Impact of Baojixia water diversion works on the hydrologic regime in the Wei River basin

Abstract

Abstract Baojixia water diversion works have direct impacts on river hydrology, primarily resulting in the changes of the magnitude, frequency of low and high flows, ultimately generating a new hydrologic regime differing significantly from the natural flow regime. Streamflow and precipitation data from 1944 to 2008 at Linjiacun station are analyzed in this study. In order to evaluate hydrologic alteration before and after water diversion, the Range of Variability Approach (RVA) is used in this paper, and hydrologic data was divided into two periods: before and after 1972, when Baojixia diversion works brought to service in the Wei River. It is supposed that the hydrologic time series before 1972 represents the hydrologic regime for the pre-impact period, and that after 1972 for the post-impact period. The Chi-square test is used to analyze the hydrologic alteration of monthly flows, which is classified as low, middle and high hydrologic alterations. Flow Duration Curve (FDC) representing the relationship between the magnitude and frequency of streamflow was used to investigate flow characteristics from low flow to high flow. FDC is categorized as three parts on the basis of magnitude of streamflow: high flow (below 10% of exceedance frequency), low flow (over 90% of exceedance frequency) and constant flow (from 10% to 90% of exceedance frequency). The results show that the magnitude of monthly flow decreased obviously in the post-impact period, especially in dry seasons. The degree of hydrologic alteration is high. The shape of FDC in the post-impact period is different from that in the pre-impact period. There is an obvious trend for FDC in the pre-impact period, while there is no obvious regularity between magnitude of streamflow and exceedance probability in the post-impact period. According to the analysis on the data of water diversion, water withdrawn accounted for about 80 percent of natural runoff in dry seasons. This may be the reason why the alteration of monthly flow in dry seasons is highest. In summary, monthly streamflow after 1972 changed greatly because of water diversion. This analysis makes one to understand hydrologic regime well, and will be helpful for the management of water resources in the Wei River basin.