Mutual effects between morphological characteristics and variations of flow-sediment process of Dongting Lake during 1951～2009
近60年洞庭湖泊形态与水沙过程的互动响应

Based on historical references,maps and flow-sediment data from 1951 to 2009,mutual effects between the lake morphology and the flow-sediment process of Dongting Lake were comparatively analyzed.The results showed that the lake morphology interacted with the flow-sediment process so that the lake morphology characteristics were changed by the flow-sediment process in several ways.For example,the structure of the lake basin was disaggregated and broken up,the lake became shallow,and the acreage and cubage of the lake decreased by 1840 km2 and 130×108 m3 respectively.Meanwhile,flow-sediment specialties were also changed by the alteration of lake morphology.The water storage of lake basin showed the obvious increase-decrease fluctuation from 1951 to 2002;however,the water levels under the same flux in main flood periods rose by 1.2 m to 1.9 m generally,and the water levels of west,south and east Dongting Lake increased by 1.61 m,1.39 m and 1.35 m respectively.When the top 5 flood levels of each main hydrological station and the smallest acreage or cubage of the lake appeared at the same time,the silting rate would be over 70%.Due to the Three Gorges Reservoir's water storage and Returning Farmland to Lake Project,the storage amount of the lake basin under the high and middle water levels slightly decreased.The high and low water levels of Chenglingji hydrological station decreased by 1.12 m and 0.35 m respectively.Sediment output ratios of west and southeast lake showed an increasing tendency.The silting rate reduced to 35.9%.The mutual effect mechanism could be summarized as the pattern: sediment siltation→the disaggregation and the break of lake basin structures as well as the decrease of the lake acreage and cubage→the change of flow-sediment specialties→the alteration of lake morphology→the change of flow-sediment specialties.