Time series Evolution flood satellite detected waters 13 - 29 July 2018

This map illustrates a time series analysis of the evolution of satellite-detected surface waters in Sanamxay district, Attapeu province, based on satellite data collected on 13, 25 and 29 July 2018. Within the current map extent, on 13 July 2018, before the collapse of the dam, a total surface of 47,717 ha was detected as inundated and the reservoir controlled by the dam was full of water. As of 25 July 2018, two days after the dam collapsed, an additional surface of 7,531 ha of inundated areas were detected, representing an increase of the surface waters of 16%. On 29 July 2018, floodwaters are receding, especially along the riverbanks of Xe Kong River. A total surface of 30,435 ha was detected as inundated at that date, representing a decrease of the surface waters of 45%. The reservoir that was controlled by the dam has continuously decreased in its size since the dam collapsed. It is likely that flood waters have been systematically underestimated along highly vegetated areas, along main riverbanks and within built-up urban areas because of the special characteristics of the used satellite data. Additional optical VHR data are needed to validate analysis over areas covered by mud, hardly detected by radar data. This is a preliminary analysis and has not yet been validated in the field. Please send ground feedback to UNITAR - UNOSAT.

This map illustrates the evolution of satellite-detected surface waters in Sanamxay district, Attapeu province, as observed from the Radarsat-2 radar image acquired on 24 July 2018 and compared with a Radsarsat-2 image acquired on 10 July 2018. As of 10 July 2018, flooded areas and saturated soils were already visible, due to the heavy rains that happened previously to the collapse of the dam. As well, the reservoir controlled by the dam was full of water. As of 24 July 2018, an additional surface of 5,826 ha of inundated areas were detected, representing an increase of the surface waters of 66%, due to the collapse of the dam. At this date, the reservoir that was controlled by the dam has decreased in its size. Several villages and surrounding agricultural fields seems to be inundated. The villages of Ban Hinlat, Ban Thaseangchan, Ban Mai and Ban Samong-tai seems to be the most affected ones. It is likely that flood waters have been systematically underestimated along highly vegetated areas, along the main riverbanks and within built-up urban areas because of the special characteristics of the used satellite data. This is a preliminary analysis and has not yet been validated in the field. Please send ground feedback to UNITAR - UNOSAT.

This map illustrates the satellite-detected water extent in the District of Sanamay, Attapeu Province, in the southwestern part of Lao People's Democratic Republic after the tropical storm SONCA-17. The UNITAR-UNOSAT analysis used a Sentinel-1 satellite image acquired on the 30 July 2017 and detected several areas with potentially standing waters. In the district of Sanamxay ~5,225 ha are likely flooded.This is a preliminary analysis and has not yet been validated in the field. Please send ground feedback to UNITAR-UNOSAT.

This map illustrates the satellite-detected surface waters extent in Sanamxay district, Attapeu province, as observed from the TerraSar-X and Tandem-X radar imagery acquired on 27 July 2018. Satellite detected water extent analysis was performed by Centro Internazionale In Monitoraggio Ambientale Research (CIMA) & Luxembourg Institute of Science and Technology (LIST). Within the analyzed area, a total of 7,405 ha were detected as inundated, four days after the collapse of the dam. Disclaimer: Flood extent maps are derived from high quality satellite data using a scientifically validated retrieval algorithm. No liability concerning the contents or the use thereof is assumed by the producer. The information has limitations due to the quality and resolution of the original data sources, as well as the uncertainties associated with the retrieval algorithm. Please be aware that the thematic accuracy might be lower in urban and forested areas due to inherent limitations of the SAR analysis technique. This is a preliminary analysis and has not yet been validated in the field. Please send ground feedback to UNITAR - UNOSAT.

This map illustrates the satellite-detected surface waters extent in Sanamxay district, Attapeu province, as observed from the Radarsat-2 radar image acquired on 24 July 2018. The previous day, the Xe-Namnoy dam collapsed, inducing flash floods along the Vang Ngao river and affecting several villages located 50 km downstream. Within the analysed area 14,692 ha of surface waters were detected after the heavy rains that happened on 22 July and as well the collapse of the dam. Several villages and surrounding agricultural fields seems to be inundated. The villages of Ban Hinlat, Ban Thaseangchan, Ban Mai and Ban Samong-tai seems to be the most affected ones. It is likely that flood waters have been systematically underestimated along highly vegetated areas, along the main riverbanks and within built-up urban areas because of the special characteristics of the used satellite data. This is a preliminary analysis and has not yet been validated in the field. Please send ground feedback to UNITAR - UNOSAT.

This map illustrates the satellite-detected surface waters extent in Samakkhixay district, Attapeu province, as observed from the KOMPSAT-5 imagery acquired on 30 July 2018. Satellite detected water extent analysis was performed by Centro Internazionale In Monitoraggio Ambientale Research (CIMA) & Luxembourg Institute of Science and Technology (LIST). Within the current map extent, a total of 1,617 ha were detected as inundated along the Xe Kong river. Disclaimer: Flood extent maps are derived from high quality satellite data using a scientifically validated retrieval algorithm. No liability concerning the contents or the use thereof is assumed by the producer. The information has limitations due to the quality and resolution of the original data sources, as well as the uncertainties associated with the retrieval algorithm. Please be aware that the thematic accuracy might be lower in urban and forested areas due to inherent limitations of the SAR analysis technique. This is a preliminary analysis and has not yet been validated in the field. Please send ground feedback to UNITAR - UNOSAT.