Flood is one of the critical hydrological issues and results from the combination of meteorological and hydrological conditions. Floods can have disastrous short and long-term effects on people and their economies. Flood impacts are functions of valley characteristics and dependent not only on the river discharge/flow depths, but also on the topography of the landform around a river section. The top width of flow at a section corresponding to a depth of flow can be determined by using Digital Elevation Models (DEM). River flow models can be redefined using flow top width variable(s) and used to quantify downstream inundation area on the basis of upstream flow depths/discharges in a river system. The book describes applications of data-driven model, ANFIS, time-series model, ARIMA and the hybrid Muskingum models in simulating and forecasting downstream flow depths, discharge and flow top width in a river system. Models applications and the results obtained for a river system in Barak basin in India are presented in the book.