HYDRO 2013_Pradyumna

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<ul><li><p> Lahmeyer International (India) Pvt. Ltd. Lahmeyer International (India) Pvt. Ltd. </p><p>One-dimensional sediment modelling for Chuzachen and Devsari hydroelectric power projects to check the feasibility of reservoirs usage as pseudo-desanders Author and Presenter : Pradyumna Machhkhand Senior Manager (Hydropower &amp; Water Resources)| Lahmeyer International (India) Pvt. Ltd. | Gurgaon-122002 </p><p>1 </p></li><li><p> Lahmeyer International (India) Pvt. Ltd. </p><p>Outline of the presentation </p><p>2 </p><p>Introduction </p><p> Background Information </p><p>Reservoir Sedimentation </p><p>Sediment Modelling </p><p>Theory </p><p>Case Studies </p><p>Modelling Scheme </p><p>Model Set Up </p><p>Data Organization </p><p>Results </p><p>Comparison </p><p>Conclusion </p><p>Model Description </p></li><li><p> Lahmeyer International (India) Pvt. Ltd. </p><p> Reservoir sedimentation in hydroelectric projects (HEP): a major problem that interrupts the smooth functioning of hydropower plants. </p><p> A schematic and classical illustration of reservoir sedimentation </p><p>Introduction </p><p>3 </p></li><li><p> Lahmeyer International (India) Pvt. Ltd. </p><p> In general, the problem is seen as a big hindrance and therefore, as a remedial measure n number of desanders, based on studies, are usually proposed to manage the sediment removal operation. </p><p> The presented case studies foray into the primary investigation of reservoir sedimentation prior to making decisions on sediment management. </p><p> The investigation of sediments lies on two basic searches: </p><p> Where &amp; How Much </p><p>Introduction </p><p>4 </p><p>To examine the location and capacity of the reservoir in discrete form </p><p>To understand the relation between sediment concentration and discharge in the reservoir </p></li><li><p> Lahmeyer International (India) Pvt. Ltd. </p><p> Two different hydroelectric projects have been studied: a. Devsari HEP (Devsari Reservoir) b. Chuzachen HEP (Rangpo Reservoir &amp; Rongli Reservoir) Project features: </p><p> contd... </p><p>Background information </p><p>5 </p><p>Project features Devsari HEP Chuzachen HEP </p><p>(Rangpo) </p><p>Location Uttarakhand, India Sikkim, India </p></li><li><p> Lahmeyer International (India) Pvt. Ltd. </p><p>Background information </p><p>6 </p><p>Project features Devsari HEP Chuzachen HEP </p><p>(Rangpo) </p><p>Type of structure Dam Dam </p><p>Height of structure 35m 48m </p><p>Extent of reservoir 4.8Kms from dam axis 508m from dam axis </p><p>Storage 9.026 Mm3 0.360 Mm</p><p>3 </p><p> contd </p></li><li><p> Lahmeyer International (India) Pvt. Ltd. </p><p> Empirical methods </p><p>a. Advantage : explicit methods (such as, Hazen, Vetter, and Camp), computational ease while computing the sediment trap efficiency. </p><p>b. Limitations : i. cover only the settling phase of reservoir operation, ii. and other factors which are NOT included in the empirical methods are: </p><p> the sediment transporting capacity of flow in a settling reach, the change in conditions as reservoir fills with sediment, the effect of variation in flow depth down a basin or reservoir, and the additional turbulence caused by inlet condition to a basin or </p><p>reservoir. contd... </p><p>Reservoir sedimentation </p><p>7 </p></li><li><p> Lahmeyer International (India) Pvt. Ltd. </p><p> 1-dimensional numerical model </p><p> a. Advantages : </p><p> models the effect of