Poyang Lake: a water coordinator of Yangtze
What is the relation between the Yangtze River and Poyang Lake in terms of water exchange?
Overall speaking the Yangtze River and Poyang Lake function as water complement to each other.
This complementary relation is season based. A water engineering expert of Jiujiang told us that from April to June when there is a lot of rain in the upstream and midstream Yangtze, the water from Yangtze River majorly flows into Poyang Lake. In this way the lake functions as a cushion for the farmland and cities downstream the Yangtze in case of serious floods. Then the water flow direction would become the other way around from July to September when the rainfall capacity decreases along the upstream Yangtze and in winter when Three Gorges Dam started to store water for upstream Yangtze. The lake in this sense has turned into water supply to Yangtze and facilitates downstream river transportation and farmland irrigation.
I was told that the water flowing from Poyang Lake to Yangtze could reach 150 billion cubic meters in volume per year. That is about 15 percent of the total water flowing into Yangtze from tributaries, lakes and wetlands. It is a very significant number. The big volume of fresh water that is added to the Yangtze along its way to the sea would also improve the water quality of down stream Yangtze.
What measures have been taken by the local government to resume the water quality of Poyang Lake?
The measures are mainly targeted at restricintg sand quarrying activities. Overly sand quarry would make the river more turbid and more importantly lower the bottom level of Poyang Lake, affecting its water exchange with Yangtze due to bottom level differences. Additionally sand quarry would kill the aquatic plants in the lake and therefore weaken the water self-purification of the lake.
Yesterday we took a cruiser to observe the Poyang Lake and saw a clear boundary of two waters. The water from Yangtze River is clearly muddier and yellowish in color while that of Poyang Lake is cleaner and green. Two waters’ meeting forms a visually very distinct line on the water surface seemingly separating two water bodies. Local officials told me that in the past few years, the situation was the other way around: lake water was muddier and river water was clearer. The changes have been made thanks to government’s efforts to ban sand quarry activities.
Meantime Jiujiang also strengthened its river chief and lake chief systems, aiming to eliminate the pollution source from the first place. And a green plant belt has been restored along the banks of the lake for ecological protection and prevention of land runoff.
With these efforts the size of the lake has been solidified in recent years and the lake water quality could reach Grade 2 or Grade 3, which means the water is drinkable after process.
That was CRI's Yang Guang with the Streaming down the Yangtze team.