Measuring Ground Subsidence Rate in Bulacan and Pampanga Delta using Geodetic Techniques

Based on the map produced from Sentinel-1 images using Permanent Scatterer Interferometric Synthetic Aperture Radar (PSInSAR), the Pampanga River basin is undergoing ground subsidence. Ground measurements using geodetic techniques such as differential levelling and Global Navigation Satellite System (GNSS) levelling can validate the deformation map. Several ground control points (GCPs) established previously were re-occupied by GNSS receivers. The results indicate similar trend i.e. land subsiding. Only 3 BMs were found in Bulacan and were given new elevations during the levelling campaign in 2021. The differences of the old and new values also indicate downtrend. Six (6) low-cost GNSS monitoring stations were installed in areas where subsidence rates are high based on the SAR deformation map to monitor the ongoing land subsidence. The initial results from 4 out of 6 GNSS monitoring stations for the 3-month observations showed a downtrend indicating land subsidence is occurring in the area.