The remarkable growth in China’s population and economy over the past several decades has come to realize at a tremendous cost to the country’s environment, particularly around water. China’s water resources are over-allocated, inefficiently used, and grossly polluted by domestic and industrial wastes, to the point that vast stretches of rivers are dead and dying, lakes are cesspools of waste, groundwater aquifers are over-pumped and unsustainably consumed, and direct adverse impacts on both human and ecosystem health are widespread and growing. For addressing these crippling water problems, a new strategy of Interconnected River System Network (IRSN) is put forward, which is of great necessity for improving the capacity of water resources allocation, sustaining river’s heath and enhancing flood and drought control. However, up to now both the theory and technology of IRSN have still been a blank, far from the practices. Based on the further requirement of national water security and the improvement of the ecological civilization, with the new idea of human-water harmony and water resources livelihood, this paper presents a concept of IRSN, which can be defined as a river system network formed by constructing the hydraulic connection of water bodies of rivers, lakes and wetlands with various kinds of water projects, characterized by proper diversion and drainage,reasonable storage and discharge, adjustment of low and high runoff, complementary water multisource, controllable capacity, and the river system network appears to be complex, systematic, dynamic, temporal and spatial. Then the general thoughts of IRSN is proposed on the basis of the river system connection goal, the study of the IRSN can be carried out at four steps: 1) mechanism analysis, the theoretical basis of the whole study; 2) system identification and assessment, the analysis of the current status of IRSN in the researched region/basin, and the construction of Safety Evaluation Model with the complete indicators; 3) IRSN project plan, the make-out of the programmers with the requirement and problems of the society, and choosing the optimal decision from the solutions set; and 4) river system optimization and adjustment, the river system network will be reevaluated with the information of the monitoring system, and adjusted according to the principle of realizing the goal of sustainable development. According to the general thought of IRSN, some key problems worth specially concerning in the study are discussed, including different scales of IRSN, the process of river network connection, the pattern matching, the function of IRSN and the control methods.

流域地貌和河网结构是地球内外营力长期综合作用的结果，是一个地区构造、气候、植被和生物等因素相互作用的最终表现。由于各地区构造、岩性以及气候等条件的不同导致流域地貌和河网结构存在显著差异，进而对流域水文响应机制与特点产生影响。首先，对定量描述流域地貌和河网形态的特征参数进行了梳理与总结，并详述了构造、岩性以及气候等因素对流域地貌和河网结构影响的研究历程；其次，指出如何再现流域地貌演化过程以及定量研究流域地貌形态的主控因素是当前面临的主要问题；第三，对地貌演化模型的诞生、发展及应用进行了回顾与评述；最后，指出将传统地貌学研究方法与地貌演化模型相结合开展流域地貌及河网结构影响机制的研究是未来的主要发展方向。

Watershed geomorphology and river network structure controlled by tectonic frameworks, regional climate, vegetation, and biological factors are the combined results of the long-term internal and external forces of the Earth. Owing to the different tectonic, lithological, and climatic conditions in various regions, different watersheds have different geomorphic and river network structural characteristics that influence hydrological response mechanisms. In this study, the characteristic parameters for a quantitative description of the watershed geomorphic system and river network morphology are presented, and the impacts of tectonics, lithology, climate, and other factors on watershed geomorphology and river network structures are reviewed. Based on this, it is emphasized that reproducing the evolution of watershed geomorphology and quantifying its main controlling factors is the main problem. Subsequently, the birth, development, and application of the geomorphic evolution model are expounded. Finally, it is suggested that the main future development direction should involve combining traditional geomorphological research methods and geomorphic evolution models to study the influencing mechanisms of watershed geomorphology and river network structure.

