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sluices and pumping stations, with a capacity comparable to the average discharge from Datong in dry months. Such large-scale water diversions may greatly ...
Hydrological Sciences-Jkmrnal-des Sciences Hydrologiques, 47( 1 ) February 2002

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Large and episodic decrease of water discharge from the Yangtze River to the sea during the dry season

CHEN XIQING, ZHANG ERFENG Stale Key Laboratory of Estuar'me and Coastal Research, East China Normal Shanghai 200062. China [email protected]

University,

XU JIANGANG Geography Department, Nanjing University, Nanjing 210093,

China

Abstract A diagnostic study on the large and episodic decrease of discharge from the Yangtze River to the sea is presented. No trend has been detected so far in the time series of river flow recorded at Datong, but a large and short-term drop is evident through analysing the yearly minimum discharges. Water abstractions in the middle reach are evidently responsible for the large and episodic drop recorded at Datong. Downstream of Datong the discharge further decreases due to water abstraction by sluices and pumping stations, with a capacity comparable to the average discharge from Datong in dry months. Such large-scale water diversions may greatly reduce the water discharge into the sea during droughts, if countermeasures are not prepared. An increasing seasonal variability will exacerbate the existing water and environmental problems in the Yangtze Delta and estuary. An integrated management system is necessary for sustaining sufficient freshwater discharge into the sea. Key words Yangtze River; river runoff; water diversions; streamflow droughts; trend detection; How regimes

Baisse importante et brève du débit du Fleuve Yangtze déversé en mer durant la saison sèche Résumé Une recherche diagnostique a été menée au sujet de la baisse importante et épisodique du débit du Fleuve Yangtze déversé en mer. Jusqu'à présent, aucune tendance n'a été détectée dans des séries temporelles de débit à Datong, mais l'analyse des débits minimum annuels montre l'existence d'une baisse importante et brève, dont les prélèvements d'eau sont évidemment responsables. Le débit continue de baisser en aval de Datong à cause des prélèvements des canaux et des stations de pompage, dont l'ampleur est équivalente au débit moyen des mois secs. Ces prélèvements d'eau à grande échelle peuvent lourdement réduire le débit arrivant à la mer lors des sécheresses, si des mesures palliatives ne sont pas mises en œuvre. L'augmentation de la variabilité saisonnière va mettre plus encore en péril les ressources en eau et les écosystèmes dans le delta et l'estuaire du Yangtze. 11 est donc nécessaire d'avoir une gestion intégrée pour maintenir un débit d'eau douce déversé en mer suffisant. Mots clefs Fleuve Yangtze; écoulement de cours d'eau; prélèvement d'eau; étiages; détection de tendance; régimes hydrologiques

INTRODUCTION Being the largest river in China, the Yangtze (Changjiang) covers an area of about 1.8 million km" with an average annual discharge into the sea of 28 600 m J s"1 between 1951 and 1999. The seasonal variability of water discharge is relatively small in comparison with that of the large rivers in North China, such as the Yellow River.

Open for discussion until I August 2002

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Chen Xiqing et al.

Human activities already have a strong influence on the hydrological processes in the middle and lower reaches. The most notable is the large and episodic drop in flow and water stage during the dry seasons. Even if it is not as extreme as in North China (cf. Feng et al, 2001; Xia & Chen, 2001), it causes severe environmental, economic and water supply problems. Meanwhile, global warming is expected to cause an increase of the seasonal variability of discharge from the Yangtze into the sea.

DATABASE The water discharge records are published by, or obtained from, the national hydrometric stations. Information about water abstractions along the river banks are based on field surveys and documented material from local government agencies. The data of water chloride concentrations in the Yangtze estuary are obtained from the local waterworks. Some recent information comes from official reports.

DECREASE OF L O W FLOW RECORDED AT DATONG The Datong hydrometric station (Fig. 1) is located at the tidal limit. It provides continuous records since 1950 which allow the study of the changes in water discharge from the Yangtze basin. The relationship between water levels and water discharge downstream of Datong is influenced by tides and tidal flows. The three highly populated provinces in this area—Jiangsu, Anhui and Shanghai—have rapidly developed industries and agriculture. The monthly mean discharge at Datong shows large seasonal fluctuations, ranging from 84 2 0 0 m V in August 1954 to 6730 m3 s~' in February 1963. Chen (1991) in»

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