turbulence in sediment movement and mass deposition, </p><p> not only simulates deposition, but also sluicing, </p><p> does not require grids to approximate cross-sections, </p><p> and requires less field data to set up. </p><p>Reservoir sedimentation </p><p>8 </p><p>contd </p></li><li><p> Lahmeyer International (India) Pvt. Ltd. </p><p> 1-dimensional numerical model </p><p>b. Limitations: </p><p> does not offer a detailed view of hydrodynamics of reservoir </p><p>system like 2-D or 3-D models. </p><p>Although 2-D or 3-D models have certain advantages, but at the cost of a </p><p>longer computational time and substantial amount of field data to </p><p>capture the complexities of 2-D or 3-D flow. </p><p> contd... </p><p>Reservoir sedimentation </p><p>9 </p></li><li><p> Lahmeyer International (India) Pvt. Ltd. </p><p> SHARC , a software developed by HR Wallingford, UK, is a suite of integrated </p><p>programs designed to assist in the identification and solution of sediment problems at intakes in rivers and canal systems. </p><p> DOSSBAS stands for Design of Sluiced Settling Basins. </p><p> DOSSBAS is tool built within SHARC to model sediment depositions in basins/reservoirs and can model both regular and irregular basins. </p><p> Two suites of DOSSBAS: 1) Deposition Model. 2) Sluicing Model. </p><p>Model description : DOSSBAS tool of SHARC </p><p>10 </p><p>contd </p></li><li><p> Lahmeyer International (India) Pvt. Ltd. </p><p> Deposition model </p><p> Assumptions: o the flow is steady, </p><p> o the velocities and concentrations are constant across the width of the </p><p>channel, </p><p>o and the concentrations in one size fraction do not affect other size fraction. </p><p>Model description : DOSSBAS tool of SHARC </p><p>11 </p><p>contd </p></li><li><p> Lahmeyer International (India) Pvt. Ltd. </p><p> Deposition model [Basic equation of turbulence (Dobbins ,1994)] </p><p> Equation (1) </p><p> = sediment diffusion coefficient in y-direction (m2/sec) , = sediment diffusion coefficient in x-direction (m2/sec), = and settling velocity (formula by Gibbs et al, 1971) of sediment for the sediment size fraction (j) (m/sec). </p><p>Model description : DOSSBAS tool of SHARC </p><p>12 </p><p>contd </p><p>2</p><p>2</p><p>2</p><p>2</p><p>x</p><p>C</p><p>y</p><p>C</p><p>yV</p><p>y</p><p>C</p><p>x</p><p>Cu</p><p>j</p><p>x</p><p>jy</p><p>sj</p><p>j</p><p>y</p><p>j</p><p>where, u = flow velocity at height y above the bed (m/sec), y = height above bed (m), Cj = sediment concentration at height (y) above bed for size fraction( j), x = distance co-ordinate along channel (m), </p><p>y</p><p>x</p><p>sjV</p></li><li><p> Lahmeyer International (India) Pvt. Ltd. </p><p> Deposition model </p><p>Model description : DOSSBAS tool of SHARC </p><p>13 </p><p>contd </p></li><li><p> Lahmeyer International (India) Pvt. Ltd. </p><p>Deposition model : Turbulent diffussion within a sub-reach </p><p>14 </p></li><li><p> Lahmeyer International (India) Pvt. Ltd. </p><p>Deposition model : Boundary conditions </p><p>15 </p></li><li><p> Lahmeyer International (India) Pvt. Ltd. </p><p>Overall structure of deposition model </p><p>16 </p></li><li><p> Lahmeyer International (India) Pvt. Ltd. </p><p> Sluicing model </p><p> Sluicing model simulates only sand movements. It is assumed that any silt in the exposed bed material is sluiced instantly and therefore, only sand transport controls the sluicing rates. </p><p> Diffusion is not a dominant process in sluicing. Sluicing is modelled using equation, </p><p> Note: