Flood scenario in the Yongding River flood detention area with impacts of rain belt northward-moving
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Abstract:
As one of the main sub-catchments of Haihe River basin, the Yongding River covers Beijing, Tianjin and Hebei, Inner Mongolia and Shanxi province, with control area more than 47,000 km2. Since the beginning of 20th century, the Yongding river has frequently suffered super large flood disasters which often caused serious economic damages and casualties. Under this condition, many big reservoirs at the upstream and one detention area at the downstream of the catchment had been set up for intercepting the flood flow and reducing the peak to the cities in this area. Nowadays, the Yongding detention area with 522.65 km2 is the most important construction measure of flood defense and prevention which demands scientific management according to different flood scenarios. In order to have comprehensive understanding of the flood evolution process in the detention area for supporting the decision-making process, many hydrodynamic studies and models were set up in this area for assessing the effects of applying different regions of the detention area under various flood conditions. However, most of previous studies were either based on the modeling representation of past flood events or according to the simulation of designed scenarios. The modelling analysis of the future flood condition under the influence of rain belt northward-moving affected by the climate change was still missing in this area. By the Integrated Flood Model System (IFMS) developed by China Institute of Water Resources and Hydropower Research (IWHR), the flood progress of “23?7” super large flood in Yongding detention area was simulated and validated with the real-time monitoring data collected by satellite remote sensing during the flood period. The model was set up with 76,349 unstructured mesh based on 2 m resolution DEM which could well represent the topography variation in the modelling area. The difference between simulated and observed maximum flooded area was only 8.8%. And the accumulated flood storage calculated by IFMS model was 0.23 billion m3 which is almost as same as observation (0.24 billion m3). Therefore, the model applied for the Yongding detention area had been approved to be able to represent the flood progress and to be further used as one of operational tools for estimating future conditions. With the increasing ratio calculated with RegCM4.4 mode, the future summer heavy rainfall in 2025, 2035 and 2050 were estimated based on the “23?7” super large flood rainfall records. Integrated with the designed flood of 10, 20 and 50 year return periods at the upstream boundary, the modelling simulation shows that under the estimated rainfall in 2025, the maximum flooded area caused by 20 year return period designed flood would be similar as 50 year return period without taking into account the impacts of rain belt northward-moving. The modelling results of this study had indicated the amplification effect of rain belt northward-moving on the flood disaster. The potential flood risk of the Yongding detention area will show an increasing trend in the future. Therefore, for the future flood defense, it is important to the decision-makers to take into account the enlargement ofdisaster caused by the rain belt northward-moving impacts. Moreover, the model applied in this study showed higherpotentiality to be applied as one of the main reference tools for the future flood management in other river basins.
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