RESERVOIR SEDIMENTATION ASSESSMENT GUIDELINE - Aneel

Reservoir Sedimentation Assessment Guideline9. SPECIFIC WEIGHT OF DEPOSITSThe runoff load is usually computed in terms of weight by time, as t/year, andshall be converted into equivalent volume, as m 3 /year, by knowing the specific weight.Lara and Pemberton realized - by performing researches with samplings from existingreservoirs – that the specific weight for sediment deposits may be computed accordingto the kind of operation for the specific reservoir, the level of sediment compaction andgranulometry, which are the most influent factors for deposits consolidation. Lessinfluent facts may be mentioned, such as the density of the reservoir’s stream sediment,the slope for the tributary stream thalweg and the vegetation effect on the reservoirheadwaters area.9.1 ComputedThe computation for initial specific weight, and after compaction, for a giventime, is performed by using the following equations; the parcel factors for suchequations are obtained based on the kind of operation for the reservoir (Table 9.1).γi= W . P + W . P + W . Pccmmssγ = γ + K.logTfor specific layerTior⎡ T ⎤γT= γ i+ 0,4343.K ⎢ ( LnT ) −1⎥ for total deposit⎣T−1⎦K = Kc. Pc+ Km.Pm+ Ks. Pswhere:γ i = initial specific weight (t/m 3 );W c , W m , W s = coefficient of compaction for argyle, silt and sand, respectively, obtainedaccording to the kind of reservoir operation (Tables 9.1 and 9.2);P c , P m , P s = fractions of quantities of argyle, silt and sand contained in the tributarysediment;γ T = average specific weight in T years (t/m 3 );T = settled sediment compaction time (years);K = constant depended on sediment granulometry and based on the kind of reservoiroperation (Table 9.2);Ln = Neperian logarithm.The values for coefficients γ i , γ T and K, as presented by Strand, were adjusted tobe used in the metric system (Carvalho, 1994).ANEEL – Brazilian Electricity Regulatory Agency / SIH – Hydrologic Studies and Information Department43