Abstract: The basis of managing river ecosystem lies in the assessment of river ecosystem health. A cloud model for assessing the health of river ecosystem in plain river network area is presented. The index system of the assessment model includes six aspects: river hydrology, river morphology, riparian zone, physical and chemical properties of water, river biology, and social service function; the weight of each index is determined via improved order relation analysis. The health of river ecosystem is classified into five levels: healthy, sub-healthy, unhealthy, ill-conditioned, and severely ill-conditioned. The model was applied to the Shuiyang River (Gaochun Section), a typical river in plain river network area, as a case study, and the result was compared with that of the fuzzy analytic hierarchy process model. The comparison demonstrates that the cloud model with improved order relation reduces the subjectivity while fully reflecting the fuzziness and randomness in the evaluation process. The assessment results are reasonable and comform with the reality.

Key words: river ecosystem, health assessment, evaluation index system, plain river network, improved order relation analysis, cloud model