Evaluasi Kerusakan Groundsill dan Rekomendasi Mitigasi AwaSl Berdasarkan Survei Pesawat Udara Nirawak dan Analisis Model Elevasi Digital

Abstract

The collapse of the Srandakan groundsill on the Progo River caused riverbed degradation and triggered headward erosion that potentially threatens the stability of the new Srandakan Bridge. Unstable post-collapse field conditions limited the use of conventional terrestrial surveys to obtain damage geometry data quickly and safely. This study evaluated damage to the Srandakan groundsill through the integration of Unmanned Aerial Vehicle (UAV) surveys, GNSS control, and Digital Elevation Model (DEM) analysis, applying a relative risk classification among piers based on geometric indicators, given the unavailability of pier foundation depth data. Unlike previous UAV-DEM studies that focused on post-earthquake damage mapping or riverbank erosion characterization, this study represents one of the first applications of this approach specifically to post-collapse groundsill damage evaluation. Accuracy testing yielded a CE90 of 0.052 m and an LE90 of 0.066 m, meeting Class 1 standards of the Geospatial Information Agency Regulation. Results showed the lowest riverbed elevation reached 3.23 m, a decrease of 7.12 m from the reference elevation of 10.35 m, with headward erosion identified extending approximately 250 m toward the new Srandakan Bridge. The relative risk classification indicated that Pier 6 fell into the highest risk category, followed by Pier 7 (moderate) and Pier 8 (moderate-low), while Pier 5 could not be classified using the vertical indicator due to its position at the edge of the active channel. These findings form the basis for preliminary mitigation recommendations prioritizing high-risk piers, serving as an initial basis prior to further hydraulic studies and structural design