Water storage reservoirs along the river drainage network are built and used for various purposes, such as human supply, hydroelectricity, irrigation, flood control, and downstream flow regulation. A particular river point is chosen, and a dam is built at this cross-section, allowing for water accumulation as a lake. This chapter demonstrates how DEMs can estimate artificial reservoirs’ flooded area and volume, producing area–volume–elevation relationships essential for reservoir design, operation, and environmental impact assessment.