Abstract
Instream ecological flow is an essential determinant of river health. Intra- and interannual distribution characteristics of runoff have been altered to different degrees by dam construction. Historical runoff series with alterations, as basic data for ecological flow calculation, provide minimal instream hydrological process information, which affects the credibility of calculation results. Considering the influence of the alterations in runoff series on ecological flow calculation, the Gini coefficient (GI) is introduced to study the evenness degrees of the intra-annual runoff distribution of four hydrological stations located in the Naolihe basin of the Sanjiang Plain. The hydrological alteration diagnosis system is used to examine the alteration points in the GI series of each hydrological station for selecting reasonable subsequences. Based on the selected subsequences, the ecological flow of each station is calculated using three hydrological methods, and the comprehensive ecological flow is calculated using weighted calculation results from the three hydrological methods. The study results show that ecological flow and natural flow have similar processes with two peaks occurring in the process in May and August, respectively. Also, dams decrease the ecological water requirement damage frequency in dry seasons, but overuse of water resources increases the ecological water requirement damage frequency in flood seasons.
Highlights
Riverine ecosystems play a significant role in the survival and development of human society, so protecting riverine ecosystems is vital
The results revealed that monthly ecological flow calculated using the monthly frequency method was higher than that calculated by other ecological methods
Based on the selected subsequence above, the range of variability approach (RVA) method, monthly frequency method, and annual daily mean flow frequency method were used to calculate the ecological flows of the four hydrological stations
Summary
Riverine ecosystems play a significant role in the survival and development of human society, so protecting riverine ecosystems is vital. Ecological flow is the runoff that maintains the riverine ecosystem health and biodiversity [1,2,3]. Studies on ecological flow have developed rapidly [4]. Many methods have been presented to calculate ecological flow [5,6], of which hydrological methods are widely used due to the simplicity of the data requirements and low calculation costs. The hydrological method calculates ecological flow by analyzing the frequency distribution characteristics of historical runoff series. Some representative hydrological methods, such as the Tennant method [8], NGPRP (Northern Great Plains Resource Program) method [9], minimum monthly mean flow method [10], month-by-month minimum ecological flow method [11], flow duration curve method [12], and the 7Q10 (seven-day low flow with a 10-year recurrence interval)
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