文献翻译-水循环和水资源开发规划

The Hydrologic Cycle and Planning for Water Resources DevelopmentIn nature , water is constantly changing from one state to another , The heat of the sun evaporates water from land and water surfaces . This water vapor (a gas ) , being lighter than air , rises until it reaches the cold upper air where it condenses into clouds . Clouds drift around according to the direction of the wind until they strike a colder atmosphere. . At this point the water further condenses and falls to the earth as rain , sleet , or snow , thus completing the hydrologic cycle. The complete hydrologic cycle, however , is much more complex . The atmosphere gains water vapor by evaporation not only from the oceans but also from lakes , river , and other water bodies , and from moist ground surfaces. Water vapor is also gained by sublimation from snowfields and by transpiration from vegetation and trees.Water precipitation may follow various routes . Much of the precipitation from the atmosphere falls directly on the oceans . Of the water that does fall over land areas, some is caught by vegetation or evaporates before reaching the ground ,some is locked up in snowfields or ice-fields for periods ranging from a season to many thousand of years , and some is retarded by storage in reservoirs , in the ground, in chemical compounds , and in vegetation and animal life.The water that falls on land areas may return immediately to the sea as runoff in streams and rivers or when snow melts in warmer season . When the water dose not run off immediately it percolates into the soil. Some of this groundwater is taken up by the roots of vegetation and some of it flows through subsoil into rivers, lakes, and oceans.Because water is absolutely necessary for sustaining life and is of great importance in industry , men have tried in many ways to control the hydrologic cycle to their own advantage . An obvious example is the storage of water behind dams in reservoirs , in climates where there are excesses and deficits of precipitation (with respect to water needs ) at different times in the year. Another method is the attempt to increase or decrease natural precipitation by injecting particles of dry ice or silver iodide into clouds . This kind of weather modification has had limited success thus far , but many meteorologists believe that a significant control of precipitation can be achieved in the future.Other attempts to influence the hydrologic cycle include the contour plowing of sloping farmlands to slow down runoff and permit more water to percolate into the ground ,the construction of dikes to prevent floods and so on . The reuse of water before it returns to the sea is another common practice . Various water supply systems that obtain their water from rivers may recycle it several time (with purification ) before it finally reaches the rivers mouth.Men also attempt to predict the effect of events in the course of the hydrologic cycle. Thus ,the meteorologist forecasts the amount and intensity of precipitation in a watershed, and the hydrologist forecasts the volume of runoff.Planning can be defined as the orderly consideration of a project from the original statement of purpose through the evaluation of alternatives to the final decision on a course of action. It includes all the work associated with the design of a project except the detailed engineering of the structures. It is the basis for the decision to proceed with (or to abandon) a proposed project and is the most important aspect of the engineering for the project. Because each water-development project is unique in its physical and economic setting, it is impossible to describe a simple process that will inevitably lead to the best decision. There is no substitute for “engineering judgment” in the selection of the method of approach to project planning, but eachindividual step toward the final