Determination of the proportion thresholds of ecological base flow in rivers with different scales in different watersheds of China
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Abstract:
The ecological base flow is very important for coordinating the ecological protection and development of rivers.However,the threshold system that can effectively guide the determination of China′s ecological base flow is still lacking.In previous studies,it is generally required that the proportion of river ecological base flow to its multi-year average natural flow (referred to as “ecological base flow proportion”) should not be less than 10%.Considering the different hydrological and ecological conditions in different regions of China,it is difficult to effectively meet the macromanagement needs of China′s ecological flow by adopting a unified threshold standard. Through the analysis of natural and measured hydrological data of 439 sections,a threshold system is proposed for the ecological base flow proportion of rivers distributed in 10 Class I water resources zones and different catchment areas of China (excluding Hong Kong,Macao and Taiwan).The proportion thresholds of ecological base flow are composed of the upper limit,lower limit and recommended values. The results show that:When there is no controlled engineering control,the ecological base flow proportion shows an upward trend with the increase of catchment area.The average recommended values in small,medium and large sections are 4.4%,6.6% and 9.2% respectively in dry season and,9.4%,11.6% and 16.2% respectively in wet season.In terms of large sections with a catchment area of more than 10,000 km2,the recommended value in the dry season in the water resources zones is 9.2% on average.Among them,the highest in the Yellow River,southwestern rivers and northwestern rivers regions,reaching 16%,while the lowest is only 1% ~ 3% in Songliao and Huaihe regions.the average recommended value in the dry season in the water resources zones is 15% under the regulation of water conservancy projects. The proposed threshold values can provide support for the determination of ecological base flow considering different regions,section types,and periods.
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