The threshold value to differentiate between silt and sand in DOSSBAS is 63 micron (default). </p><p>Model description : DOSSBAS tool of SHARC </p><p>17 </p><p>contd </p></li><li><p> Lahmeyer International (India) Pvt. Ltd. </p><p>Overall structure of sluicing model </p><p>18 </p></li><li><p> Lahmeyer International (India) Pvt. Ltd. </p><p> Modelling scheme of reservoir sediment management plan </p><p>Modelling scheme </p><p>19 </p><p>contd </p></li><li><p> Lahmeyer International (India) Pvt. Ltd. </p><p>Modelling scheme </p><p>20 </p><p>contd </p><p> Set of parameters </p><p> X1 is the set of input parameters, viz., reservoir geometry, and sediment data </p><p> X2 is the set of parameters that includes the temperature, and the sand concentrations to be applied in both deposition and sluicing model. </p><p> The input parameters for deposition model can be expressed as, (X1 X2). </p><p> The set X3 is composed of additional parameters such as, flushing/sluicing discharge, the water level at the time of sluicing, and the duration of sluicing. </p><p> Y1 is the set of longitudinal bed profiles, which are results of deposition models. </p><p> The input parameters for sluicing model can be expressed as, (Y2 X2 X3). </p><p> The set Y2 comprises results of sluicing models in terms of elapsed time for flushing out the sediments and change in bed profiles at different time. </p></li><li><p> Lahmeyer International (India) Pvt. Ltd. </p><p> Hydrological year mean flow duration curves </p><p>Data organization </p><p>21 </p><p>contd </p><p>0</p><p>20</p><p>40</p><p>60</p><p>80</p><p>100</p><p>120</p><p>140</p><p>160</p><p>180</p><p>200</p><p>220</p><p>240</p><p>0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%</p><p>Dis</p><p>char</p><p>ge (m</p><p>3/s</p><p>ec)</p><p>Exceedance probability (%)</p><p>Flow duration curve divisions: Devsari HEP</p><p>Flow duration curve</p><p>Qdesign (Intake) = 120.76 m3/sec</p><p>Division3 Qm = 44.8 m3/sec</p><p>Division2 Qm = 160.1 m3/sec</p><p>Division1 Qm = 205.3 m3/sec</p><p>0</p><p>20</p><p>40</p><p>60</p><p>80</p><p>100</p><p>120</p><p>140</p><p>160</p><p>0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%</p><p>Dis</p><p>ch</p><p>arg</p><p>e (cum</p><p>ec)</p><p>Exceedance Probability (%)</p><p>Flow duration curve divisions : Rangpo</p><p>Flow duration curve</p><p>Qm = 33.2 m3/sec (Division 3)</p><p>Qm= 95.8 m3/sec (Division 1)</p><p>Qm= 58.1 m3/sec (Division 2)</p><p>Qm= 8.4 m3/sec (Division 4)</p><p>Qdesign = 21.5 m3/sec</p></li><li><p> Lahmeyer International (India) Pvt. Ltd. </p><p> Pre-processed data: average discharge and mean concentration </p><p>Data organization </p><p>22 </p><p>contd </p><p>Divisions </p><p>Devsari Rangpo </p><p>Qm </p><p>Mean conc. </p><p>Qm </p><p>Mean conc. </p><p>m3/s ppm m3/s ppm </p><p>1 205.3 511 95.8 707 </p><p>2 160.1 436 58.1 389 </p><p>3 44.8 192 33.2 187 </p><p>4 - - 8.4 47 </p></li><li><p> Lahmeyer International (India) Pvt. Ltd. </p><p> Optimization of input parameters </p><p>Data organization </p><p>23 </p><p>contd </p><p>y = 16.54x0.6445</p><p>R = 0.6115</p><p>0</p><p>100</p><p>200</p><p>300</p><p>400</p><p>500</p><p>600</p><p>700</p><p>800</p><p>900</p><p>0 50 100 150 200 250</p><p>Me</p><p>an</p><p> Co</p><p>nc</p><p>en</p><p>tra</p><p>tio</p><p>n [</p><p>pp</p><p>m]</p><p>Mean Discharge [m3/s]</p><p>Mean discharge vs mean concentration</p><p>Obs.Mean Power (Obs.Mean </p><p> Devsari Reservoir </p><p> 6445.054.161 xCm</p></li><li><p> Lahmeyer International (India) Pvt. Ltd. </p><p> Optimization of input parameters </p><p>Data organization </p><p>24 </p><p>contd </p><p> Rangpo Reservoir </p><p>o from the table of the pre-processed data, the annual sediment volume of Rangpo is about 70% the capacity of the Reservoir, and therefore, it is quite conservative to adopt the same values. </p></li><li><p> Lahmeyer International (India) Pvt. Ltd. </p><p> Bed gradation curves </p><p>Model setup </p><p>25 </p><p>contd </p></li><li><p> Lahmeyer International (India) Pvt. Ltd. </p><p> Input parameters </p><p>Model setup </p><p>26 </p><p>contd </p><p>Divisions </p><p>Flow </p><p>Sediment concentration </p><p>Deposition cycle time </p><p>Flushing discharge </p><p>Silt Sand </p><p>m3/sec ppm ppm Days Hours m3/sec </p><p>1 205.3 465 199 37 876 84.5 </p><p>2 160.1 397 170 44 1051 39.3 </p><p>3 44.4 174 74 285 6833 NA </p><p>Divisions </p><p>Flow </p><p>Sediment Concentration </p><p>Deposition cycle time </p><p>Flushing discharge </p><p>Silt Sand </p><p>m3/sec ppm ppm Days Hours m3/sec </p><p>1 95.8 495 212 37 876 74.3 2 58.1 273 117 37 876 36.6 3 33.2 131 56 73 1752 11.7 4 8.4 33 14 219 5256 NA </p><p> Devsari Rangpo </p></li><li><p> Lahmeyer International (India) Pvt. Ltd. </p><p> Input parameters </p><p>Model setup </p><p>27 </p><p>contd </p></li><li><p> Lahmeyer International (India) Pvt. Ltd. </p><p> Deposition model: Devsari </p><p>Results </p><p>28 </p><p>1265</p><p>1270</p><p>1275</p><p>1280</p><p>1285</p><p>1290</p><p>1295</p><p>1300</p><p>1305</p><p>0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000</p><p>Distance downstream (m)</p><p>Minimum bed lev el (m)</p><p>Bed lev els at time 0.00 (hours )</p><p>Bed lev els at time 146.00 (hours )</p><p>Bed lev els at time 292.00 (hours )</p><p>Bed lev els at time 438.00 (hours )</p><p>Bed lev els at time 584.00 (hours )</p><p>Bed lev els at time 730.00 (hours )</p><p>Bed lev els at time 876.00 (hours )</p><p>Final w ater lev el</p><p>Longitudinal Profile Down Basin</p><p>Ele</p><p>vati</p><p>on</p><p> (m</p><p>)</p><p>Divisions </p><p>Sediment Volume </p><p>Outflow Sediment </p><p>Trap Efficiency </p><p>Reservoir Storage </p><p>Silt Sand Silt Sand Silt Sand Before run </p><p>After run </p><p>Mm3 Mm3 PPM PPM % % Mm3 Mm3 1 0.1 0.1 215 0 53.7 100.0 9.1 8.9 2 0.1 0.1 164 0 58.6 100.0 9.1 8.9 3 0.1 0.1 35 0 79.8 100.0 9.1 9.0 </p><p>contd </p></li><li><p> Lahmeyer International (India) Pvt. Ltd. </p><p> Sluicing model: Devsari </p><p>1265</p><p>1270</p><p>1275</p><p>1280</p><p>1285</p><p>1290</p><p>1295</p><p>1300</p><p>0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000</p><p>Distance downstream (m)</p><p>Minimum bed lev el (m)</p><p>Bed lev els at time 0.000 (hours )</p><p>Bed lev els at time 3.000 (hours )</p><p>Bed lev els at time 6.000 (hours )</p><p>Bed lev els at time 9.000 (hours )</p><p>Bed lev els at time 12.000 (hours )</p><p>Bed lev els at time 14.442 (hours )</p><p>Longitudinal Profile Down Basin</p><p>Elev</p><p>atio</p><p>n (m</p><p>)</p><p>Results </p><p>29 </p><p>contd contd </p><p>Divisions </p><p>Volume removed Elapsed time for </p><p> flushing Silt Sand </p><p>Total sediment </p><p>Mm3 Mm3 Mm3 Hours </p><p>1 0.1 0.1 0.2 14.44 </p><p>2 0.1 0.1 0.2 28.59 </p><p>3 NA </p></li><li><p> Lahmeyer International (India) Pvt. Ltd. </p><p> Deposition model: Rangpo </p><p>Results </p><p>30 </p><p>contd </p><p>880</p><p>885</p><p>890</p><p>895</p><p>900</p><p>905</p><p>910</p><p>915</p><p>0 100 200 300 400 500 600</p><p>Distance downstream (m)</p><p>Minimum bed lev