decision should be supported by quantitative analysis rather than estimates or judgment whenever possible. One often hears the phrase “river-basin planning” , but the planning phase is no less important in the case of the smallest project. The planning for an entire river basin involves a much more complex planning effort than the single project, but the difficulties in arriving at the correct decision may be just as great for the individual project.The term “planning”carries another connotation which is different from the meaning described above. This is the concept of the regional master plan which attempts to define the most desirable future growth pattern for an area. If the master plan is in reality the most desirable pattern of development, then future growth should be guided toward this pattern. Unfortunately, the concept of “most desirable”is subjective, and it is difficult to assure that any master plan meets this high standard when first developed. Subsequent changes in technology, economic development, and public attitude often make a master plan obsolete in a relatively short time. Any plan is based on assumptions regarding the future, and if these assumptions are not realized the plan must be revised. Plans generally must be revised periodically.An overall regional water-management plan, developed with care and closely coordinated with other regional plans, may be a useful tool in determining which of many possible actions should be taken. But it must always be considered subject to modification as the technological, economic and social environment change or as new factual data that are develop. A master plan that is no more than a catalog of all physically feasible actions is likely to prove of little value.Planning occurs at many levels within each country with the purpose and nature of the planning effort differing at each level. Many countries have a national planning organization with the goal of enhancing the economic growth and social conditions within the country. Even if no such organization exists, the national goals remain, and some form of national planning occurs in the legislative or executive branches of government. The national planning organization will rarely deal with water problems directly, but in setting goals for production of food, energy, industrial goods, housing, etc, it may effectively specify targets for water management.To allow for differences between the various of the country, regional planning groups may exist and equivalent regional water planning may occur. However, a natural “region”for water planning is the river basin and the tendency is to create river basin commissions, or river basin management units (authorities). These groups must assure coordination between the various activities within the river basin. Each specific action in water management is likely to have consequences downstream (and sometimes upstream), and thus these specific actions should not be planned in isolation but must be coordinated.Planning of specific actions is the lowest level of planning, but it is at this level that important decisions which determine the effectiveness of water management are made. This level is often called project planning although a physical project may not necessarily result. For example, a study leading to a plan for flood-plain management is a legitimate project plan.Project planning usually passes through several phases before the final plan emerges. In each country there is a specified sequence with specific names. The first phase or reconnaissance study is usually a coarse screen intended to eliminate those projects or actions which are clearly infeasible without extensive study, and hence to identify those activities which deserve further study. Following the reconnaissance phase may be one or more phases intended to thoroughly evaluate the feasibility of the proposed activity and