Abstract:

As river degradation becoming the primary problem faced by the river ecosystem of countries all over the world,more attention has been paid to river health assessment.Determination of reference condition and identification of spatial and temporal features are described as the critical components of river health.The spatial and temporal features aids to the selection of indicator of river health assessment,while establishment of reference condition contributes to the determination of criterion.Considering river hierarchy theory,river continuum concept and a fourdimensional matrix,main characteristics of river system and features of its spatial and temporal scale were analyzed.The paper profiled spatial scale of river health assessment from dot (section and site),line (stream and reach),and surface (river basin and river system) grades,and demonstrated temporal scale from short (temporal dot),middle (temporal segment) and long (temporal section) hierarchies.Reference baselines of river health assessment,including minimally disturbed conditions (MDC),historical condition (HC),least disturbed condition (LDC) and best attainable condition (BAC) were defined.Determination procedure and application scope of reference baseline calculating methods using reference site,historical data,expert opinion or simulation models were discussed.Finally,some suggestions to improve the effectiveness of river health assessment were presented