An eco-functional classification for environmental flow assessment in the Pearl River Basin in Guangdong, China

River classification has emerged as a major application of environmental science, which can overcome the defects of traditional methods in focusing on the single objective of maintaining specified, valued features of ecosystems. However, current efforts to classify rivers by hydrologic processes may result in a growing temptation to ignore ecological variability across basins. Thus, an eco-functional classification is proposed for river management in the Pearl River Basin. This method views ecological functions as fundamental characteristics of riverine systems and provides a framework for dividing a basin into eco-specific categories according to the heterogeneity of the primary ecological functions. In addition, we proposed specific environmental flow methodologies corresponding to three typical river reaches of the basin by perceiving the key attributes of flow variability. In the upstream region of the West River, flow velocity and wetted perimeter are considered as the key attributes of maintaining fish habitat; in a small-sized mountainous tributary of the North river, we choose water surface area to maintain the continuity and biodiversity of the river; while for the aspect of river landscape in the midstream reach of the East River, water level is crucial for maintaining the aesthetic value. This research highlights the ecologically relevant heterogeneity that occurs within and among regions of a basin, and is expected to contribute to a simpler and more comprehensive river management.