, only monthly water volumes are used to estimate sediment yield in the reservoir. The methodology involved in this study is developed by a conventional sediment rating curve and a multiple regression model. The former method is investigated with the mean discharge classes derived from the recorded suspended sediment concentrations and water discharges for the Cherf drainage basin (1710 km²), prior to the reservoir construction. The later is based on rock type erodibility, mean annual runoff and basin area variables, and which is applied for the ungauged reservoir basin of 1735 km². For the rating curve model, a regression analysis is made between the instantaneous suspended sediment concentration (C) and the instantaneous water discharge (Q) based on all recorded data and seasonal ratings. Optimization of rating curve method is validated by comparing the predicted against observed values on scatter plots.

Predicting soil erosion risk at the Alqueva dam watershed

Abstract: Soil erosion is serious economic and environmental concern. Assessing soil erosion risk in the Alqueva dam watershed is urgently needed to conserve soil and water resources and prevent the accelerated dam siltation, taking into account the possible land-use changes, due to tourism development, intensification of irrigated farming and biomass production, as well as climate change. A comprehensive methodology that integrates Revised Universal Soil Loss Equation (RUSLE) model and Geographic Information Systems (GIS) with geostatistical techniques was adopted to study different land-use and management scenarios. The main objective of this study stage is to determine the soil erosion vulnerability of an agro-silvo pastoral system. The resultant soil erosion map shows an average of 14.1 t/ha/ year, with serious erosion risk (higher than 50 t/ha/year) in 4.3% of area. The highest values are associated mainly to high slopes and low vegetation. The final prediction maps for soil erosion and for each factor considered, can be used as a solid base to create a Decision Support System so as to provide specific procedures for decision-makers, promoting for sustainability of the ecosystems, reducing the risk of erosion and consequently increase lifetime of dam, under various land use and management scenarios

Influence of water and sediment regulation of the Xiaolangdi reservoir on the channel scouring and silting of lower reaches of the Yellow River

Abstract: The function of water and sediment transfer of Xiaolangdi Reservoir to the river erosion of the lower reaches of the yellow river has been analysed since 2002 and pointed out that the water and sediment transfer is benefit to the river erosion.However,according to recent data,river erosion amplitude is becoming smaller year after year.Therefore,proper evaluation of the function for current water and sediment transfer is quite necessary.

Influence of reclamation on macrobenthic community in the hengsha east shoal of yangtze river estuary

Abstract: Using ecological methods,we investigated the influence of reclamation on macrobenthic community in the terrestrial zone,the siltation zone and the nature tidal flat of the Hengsha East Shoal from April to December in 2011.The investigation showed that a total of 28 species were found.The rank of the number of macrobenthos species were the nature tidal flat(22 species) the siltation zone(19 species) the terrestrial zone(7 species).The rank of the dominant species were the nature tidal flat(6 species) the siltation zone(5 species) the terrestrial zone(2 species).The rank of the average abundance of macrobenthos were the siltation zone(118.68ind/m 2) the terrestrial zone(100.67ind/m 2) the nature tidal flat(57.67ind/m 2).The rank of the average biomass were the siltation zone(35.71g/m 2) the nature tidal flat(27.56g/m 2) the terrestrial zone(1.52g/m 2).The rank of the diversity indices(H',J,d) of macrobenthos were the nature tidal flat the siltation zone the terrestrial zone.The results of CLUSTER and MDS showed that there were significant differences among the three different habitats.The ABC curves also indicated that the macrobenthic community of the siltation zone and the terrestrial zone had been changed while the nature tidal flat were relatively undisturbed.In conclusion,reclamation has significantly changed the composition of macrobenthos.

A long-term numerical model of morphodynamic evolution and its application to the Modaomen Estuary

Abstract: Because of the influence of human activities, the evolution of the Modaomen Estuary is no longer a purely natural process. We used a long-term morphodynamic model (PRD-LTMM-10) to study the evolution of the estuary from 1977 to 1988. The model incorporated modules for riprap-siltation promotion and waterway dredging. The model can simulate the morphodynamic evolutionary processes occurring in the Modaomen Estuary during the period of interest. We were able to isolate the long-term influences of various human engineering activities and the roles of natural factors in estuarine evolution. The governance projects had the largest effect on the natural development of the estuary, resulting in larger siltation on the west side. Installation of riprap and reclamation of submerged land resulted in scouring of the main Hengzhou Channel causing deep trough out-shift. Severe siltation narrowed the upper end of the Longshiku Deep Trough.