in the process to formulate a description of the most desirable actions, I.e. the plan. In many cases a single feasibility study is adequate becausethe nature of the action is relatively easily evaluated. In other cases one or more pre-feasibility studies studies may be undertaken to examine various aspects of the proposal. The idea of several sequential studies is to reduce planning costs by testing the weakest aspects of the project first. If the project is eliminated because of some aspect, the expense of studying all other aspects will have been avoided. If the series of studies is allowed to become a series of increasingly more thorough reviews of all aspects of the project, the cost may be increased because many things will have been redone two or more times.The feasibility study usually requires that the structural details of a project be specified in sufficient detail to permit an accurate cost estimate. In the final phase of the effort, the details of design must be examined carefully, and the construction drawings and specifications produced. Although, in principle, the issue of feasibility was decided on the basis of the feasibility study, the possibility always exists that the more thorough study may develop information that alters feasibility. Consequently, the decision to proceed should not be made irrevocable until the final design is complete.水循环和水资源开发规划在自然界中,谁总是不断地从一种状态改变成另一种状态.太阳热使陆地和水面上的水蒸发.这些水蒸气(一种气体)由于比空气轻,会上升直至达到高空冷气层,并在那里凝结成云.云层随风飘荡,直至遇到更冷的大气层为止.此时水便进一步冷凝,并以雨,雹或雪的形式落到地面.这样便完成了水的循环.然而,完整的水循环要复杂的多.由于蒸发作用,大气不仅从海洋而且从湖泊,河流和其他水体,以及从湿的地表面获得水蒸气.也可从雪地中雪的升华和从植物与树木的蒸腾获得水蒸气.江水刻有各种不同的出路.大部分的江水都直接落到海洋.落在陆地区域的水,有些被植物所摄取,或再降至地面之前就蒸发了;有些被封冻在雪原或冰川重达一个季度乃至成千上万年;有些则因储存在水库,土壤,化合物以及动植物体内而滞留下来.降到陆地区域的水可能作用溪流与江河的径流,或再温暖季节融化的雪水直接汇到海洋.当降水不立即流走时,它会渗入土壤.这些地下水中有一些被植物的根系手,有一些则通过下层土壤流入河流,湖泊和海洋.因为水对于以维持生命来说绝对必要,在工业上也很重要,所以人们为了自身的利益试图以各种方式来控制水的循环.一个明显的例子就是在一年中不同的实践根据当地降水的多寡(按对水的需要来说)将水储存在水库中.另一种方法是试图将干冰或碘化银微粒射入云层来增多或减少天然降雨量.虽然这种改造其后的方法迄今只取得了有限的成功,但许多气象学家都认为,有效的控制降水在将来是可以做到的.其他一些影响水循环的努力包括沿等高线耕作梯田,以使径流减速,让更多的水渗入地下;建筑堤坝以防洪水等.在水回归大海之前将它重复使用,也是一种常用的办法.自河道取水的各种供水系统可江水在最终到达河口之前,经过净化,可重复使用多次.人们还试图预测水循环过程中一些实践的结果.例如,气象学家预报一个流域的降雨量和降雨强度;水文学家预报径流量等.规划就是对一个工程从目的的初始陈述,方案评价到行动过程的最终决定的有序研究.除了建筑物的细部工程外,它包括与工程设计有关的全部工作.它是决定一个建设项目继续进行(或放弃)的依据,也是这个项目工程的最重要方面.因为每个水开发项目对经济和自然的调节都是唯一的,所以,一个简单的描述方法不可能获得最好的决定.在项目规划途径的方法选择中,没有什么能够代替”工程判断”.但朝着最终决定的每一独立步骤,无论何时都应采用定量分析的方法,而尽可能不用估计或判断.人们经常听到”流域规划”这个词,但规划阶段对最小工程来说是不太重要的,整个流域的规划比单个工程涉及更加复杂的规划程序.而单个工程在取得正确决定时所面临的困难可能是与整个流域规划一样大.“规划”这个词包含有不用于上面提到过的另外的涵义,这是一个区域总体规划的概念.它试图为另一个地区确定最适宜的未来发展模式.如果这个总体规划就是实际上的最适宜的发展模式,那么未来的发展就应该向这个模式方面引导.遗憾的是"最适宜的"这个概念是主观的,它很难保证任何总体规划初次被提出来就能满足这一高标准.其次,技术的变化,经济的发展和公众的态度常常使一个总体规划在一个相当短的时间内就变得过时.任何一个规划都是基于有关未来的假设,因此,如果这些假设没有实现,那么这个规划就必须修改.规划也必须定期进行全面的修改.一个经过细心研究并与其他区域规划紧密协调的区域水管理总体规划,可能是一个有用的工具,在决定许多可能方案时应当采用这一有用工具.但必须考虑技术,经济和社会环境的变化或当研究出新的有关数据时,随时对他进行调整.一个总体规划,只不过是所有可行性研究中的一种,很可能被证明是没有价值的.每一个国家许多领域都有规划,而每一个领域中规划工作的目的和性质又不相通.许多国家有国家规划机构,他们的目标是加强国内的经济发展,改善国内的社会状况.即使没有这样的组织存在,也有国家目标存在,国家规划的某些形式由立法机关或政府行政部门提出.国家规划机构很少直接处理水问题,但在调整粮食,能源,工业商品和住房等生产指标时,他可能有效地为水管理规定目标.考虑到一个国家各地区之间存在着差异,因此,一个国家可以由地区规划分支机构,并且可以存在相应的地区水规划.然而,由于水规划的一个自然"区域"是流域,因此又建立流域委员会(官方)的趋势.这些规划组织必须确保流域内各项工作之间的协调.水管理的每个具体行动可能对下游(并且有时对上游)产生影响.因此,这些具体行动不应单独进行规划,而且必须进行相互之间的协调.具体行动计划是规划的最低级,它决定了水管理有效性的实现.但决定水管理效率的重要决定就是由这以及指定的.尽管一个具体工程不一定产生,但这一级别的规划场被称为工程规划.例如,(因)一项研究而产生的一个红泛平原管理方案就是一个合法的工程搞规划.工程规划通常要经过几个阶段才能成为最终的方案.在每一个国家,规划都有一个具体名称的规定顺序.第一阶段或设计任务书阶段,通常是一个粗过滤网,这一阶段是用来淘汰那些具有明显不必广泛研究特征的工程或方案,从而确定哪些是值得进一步研究的方案.设计任务书阶段后可能有一个或更多的阶段要对建议方案的可行性进行详细的评价.在这个过程中,要对最适宜方案的作用进行系统说明,这就是计划.在许多情况下,一个单独的可行性分析是足以满足要求的,因为方案的性质比较容易评价.在其它情况下,一个或更多的初步可行性分析可以对建议方案的各个方面进行检查.几个阶段研究的目的,首先是通过考察工程的最弱方面来减少规划的费用.如果这个工程由于某方面的原因被淘汰,那么这个工程所有其他方面的研究费用就不用再花了.如果这些分析序列越来越多地成为这个项目所有各方面的一系列的更详细的观点,那么规划费用就会因许多事情将被重做两次或更多次而增加.可行性研究通常要求一个工程的结构细节应该规定得充分具体的,以便给出一个准确的费用估计.早规划工作的最终阶段,设计的细节必须进行认真的审查,并且要给出施工图和设计说明书.尽管在原则上可行性分析的结果却绝于可行性研究的基础,但更详细的研究可能开发出使可行性改变的资料的可能性总是存在的.所以,不到最终设计完成就不能取消继续做下去的决定.。