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Geohazard event: Matai’an Land...
Geohazard event: Matai’an Landslide Dam Breach in Hualien, Taiwan
Leveraging high-resolution satellite imagery to assess disaster extent and geomorphological changes.
Challenge
In July, heavy rainfalls associated with the peripheral circulation of Typhoon Wipha triggered a large-scale landslide in the upper reaches of the Matai’an Stream, subsequently forming a significant landslide dam. Risk mitigation during the early stages was significantly constrained by the steep, remote, and inaccessible terrain.
Over the following two months, a series of typhoons caused the landslide-dammed lake to expand significantly. The situation reached a critical point on the afternoon of 23 September 2025, after the passage of Typhoon Ragasa, when the natural dam suddenly breached. This failure released an estimated 10 million cubic metres of water and sediment-laden debris downstream.
The outburst flood caused significant geomorphological and hydrologic changes in the downstream reaches, particularly across Guangfu and Fenglin townships. Large segments of the main channel and adjacent floodplains were covered by substantial sediment deposits, resulting in environmental impacts and infrastructure damage.
Full-length view of Matai’an Stream Pléiades © CNES 2025, Distribution Airbus DS, processed by CSRSR
Pre- and post-event images from the Matai’an landslide-dammed lake to the middle reaches. Pléiades © CNES 2025, Distribution Airbus DS, processed by CSRSR
The critical requirement: rapid damage assessment
In such high-impact geohazard events, the immediate provision of high-resolution satellite imagery is paramount for effective emergency response.
Geomorphological changes: The post-event imagery demonstrates the significant reduction in the lake’s surface area following the dam breach.
Pre- and post-event images of Guangfu and Fengling townships (lower reaches of Matai’an Stream). Pléiades © CNES 2025, Distribution Airbus DS, processed by CSRSR
Solution leveraging direct reception
Pléiades 1A/1B satellites were rapidly tasked, leveraging their high-resolution capabilities to provide essential data throughout the event:
1. Rapid, high-resolution damage mapping
The 50 cm resolution Pléiades imagery provided the necessary details for rapid damage assessment, enabling accurate delineation and mapping of all affected areas.
Spatial delineation: Precise identification of the disaster footprint, including buried floodplains.
Morphological tracking: Clear documentation of channel morphology changes resulting from the sediment deposition.
Quantitative sediment deposition analysis via DoD map. Pléiades © CNES 2025, Distribution Airbus DS, processed by CSRSR
2. Quantitative sediment analysis via DSM differencing
By combining pre-event Pléiades stereo archive data (21 August 2025) with urgent post-event stereo tasking (25 September 2025), highly precise Digital Surface Models (DSMs) were generated.
This critical data was processed rapidly to conduct comparative elevation analysis, producing a Difference of DSM (DoD) map that visually and quantitatively identified areas of sediment and debris accumulation.
Critical accumulation zones: Significant sediment accumulation was identified within the middle reaches' channel, with localised maximum depths reaching up to 56 metres.
Spatial dispersion trends: Sediment thickness exhibits a distinct distal decrease, with most deposits across the wider, flatter lower reaches measuring less than 4 metres.
Pléiades © CNES 2025, Distribution Airbus DS, processed by CSRSR
3. Long-term recovery tracking
The multi-temporal data acquisition capability supports the verification and tracking of ongoing debris removal operations and provides a reliable baseline for long-term recovery and reconstruction planning.
Benefits
The deployment of Pléiades imagery and advanced products delivered crucial, multi-faceted benefits throughout the crisis:
- Rapid response and deployment: The system's high agility ensured rapid acquisition and processing, equipping response teams with timely, location-specific data to enable the effective mobilisation and direction of emergency operations within the initial response phase.
- Topographic analysis and reconstruction planning: Derived topographic products provided an accurate, quantifiable analysis of sediment accumulation volume and distribution, serving as an essential input for detailed hydraulic modelling as well as long-term riverbed stabilisation and dredging plans.
- Continuous monitoring and management: The multi-temporal archive created a continuous, objective record used to monitor and verify the progress of recovery operations, supporting data-driven management and resource optimisation for the extended reconstruction and long-term river management phases.
Organisation involved
The Center for Space and Remote Sensing Research (CSRSR) is a prime research center established in 1984 at National Central University (NCU) in Taiwan.
As a pioneer in remote sensing and geoinformatics, CSRSR operates Taiwan's first resource satellite receiving station, actively conducting research and development across various fields, including land monitoring, disaster investigation and atmospheric analysis. Its core mission is to produce and apply geoscientific knowledge to support national needs, technological advancement and sustainable development.
