南流江入海水沙通量响应热带气旋作用的变化过程

Variations of fluvial discharge and sediment to sea are the research focus of Future Earth Coast plan. Due to intensive interference of anthropogenic activity, water discharge and sediment load from river to sea are characterized by high mutability and variety. This is particularly obvious in mountainous river. However, there have to date been very few researches on the water discharge and sediment load variations from mountainous river to sea.Taking the Nanliu River, a small-medium mountainous river in subtropical oceanic monsoon climate zone, as an example, spatial-temporal variation characteristics of tropical cyclone, water discharge and sediment load of the Nanliu River and their relationships are expounded by analyzing the observations on geomorphology, hydrology and sediment from LiDAR, ADCP and ASM as well as additional historical records.Through a series of techniques, such as numerical model, 3S, and mathematical statistics, the discharge-sediment rating curve of normal and storm states can be explored, the water and sediment characteristics of different storm states can be analyzed, the contribution of tropical cyclone to water and sediment supply from the Nanliu River to the sea can be quantified, the response mechanism of fluvial water and sediment to tropical cyclone can be revealed.The expected results can enrich the knowledge on water discharge and sediment load characteristics as well as their response to extreme climate in mountainous rivers over the southwest region and provide some scientific and technical supports for disaster prevention and reduction in the coastal zone along the Northern Beibu Gulf.

河流入海水沙通量的变化研究是未来地球海岸计划的焦点内容。在高强度人类活动干扰和极端水文事件的影响下，河流尤其是山区型河流入海水沙通量极具突变和多样性。但山区型河流入海水沙变化过程研究甚少。本项目拟选择地处亚热带海洋性季风气候区的山区型中小河流—南流江为研究区域，基于LiDAR、ADCP、ASM等仪器，观测河槽地形、流量、含沙量等要素，结合历史和实测数据，采用数学模型、3S和数理统计等技术，分析影响南流江流域热带气旋时空变化特征和水沙通量变化特征及两者的关联性。弄清南流江常态和风暴态水沙比率曲线，分析不同风暴状态水沙特性，甄别热带气旋对南流江入海水沙通量的贡献率，揭示南流江入海水沙通量对热带气旋的响应机制。项目预期研究成果将有助于揭示我国西南地区入海河流的水沙输运特征及其对极端天气的响应特征，为北部湾海岸带防灾减灾提供理论基础和技术支撑。

水是生命之源，沙是沉积性地貌之本。入海水沙的输运是地球生物化学循环的重要途径，河流入海泥沙是海岸带地质地貌以及生物地球化学过程的基础，河流入海水沙通量对陆海相互作用、物质循环与物质迁移具有重要的意义。然而，近几十年来高强度的人类活动、海平面上升和极端天气频发等背景下，河流入海水沙通量发生变异，导致河口三角洲遭受侵蚀，流域-海岸-海湾生态系统压力增大。.本项目围绕“河流入海水沙通量响应热带气旋作用的变化过程”主题，开展了南流江水沙及影响流域热带气旋的时空变化特征、南流江常态和风暴态的水沙特性、热带气旋对入海水沙的作用机制及对入海泥沙的贡献量等方面的研究，主要进展和成果具体表现在：（1）基于年平均气温、年最高气温、年平均日照时数、年平均风速和年海表平均温度等参数构建了北部湾热带气旋发生频数模型，预测准确率达79.3%。（2）揭示了近60年来南流江悬沙浓度变化特征，甄别了流量与悬沙浓度之间的关系，刻画了水沙比率曲线变化特性，分析总结了悬沙浓度变化的影响因素。（3）通过对比研究注入北部湾的两条中小河流——钦江和南流江，揭示热带气旋对南流江水沙通量的影响机制。（4）计算热带气旋、洪水等极端天气事件对南流江入海水沙通量的贡献率，热带气旋对径流量和输沙量的多年平均贡献率分别为6.78%和19.31%。（5）分析采砂活动对水沙变化及海岸侵蚀的影响机理。采砂活动是南流江含沙量下降的主要原因之一，它导致南流江河床面积在1988~2018年期间总共减少了7.23km2。（6）分析基于SWAT模型的南流江流域径流变化特征。基于南流江流域的15个雨量站分别在日尺度和月尺度下构建了SWAT水文模型，采用SWAT-CUP进行参数率定后，再用实测径流的验证期进行验证，精度达到模型要求。（7）其他拓展性研究成果：在南流江入海口海岛资源保护与利用、邻近海滩（北海银滩）冲淤变化和海滩旅游等方面取得相关研究成果。.项目实施期间，共发表学术论文16篇，出版编著1部，授权专利4项和软件著作权1项。培养研究生6名。