Abstract: As a large-scale (Category 2)water conservancy hub within the Longjiang River basin of Fuqing city, Fujian province, the Dongzhang reservoir has long faced the combined risks of seepage erosion and deformation due to the influence of its gently dipping, weathered clayey interbedded layers in the dam foundation.This study integrates 2024 full-cycle monitoring data to establish a multi-source monitoring system combining Sentinel-1 satellite InSAR, 3D laser scanning, and BOTDA distributed fibre optic sensing.It analyses the evolution patterns of dam horizontal displacement, circumferential seepage, and foundation uplift pressure.Results indicate, reservoir volume fluctuations predominantly drive displacement, with an extreme displacement range of 5.05 mm at monitoring points YZ10—YZ13, and a mere 2.8%deviation between GNSS and tension-line data.The primary seepage channel RS-1 exhibits an extreme water level variation of 3.318 m, correlating with the 8～15m depth dielectric constant anomaly zone identified by ground-penetrating radar.The uplift pressure variation at the new Y3-2 monitoring point in the dam foundation reached 3.714 m, coinciding with the downstream thermal anomaly zone and fissure belt, where a 10% increase in seepage corresponded to a 0.3℃ temperature decrease.The study innovatively establishes a dynamic coupled model of seepage, displacement, and temperature.It proposes prevention and control paradigms including BeiDou positioning-optimised monitoring grids, digital twin extreme condition simulations, and curtain grouting reinforcement, providing support for the safety management of reservoirs in complex geological settings.

Key words: Dongzhang reservoir, safety monitoring, horizontal displacement, seepage flow around dam, lift pressure