| 摘要: |
| 赣江尾闾是赣江汇入鄱阳湖的关键通道，也是赣江尾闾水利枢纽的主要调控区域。枢纽工程通过枯水期抬升尾闾水位，并调控主支、北支、中支和南支分流过程，改变上游分汊河道水动力格局，进而影响区域流速分布与水体交换能力。为揭示枢纽运行后低枯流量条件下不同分流比对尾闾水动力条件及水体更新能力的影响，本文基于 MIKE21 FM 构建二维水动力—对流扩散耦合模型，并采用保守示踪剂法计算换水周期。根据外洲站 1957—2022 年 8 月至次年 3 月水文资料，其最低月平均流量主要处于 253～484 m³/s，低流量过程集中出现在枢纽调控期内；据此选取赣江外洲站来流量 300、400 和 500 m³/s 作为典型低枯流量工况，模拟分析不同分流情景下尾闾水动力及换水周期变化。结果表明：提高中支和南支分流比例可有效改善尾闾流场均衡性。在赣江外洲站来流量分别为 300、400 和 500 m³/s 条件下，东河流速分别提高 37%～61%、70%～76% 和 45%～63%，西河流速分别降低 17%、17%～20% 和 14%～18%。赣江尾闾换水周期具有显著空间异质性，整体呈沿水流方向递增特征，表现为主支最短、中支最长，南支居中，北支变化趋势与主支较接近。分流比例优化可明显提升区域水体更新效率，其中主支、北支、中支和南支分流比分别为 55%、2%、19% 和 24% 的GK3方案在本文设定工况下表现较优，赣江外洲站来流量为 500 m³/s 时，整体换水周期由 504 h 缩短至 348 h；来流量为 400 和 300 m³/s 时，90% 水体分别可在 320 h 和 420 h 内完成更新，全部水体换水周期分别由 476 h、664 h 缩短至 424 h、564 h。总体来看，GK3方案能够增强中支和南支水体交换能力，相关结果可为赣江尾闾水利枢纽枯水期优化调度提供参考。 |
| 关键词: 水动力模拟 尾闾分叉河道 分流比 赣江尾闾水利枢纽 换水周期 |
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| 基金项目:国家自然科学基金(42471048)；江西省水利厅科技项目(202325ZDKT13；202527ZDKT18)；中央高校基本科研业务费专项资金(B240201015)；国家重点研发计划(2023YFC3206002)；赣江下游尾闾综合整治工程科研课题研究项目；江西省鄱阳湖流域生态水利技术创新中心(2023SKLS05)。 |
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| Numerical Simulation of the Effects of Flow Allocation among Four Branches on Water Exchange Time in the Lower Ganjiang River under Low-Flow Conditions |
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zhu qisheng1, qiuyong2, zhangqi3, wentianfu4, gexiaobing5, LI Shuqing6, LIU Yudong7
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1.College of Water Conservancy and Hydropower Engineering, Hohai University;2.Jiangxi Ganfu Water Conservancy Co., Ltd.;3.State Key Laboratory of Water Disaster Prevention, Yangtze Institute for Conservation and Development, Hohai University, Nanjing, 210024, China;4.Jiangxi Academy of Water Science and Engineering;5.Ganjiang River Lower Reaches Hydrological and Water Resources Monitoring Centre;6.Xiuhe Hydrological and Water Resources Monitoring Center;7.Poyang Lake Hydrological and Water Resources Monitoring Center
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| Abstract: |
| The Ganjiang River estuary is a key channel through which the Ganjiang River flows into Poyang Lake, and it is also the main regulation area of the Ganjiang River estuary water conservancy hub. During the dry season, the hub project raises the water level in the estuary and regulates the flow diversion among the Main, North, Middle, and South branches, thereby altering the hydrodynamic pattern of the upstream braided channels and further affecting the regional flow velocity distribution and water exchange capacity. To reveal the effects of different diversion ratios on hydrodynamic conditions and water renewal capacity in the estuary under low-flow conditions after hub operation, a two-dimensional hydrodynamic–advection-diffusion coupled model was established using MIKE21 FM, and the water exchange period was calculated using a conservative tracer method. According to hydrological data from Waizhou Station from 1957 to 2022 during August to March of the following year, the minimum monthly average discharge mainly ranged from 253 to 484 m³/s, and low-flow processes were concentrated within the hub regulation period. Therefore, inflows of 300, 400, and 500 m³/s at Waizhou Station were selected as typical low-flow conditions to simulate the variations in hydrodynamics and water exchange period under different diversion scenarios. The results show that increasing the diversion ratios of the Middle and South branches can effectively improve the flow-field balance in the estuary. Under inflows of 300, 400, and 500 m³/s at Waizhou Station, the flow velocity in the East River increased by 37%–61%, 70%–76%, and 45%–63%, respectively, while that in the West River decreased by 17%, 17%–20%, and 14%–18%, respectively. The water exchange period in the Ganjiang River estuary showed significant spatial heterogeneity and generally increased along the flow direction, with the shortest period in the Main Branch, the longest in the Middle Branch, an intermediate value in the South Branch, and a variation trend in the North Branch similar to that in the Main Branch. Optimizing the diversion ratio can significantly improve regional water renewal efficiency. Among the scenarios, the GK3 scheme, with diversion ratios of 55%, 2%, 19%, and 24% for the Main, North, Middle, and South branches, respectively, performed better under the conditions set in this study. When the inflow at Waizhou Station was 500 m³/s, the overall water exchange period was shortened from 504 h to 348 h. Under inflows of 400 and 300 m³/s, 90% of the water body could be renewed within 320 h and 420 h, respectively, and the complete water exchange period was shortened from 476 h and 664 h to 424 h and 564 h, respectively. Overall, the GK3 scheme can enhance the water exchange capacity of the Middle and South branches, and the results can provide a reference for optimizing the dry-season operation of the Ganjiang River estuary water conservancy hub. |
| Key words: Hydrodynamic simulation tail gate bifurcated channel diversion ratio Ganjiang river trail channel hydraulic project water exchange period |
