Runoff analysis of the Chang Jiang ( the Yangtze River )

The daily discharge of the Chang Jiang (the Yangtze River) at Yichang (catchment area about one million square kilometres) is derived by routing the daily discharge of the Jinsha Jiang at Pingshan (catchment area about half a million square kilometres) with modelled runoff based on daily precipitation at 14 rainfall stations in the downstream Sichuan basin. Precipitation at each station is transformed into runoff by means of a tank model composed with a time lag. The time lag is assumed to obey a normal distribution, the mean and the standard deviation of which are determined by the discharge on the same day at Three Gorges. Analyse hydrologique de l'écoulement du fleuve Chang Jiang (Yangtze) Résumé Le débit moyen journalier du fleuve Chang Jiang (Yangtze) à Yichang (où la superficie du bassin supérieur est de un million de kilomètres environ) se calcule à partir du débit journalier du Jinsha Jiang à Pingshan (où la superficie du bassin supérieur couvre un demi-million de kilomètres carrés environ) et des précipitations journalières en quartorze points du bassin de Sichuan. Les précipitations à chaque station pluviométrique sont transformées en écoulement par un modèle à reservoirs, et on ajoute un certain délai pour aboutir à l'écoulement donné à l'écoulement obtenu. En supposant que ce délai suive une distribution normale, sa moyenne et son écart-type se déterminent à partir des débits du même jour aux "Trois Gorges". PURPOSE AND AVAILABLE DATA Purpose The purpose of the study is to derive the daily discharge of the Chang Jiang at Yichang from the daily discharge of the Jinsha Jiang at Pingshan and daily precipitation measured at 14 points in the downstream part of the catchment, namely the Sichuan basin (Fig. 1). The main part of the study is the runoff Open for discussion until 1 October 1991 135 M. Sugawara & E. Ozaki 136 2te££_Jâ, I, Or, \ I ^0 Yichang O Precipitation station • Evaporation station Y River gauge Fig. 1 o ioô âoô 300 ç 5 ô — ^ 0 k n Map of the Sichuan basin. analysis of the Sichuan basin, the catchment area of which is about half a million square kilometres. Discharge data The daily discharges of the Jinsha Jiang at Pingshan (catchment area 485 090 km) and of the Chang Jiang at ' Yichang downstream of Three Gorges (catchment area 1 005 501 km) are available for five years from 1978 to 1982.