Trapping of sediment in tidal estuaries

Abstract: An estuary is an ideal habitat for various aquatic species. At the same time, estuaries and adjacent rivers are used as fast navigation routes between the coastal and inland territories. The fast industrial development and the subsequent growth of cities and trade have led to large-scale anthropogenic alterations of estuarine systems. Estuaries are streamlined and deepened to ensure a safe navigation for larger ships. Dams are constructed to protect the farmland, households and industrial buildings from floods. Moreover, land reclamation, deforestation and various agricultural activities result in higher sediment and freshwater input into estuaries. All these activities lead to fundamental alterations of the hydro- and sediment dynamics, mixing and circulation processes within estuarine systems. An estuarine system, taken out of its natural balance, is always trying to restore this equilibrium or reach a new balance. This can result in, for example, an increased siltation such that the estuarine depth has to be constantly maintained via annual dredging activities. Engineering interventions are expensive and they create a substantial load on the local ecosystem, because a biological system cannot readjust to new conditions within a short period of time. Hence, these activities pose many problems from both the ecological and economic point of view. A proper understanding of estuarine processes is essential to minimize the negative consequences of human influence and to develop a long-term restoration and development plan for many problematic estuaries. The main objective of the thesis is to investigate physical mechanisms in the along-estuary direction that result in the trapping of suspended sediment in partially and well mixed tidal estuaries and to analyze the influence of individual mechanisms on the trapping location.

Predicting of Soil Loss in Tisovec Catchment, Slovakia

Abstract: Soil erosion is a major form of land degradation and has been recognized as a severe environmental problem since late 18 th century. In Europe soil erosion affects large areas and it is estimated that about 17 % of the total land area is affected. Sediments, originated by erosion, cause silting of water basins and they also affect water quality in reservoirs because they play an important role by being the ultimate sink of pollutants. Nowadays, it should be rather a preference to predict the erosion and its control. There are a lot of mathematical models for predicting of reservoir sedimentation. The most widely accepted and utilized empirical model for prediction of water erosion hazards throughout the world is Universal soil loss equation (USLE), developed by Wischmeier and Smith, which computes the average annual soil loss as the product of six major factors whose most likely values at a particular location can be expressed numerically. This paper is focused on the soil loss calculation using the USLE in the Tisovec catchment situated in the east of Slovakia, with emphasis on the suggestion of the crop/vegetation and management factor (the C factor) calculation, which is related to the land-use and represents the ratio of soil loss from a given vegetal cover. The determination of the average annual C factor is divided into five periods for each of the main periods of the cropping cycle. In accordance with the suggested calculation the total average annual soil loss from the arable land and also soil loss from the whole watershed of the Tisovec river is determined.

Morphodynamic evolution of the Xiaoqing River mouth: a Huanghe River-derived mixed energy estuary

Abstract: In an estuary, tidal, wave and other marine powers interact with the coast in different ways and affect estuary morphology as well as its evolution In the Huanghe (Yellow) River estuaries and nearby delta, there are many small sediment-affected estuaries with a unique morphology, such as the Xiaoqing River estuary In this study, we investigated the special evolution and genetic mechanism of the Xiaoqing River estuary by analyzing graphic and image data with a numerical simulation method The results show that NE and NE-E tide waves are the main driving force for sandbar formation Sediment shoals have originated from huge amounts of sediment from the Huanghe River, with consequent deposition at the Xiaoqing River mouth The lateral suspended sediments beyond the river mouth move landward Siltation takes place on the northern shoreline near the river mouth whereas erosion occurs in the south The deposits come mainly from scouring of the shallow seabed on the northern side of the estuary Storm surges speed up deposition in the estuary Development of the sediment shoals has occurred in two steps involving the processes of growth and further southward extension Although the southward shift increases the river curvature and length, the general eastward orientation of the estuary is unlikely to change Processes on the adjacent shorelines do not affect the development of the sediment shoals The study presents a morphodynamic evolutionary model for the Xiaoqing River estuary, with a long-term series cycle, within which a relatively short cycle occurs