Abstract:

The Danjiangkou Reservoir located at the junction of Hubei and Henan province, is the water source area of the Middle Route of China's South to North Water Transfer Project. Monitoring of the water resource in the reservoir is critical for the interbasin water transfer project. In this study, we collected 47 Landsat TM/ETM and HJ1A/B remotelysensed imageries for monitoring changes of water surface using Normalized Different Water Index(NDWI) based on the threshold segmentation method in the reservoir from 2002 to 2011. The results indicated that water surface decreased from December to March of the next year, increased from March to December, and the minimal and maximal water area appeared in February and December respectively. Water area had larger variations in the wet season than that in the dry season due to the seasonality of precipitation in the upper Han river and reservoir management, and the water area standard deviation was 66.8 and 44.2, respectively. The inundation area ranged between 316.4 km2 on September 25, 2002 and 562.3 km2 on December 13, 2011 in the wet season because of the anomalous weather, but fluctuated between 291.5 km2 on April 18, 2011 and 483.2 km2 on June 24, 2009 in the dry season. Significant seasonality variability was also found during the past ten years. The water surface area was relatively stable in spring (water area ratio and standard deviation were 1.55 and 44.11) and summer (water area ratio and standard deviation were 1.40 and 44.56 ), but fluctuated dramatically in autumn(water area ratio and standard deviation were 1.67 and 73.16 ) and winter(water surface area ratio and standard deviation were 1.63 and 70.87 respectively). In order to ensure water storage in the dry season, the management department should strengthen monitoring and increase storage reasonably so that there are enough water to supply to the North China after the project finished. Water surface area of the Danjiangkou Reservoir was almost kept larger than 300 km2, and presented a growth trend in May, in which the water area was most stable. The same growth trend was also found in wet season, dry season and the whole past 10 years. The increased water area was mostly located in the east and north of the reservoir, where soil erosion and nonpoint source pollution should be concerned