Weirs are one of the world wide water resources management structures, which are beside their activity in rising water surface to become important source for electricity by using low head hydropower turbines, it improve the hydraulic and the environment of the river reach.140,000m long of Tigris River reach between Al-Fatha and Samraa cities at Salahaldeen province in Iraq was selected to evaluate the usefulness of constructing system of weirs series by calculating the range of improvements in the hydraulic properties, in the environment and estimating the hydroelectric power potential of the study reach. GIS, Global Mapper (Ver.11) and DEM (digital elevation model) combined with surveyed cross-sections of the river bed were used for the delineation and knowing the number of cross – sections and its area. 30 cross sections were used for river reach in this study. One dimensional and steady flow HEC-RAS model was used .It was calibrated to estimate water surface profiles through a group of equations and to calculate the suitable hydraulic conditions along the study reach. The optimum value of manning coefficient was 0.027. The study area was evaluated and the system of five weirs with heights of (3.7 – 6.0 m) was proposed along the river reach. Their locations depend on trial and error process, geometric of the cross – sections and the ratio of the height of the weirs to the design head. The simulated results by using HEC-RAS model were tested to know the reach behavior against three different discharge values (200, 1242, 8616 m3/s), with return period of 1, 1.15 and 42.50 years respectively, and to compare the hydraulic changes in the study reach before and after installing the weirs and to know the net heads for running the low head hydropower turbines. The results illustrate improvement in the reach hydraulic properties of the river reach. According to the criteria of hydro – power system classifications, the type of hydro – power in this case study was small and the suitable turbine was Kaplan turbine with flow rate of 30m3/sec and with ranges of net heads of (3.29 – 6.08 m). 7 and 41 turbines were chooses for the flow rates of 200 and 1242 m3/sec respectively. The Kaplan turbine is running with very high efficiency below the design flow and with suitable runner diameter. The total estimated capacity of one turbine was (5.38 –7.60 MW) and for seven units, it was (37.66 - 53.20 MW) at one weir. These capacities will cover some of the growth in demand to the electricity in Iraq. It covers about (300, 000) capita of population in the study area. It was found that the maximum cost of the electromechanical equipment for hydro project was 42.91 million US$ .