Innovated method applied to adapt Hatra Bridge on Tharthar valley as discharge monitoring station, to estimate the water income of the valley near the site of proposed dam. The section of the valley was geometrically surveyed before the first rainfall storm to build the equation of relationship between water level and area of flow section which required for the discharge estimation. Six flood waves were monitored along the period of raining season of 2012-2013, the flow velocity were measured on the surface of flow section, with 30 minutes time interval, the same time interval used for the measurements of water level. The average velocity estimated by innovated method according to the measurements of surface velocity, the equation of the relationship between average velocity and water level were derived and applied with the cross sectional area of flow to estimate the discharge, then the accumulated discharge measurements converted to the total volume of water income for each flood wave. The total volume of water income in the studied section reached to 141719509 m3.