The aim of the present study is a hydrological approach on Lithaios river (Central Greece) streamflow 2D modelling, using GIS and geostatistics in order to investigate flow velocity, discharge rate, stage, river bed variations and the hydraulic properties (water depth, flow area, wetted perimeter, hydraulic radius and depth, Manning’s coefficient of roughness, Froude Number, etc.). Also, the study aims to the compilation–validation of a rating curve (RC) from a series of stage h(t)–discharge Q(t) pairs measurements, in order to use them as tools to assist environmental and agricultural water resources management, support environmental flows estimation, monitoring and irrigation planning in local basin scale. The results and statistical analysis, showed that Froude number during the measurement period was Fr < 1 which means that streamflow of the River Lithaios, is classified as subcritical. The results of model’s validation using different statistical and geostatistical methods, model simulation, error statistics criteria, were converge to the same output that the data fitting the selected power model for the curve RC and the modelling and 2D GIS mapping of river discharge were very satisfactory since the stabilities of the developed relationships were robust. The resulted outputs are proposed to serve as hydrological assisting tools for environmental water resources and irrigation management at the study area. These assisting tools will help water authorities accurately and quickly estimate river’s water quantities and variation with a minimum cost and effort, and they could be used for irrigation management, environmental flow estimation, flood protection, groundwater recharge and other purposes.