{"id":1047,"date":"2017-07-25T21:58:14","date_gmt":"2017-07-25T21:58:14","guid":{"rendered":"https:\/\/progroupe.net\/?p=1047"},"modified":"2018-11-28T12:24:22","modified_gmt":"2018-11-28T11:24:22","slug":"dredging-dewatering-1-sediment-origin","status":"publish","type":"post","link":"https:\/\/progroupe.net\/sk\/dredging-dewatering-1-sediment-origin\/","title":{"rendered":"DREDGING & DEWATERING: 1 Sediment origin"},"content":{"rendered":"

Almost every water area comes to a\u00a0stage when it is necessary to clean it from bottom sediments or other kind of pollution. Most of the time the realization and decision to remove the sediments and clean the area lies upon the governor of the water area. It is not a rare occasion when the governor himself is not sure how to carry out the cleaning in the most effective way. That is the main reason we decided to prepare several articles on the matter.<\/span><\/strong><\/p>\n

<\/a> Step by step we will reveal the sequence of actions to be taken even prior to the very cleaning and only after all these processes are cleared out of the table we can proceed to the description of the cleaning process itself. First, we will elaborate on the pollution by sediment, how it occurs and its consequences when the matter of pollution is not handled properly or at all.<\/span><\/p>\n

Pollution by Sediment<\/b><\/span><\/span><\/span><\/span><\/h1>\n

Soil erosion is a natural process accelerated by human activities. Each year, erosion of surface soil from river basins amounts to 60 billion tons, resulting in 24 billion tons of sediment flux to the oceans in the world and almost 25 billion tons of soil lost from agricultural land. From a global point of view, this currently represents a redistribution of soil resources by about 7\u00a0% each decade with multiple consequences.<\/span><\/p>\n

Geologic erosion varies in different places on the earth\u2019s surface because of differences in character of the minerals and of the climatic and vegetative conditions. The control over geologic erosion is often difficult to achieve because the natural conditions that have prevailed over centuries cannot be hanged significantly to effect any great reductions in erosion. Under certain local conditions, however, improvements can be made to reduce erosion. Accelerated erosion is brought about by human activity. It is not uncommon that erosion rates have increased by more than 100 times that of the geological erosion. Agricultural activities, urbanization, road and highway construction, mining operations, and altering runoff conditions and river control works are those which induce accelerated erosion.<\/span><\/p>\n\n\n\n\n<\/colgroup>\n\n\n\n
Fluvial erosion<\/span><\/td>\nAerial Erosion<\/span><\/td>\nGlacial erosion<\/span><\/td>\n<\/tr>\n
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Source: w<\/span>ww.arrc.com.au<\/span><\/p>\n<\/td>\n

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Source: www<\/span>.reference.com<\/span><\/p>\n<\/td>\n

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\"\"Source:www.beyondpenguins.ehe.osu.edu<\/span><\/p>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Sediments, created by erosion, are most often transported by water (<\/span>fluvial processes<\/span><\/span><\/a>), wind (<\/span>aerial processes<\/span><\/span><\/a>) and ice (<\/span>glaciers<\/span><\/span><\/a>). <\/span><\/p>\n

Water can wash sediment, such as gravel or pebbles, down from a creek, into a river, and eventually to that river’s delta. Deltas, river banks, dams, and the bottom of waterfalls are common areas where sediment accumulates. Reservoirs are built for many purposes, including flood control, water supply (for agriculture, industry, and urban usage), power generation, navigation and recreation, etc. As rivers carry sediment load, whether in large or small amounts, reservoir sedimentation occurs simultaneously with the impounding of water. Making full use of the benefits of reservoirs and developing appropriate measures to mitigate the side effects of dam construction are a necessity for the sustainable development of reservoirs. Many reservoirs have been filling with sediment, which depletes their storage capacity, and many have exceeded their life expectancy.<\/span><\/p>\n

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Capacity curve of Nyumba ya Munga reservoir in Tanzania (Belete K., et al, 2006)<\/span><\/em><\/p>\n

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There are three basic methods of sediment control for reservoirs:<\/span><\/strong><\/p>\n