Περίληψη σε άλλη γλώσσα
Soil erosion is a serious environmental problem in the world. Generally, with high erosion rates in many parts of the world, efforts should be directed towards curtailing its hazard. This requires quantitative data to identify critical areas where urgent conservation is needed especially in reservoir’s catchment areas. Traditional approaches based on runoff plots are expensive, time consuming and generate point-based data. Modern tools can be used instead to assess soil erosion. Understanding the hydrologic and topographic characteristics of reservoirs, and how those characteristics have changed over time, is essential for the effective management of these valuable resources. Reservoirs experience physical changes as a result of sediment deposition, shoreline erosion, and wind processes over time. The purpose of this study was the comparison of a current bathymetric survey with data collected during reservoir construction, in order to assess quantities and rates of reservoir sedimentat ...
Soil erosion is a serious environmental problem in the world. Generally, with high erosion rates in many parts of the world, efforts should be directed towards curtailing its hazard. This requires quantitative data to identify critical areas where urgent conservation is needed especially in reservoir’s catchment areas. Traditional approaches based on runoff plots are expensive, time consuming and generate point-based data. Modern tools can be used instead to assess soil erosion. Understanding the hydrologic and topographic characteristics of reservoirs, and how those characteristics have changed over time, is essential for the effective management of these valuable resources. Reservoirs experience physical changes as a result of sediment deposition, shoreline erosion, and wind processes over time. The purpose of this study was the comparison of a current bathymetric survey with data collected during reservoir construction, in order to assess quantities and rates of reservoir sedimentation and compare them with the rates predicted using three soil erosion models (RUSLE, RMMF and Gavrilovic) in reservoir basin area. Marathon reservoir in Attica, Greece was used as study area. The study was in cooperation with the Athens Water Supply and Sewerage Company (EYDAP), which owns the reservoir. Marathon reservoir is situated in Attica prefecture in central Greece, near Athens. It was created by the construction of a concrete dam, 54 meters high at the junction of the Charadros and Varnavas torrents. The construction began in 1925 and the project began its operation in 1931. The reservoir has a surface area of 2.4 square kilometers, a watershed of 117.8 square kilometers, a maximum capacity of 41 million m3 of water and an operational volume of 34 million m3. The reservoir operates as a backup source for the water supply system of the greater Attica region and as a primary regulating reservoir. A bathymetric survey was conducted in Marathon reservoir with a transducer (echosounder) equipped with a GPS unit. Approximately, 32000 readings were taken from the survey and corrections were made based on fluctuations in the water surface elevation that occurred during the survey. Once data were edited for obvious errors with survey software, the soundings were converted to elevation in meters and then exported to text files for import into GIS software. The individual points were then mapped to produce a Digital Elevation Model (D.E.M.) of the current morphology of the reservoir bottom. Digitalization of old maps produced a D.E.M. of the old morphology of the reservoir bottom, before the construction of the dam. The two DEMs were subtracted in order to estimate the volume of sediments that were placed in the reservoir. The volume of sediments were estimated 4,68 hm3. In order to evaluate the results of hydrographic survey, a geoelectric resistivity survey was also carried out by applying electrical soundings, which measured the electrical resistivity of sediments. Schlumberger array was applied in this study. Lots of vertical electrical soundings were measured along 2 profiles situated near the part of the reservoir, where Charadros torrent flows. The thickness of the sediments along the profiles was 4 to 7 m, which was the same that estimated with the bathymetric survey. Soil samples were collected directly from the basins of Charadros and Varnavas torrents based on maps and random sampling. Soil sampling was carried out with a soil auger from representative sites of the study area. Soil descriptions were made according to the FAO guidelines for soil description. Vegetation parameters were also collected, which included surface cover (%), plant canopy (%) and plant height (m) from the major land uses of the study area. Three soil erosion models: the Revised Soil Loss Equation (RUSLE), the Revised Morgan Morgan and Finney (RMMF) and Gavrilovic model were applied in a GIS environment. Results from chemical and physical soil laboratory analysis were used to estimate the K factor of RUSLE model and also many factors of RMMF and Gavrilovic model. Software was used to generate the slope length (LS) factor of RUSLE model. Estimates were made for surface cover factor (C) of RUSLE and RMMF models to compare with the typical values used in Greece. The results show that the predicted sediment volume from RUSLE and RMMF models was lower than that of the bathymetric survey. Gavrilovic model provide a good estimation of reservoir sediment volume, 4.69 hm3, almost the same prediction with hydrographic survey. The sediment volume prediction by the RUSLE and RMMF model was 1.64 hm3 and 0.29 hm3 accordingly. Overall, the Gavrilovic model performed better than RUSLE and RMMF models and is recommended for the study area.
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