Today with the advancement in remote sensing technology, very high resolution imaging together with the capability of stereo data acquisition has greatly enhanced the disaster management of high hazardous and inaccessible mountainous terrain. The Rishiganga valley in the Chamoli district of Uttarakhand (North India) was impacted by sudden flash floods triggered due to a massive rockslide, caused by wedge failure on 7th February, 2021. This event caused loss of more than 200 lives besides widespread damage to hydropower projects downstream. Due to the high altitude of the terrain, huge flow of mud and debris down the valley and disruption of road connectivity, made the disaster site inaccessible through conventional means. Therefore most of the preliminary and subsequent studies carried out to assess the impact and the causes of the rockslide have heavily relied on the space based observations. The Indian Space Agency (ISRO) activated (Call Id-803) the International Charter “Space and Major Disasters” (ICSMD) to image the area of the disaster in Uttarakhand. The ICSMD is a consortium of space faring members having a constellation (61 as on date) of highly agile, multi-sensor and multi-resolution of satellite resources, which can be tasked based on type of disaster and requirement, very rapidly over the disaster affected areas to collect information on being activated. These satellite datasets are provided freely by the space agencies under ICSMD platform to serve humanitarian response for the disaster affected sites, keeping aside the commercial interests. The present study is carried out with two objectives first highlighting the role of space data in quick satellite based disaster response for this particular event which assisted the Uttarakhand State Disaster Management Agency (USDMA), Govt. of Uttarakhand to take immediate steps to mitigate the problem. The second objective tries to do an assessment and review of major studies published in peer reviewed journal between February and July, 2021 on this disaster globally to have a synthesised understanding of the event. The pre and post multi-temporal and multi-sensor and multi-resolution satellite data from ICSMD over Rishiganga and Dhauliganga valleys provided first-hand information on the chronology of the events, causes and process mechanism of this unique event and identifying locations impacted downstream. The high resolution images were useful in providing in depth understanding of the damage to hydropower projects, changes in the river geomorphology and the river impoundment due to the obstruction in the flow of one of the tributaries of the Rishiganga joining from the northeast. The satellite based inputs proved to be valuable source of information during this event for the state machinery. From all the analysis it has emerged that the satellite images have unequivocally allowed researchers to determine and quantify various terrain parameters (volume, ele

Researchers dealing with flood hazard and risk assessment typically refer to available in-situ gauging stations for the calibration and validation of hydrological and hydrodynamic (HD) models. However, lack of dense gauging data such as stage-discharge relationship (rating curves) results in higher uncertainty in hydrological studies. The multi-mission satellite altimetry observations are capable since long time to monitor continental water bodies at regular interval. In this study, combined use of hydrodynamic model and satellite altimetry data has been exploited for establishing virtual gauging network in flood-prone sparsely gauged river basin. The virtual gauging stations were established at locations where ground tracks of various altimeters (Jason-2/3, SARAL/AltiKa, and Sentinel-3A/3B) cross the river channel. Rating curves were generated at these virtual stations using calibrated and validated HD model. High agreement between the simulated and altimetry-based water levels at virtual stations showed the potential of satellite altimetry data for the multi-site validation of HD model and constructed rating curves. The availability of water level time series and rating curves at multiple virtual locations in addition to existing in-situ physical gauging stations provides an opportunity to expand gauging network in sparsely gauged basin. Thus, the proposed framework may open new perspectives for enhancing river flow dynamic studies considering upcoming satellite missions like SWOT which will ensure more observations in future.