Comparison of multitemporal multifrequency multibeam echosounder norbit iwbms: depth and sedimentation rate analysis of selorejo reservoir 2022-2023

Selorejo Reservoir is a reservoir constructed and located in Pandansari Village, Ngantang District, Malang Regency, East Java. The Indonesian Government built this reservoir to accommodate the water flow from several rivers, including the Konto River, Kletak Lahar, Kwayangan River, and several other small rivers. The biggest challenge for a reservoir, where the primary clean water source comes directly from rivers, is siltation caused by sediment accumulation at the bottom of the water body. Therefore, severe and continuous control in the reservoir area is necessary to prevent damage and overflow and ensure the community’s safety by engaging in activities around the Selorejo Reservoir. Bathymetric surveys are essential in obtaining information related to marine fields and precise depth values with spatial references. When using a multibeam echosounder, surveyors must consider several aspects regarding the specifications of the equipment before data acquisition, one of which is the frequency used. Different frequencies result in different penetration abilities and data quality. This study aims to estimate the sedimentation rate in the Selorejo Reservoir using multitemporal data and investigate the effect of using multifrequency on the depth measurement results obtained. The results of this study indicate that the higher the frequency used, the shallower the depth value obtained. Higher frequencies provide better representation in object detection capabilities. At the same time, the sedimentation rate was relatively high, from 3.2 to 5.3 centimetres per month.