RESERVOIR SEDIMENTATION ASSESSMENT GUIDELINE - Aneel

Reservoir Sedimentation Assessment Guidelinewhere V is the reservoir volume, D is the distance between the sections and A is thecross-sections area.11.7 Computation of settled sediment volumeThe methods presented in item 11.6 refer to the computation of the reservoirremaining volume.Similar computation, using the same equations, is performed by using theprimary or previous survey for comparison purposes, as well as for calculating thesediment volume through the difference between two reservoir volumes for thereservoir.Having the dead storage, the settled volume shall also be computed. Bycalculating the difference to the total volume, one can obtain the volume of sedimentsettled in the useful volume.Those values may also be computed as percentages, in order to review thereduction in the reservoir total volume, the useful volume reduction and to know thetrap efficiency as well.11.8 Outline of new level x area x volume curvesAmong the several results deriving from the survey, the knowledge on thesettled volume and the new reservoir capacity are outstanding.Having the areas of bathymetric curves and corresponding volume summed upto each isobathic being considered, one can trace out the level x area and level x volumecurves. For comparison purposes, the original curves are also traced out.11.9 Pivot pointIt is also important, for the survey, to verify the new geometry of the lake. Forthat, comparative cross-sections are traced out (Figure 11.13), selected from sites alongthe reservoir that may reflect the changes on geometry, concerning its original and newcondition. If there are several surveys available, one shall trace out several sections onthe same position for comparison purposes. The formation of crests, changes on thedelta area and height of sediment settled at the dam base are also surveyed.The longitudinal line for the current thalweg is also traced out for comparing itwith the previous line, intending to obtain the pivot point and its development, whichcharacterizes the delta (Figure 11.14).ANEEL – Brazilian Electricity Regulatory Agency / SIH – Hydrologic Studies and Information Department68