Calculation method of river hydrological regime alteration degree

The Range of Variability Approach(RVA) is an important method for assessing the river hydrological regime alteration degree.The original RVA only focuses on the frequency changes of hydrological indicators within target intervals, but ignores their distribution characteristic changes, which may underestimate the alteration degree of hydrological regimes.In order to quantify the degree of change of river hydrological regime more comprehensively, the mean value and coefficient of variation were introduced to reflect the changes of distribution characteristics such as central tendency and dispersion degree of hydrological index values in the target interval, and a new evaluation method for the degree of change of river hydrological regime was established by combining the original variation range method.The Hanjiang River was adopted to test the effectiveness of the improved RVA.The results showed that the improved RVA can quantify the hydrological situation change characteristics which was not considered in the original method.Taking Huangzhuang hydrological situation as an example, the original variation range method obtained a low degree of change of 20.63%,the new method obtained a moderate degree of change of 50.71%.The improved RVA can assess the river hydrological regime alteration more comprehensively and accurately, and provide more reasonable quantitative targets for ecological flow assessment.