| The connectivity of rivers-lakes system refers to the smoothness of the interconnection between the watershed units.It is the basic attribute of the watershed system,and the basic requirement to maintains the material flows,energy flows,information flows,species flows between upstream and downstream,rivers and lakes,riverways and floodplains in the watershed,which includes four dimensions:lateral connectivity,longitudinal connectivity,vertical connectivity and temporal variability.Among them,the longitudinal connectivity of rivers is the dimension most affected by barriers.In the past,the large-scale evaluation of longitudinal connectivity of rivers in China generally only considered the number of river blocking structures per unit river length,but the impact on the blocking of different types of river blocking structures and the restoration of fish pass facilities are not considered comprehensively.In order to solve these problems and analyze the different block effects caused by the distribution of river blocking structures,this paper proposes an improved barrier coefficient method that considers the location correction factor to evaluate the longitudinal connectivity of major rivers in China,and analyzes the current situation of longitudinal connectivity and the temporal-spatial variation trend of rivers in Ten First-Class Water Resources Regions in China,corresponding restoration plans and restoration goals of sub-regional management are proposed.The research content include:(1)According to the First National Water Census,the temporal-spatial distribution of the number,scale and type of river blocking structures in Ten First-Class Water Resources Regions in China were classified statistically.(2)Taking 215 rivers with the river basin area more than 10000km2 and 1409 large-scale and medium-scale of river blocking structures on these 215 rivers as the evaluation objects,the improved barrier coefficient method that considers the location correction coefficient is used innovatively for the evaluation of the longitudinal connectivity of the major rivers in China.(3)Based on the evaluation results of the longitudinal connectivity of the major rivers in China,the construction of upstream restoration measures such as the construction of fish facilities,downstream restoration measures such as proliferation and release of fish and comprehensive restoration measures of upstream and downstream were proposed,and performs scenario simulations on different restoration measures.The conclusions include:(1)In terms of the number and the scale of structures,the total number,the number of large-scale and medium-scale of river blocking structures in the Yangtze River Region are the largest in China,and far higher than the other nine regions,and the Xibeizhuhe Region has the least river blocking structures in China.In terms of types,the main structure type in the Xinanzhuhe Region,the Zhujiang Region,the Yellow River Region,the Yangtze River Region,and the Songhua River Region are dam gates.The sluices in the Liaohe Region and the Xinanzhuhe Regions are evenly distributed.The main structure type in the Xibeizhuhe Region,Huaihe Region and Haihe Region is sluice.By analyzing the construction trend of river blocking structures,it was found that most of the river blocking structures were built during the 1960s to 1980s,and the construction speed slowed down significantly after the 1980s.(2)The results show that the national average longitudinal river connectivity index was 0.05 in 1960.In 2018,the national average longitudinal river connectivity was significantly worse than in 1960,the corresponding index reached 1.07,the overall evaluation results dropped from "excellent" to "poor".At present,the Xinanzhuhe Region,the Zhujiang Region and the Yangtze River Region have the lowest three scores for longitudinal vertical connectivity,the Songhua River Region has the best longitudinal connectivity,and the evaluation level is still maintained as "excellent".Regarding the variation trend of longitudinal connectivity of rivers,the average longitudinal connectivity of major rivers in China has shown an accelerated deterioration trend in the past 60 years,and the deterioration trend has become more obvious in the past 20 years.(3)The results show that the comprehensive recovery measure is the best way for the restoration of the longitudinal connectivity of rivers.The national average index of the longitudinal connectivity of rivers after restoration is 0.59,which is 44.9%lower than 2018.By comparing the results of the functional connectivity prediction at each First-Class Water Resources Region with only the upstream or downstream restoration measures,it is found that the use of upstream restoration measures such as the fish pass structures are effective for the region with more dam gates and poor the current longitudinal connectivity of rivers;the downstream restoration measures such as proliferation and release of fish are effective for the region with few dam gates and good longitudinal connectivity of rivers.In addition,according to the scenario simulation results of different restoration measures,combined with the current situation of each First-Class Water Resources Region and future water conservancy project construction planning,corresponding management and restoration goals are proposed for each First-Class Water Resources Region,which provide reference for engineering planning of the development and utilization of water resources,conservation and restoration of water ecological. |
