Seasonal variability of Total Suspended Sediment off the Banjir Kanal Barat River, Semarang, Indonesia estimated from Sentinel-2 images

Abstract

Total Suspended Sediment (TSS) is one of the important variables determining water quality since it controls the biological process in the coastal waters. TSS distribution off the Banjir Kanal Barat (BKB) River, Semarang, Indonesia previously has been investigated using remote sensing method. However, they did not use the TSS algorithm which is designated for coastal area of Semarang or they did not do proper validation process. In the present study, we generated TSS algorithm using Sentinel-2 images for the coastal waters off the BKB River based on 164 match-up data, which consists of the in-situ TSS as the truth TSS and collocated satellite measurements. With the Root Mean Square Error of 6.27 mg/L and bias of -0.29 mg/L, TSS off the BKB River can be estimated by the linear regression of red band. The seasonal variation of TSS off the BKB River is obtained by applying the linear regression equation on the cloud free Sentinel-2 images which represent each month in 2020. The maximum (minimum) TSS occur in February (May) i.e., > 150 mg/L (< 96 mg/L). High TSS plume is clearly seen off the BKB River which indicates the dominant role of BKB River as a suspended sediment source. Based on the TSS distribution criteria by Ministerial decree of environment of the Republic of Indonesia no. 54 of 2004, the coastal waters off the BKB River is categorized as polluted water. The seasonal variation of TSS follows the variation of precipitation. The high (low) precipitation causes the high (low) TSS off the BKB River. The precipitation over land may bring eroded soil that increase TSS. Thus, the management uphill land use may play an important role to control the TSS off the BKB River.