长江对鄱阳湖退水期洲滩出露特征的影响

Influence of the Yangtze River Droughts on the Exposure Characteristics of the Poyang Lake Wetlands

采用具有物理机制的二维水动力模型MIKE 21,基于2006年长江枯水与1953―2000年长江平均来水条件(平均条件)2种情景,模拟比较2种情景下鄱阳湖退水期(7―12月)洲滩出露过程,阐释长江来水变化对鄱阳湖洲滩出露特征的影响。结果表明:2006年长江来水减少导致鄱阳湖洲滩出露开始时间提前,与平均条件相比提前1个月;洲滩出露50%面积仅历时约0.5个月,比平均条件缩短约1.5个月;长江枯水对鄱阳湖洲滩出露分布影响最显著的时段为8―11月,8月上旬洲滩增加的出露面积主要分布在赣江入湖三角洲和东部湖湾,而8月中旬―11月末增加的出露面积主要分布在中部开敞湖区和北部入江通道洲滩;长江枯水对鄱阳湖中北部洲滩出露天数的影响大于南部湖区,对修水和赣江北支入湖三角洲的影响大于赣江中支和南支入湖三角洲,对鄱阳湖国家级自然保护区的影响明显大于南矶山自然保护区;长江来水变化还显著影响洲滩出露速率,2006年长江水情下洲滩自开始出露至到达最大出露面积(8月初―10月中旬)期间的平均出露速率(25 km2/d),与平均条件下洲滩自开始出露至到达最大出露面积(9月初―12月末)期间的平均出露速率(14.5 km2/d)相比增大了72%。

The variations in flow regime of the Yangtze River inevitable affect the hydrological condition in the Poyang Lake, and thus affect the spatial pattern of the exposure characteristics of the lake wetlands. In this study, we used a physically based hydrodynamic modeling（MIKE 21） to explore the influence of the Yangtze River droughts on the characteristics of spatial-temporal distribution of exposure area of the Poyang Lake. The objectives were achieved through the comparison of two simulation scenarios. One was the reference case representing for an average condition over a long period of 1953-2000（marked as S0）. The other represented the typical dry year in 2006 for the Yangtze River（marked as S1）. Simulation results were assessed for the lake＇s recession period from July to December. Results indicated that the Yangtze River drought caused the onset of the exposure of wetland about one month earlier compared to that for the reference case. In 2006, it took only half month to reach an exposure area of 50% of the maximum, which was 1.5 months shorter than that for the reference case. Simulation results also showed that the most significant period affected by the Yangtze River discharge was from August to November. In early August, the expansion of wetland mainly distributed in the Ganjiang delta and the eastern bay of the Poyang Lake. During the period from middle August to November, the expansion of wetland shifted to the northern（downstream） and middle regions of the Poyang Lake. It was found that the flow regime change in the Yangtze River had more impacts on the northern-central parts of the Poyang Lake than the southern（upstream） regions. It was also found that the average wetland expansion rate for 2006 was 25 km^2/d, which was 72% more than that for the reference case（14.5 km^2/d）. This paper was the first attempt to use a physically based hydrodynamic modeling to reveal the interaction between the wetland exposure characteristics of the Poyang Lake and the seasonal flows of the Yangtze River.