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JSPM NARHE TECHNICAL CAMPUS STUDY OF SILTING, ITS CAUSES, EFFECTS AND REMEDIAL MEASURES ON RESERVOIR NARHE, PUNE-41 SEMINAR REVIEW GuideName : Prof. INDI P.M Student Name : AJINKYA DAREKAR Department of CivilEngineering 2017-2018
CONTENT OF SEMINAR • INTRODUCTION • SILTING OF RESERVOIR • CAUSES • EFFECT DUE TO SILTING • DISILTING OF RESERVOIR • NEED OF DISILTING • REMEDIAL MEASURES
INTRODUCTION • Reservoirs are used for water supply, power generation, flood control etc. • When sediment transported in reservoir which decrease Storage capacity of reservoirs. • In this report is a review of information and techniques are available to avoid sediment deposition in reservoirs and how to remove deposited sediment.
SILTING OF RESERVOIR The silting process of reservoir is determined by several natural causes such as :- • Sediment transport in the river system. • Bank and Shore erosion. • Bank and Slop sliding.
Siltation in the reservoir is due to stagnant water in huge water storage. All rivers naturally carry Silt in their flow due to velocity of flow. Silt is deposited all along river banks in normal floods. Formation of big reservoirs disturbs silting pattern all along the banks. • Silting in the reservoir reduces the live storage. Hence Reservoir capacity is designed to accommodate the expected quantity of Silt in life time of dam. Normally big dams and reservoirs are designed for 100 years of life time. • Silting pattern in reservoir is studied with data of the catchment area and model studies.
CAUSES • The origin of the increased sediment transport into an area may be erosion on land, or activities in the water. • Another important cause of siltation is the septage and other sewage sludges that are discharged from households or business establishments with no septic tank or waste water treatment facilities to bodies of water. • climate change also affect the disiltation rates.
Lack of vegetation • If landslide is occurs due to earthquake in reservoir zone then it cause siltation
EFFECTS • Reduction of useful and economic life reservoir. • The reduction of hydropower generation, water supply . • Additional lateral force on the dam wall exerted by deposited sediments. • The abrasion and damage of tunnels, galleries, guiding slots and other equipments.
Siltation and secondary effects of erosion The direct loss of production due to the loss of soil is only part of our annual erosion bill. The secondary effects of erosion cause losses as great or greater. These include: Adverse Effect on other Land - Rich areas of river flat are often smothered with barren clay or sand from the scouring of the subsoil of other land above. Choking of streams with debris may cause flooding or a breakaway of the stream, with consequent erosion. Adverse Effect on Communications - Bridges often are undermined or their approaches scoured away; or their capacity is so reduced by siltation that they can no longer safely carry the floodwater of the streams. Roads are sometimes blocked by landslides or the debris from sudden scours.
Supply Adverse Effect on Water - Storages, from small dams to important reservoirs, are silted up and rendered useless. (It is, of course, recognized that practically all reservoirs on streams will ultimately fill with silt; but the longer this can be delayed, the greater the return from the money expended on them.) Natural waterholes along streams are filled, leaving them dry in summer. Water channels are blocked by sand drift, causing an annual expenditure of many thousands of pounds for clearing them. (4) Other Ill Effects - Fencing may be destroyed and buildings threatened by landslides, stream erosion. Pollution of streams and filling of waterholes have adverse effect on fisheries. The scenic value of an area is often greatly depreciated by scours and soil washing. A still more important matter is the silting up of costly drainage systems.
What is De-silting ? Desilting as the name indicates is removal of silt (fine grained clay/lake-bed soil) from a lake-bed or Reservoir, which can be done manually, or mechanically.
NEED OF DE-SILTING • TO REMOVE DEPOSITED SEDIMENTS FROM RESERVIOR. • TO INCREASE STORAGE CAPACITY OF RESERVIOR. • TO AVOID FLOOD CONDITION.
REMEDIAL MEASURES • Sediment Traps and Detention Basins • Vegetative Screens
1.SEDIMENT TRAP AND DETECTION BASIN • Sediment trap is the technique of construction of small dam upstream site of major reservoir to trap sediment . • When small dam fill by sediment then silt dredged out by mechanical technique and use for construction purpose. • In Japan there are more than 500 sediment storage dam with height of 15 m or above.
Sedimentation Trap Settling Basin
2.VEGETATIVE SCREENS • Vegetative screen is a dense growth of vegetation through which sediment must flow to enter into the Reservoir. • The main purpose of vegetation is to reduce velocity of sediment and deposit around the plant.
CONCLUSION • Siltation is measure problems in case of many of dams or reservoir as it reduces the storage capacity of reservoir. • So it essential to overcome the this problem by applying proper techniques to avoid losses due to siltation. • Vegetation is the best preventive measure for siltation. • Sediment trap is also helpful technique to overcome siltation.
