EFFICIENT MANAGEMENT OF MULTIPURPOSE AND MULTI-STAKEHOLDER WATER PROJECTS
RESERVOIR SEDIMENTATION AND ITS REMEDIES -A CASE STUDY ON PANCHET RESERVOIR DIPANKAR CHAUDHURI SATYABRATA BANERJEE
HISTORY OF CIVILIZATION
NEED OF RESERVOIR • UNCERTAINTIES • ASSURED WATER • QUALITY WATER
EROSION Little drops of water, Little grains of sand Run away together And destroy the land. - Robert Horton • NATURAL PROCESS • HUMAN ACTIVITIES (Rate of erosion increases by 10 – 40%) EFFECT OF EROSION : Changes in the configuration & character of soil mass . : Loss of productivity of soil / destruction of agricultural land. : Advancement of deserts. : River problems, instability of bed & banks. : Change of course / bank sloughing / floods. : Reservoir sedimentation / economic & environmental damages
FACTOTS INFLUENCING THE RESERVOIR SEDIMENTATION The factors Hobbs (1969) identified to be the most significant in reservoir sediment deposition problems are: RESERVOIR SIZE AND SHAPE; SEDIMENT QUANTITIES AND CHARACTERISTICS; SEDIMENT SOURCES; PROGRESSIVE VEGETATIVE GROWTH ON FREQUENTLY EXPOSED DEPOSITS; (E) CONSOLIDATION OF DEPOSITS; MAGNITUDES, FREQUENCY, AND SEQUENCES OF HYDROLOGIC EVENTS; (G) RESERVOIR REGULATION PRACTICES.
EXTENT OF INFLUENCE SILT CONTRIBUTING AREA (0.985) DRAINAGE AREA (0.955) MEAN ANNUAL RESERVOIR INFLOWS (0.955) MEAN ANNUAL PRECIPITATION (-0.341) Salas and Shin (1999) also observed that sediment load and annual stream flow is the most important factor in determining the variability of accumulated reservoir sedimentation; Similar week correlation was also observed for mean annual precipitation (Water, 2001) in cases of the reservoirs in Britain.
SEDIMENT ROUTING THROUGH AND AROUND THE RESERVOIR THROUGH THE RESERVOIR • RESERVOIR DRAWDOWN (SEDIMENT FLUSHING ALSO TAKES PLACE) • RESERVOIR EMPTYING • RESERVOIRS IN SERIES • VENTING OF DENSITY CURRENT AROUND THE RESERVOIR • SEDIMENT BYPASS • OFF STREAM RESERVOIR • PARALLEL RESERVOIR
REMOVAL OF DEPOSITED SEDIMENT •HYDRAULIC FLUSHING •EXPLOSIVE MOBILIZATION •DREDGING
SALIENT FEATURES OF PANCHET RESERVOIR Inception of Reservoir Panchet: 1959 Dead: Up to 119.5 Mt.; Conservation : 119.5 – 125.0 Mt.; Flood: 125 – 135.7 Mt.; Land acquired up to 129.5; House acquired up to 132.6 Mt. Inception of Reservoir Tenughat: 1970 Average yearly Inflow: 4245 MCM (1993-2012) Trap Efficiency : 90% Zone wise storage Prediction carried out: Up to 2060. Base Period for Prediction: Up to 1985. Reservoir Type : Type – II YEAR
SEDIMENT DEPOSITION MCM
YEAR
MCM/YR
SEDIMENT DEPOSITION MCM
MCM/YR
1956-62
79.16
13.19
1956-62
79.16
13.19
1956-64
96.54
12.07
1962-64
17.39
8.69
1956-66
105.79
10.58
1964-66
9.25
4.62
1956-74
145.12
8.06
1966-74
39.33
4.92
1956-85
185.32
6.39
1974-85
40.20
3.65
1956-96
222.80
5.57
1985-96
37.48
3.41
REDUCTION OF DEAD STORAGE ZONE
REDUCTION OF CONSERVATION STORAGE ZONE
REDUCTION OF FLOOD STORAGE ZONE
SEDIMENT CONTROL STRATEGIES IN THE RESERVOIR AT PANCHET •Respective capacities 130, 83, and 66 MCM have been lost from the original dead, conservation and flood storage. •Mechanical dredging project may be considered in phase wise routine manner in the area of the flood and conservation zone. •To reduce the cost of transportation , rolling buckets placed on a conveyer belt may be used for removing and dumping of sediment. •Working period may be considered as 242 days during non-monsoon period in a year. •Venting of density current & Hydraulic flushing is to be carried out in a routine manner in every year as prevention is better than cure. •Performance of Hydraulic dredging may also be explored. •Simultaneously erosion control measures are also to be taken up to reduce sediment delivery.
CONCLUSION Only Solution of Sedimentation Problem is to carry out the eroded silts and to throw in to the ocean. •Good will • Steady effort • & Promise - may bring success to fight sedimentation problem
THANKS