Factors Of The Relationship Variation Between Water Level And Surface Area In Dongting Lake

Dongting Lake is an important lake for catchment in the middle reaches of the Yangtze River,and is also the second largest freshwater lake in China.The water from the upper reaches of the Yangtze River is discharged into the Dongting Lake from the North of “Three Ports”(Songzikou,Taipingkou,and Dianchikou).The water was poured into the Dongting Lake from the east,west,and south respectively of“Four waters”(Xiang,Zi,Ruan,Li).In recent years,frequent floods and droughts have occurred in the middle reaches of the Yangtze River.The operation of the Three Gorges Project has had a tremendous impact on the mainstream of the middle reaches of the Yangtze River and Dongting Lake.The hydrological characteristics of the Dongting Lake have undergone a series of changes that have affected the changes in the relationships between Yangtze River and lakes.Under the background of the construction and operation of the Three Gorges Project,the relationship between the Yangtze River and the Dongting Lake and the changes and causes thereof are not only related to the evolution and development of the Dongting Lake,but also have important implications for the development of the Tongjiang Lake.The surface area of Dongting Lake from 2000 to 2012 was extracted from the Terra / MODIS,Aqua / MODIS L1 A and L1 B remote sensing data.In Combination of the observation data of the water level of Chenglingji in the same period,the temporal and spatial variation of water conditions in Dongting Lake from 2000 to2012 was analyzed.For the first time,the relationship curve between the water level and the surface area of the Dongting Lake was discovered,which revealed the characteristics of the relationship between the water level and the water surface area of the Dongting Lake in different periods and different typical years.The BP neural network was used to simulate the water level of the Chenglingji River under the natural runoff process of the Yangtze River.The influence of the Three Gorges Project's operation on the water surface area of Dongting Lake and the water level of Chenglingji was analyzed.Research indicates:1.From 2000 to 2012,the annual average water level in Chenglingji showed an overall decrease trend,and there was an obvious rhythm of rising-abundance-dry-retreating within the year.The average annual water surface area of Dongting Lake also shows an overall decrease trend,showing a regular fluctuation during the year,and also has the change characteristics of upswing-feng-bun-retreat.From the perspective of spatial changes in the water surface area of the Dongting Lake,during the growth period,the water surface area grows outward from the center of the lake,and the decrease period is gradually reduced from the center of the outer lake body.2.There is a high correlation between the water surface area of Dongting Lake and the water level of Chenglingji from 2000 to 2012.The relationship between water level and water surface area shows a multi-value change,which shows the shape of the rope trap.However,the correlation between the water level and the water level in different periods is different.The influence of the factors changed,the dry season and the wet season water level of the Dongting Lake-water surface area were mainly affected by the water supply from the Yangtze River,and the rope-set relationship between the water level and the water surface area during the flooding period and the water withdrawal period was affected.The size of Dongting Lake has a certain influence.3.After the operation of the Three Gorges Project,during the period from April to May,the water level of Chenglingji has increased.During the period from September to November,the water level of Chenglingji has decreased.During the period from April to May,the water surface area of Dongting Lake has increased.During the wet period from July to September,the water surface area of Dongting Lake has decreased.From September to November of the dispatch period,the water surface area of Dongting Lake has decreased,and the water period has decreased.From January to March,the water surface area of Dongting Lake increased,but the increase was not obvious.Since 2003-2012,the multi-year average of the water level of Chenglingji in April-June has decreased,and the decline in the average multi-year water surface area of the Dongting Lake has not been caused by the operation of theThree Gorges Project.From September to November,the operation of the Three Gorges Project had a definite impact on the decline of the multi-year average of Chenglingji water level and the decrease of the average multi-year water surface area of the Dongting Lake.4.The operation of the Three Gorges Project has little impact on the level of flat water and abundant water,and the main impact is reflected in the increase of the Dongting Lake area and the water level of the Chenglingji watershed during April-June of the season,reducing the area of the Dongting Lake from July to August.The water level of Chenglingji is reduced during September-November,which reduced the Dongting Lake area and the Chenglingji water level in October.The operation of the Three Gorges Project has a greater impact on the dry season,regulating the April-June spring drought,reducing floods during the flood season from July to August,and exacerbating the drought after September.