Assessing effects of dam operation on flow regimes in the lower Yellow River

Abstract

River flow regimes are considered to be primary drivers of riverine ecosystems, while substantially altered by human activities such as damming and reservoir construction. A number of hydrologic indices were recognized to be ecological relevant and used to describe the different characters of flow regimes. At the same time several sets of indicators were developed to assess flow regime alterations, among which Indicators of Hydrologic Alteration (IHA) character the magnitude, duration, timing, frequency and rate of change. The Histogram Matching Approach (HMA) uses the degree of histogram dissimilarity employing the quadratic-form distance between the frequency vectors of the pre- and post- histograms based on the IHA. In this study, Mann-Kendall method (MK) were applied to investigate the temporal abrupt in the lower Yellow River, and then critical influential factors were explored for flow regimes in the lower Yellow River using HMA. Pre- and post- by the year 1984 was separated based on the analysis on daily streamflow records from 1958 to 2006 at the Lijin gauge station. Results revealed that after the separating year, the frequency of low flow is much higher during all twelve months, especially for April. no middle or high flow was recorded, and the calculated distance between pre- and post- equals to 1.0704. The 1-day, 3-day, 7-day, 30-day and 90-day minimum and maximum flow magnitude are shrinking, with the average distances are 0.337 and 0.417, respectively. Duration of low pulse has extended and high pulse has shortened. It can be concluded that the flow magnitude of YR (the Yellow River) is much smaller; the high flows are cut as well as postponed temporally. April should be taken as the critical periods for water resources management because of high frequency of low flow, and important water demands for most vegetation's germination in downstream of the Yellow River Basin.