Preface 

Water is the source of human life. From ancient times cities in various countries have been built near the water. Thanks to the water, cities have become prosperous, and generated different types of water culture. The emergence and development of any city are closely related to water at all times and all over the world. Both the expansion of city and the growth of population need water resources. Water is an important part of the ecosystem. Water and biological communities (including animals, plant and microorganisms) coexist in rivers and lakes, intertwined with each other through climate system, hydrological cycle, food chain, nutrient cycle and energy exchange. Water conservancy projects play a great role in the economy and society, at the same time, we should also notice that they have influenced river ecosystem to a variable extent.
   Human activities including river regulation and dam construction have artificially changed the diversity, continuity and mobility of rivers, resulting in significant changes in natural conditions such as flow velocity, water depth, water temperature, flow boundary per se, hydrological laws and so on. The influence of all these changes on river ecosystem should not be ignored. The goal of river and lake controlling is not only to develop the functionality of rivers and lakes, but also to maintain the integrity of the watershed ecosystem. Clean rivers are the arteries of a sound ecosystem. Therefore, what should be made clear in the planning of flood control projects is that the river and biological communities in its upstream and downstream, left and right bank are all in one ecosystem. We should carry out unified planning, design and construction.

前 言

水是人类生命之源，从古至今各国的城市依水而建、因水而兴，并形成不同类型的水文化现象。古今中外任何一座城市的产生与发展都离不开水，城市规模的扩大、人口的增长需要水资源的支持。水是生态系统的重要组成部分，河流湖泊中的水与生物群落（包括动物、植物微生物）共存，通过气候系统、水文循环、食物链、养分循环及能量交换相互交织在一起。在社会生产过程中水利工程对经济与社会有着巨大的作用，同时也要看到水利工程对河流生态系统造成了不同程度的影响。
       人类整治河道和修筑堤坝等活动人为地改变了河流的多样性、连续性和流动性，使水域的流速、水深、水温、自水流边界、水文规律等自然条件发生重大改变，这些改变对河流生态系统造成的影响是不容忽视的。河流湖泊治理的目标既要开发河湖的功能性，也要维护流域生态系统的完整性，洁净的河流是一个健全生态系统的动脉。因此，在进行防洪工程的规划时，应明确河流与其上下游、左右岸的生物群落处于一个完整的生态系统中，进行统一规划、设计和建设。