1. River siltation, its impact and the way forward

2. Rivers – conveyance system
Rivers may be likened to conveyance system
As the river flows from high gradient to low gradient, its stream power is lost proportionately, inducing thereby silt deposition en route
Siltation process subjected to several factors including physiography, geology, Meteorology, hydrology and flow characteristics of the particular reach.
Landslides, Climatic factors, land use pattern are important in inducing slope instability, such as fragile nature of rocks, active nature of tectonics in plate margins along with climatic factors.
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3. Impacts – In stream impacts
Biological impacts e.g. turbidity, sedimentation, reduced productivity and species diversity.
Recreational impacts e.g. restriction of swimming, boating, fishing and reduction of overall aesthetics.
Sedimentation of channels and water storage bodies e.g reservoirs sedimentation, impairment of navigation, siltation of training structures.
Increased abrasion of hydraulic equipment e.g HEP turbines.
River Morphological changes e.g. Shifting of river course, aggradations / degradation
Sand/Gravel Minning.( +ve Impact)
Contd.
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4. Impacts – Off stream impacts
Flood damage e.g. aggradation, increased damage from muddy water. (This may either be beneficial or may create serious problems depending on its nature, quantity and quality.)
Sedimentation of conveyance system e.g. Irrigation and drainage channels.
Increased cost of water treatment e.g. increased sedimentation times, clogging of filters.
Impairment of Industrial water use e.g.reduced cooling efficiency, abrasion of pumps and turbines.
Sealing of Irrigated soils.
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5. Impacts – remedial measures
Afforestation and forest management
Regrading and grassland management
Cultivation practices, such as crop rotation, increasing organic matter, mulching, seasonal cover crops, contour cultivation, strip cropping and terracing.
Gully control and check dams- contour bunding and trenching.
Contd.
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6. Impacts – remedial measures
Storage Reservoirs
Desilting basins.
River training works such as bank protection, spurs etc.
River training works for local sediment control e.g Sumerged vanes, bed bars, Bundalling etc.
Desilting- There are different methods of desilting such as flushing, sluicing, siphoning, dozing, dredging etc.
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7. Committee/ Select Group/ Seminars on Silting of rivers
Committee to study the problems of silting in rivers
(Dr B.K.Mittal committee)
Constituted by Ministry of Water Resources in 2001 under chairmanship of Dr. B.K. Mittal, former Chairman, CWC
studied problem of silting in rivers and related aspects including feasibility of desilting
Expertise from G/o Bihar, Orissa, Assam, West Bengal, Brahmaputra Board, GFCC, Irrigation & Waterways Department, Dredging Corporation of India, CWPRS, NRSC, IWAI, GSI, JNU, NIH & CWC
studied the siltation pattern in a few rivers in India and concluded that siltation is not pronounced and alarming.
Contd.
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8. Committee/ Select Group/ Seminars on Silting of rivers
Concluded that method of minimizing siltation may be of two fold viz., those required in catchment and other in the river itself.
In catchment method may include afforestation, right practice of land use, catchment area treatment
‘the river itself’ method may include construction of suitable hydraulic structures that may trap silt.
Desilting of rivers, in general, not feasible technically, due to several reasons like non-sustainability, non-availability of vast land required for the disposal of dredged material etc.
Contd.
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9. Committee/ Select Group/ Seminars on Silting of rivers
Dredging in general should not be resorted particularly in major rivers except some locations such as tidal rivers, confluence points with narrow constrictions and the likes which can be tackled by desilting after thorough examination and techno-economic justification.
Desilting of rivers can marginally minimize the magnitude of floods and be effective only for a short period.
Cannot be viewed in isolation of other approaches to manage floods.
Desilting of rivers for flood control is not an economically viable solution.
Contd.
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10. Committee/ Select Group/ Seminars on Silting of rivers
Desilting of rivers in vulnerable reaches may be suggested based on model study if it is found techno-economic viable.
For navigation purpose the river reaches in the waterway path may be dredged to have minimum depth of water.
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11. Committee/ Select Group/ Seminars on Silting of rivers
Select Group constituted by MoWR in 2003 under the Chairmanship of Chairman, CWC, to examine the report of Mittal Committee also endorsed the views of Mittal Committee and also suggested some action points
Desilting can be done in vulnerable reaches for some specific purpose which are to be identified by the State Governments and the experience should be evaluated for further applicability.
For navigation purpose, the river reach in the water way path may need to be dredged regularly to have minimum depth of water.
Contd.
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12. Committee/ Select Group/ Seminars on Silting of rivers
Catchment area treatment to be made mandatory in water resources projects
In respect of rivers flowing from other countries such as Nepal/Bhutan/ Myanmar, since the catchment area treatment will necessitate an understanding with these countries, necessity for reaching an understanding with all these countries to implement schemes, which may reduce the silt load in these rivers.
The feasibility of conducting studies upstream of Farakka in order to manage the silt problem
Contd.
Central Water Commission

13. Committee/ Select Group/ Seminars on Silting of rivers
Carrying capacity of the rivers be monitored on regular basis to obtain complete knowledge regarding aggradation / degradation. The scope of such studies may be included in the existing schemes under operation in the respective organization/agencies.
