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Basin characteristics

The Yongding river basin is the largest sub-catchment of the Hai River watershed. The catchment area of the Yongding River is 47.016 km2. The catchment share above the Guanting Gorge (Guanting basin) amounts to 95%, 3% is in the Guanting Gorge and the remaining 1% lies in the plain area. From the Guanting basin, about 70% are mountainous regions. The rests are hilly areas of red soil, loess and alluvial soil, which provide a large amount of sediment (average 40 kg/m3 with daily peaks of 450kg/m3) to the Yongding River.

The main parts of the catchment area lay across two provinces: the North-eastern part of Shanxi (total ca. 35 mio inhabitants, 205.000 km2) and the North-western part of Hebei (total ca. 65 mio inhabitants, 190.000 km2).

The annual precipitation in this area is about 450 mm. The combination of loose soil and serious seepage is responsible for low annual runoff values. But the storms and corresponding floods are fierce and concentrated in a short period of time. The river flows in a largely man mad riverbed. A levee system exists since 1180. At present the old floodplains between the levees are 5-7 m higher than the ground surface outside the levees due to past river bed sedimentation.

The Guanting Gorge with an area of 1.520 km2 is a mountainous area with steep slope. Heavy rainfall may induce big floods in this area. In 1954 the Guanting dam was primarely built in order to safeguard Beijing and Tianjin for big flood events. Since its first operation year, four reconstructions (including dam heightening and consolidation) have been carried out. In 1989 the total storage capacity of the reservoir was 4.16 billion m3 (ISI 2004). This is more than all German dammed storage lakes and reservoirs combined. Two other major reservoirs built in the upper basin parts increased the storage capacity during the 1960’s: the Cetian reservoir on the Sanggan River completed in 1960 and the Youyi reservoir on the Dongyang (Yanghe) River finished in 1963.

A large amount of sediment deposited in the reservoir during the first ten years of operation in the Guanting reservoir. Additionally built middle and smaller-size dams in the upper basin parts helped to reduce sedimentation since the 1970’s. (ISI 2004). However, approx. 640m m3 of sediments have been deposited in the reservoir and many million m3 more are added each year (depending on runoff conditions).

Original planning projections for reservoir discharge amounted to 44 m3/s. The current mean discharge rate is about 5 m3/s only.

The mean discharge is reduced by decreasing storage capacity but also by the increasing water use in the upper basin parts for irrigation in combination with recent climate trends.

The drastic decrease of water discharge in combination with increasing nutrient and matter loads from point and diffuse basin sources lead to a decrease in water quality as well. Thus, the water availability and suitability for the Beijing administrative area below the reservoir decreased drastically during recent years.  Currently, water from the Guanting reservoir is practically only used downstream for irrigation in agriculture and energy production (intermittent production is heavily limited due to lack of water).

 (source: Wechsung, project proposal)

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