Erhai

@Erhai Lake has an area of 251 square kilometers (with a water level of 1974 meters), a total capacity of 2.53 billion cubic meters, a catchment area of 2565 square kilometers, a length of 42.5 kilometers, an average width of 6.3 kilometers, a maximum depth of 22 meters, an average depth of 10.2 meters, and a circumference of 117 kilometers. At a water level of 1966 meters (elevation 85), Erhai Lake has a length of 42.0 kilometers from north to south, a maximum width of 8.8 kilometers from east to west, a minimum width of 3.05 kilometers, a maximum depth of 21.5 meters, an average depth of 10.8 meters, a lake surface area of 252.91 square kilometers, a water storage capacity of 2.794 billion cubic meters, an island area of 0.748 square kilometers, and a shoreline of 129.14 kilometers. It is the second largest freshwater lake in Yunnan Plateau after Dianchi Lake

The annual lake surface water temperature is 12 ℃ -21 ℃. The minimum operating water level is 1962.84 meters above sea level (coastal defense elevation 1971 meters), and the highest water level is 1965.84 meters above sea level (coastal defense elevation 1974 meters). The normal water level range is between 1962.84-1965.84 meters above sea level (coastal defense elevation 1971-1974 meters, all below the Yellow Sea elevation)

Due to the favorable storage and infiltration of groundwater by the interlayer of marble, the Eighteen Streams are mostly formed by transverse faults and physical geological processes, and have become a concentrated area for the convergence of surface water and groundwater in Cangshan. In the north-south marble interlayer on the mountainside of Cangshan Mountain, karst is developed. In the east-west transverse section, there are large streams of spring water gushing out, such as the Mangyong Creek along the foot of the mountain; Some exposed areas in rock contact zones or fault zones, as well as varying degrees of spring water exposure in alluvial layers, such as Butterfly Spring

The east bank of Erhai Lake is composed of limestone and sandstone, which have strong permeability and are not conducive to water storage, resulting in a relatively short water supply. The water volume of Erhai Lake is not only replenished by surface water, but also receives good groundwater conditions. The groundwater discharged from the surrounding mountains is all included in Erhai Lake@The annual water temperature on the surface of Erhai Lake ranges from 1 ℃ to 20 ℃, and the vertical distribution of water temperature has the characteristics of a positive temperature layer. It does not freeze all year round and belongs to a subtropical lake (warm lake). Transparency is 4 meters, with significant seasonal variations, smaller during the rainy season and higher during the dry season. According to the monitoring results in December 1985, the average transparency was 5.4 meters, with a maximum transparency of 8 meters. The water color was light blue and the chromaticity was 6.625. The water quality is colorless and odorless, belonging to the clean grade calcium magnesium carbonate type freshwater lake, with a nutritional status of moderate nutrient

The water level of Erhai Lake plays a decisive role in the biological community and natural ecology of Erhai Lake. The record of Erhai Lake water level has been established since 1951. After more than 50 years of repeated practice and scientific demonstration, the control elevation of Erhai Lake water level was formulated five times in 1966, 1982, 1989, 1998, and 2004. On March 26, 2004, the 8th meeting of the Standing Committee of the 10th People's Congress of Yunnan Province approved and promulgated the "Management Regulations of Erhai Lake in Dali Bai Autonomous Prefecture, Yunnan Province", which stipulated that the lowest operating water level of Erhai Lake is 1964.30 meters and the highest operating water level is 1966.00 meters