 This research paper compares four open-source digital elevation models, DEMs, for hydrodynamic, HD, modeling and flood risk mapping in the Dhaman Ganga Basin in India. It also uses two methods, Gumbel's Extreme Value Distribution, GEV, and Log Pearson Type 3, LP3, to calculate the peak flood depths corresponding to different return periods. The study concludes that CARDASAT-1 DEM provides reliable results with the observed flood depth, while the GEV method gives more reliable estimates for lower return periods and the LP3 method for higher return periods. This study highlights the importance of evaluating different open-source data and techniques for developing reliable flood mitigation, plans with practical implications. This article was authored by Parth Gangani, Nikunj K. Mangukia, Darshan J. Mehta, and others.