RESERVOIR SEDIMENTATION ASSESSMENT GUIDELINE - Aneel

Reservoir Sedimentation Assessment GuidelineSpecific weight γ apAnnual average sediment volume(computed based on the equation forsediment transportation and dischargesseries)Sedimentation time for total volume,in max. normal water levelSedimentation time for total volume,in min. normal water levelSedimentation time for a volumeequivalent to the volume at the intakesill (reservoir useful life)Sedimentation time for total volume,considering the increase on sedimenttransportation since when sedimentdischarge measurements took place(1982)E r = 45% (adopted 50%)According to Lara and According to Lara andPembertonPemberton1,13 t/m 3 1,5 t m 323,37 x 10 6 m 3 /year 330.325 m 3 /year1240 years 14 years430 years 12,7 years200 years 12 years------15 months10.3 Assessment of a reservoir useful lifeUnder a sedimentological perspective, a reservoir useful life is considered aswhen sediments reach the intake sill and starts disturbing or hindering the operation.For a computation more accurate than the one presented in Table 10.1, thesediment distribution in the reservoir and the increase on either erosion index orsediment transportation must be taken into consideration. One may calculate the heightof the sediment deposit at the dam’s base, or at the intake position for different times,and depict an assessment graph in order to get the forecast on how long will it take forthe deposits to reach the sill. The methods for performing such computation werepresented in item 10.1.10.4 Sediments distribution in reservoirsAs presented in Chapter 3 (see Figure 3.1), the sediments deposits in a reservoirare irregularly formed, occurring the formation of a delta in the backwater area thatexpands towards the lake along time and in face of greater bed sediment. Fine sedimentsbecome settled inner and closer to the dam.The assessment of such distribution may be performed through several methods,as mentioned in item 10.1.10.5 Increase on basin erosionThe increase on sediment transportation along a stream is a consequence of anincrease on the basin’s erosion. Having data on annual average sediment discharge for49ANEEL – Brazilian Electricity Regulatory Agency / SIH – Hydrologic Studies and Information Department