el (m)</p><p>Bed lev els at time 0.00 (hours )</p><p>Bed lev els at time 146.00 (hours )</p><p>Bed lev els at time 292.00 (hours )</p><p>Bed lev els at time 438.00 (hours )</p><p>Bed lev els at time 584.00 (hours )</p><p>Bed lev els at time 730.00 (hours )</p><p>Bed lev els at time 876.00 (hours )</p><p>Final w ater lev el</p><p>Longitudinal Profile Down Basin</p><p>Ele</p><p>va</p><p>tio</p><p>n(m</p><p>)</p><p>Divisions </p><p>Sediment Volume </p><p>Outflow Sediment </p><p>Trap Efficiency </p><p>Reservoir Storage </p><p>Silt Sand Silt Sand Silt Sand Before </p><p>run After run </p><p>Mm3 Mm3 PPM PPM % % Mm3 Mm3 1 0.013 0.045 350.0 5.0 12.6 97.5 0.36 0.31 2 0.009 0.015 217.0 1.0 20.4 99.3 0.36 0.34 </p><p>3 0.007 0.008 89.0 0.0 31.7 100.0 0.36 0.35 </p><p>4 0.003 0.002 14.0 0.0 58.8 100.0 0.36 0.36 </p></li><li><p> Lahmeyer International (India) Pvt. Ltd. </p><p> Sluicing model: Rangpo </p><p>Results </p><p>31 </p><p>contd contd </p><p>880</p><p>885</p><p>890</p><p>895</p><p>900</p><p>905</p><p>910</p><p>0 100 200 300 400 500 600</p><p>Distance downstream (m)</p><p>Minimum bed lev el (m)</p><p>Bed lev els at time 0.000 (hours )</p><p>Bed lev els at time 0.200 (hours )</p><p>Bed lev els at time 0.400 (hours )</p><p>Bed lev els at time 0.410 (hours )</p><p>Longitudinal Profile Down Basin</p><p>Ele</p><p>vati</p><p>on</p><p>(m)</p><p>Divisions </p><p>Volume removed Elapsed time for </p><p> flushing </p><p>Silt Sand Total </p><p>sediment </p><p>Mm3 Mm3 Mm3 Hours </p><p>1 0.014 0.043 0.06 0.41 </p><p>2 0.009 0.015 0.02 0.35 </p><p>3 0.005 0.008 0.01 0.79 </p><p>4 NA </p></li><li><p> Lahmeyer International (India) Pvt. Ltd. </p><p> Velocities and required length of reservoirs to settle 0.2mm particle: </p><p>Comparison with empirical method </p><p>32 </p><p> Devsari Rangpo Units </p><p>Full reservoir level (FRL) = 1300 910 MASL </p><p>Minimum drawdown level(MDDL) = 1295 893 MASL </p><p> Division1 average discharge (Qa) = 205 90 m3/sec </p><p>The approximate average area of flow (A) = 4700 1978 m2 </p><p>The corresponding flow through velocity (V) = Qa/A = 0.044 0.046 m/sec Mean flow through velocity for 0.2mm particle to </p><p>settle down, v = 0.2 0.2 m/sec </p><p>Settling velocity of 0.2mm particle, w = 0.022 0.022 m/sec Length of reservoir required to settle 0.2mm particle, </p><p>L*= v/w x ( FRL-MDDL) = 45.5 154.5 m </p><p>Mid-Length from dam axis of reservoir, L = 2500 254 m </p><p>contd </p></li><li><p> Lahmeyer International (India) Pvt. Ltd. </p><p> It can be safely inferred from the model results that the sediment grain size of 0.2mm and greater than 0.2mm shall be settling down in the reservoirs. </p><p> If periodical flushing operations are realized during the whole life of the </p><p>reservoir, the entrance sill of the intake will not be affected by the deposited sediments; as it is already being witnessed in the model studies. </p><p> The model studies have potential scopes to enhance the analysis; the sensitivity analysis of the models is one of them. </p><p>Conclusion </p><p>33 </p><p>contd </p></li><li><p> Lahmeyer International (India) Pvt. Ltd. </p><p> It would be in the interest of HEPs, if the utility of the desanders decelerates before placing them in the planning stages, thereby encouraging physically-based hydraulic modelling study of the sediments in the interim to assess whether the reservoirs are self-sufficient for managing the sediment processes or not. </p><p> The case studies of this paper offer supporting re...</p></li></ul>