Estimating Reservoir Capacity Loss From Sedimentation David C. - PowerPoint PPT Presentation

Estimating Reservoir Capacity Loss From Sedimentation David C. Froehlich, Pramod Narayan, and M anoj Kumar Dam Rehabilitation and Improvement Project (DRIP)

Estimating Sedimentation – Three Approaches • From sediment discharge rating curves combined with flow-duration relations. • From calculations of the total amount of land surface erosion, the ability of the sediment to be transported to the reservoir, and the reservoir trapping efficiency. • From predictions based on sedimentation in existing reservoirs in which the accumulated deposits have been surveyed over a sufficiently long period.

General Form of Capacity Loss M odel           ˆ ln ln ln ln ln Y A A C T 1 2 3 4 5 c r o where  ˆ 3 Y expected reservoir capacity loss (Mm )  2 A reservoir catchment area (km ) c  2 A reservoir surface area (km ) r  3 C initial reservoir storage capacity (Mm ) o  T time s ince initial filling of reservoir (years)   model parameters i

 0.10 0.05 0.8 0.9 0.0064 A A C T ; eastward flowing rivers  c r o   ˆ Y  0.15 0.30 0.50 0.65  0.030 ; westward flowing rivers A A C T c r o   2 2 0.930 0.881 r r ln Y ln Y east west   s 0.601 s 0.492 ln Y ln Y east west

Reservoir Half-life T 50% (years) 1    0.5   5         1  T A A C 4 2 3    50% c r o    exp  1    1.11   0.15 0.1 0.3 78.0 A A C ; eastward flowing rivers  c r o   T (years) 50%    1.54   0.15 0.3 0.5 16.6 ; westward flowing rivers A A C  c r o

100 x (1- α )% Prediction Interval            1 ˆ 2 ln 1 f F F f Y t s     2 , ln 0 0 n p Y ln Y  two-tailed Student's t-distributio n t  130 (eastward), 90 (westward) n         5 , , , , p 1 2 3 4 5     f 1,ln ,ln , n l ,ln A A C T 0 c r o           0.53544 0.01893 0.02723 0.01289 0.11471 0.71542 0.04684 0.05769 0.02803 0.13602           0.01893 0.00406 0.00194 0.00135 0.00102 0.04684 0.01149 0.01089 0.00054 0.00148                  1    1    F F 0.02723 0.00194 0.01194 0.00777 0.00253 F F 0.05769 0.01089 0.05549 0.03532 0.00830     ln Y ln Y east west         0.01289 0.00135 0.00777 0.00832 0.00080   0.02803 0.00054 0.03532 0.03160 0.00854              0.11471 0.00102 0.00253 0.00080 0.030 75 0.13602 0.00148 0.00830 0.00854 0.043 25 Eastward flowing rivers Westward flowing rivers

Upper 95% prediction limit Lower 95% prediction limit

Upper 95% prediction limit Lower 95% prediction limit

Summary and Conclusions  0.10 0.05 0.8 0.9 0.0064 A A C T ; eastward  c r o ˆ   Y  0.15 0.30 0.50 0.65  0.030 A A C T ; westward c r o    1.11   0.15 0.1 0.3 78.0 ; eastward A A C  c r o   T 50%    1.54   0.15 0.3 0.5 16.6 A A C ; westward  c r o            1 ˆ 2 ln Y t s 1 f F F f     2 , n p ln Y 0 0 ln Y