Abstract: Upstream-downstream relationship among cascade reservoirs is a key component of water resources system modelling. This paper builds a framework for identifying this relationship based on the river coding method, and applies it to analysis of the spatial characteristics of a cascade reservoirs system and its watershed development and utilization. In a case study of the Xijiang River watershed, the results show the cascade reservoirs are connected only by a few of them, and more than 70% are functionally headwater reservoirs. Only five of them are leading reservoirs that have the largest confluence areas and totally control 23.6% of the watershed area, but they play a key role in flood control, water supply, and power generation through their hydraulic connections with many upstream reservoirs. Overall, each tributary in this watershed presents obvious characteristics of typical cascade development, and the number of its upstream reservoirs increases exponentially with the raising in its grade. The results are of great significance for analyzing the function of cascade reservoirs.

Key words: cascade reservoirs, river network, river coding, upstream-downstream relationship, watershed development and utilization