Calculation of ecological basic flow of Weihe River based on basic flow ratio method

To make the ecological basic flow better reflect river life water demand inter-annual and years change in the north of China, the basic flow ratio method was proposed, which divided long-term runoff statistical data into different hydrological years such as wet, normal, dry and special dry. By using traditional methods to determine the basic flow ratio of a certain hydrological year and counting the ratio of average runoff between this hydrological year and other years, the relationship between each basic flow ratio could be ascertained. Thus, the basic flow ratio of other hydrological years and ecological basic flow values could be calculated. Also, the value of ecological basic flow could be calculated for different periods in a year respectively. Taking mainstream of Weihe river in Baoji section as an example, the ecological basic flow was calculated based on basic flow ratio method. The results showed that the ecological basic flow for different hydrological years and periods calculated with this method was 5.00-36.00 m3/s. Results of other methods, such as Tennant and Texas method, were in this scope and guarantee degree of every hydrological year could reach 90%. This method could be applied to calculating the river ecological basic flow in northern China.