Specific scientific study needs to be taken up by NEHARI under Brahmaputra Board, IRI, Roorkee, River Research Institute (RRI), Kolkata, CWPRS, Pune and other similar organizations to establish the cause of aggradation/ degradation in rivers and to suggest short term/long term remedial measures to minimize/remove the siltation problem
Contd.
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14. Committee/ Select Group/ Seminars on Silting of rivers
Seminar on “Silting of Rivers-Problems & Solutions” held on February, 2004 at New Delhi
A. AGGRADATION/DEGRADATION IN FLUVIAL RIVERS
Systematic data collection and analysis be carried out to study the aggradational and degradational behavior of river, especially in rivers carrying large quantities of sediment load.
In the existing projects necessary data on changes in river slope, bed material size and river cross sections be taken periodically as this information will be useful in improving methods of prediction of degradation/aggradation.
Contd.
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15. Committee/ Select Group/ Seminars on Silting of rivers
Regular monitoring of various morphological changes such as formation of shoals, meandering tendency of the river, effect of construction of hydraulic structures , damages to the bank, effect of afforestation/deforestation and tectonic occurrences should be done together with model studies as per the requirements, to take timely corrective measures to maintain its morphology and to check local erosion damages.
Results from R&D activities being carried out in different institutes/organizations should be pooled together which could be used as a data base for river management.
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16. Committee/ Select Group/ Seminars on Silting of rivers
While taking up a project, mathematical model, ANN and physical model studies be used to predict river behaviour after the project is made operational.
Retrogression downstream of dams be estimated using available methods and it be controlled using slope controlling structures and bank protection measures as necessary.
Studies related to basin geo-morphology on regional or sub-regional level be carried out.
Impetus should be given to measurement of bed load in streams in hilly region.
Contd.
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17. Committee/ Select Group/ Seminars on Silting of rivers
B. SILT CONTROL MEASURES AND THEIR TECHNO-ECONOMIC VIABILITY
Using knowledge of fluvial hydraulics and mathematical modeling, the effect of the construction of dams and other hydraulic structures on flood plain of the river and possible aggradation/degradation due to them needs to be studied. 3-D model on morphological behaviours should be developed as a part of the project so that necessary precautions can be taken in designing such structures for minimizing the siltation problems in rivers.
Contd.
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18. Committee/ Select Group/ Seminars on Silting of rivers
Watershed Management and CAT, specially soil conservation measures should be used in the catchment of rivers having heavy erosion problems. Particular care needs to be taken in maintaining slopes to reduce land slide.
Economics and efficacy of Watershed Management programme needs to be examined considering existing catchment conditions.
Increasing unplanned encroachment into flood plains may be responsible for sedimentation in rivers and flood losses and should be controlled.
Contd.
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19. Committee/ Select Group/ Seminars on Silting of rivers
A standing working group/committee with representatives from CWC, CWPRS, the concerned states and GFCC (In the case of river Ganga), Brahmaputra Board (in the case of river Brahmaputra) needs to be set up for each major river basin. This could also include experts in the field and give suitable recommendations on river morphological problems and, monitor their implementation as an immediate measure. In the long run, a single authority to oversee and implement the morphological, environmental and all other related issues need to be set up.
Contd.
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20. Committee/ Select Group/ Seminars on Silting of rivers
C. DESILTING OF RIVERS AND ITS TECHNO ECONOMIC VIABILITY
 Arrangement for flushing of sediment in reservoirs needs to be provided wherever possible, using various available methods.
Flushing of sediment at barrages and use of desilting arrangements to exclude sediment before its entry into power draft are necessary.
Extensive use should be made of satellite imageries to identify critical areas where erosion is likely to take place in the forthcoming monsoon and bank strengthening and other necessary actions be taken.
Contd.
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21. Committee/ Select Group/ Seminars on Silting of rivers
 Newer methods like submerged vanes, short spurs and geosynthetics need to be tried out in the field as the experience so far has not been conclusive.
Contd.
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22. Committee/ Select Group/ Seminars on Silting of rivers
D. EFFICACY OF DREDGING AS A SILT CONTROL MEASURE FOR REDUCING FLOOD LEVELS.
Desilting through dredging in large rivers is not economically viable due to high cost, non sustainability, non availability of vast land required for disposal of dredged materials. However, desilting in small rivers in small reaches may be economical and advisable, depending on local conditions. Reaches where dredging has been performed need to be monitored.
Removal of sediment may not be effective in reducing flood level.
Contd.
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23. Committee/ Select Group/ Seminars on Silting of rivers
Case histories on dredging and their techno economic performances should be compiled. Such database, covering the whole country will be useful as support to decisions on dredging related problems.
Techno-economic criteria for dredging as a means of river management, need to be evolved.
Sediment removal may be necessary at vulnerable locations such as i) where there is scouring in one bank and siltation in river bed near the other bank, ii) at outfall of rivers into sea, iii) in waterways to improve effectiveness of the river for navigation, and iv) for excavating Pilot channels to guide the flow in a reach for water management.
Contd.
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24. Points need to be discussed
Efficacy of dredging as silt control measure for reducing flood levels
Possible solutions for neutralizing the aggradation tendency of the rivers and how best to provide relief from the ill effects of the silting trouble.
Comparison of sediment dredging with river training devices, both of which are helpful to deepen the river bed.
For minimizing the silt trouble in rivers, the precautions to be taken in designing of hydraulic structures.
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25. Central Water Commission
THANKS
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