RESERVOIR SEDIMENTATION ASSESSMENT GUIDELINE - Aneel

Reservoir Sedimentation Assessment GuidelineTable 7.5 – Methods and equipment for sedimentometric analysisSuspended sedimentsamplingTotal concentration analysisGranulometric analysisFiltration methodEvaporation methodSettling tube methodSettling tube methodPipettingDensimeterBed load samplingGranulometric analysisSifteringDensimeterPippetingVisual accumulation tubeSettling tube methodEach method has its own restriction, thus demanding suitable quantities ofsediment contained in the sampling. The filtration method is used for low-concentrationsamplings – lower than 200mg/l – and small volume, in order to avoid obstructing thefilter. The evaporation method is used for higher-concentration and higher-volumesamplings. Both methods require the reduction of the sampling volume, by decantationor water-bath, in such a way as to hold all particles along the process. According toWMO (WMO, 1981), the required volumes for an accurate analysis are those presentedin Table 7.6.Usually, concentration is determined as the ratio between the dry sedimentweight and the volume of the water-sediment mixture, in mg/l, or the ratio between thedry sediment weight and the water-sediment mixture weight, in ppm (= mg/kg =mg/1.000.000mg). The ppm values may be used as mg/l up to 16.000ppm with nodensity adjustment. Data may be presented with three significant algorisms up to 999(0,32ppm, 3,21ppm, 32,1ppm, 321ppm).Table 7.6 – Volumes of sampling required for suspended sediments concentrationanalysis (WMO, 1981)Expected concentration of sedimentloadSampling volume(g/m 3 , mg/l, ppm)(liters)> 100 150 to 100 220 to 30 5< 20 10Granulometric analyses for suspended material are performed with smallquantity of sediments, using the principle of the particles water dropping velocity. EachANEEL – Brazilian Electricity Regulatory Agency / SIH – Hydrologic Studies and Information Department27