Siltation

About: Siltation is a research topic. Over the lifetime, 1420 publications have been published within this topic receiving 20983 citations.

Combination of Satellite Images and Numerical Model for the State Followed the Coast of the Bay of Bejaia-Jijel

Abstract: Bay of Bejaia-Jijel extends over a length of 100 km with the presence of the ports, the beaches of rivers that discharge of the bay. This area characterized by strong economic activity, namely tourism and fisheries. However, severe erosion, high hydrodynamic activity and significant silting of ports affect this bay. Hence, the interest of this study, which tries to explain these phenomena, based on multisource data with multitasking models. First, we developed an algorithm that can convert satellite images in coastline vector. This technique applied to three images LANDSAT TM and OLI sensed in 1987, 2011; 2015. The multi-temporal monitoring coastlines show that the region suffered severe erosion. This erosion is 4.6 m / year for the period of 1987/2011 and 1.5 m / year for the period 2011/2015. To explain this phenomenon we interested to do a study of hydrodynamics using the SWAN software. We used a long time series of wind speed and direction to discern extreme cases in the region. For maximum wind, the significant wave height recorded very high values and a very active orbital current with a speed that exceeds 0.7 m / s. Numerical modelling has allowed us to explain the erosion but does not explain the speed difference coastline. To find the explanation of erosion speed difference between the two periods we consulted the administrative archive of the region. In the archive, the number of authorized hourglasses is, 12 in the 90s, but 36 quarries operate haphazardly. In this period the balance of suspended matter is completely unbalanced which promotes erosion. After 2008, these quarries were closed therefore the balance of the suspended material has improved and consequently coastal erosion has decreased.

The Effect of the Exceptionally Low Water Discharge on Sediment Characteristics of the Middle and Lower Yangtze River

Abstract: Based on meteorologic data, historical sediment data and current sediment data collected in October 2006 in the Yangtze River Basin, the analyses of monthly mean water and sediment discharge characteristics, meteorologic characteristics and the effect on suspended sediment concentration and suspended sediment grain diameter under the exceptionally low water discharge were carried out. The results showed that the sediment discharge decreased remarkably in the year of low water discharge, and the sediment discharge of flood season at Datong Hydrographic Gauging Station is only 19.8% of the mean value from 1985 to 2000. The mean suspended sediment concentration in October 2006 was 0.057 kg/m3 in the middle and lower Yangtze River, being only 20.6% of the mean value in October from 2003 to 2005. The mean suspended sediment median diameter in October 2006 was 4.8 m, being only 26.3% of the mean value of historic records and 41.8% of the annual mean value recently. The synthetic analysis of suspended sediment concentration, suspended sediment diameter and scouring/silting characteristics showed that the vertical water and sediment exchange was intense in the reach from Chenglingji to Hukou, where the channel adjustment has taken place frequently in recent years. Under the background of the exceptionally low water discharge and the completion of the Three Gorges Project, the contribution of the suspended sediment concentration from Dongting and Poyang lakes to the main stream was greater than that of any other lakes and tributaries, and the contribution of Poyang Lake was greater than that of Dongting Lake. The influence of the suspended sediment diameter from the Hanjiang River and Chaohu Lake to the main stream was greater than that of any other lakes and tributaries, while the influence of Dongting and Poyang lakes was relatively small.

Regional-Scale Modeling of Water Erosion and Sediment Yield in a Semi-Arid Context: Case Study of Ziz Upper Watershed in South-Eastern Morocco

Abstract: On-site, the main impacts of soil erosion worldwide are the decrease in the productivity of agricultural land and off-site, the significant problems are the siltation dam and increased risk of flooding.Many studies showed that several natural and anthropogenic factors have combined to aggravate soil erosion of Mediterranean agroecosystems, the climate, high sensitivity to soil erosion, the intensification of human activities, and cultural practices for centuries. The severity of this problem in Moroccan mountain agroecosystems has generated a demand for soil loss monitoring.Currently, much different erosion and sediment transport models are available. Spatially distributed erosion models are excellent tools to simulate and predict the spatial distribution of soil erosion and sedimentation under different conditions. In this study, WaTEM/SEDEM was applied in Ziz upper watershed (4435 km-2) in southeast Morocco. Model calibration and validation were performed based on 37 years of recorded sediment yield at the Hassan Addakhil's dam. This application estimates the total sediment supply from hillslopes to the river network at 2.02 106 t. yr-1 and specific sediment yield at 4.58 t ha-1yr-1. These results were lower than those recorded at the catchment outlet. Water erosion was the predominant process of soil redistribution, whereas tillage erosion was not significant. This simulation allows the primary sediment sources situate in the upper parts of the southwest-facing slope and some sinks within the catchment. The spatial distribution knowledge of erosion processes is a useful tool for proposing the best strategies for erosion control.

Impact of Wind on the Spatio-Temporal Variation in Concentration of Suspended Solids in Tonle Sap Lake, Cambodia

Abstract: Even though wind, water depth, and shear stress are important factors governing sediment resuspension in lakes, their actual relations to total suspended solids (TSS) distribution in natural environments have not been well elucidated. This study aims to elucidate the impact of the wind on the spatio-temporal variation of TSS in Tonle Sap Lake, Cambodia, during low-water (March and June, 50 mg/L) than that in the high-water season. The TSS concentration during the low-water season was empirically described by wind speed (W), water depth (D), and shear stress (τ_wave) with a function of W3, W3/D, and exp(W/D) or exp(τ_wave), depending on the location in the lake. The critical shear stress due to wind-induced waves at most of the places in the lake was higher than the total shear stress indicated. Sedimentation was predominant in December and June, and erosion (siltation) was dominant in March. Most of the siltation in March was dominant in the southern part of the lake.

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.