KAJIAN LOKASI PENGAMBILAN SAMPEL SEDIMEN SUSPENSI ARAH TRANSVERSAL TERHADAP NILAI KONSENTRASI SEDIMEN SUSPENSI RATA-RATA TAMPANG (Perbandingan Data Pengukuran Laboratorium dan Lapangan)

Abstract

Sampling of suspended sediment in the field is often conducted not in accordance with the appropriate sampling standards due to many constraints found in the field. Theoretically, sampling of suspended sediment should be taken in the whole flow-cross section, from the left to the right side of channel, and from the bottom to the free water surface. However, due to constraints found in the field, sampling of suspended sediments are often only taken at certain (transversal) positions of the channel. This will lead to inaccuracies in the prediction of suspended sediment discharge. This article analyzes how the sediment concentration taken in certain transversal positions of the channel relate to their cross-sections averaged values, either for data obtained in the laboratory, and for data obtained in the field. 125 profiles of suspended sediment concentration of laboratory data − measured in the flume at 5 different positions in transversal direction −, and 50 profiles of field data − measured in Mataram irrigation channel at 5 different positions − are analyzed in this article, in which, for each flow run, the depth averaged of and the cross-section averaged of suspended sediment concentrations are calculated and compared. The findings of the data analyzed in this article show that the nearer to the wall, the suspended sediment concentration, y C /C , tend to decrease, whereas the nearer to the center of the channel, y C /C , tend to increase. The values of , y C /C , of the field data are found to be smaller than the ones of laboratory data, that is for the data near to the wall; whereas to be larger in the center of the channel. Although the trend curves of y C /C for the laboratory and the field data are relatively difference, however the positions where, y C /C , = 1, are almost the same, i.e., at z/B  0,2. This results mean that the cross-section averaged of suspended sediment concentration can be obtained from the sampling of suspended sediment concentration at a point of z  0.20 B, where B is the channel width. Keywords : sediment sampling