平原河网地区地势平坦流速较缓，水体抗污染能力弱，改善水系连通性对水环境质量提升至关重要。以水系连通性较差的盛泽镇跃进联圩为研究对象，通过开展引调水试验，构建圩区河网水动力模型，探索圩区水利工作调度运行规则、河网水系连通方法以及相应的水环境变化规律。研究以水龄作为水系连通性的一种时间尺度参量，建立了跃进联圩水动力-水质-水龄的河网水环境模型，模拟了5种引调水方案下，圩内水系连通性及水质改善情况，并构建了压力、状态与响应的引调水连通效果评估体系，实现了对水系连通性变化与水环境改善水平的定量分析。结果表明：从水体交换时长来看，研究区域主要河道水体交换时间在5天以内，水体连通性越好的河道，水龄越短；从水质指标变化来看，调水实验中圩内的水环境氨氮变化最为明显，对引调水响应度高，模拟结果显示水龄与氨氮浓度变化趋势基本一致，水体连通性越好，水龄越短，有利于氨氮的削减；从引调水方案来看，单一调度方式对圩内水系连通性改善能力有限，特别是在河网内水体流动性弱的区域，同时使得圩区内水体流动性差异增大，更容易造成河网内水系连通性以及水质的空间分布差异，形成局部的滞水区或死水区。因此，采用多源引水与多区域排水相配合的调度方式，可以加强水系连通性，改善水环境质量。

The plain river network area has a flat terrain and slow flow velocity， resulting in a limited ability to resist pollution. Therefore， enhancing the connectivity of the water system is crucial for improving the quality of the water environment. This article focuses on the Yuejin polders which has poor water system connectivity in Shengze Town as the subject of research. By conducting water diversion experiments and constructing a hydrodynamic model of the river network in the polders area， the study explores the scheduling and operation rules of water conservancy work， methods of connecting the river network， and the corresponding changes in the water environment. The study utilizes water age as a time scale parameter to measure the connectivity of the water system. It establishes a river network model for hydrodynamics， water quality， and water age in the Yuejin polders. The simulation evaluates the connectivity and water quality improvement in the polders area under five water diversion schemes. Additionally， an evaluation system of pressure， state and response is constructed to quantitatively analyze changes in water system connectivity and the level of water environmental improvement resulting from water diversion. The results reveal that from the perspective of the length of water exchange， the exchange time of water bodies in the main river channels of the research area is within 5 days. The greater the connectivity of these water bodies， the shorter the water age becomes. From the perspective of changes in water quality indicators， during the water diversion experiment， the most noticeable change in the water environment inside the polders is the level of ammonia nitrogen. It shows a strong response to water diversion， and simulation results indicate that water age generally aligns with the concentration of ammonia nitrogen. Enhanced connectivity of water bodies leads to a shorter water age， which aids in reducing ammonia nitrogen levels. From the perspective of water diversion scheme， the uni-source water diversion and uni-region drainage scheme has limited effectiveness in improving the connectivity of the water system within polders， especially in areas with weak water flow in the river network. This scheme also increases variations in water flow within the polders， resulting in spatial differences in connectivity and water quality in the river network. Consequently， local stagnant water areas or dead water areas may be formed. Therefore， the combination of multiple sources of water diversion and multi-regional drainage scheme can enhance the connectivity of the water system and improve water environmental quality.

The turbulent surfaces of rivers and streams are natural hotspots of biogeochemical exchange with the atmosphere. At the global scale, the total river-atmosphere flux of trace gasses such as carbon dioxide depends on the proportion of Earth's surface that is covered by the fluvial network, yet the total surface area of rivers and streams is poorly constrained. We used a global database of planform river hydromorphology and a statistical approach to show that global river and stream surface area at mean annual discharge is 773,000 ± 79,000 square kilometers (0.58 ± 0.06%) of Earth's nonglaciated land surface, an area 44 ± 15% larger than previous spatial estimates. We found that rivers and streams likely play a greater role in controlling land-atmosphere fluxes than is currently represented in global carbon budgets.Copyright © 2018, American Association for the Advancement of Science.