The course of the Nile in northern Sudan follows a contorted path creating the Great Bend. Few years ago, the satellite images showed a fertile strip of land with villages, where paleochannels of the river hosted many fields with cultivations and archaeological sites. Now, a huge part of this valley is under the waters of Merowe Dam reservoir. Comparing the images of the region before and after the dam gates were closed, we can show how the reservoir created itself through flooding the paleochannels. The comparison of satellite images is performed using an image processing program based on the calculus of a fractional gradient.