Usually projects are implemented to meet their primary objective. Ribb Dam is going to be constructed in Ribb River of Amhara Region Lake Tana Basin primarily to irrigate 20 thousand hectares of land. However, this thesis identifies to what extent does the Ribb Dam is capable to reduce flood magnitude downstream at Bahir Dar Gonder road Bridge outlet. A river cross section field survey is conducted along the course of the river to confirm the ortho photo data if it represent the existing river condition. A GIS tool is used to overlay the surveyed data & the ortho photo data for the purpose of ground truth & the data is found best to represent the existing river situation.