Introducing a Holistic Ecological Model under Data Shortage for Determining River Ecological Water Requirements

River flow regime is dynamic and comprises different characteristics. Low flows, small floods, and high floods are among the most important components of the regime and play special roles in retaining the river in a healthy condition. Allocating the minimum environmental flow as a fixed figure, disregarding these important components of the river regime, is common in river management in the country. The present research, noticing the imposed danger to environment through such policies and using the ideas embedded in Building Block Method (BBM) as a holistic method, obtained the river environmental flows under the condition of data shortage. The employed criteria used in this research for defining the required thresholds to achieve the proper regime were; providing living creatures in the river with appropriate hydraulic conditions, retaining river bed morphology, protecting main channel shape, saving riparian vegetation cover, and coinciding with the watershed climate. Based on the results, wetted perimeter technique was employed when supplying drinking and industrial water, a combination of historical minimum discharge and Q95 was used when supplying agricultural water, a 2-year flood was used for saving river morphology and flushing sediment from its bed, and a 5-year flood was employed for supplying water to the river flood plain. As the main achievement, this research introduced a comprehensive ecological regime defining the required thresholds for a healthy river in an IWRM framework.