Central Java’s Flood Extent Result of Failed Canals, Embankment Collapses

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Heavy rainfall in the central Java province of Indonesia between March 13 to March 18, 2024 has caused the failure of two embankments at four different points near Kudus in the Demak Regency. The most significant failure occurred on the Wulan River, exacerbating flooding in the area and causing many canals to fail as a result.

Leveraging cutting-edge satellite analytics, specifically synthetic aperture radar (SAR) imagery and interferometric synthetic aperture radar (InSAR), Ursa Space unravels the intricacies of the disaster’s aftermath, offering insights into the extent of damage and its ramifications.

Central Java Province

Many news sources focused their reporting on a singular embankment failure, though our detections reveal many other canals failed as well. A culmination of the failed embankment at Wulan, failed canals in the surrounding agricultural areas, and the extreme, unseasonably high rainfall contributed to the extent.

Flooding covered 43% of the total area of Demak (430 of 995 sq. km), and 24% of Kudus (104 of 425 sq. km) according to Ursa Space’s analytics. The necessary basis for this output is SAR satellite imagery, an all-weather, 24/7 technology. 

Although the Central Java province averages 12 hours of daylight in March, the area is obscured by cloud coverage 80% of the month, making optical imagery a nearly impossible data point to map the region.

Umbra Space, known for its cutting-edge space radar technology, provided two high-resolution synthetic aperture radar (SAR) images collected on March 21, 2024.

The images narrow in on two key locations: the Wulan river embankments near Demak and Kudus, and the Tawang Station in Semarang

Demak and Kudus

Four total embankment failures were detected in the imagery, with three of them being along a canal just west of the Wulan River embankment.

The Wulan River embankment, which had also been breached during flooding in early February, failed again on March 17th, exacerbating the widespread flooding in the area.

Standing water was still visible in the residential area north of the Wulan River as of March 21st.

A portion of the Wulan river embankment is visibly broken and bright returns indicate construction equipment beginning repair efforts.

Semarang

As of March 21st, flood waters have receded throughout the city of Semarang, Central Java.

Tawang station had been widely reported as having been affected by flooding, however at the time of image capture flooding had receded.

The station may still be inactive however, suggested by the lack of bright returns over the railyard which would indicate the presence of railcars.

By comparison, Poncol train station was reported to have been unaffected by flooding.

DinSAR

Land subsidence has been cited as a major contributing factor to flooding in Semarang.

Ursa Space’s DinSAR tool measured a max subsidence of 35mm from January 3rd to March 3rd 2024 using Sentinel-1 imagery, finding that most of this subsidence was located close to port to the east.

DInSAR is used to observe the differences in phase between two images, allowing physical ground movement changes to be measured over a period of time. DInSAR has emerged as a powerful tool for monitoring ground movements with precision.

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