A NEW METHOD TO ASSESS THE FLOW REGIME ALTERATIONS IN RIVERINE ECOSYSTEMS

Assessing alterations of a river's flow regime provides the basis for river protection and restoration planning. The range of variation approach (RVA) is a commonly used method to evaluate alterations in a river's flow regime. However, RVA underestimates the degree of flow regime alteration potentially, because it only considers the difference in frequency between the pre-impact and post-impact hydrologic indicator values within certain target ranges and does not consider alteration of the order of hydrologic year types (HYTs; i.e. wet, average and dry years). The HYT order is an important holistic feature of the flow regime. The human-induced change of HYTs, such as from a dry year to a wet year or from an average year to a dry year, can be a major cause of ecosystem alteration. For some species, the order of the HYTs was more important than single-year events (such as the flood magnitude during a given year). To address this problem with the RVA, we proposed a modification of this method that accounts for alteration of the order of HYTs. We developed a metric for assessing the alteration of the HYT order based on Euclidean distance and then combined this metric with the RVA. We applied the revised method to a case study of the Sha River in northern China to test its effectiveness. The results demonstrated that the new method solved RVA's problem of potentially underestimating the degree of flow regime alteration and enabled a more comprehensive analysis of the alteration of the flow regime. Copyright (c) 2014 John Wiley & Sons, Ltd.