River Management for Ecosystem Conservation- Policy-Making Support through Mathematical Modelling-

Human activity is developed on a river basin, which is a unit of hydrological cycle of the surface of a globe, In a river basin, rainfall is converted to flow regime in a river. Not only water but also various materials are transported along a river, and they support various organisms. Our activity is closely related to these processes and river basin management is a key for sustainability of human activity. In particular, management of rivers must be efficient where the above processes are dynamic. Since the revision of River law in 1997, ecosystem conservation has become one of the objectives of river management, and we have tackled with the research topics how to recognize the mechanism of river ecosystem where it would be described quantitatively and mathematical modelling is one of powerful means. We regard ecosystem as an interrelating system among (1) physical basement, (2) material cycles focusing on the bioelements and (3) biological aspects, and mathematical models to describe respective subsystems are developed in addition the interactions among subsystems. This paper introduces the framework of mathematical modelling and some examples, where it is able to how we are able to recognize not only degradation of ecosystem by human impacts but also rehabilitation effects by new policies and measures of river management