Linear models for river flow routing on large catchments

Following a brief review of the place of linear input-output models in applied hydrology, the algebraic analysis of multiple input single output linear systems is presented and applied in the context of flood routing on the Changjiang (Yangtze River) in China. Two different stretches of the river and one tributary catchment are chosen and the outflows are forecast in terms of observed flows at the upper ends of the river reaches and rainfall on the intervening catchment. It is shown that very high accuracy indeed can be obtained with multiple input linear models whether applied to the total flows and rainfall or to the departures in these quantities from their seasonal expectations. The paper concludes with some analysis of the residual errors which could provide the basis of an updating procedure if the linear models were used for forecasting purposes.