Abstract:

Healthy river is acknowledged as the object of river management and the basis of environmental flows assessment, thus in terms of river health assessment theory is of great significance in theory and practice for improving the river ecosystem environment.The study is undertaken in the Liao river basin that based on the changes between four seasons in the northern region of China.Affected by indicators such as hydrological conditions and human disturbance,the river health also has seasonal characteristics.The aim of this paper is to access the river health by month and study its changing rule within Main Liaohe River basin.River health assessment used indicators as water quality,biological indicator,riparian vegetable,the physical form of the river system and the socioeconomic indicators.The study used AHP method for assessing the health of the Liao river and a score from 15 was assigned for each indicator.These scores were then aggregated to produce combine score to evaluate the river health condition.And the fivegrade assessment standard described as" healthy,subhealthy,normal,subsick and sick” were established.The result showed that the river health in Main Liaohe River changed by stages and obviously.The hydrology and water quality indicators were the mainly disturbance of river health management.The month within DecFeb was on the sick level,MarMay and OctNov were on the subsick level,JunSep was on the normal level.Based on this characteristic,the idea of ecological regulation by stage was suggested to restore the river health condition.This study divided a year into four seasons:frozen season, dry season before flood,flood season,and dry season after flood.It also confirmed the minimum ecological water demand in frozen season,river selfpurification water demand in dry season,the sediment water demand in flood season.At last the study coupled the ecological flow process of the Liaohe River,and compared with the Tennant method.The result indicated the flow process met the natural runoff rhythm which was able to maintain river health better.The advise is health changes in the Liaohe,a major river in northern China,could provide the basis for health management of the rivers of northern China.The accuracy of the data would have a great impact on the accuracy of the evaluation results during the process of evaluation of river health trends.Because of the lack of ecological information of the riparian zone vegetation, long series river health status can only have a limited analysis instead of comprehensive analysis.Therefore,river health management should be concerned to strengthen the collection and monitoring of ecological data,which also contributes to longterm maintenance of river health