Water balance and water quality

The lake is located in the Jinsha catchment area. The lake’s total volume sums up to 1.56 bn. m³ with a surface area of 310 km² and an average depth of 4.7 m (World Lakes, 2005). The northern part of the lake, the Caohai, is separated from the main lake, the Waihai, and discharges into the Xiayuan channel under standard conditions. The Waihai lake outflow is located at Haikou. With a catchment area of approximately 2900 km² and more than 20 natural rivers discharging into Caohai and Waihai, the lakes receive an annual volume of 5.5*108 m³ of water and have a combined outflow of 4.07*108 m³ per annum (cf. picture below).  Due to the location of inflows and outflows the flow through the lakes is extremely non-uniform, resulting in a local concentration of contaminants from point sources such as waste water discharges. With the lake being used for industrial and agricultural purposes, water supply, flow control, flood protection, aqua culture, boat traffic, tourism, and last but not least, drinking water supply, the total water withdrawal exceeds 25 % of the lake’s inflow.

Mittlere Jahreswasserbilanz des Dianchi Sees, Angaben in 108 m³ (Jin et al 2006)
(Jin et al., 2006)

The water quality parameters BOD5, COD, total nitrogen, and total phosphorous indicate a slight water quality improvement as of 2007, after the tenth Five-Year-Plan and the plan’s environmental protection agenda for Yunnan had been put into action. Nonetheless, the target values for good water quality are still not met.

Entwicklung der org. Parameter BSB5 und CSB sowie N-ges. und Pges. im Dianchi-See von 1998 bis 2009 (Res. Center of Ecology, 2013)
(Jin et al., 2006)

Location Kunming (Dianchi)

The Dian Lake is the sixth-largest Chinese fresh water lake. It is located in the Eastern Yunnan-Guizhou-plateau at an elevation of 1880 meters and is part of the administrative district of Kunming, capital city of the Yunnan province.

Karte des Einzugsgebiets (links) des Dianchi-Sees und Entwässerungsgebiets (eingefärbt) der Stadt Kunming
(Jin et al., 2006)

The region is located in the northern sub-tropical zone and is affected by the monsoon. The region’s micro climate is advantageous to a natural flora and fauna and a high biodiversity. 70 % of the catchment area (2030 km²) are mountainous, 20 % (590 km²) are plane, and the lake itself constitutes for the remaining 10 %. The lake is used for agricultural irrigation, drinking and industrial water supply and fishery and hence is extremely important to Yunnan’s inhabitants. Yunnan has an extraordinary developmental potential: the population rapidly grew from 1.5 mn. people in 1980, to 3.16 mn. inhabitants in 2003, to 7 mn. citizens in 2012. This development has, however, also promoted the lake’s qualitative deterioration.

Considering the overall catchment area the mean population density is merely 317 inhabitants per km², whereas the population density in the inner city of Kunming sums up to approximately 23,600 inhabitants per km² (Jin et al., 2006). With the “Big Leap Forwards” campaign Dianchi’s swamps and shallow zones were redesigned with the second Five-Year-Plan (1958-1962) in order to make them accessible to agriculture, leading to a rapid population growth. The additional agricultural waste waters discharged into the lake accelerated the lake’s deterioration. Today, 45 % of the catchment area are forests, 30 % are used agriculturally, 10 % are devoted to the industry, and another 12 % are settlements and infrastructure.