Rainfall-Runoff computation of any basin plays an important role for any civil engineering project. In most of the locations the rainfall data is available but the discharge data is not available or is available in gaps. The uncertainty of data is a problem for the hydrologists as proper planning and management techniques cannot be applied. Hence, engineers and hydrologists from all over the world have bend more towards the computer softwares for the estimation of runoff in any catchment. Rainfall runoff estimation is carried out using observed discharge at Rahatgarh site by the models. In support to SCS CN, Arc GIS tool is employed for better accuracy in achieving the composite curve number for the basin. We hope that this book will provide the readers a clear approach to estimate the runoff of any watershed or basin and thus getting benefitted by proper planning and management of the water resources