Abstract:

Based on the daily flows from 1954 to 2000 in the Huangjiagang Gauge, the 47year hydrologic regimes were divided into two sequences: one as “near natural state river” before 1967 and another as “maninterfered river” after 1967. According to the Range of Variability Approach (RVA) proposed by Richter，a method using Indicators of Hydrologic Alteration (IHA) containing thirtytwo ecohydrologic parameters, the difference between the flows before and after 1967 was quantitatively evaluated.The value ranging from 25th to 75th for each parameter before 1967 was set as the management target.The impacts of the Danjiangkou Reservoir on ecosystems of the middle and lower reaches of the Han River were further analyzed.The results indicate that，after 1967，most hydrologic parameters have experienced significant alterations.The intrayear allocation of runoff has been greatly changed and the intrayear variations in discharges have been smoothed.Extreme flows are found to occur earlier and the duration has been shortened.Based on these analyses，in combination with the ecosystem characteristics of the middle and lower reaches of the Han River，fish is chosen as the representative biological indicator.The impacts of the abovementioned changes in flow regimes on the growth，reproduction and wintering of fish in the middle and lower reaches of the Han River were then preliminarily discussed. In the end，suggestions on how to reduce the negative impacts were proposed in details.

Key words: Indicators of Hydrologic Alteration/ Range of Variability Approach/ the Han River/ the Danjiangkou Reservoir/ flow regime/ fish