水利水电工程专业英语——水文与水资源篇

水利水电工程专业英语——水文与水资源篇
1. Hydrological Cycle and Budget
1.水文循环与预算
Hydrology is an earth science. It encompasses the occurrence, distribution, movement, and properties of the waters of the earth and their environmental relations. Closely allied fields include geology, climatology, meteorology and oceanography.
水文学是一门地球科学。

它包含地球水资源的发生、分布、运动和特质，以及其环境关系。

与之密切相关领域包括地质学，气候学，气象学和海洋学。

The hydrologic cycle is a continuous process by which water is transported from the oceans to the atmosphere to the land and back to the sea. Many sub-cycles exist. The evaporation of inland water and its subsequent precipitation over land before returning to the ocean is one example. The driving force for the global water transport system is provided by the sun, which furnishes the energy required for evaporation. Note that the water quality also changes during passage through the cycle; for example, sea water is converted to fresh water through evaporation.
水文循环是一个连续的过程，在这个过程中水从海洋被运输到大气中，降落到陆地，然后回到海洋。

有很多子循环存在。

内陆水域的蒸发机器后在回到海洋前在陆地上的将于就是一个例子。

全球水运输系统的运行动力由太阳提供，通过蒸发这个过程赋予水运动能量。

需要注意的是，水质在水循环通道中也会改变，比如，海水在蒸发后就会转变成淡水。

The complete water cycle is global in nature. World water problems require studies on regional, national, international, continental, and global scales. Practical significance of the fact that the total supply of fresh water available to the earth is limited and very small compared with the salt water
content of the oceans has received little attention. Thus waters flowing in one country cannot be available at the same time for use in other regions of the world. Modern hydrologists are obligated to cope with problems requiring definition in varying scales of significant order of magnitude difference. In addition, developing techniques to control weather must receive careful attention, since climatological changes in one area can profoundly affect the hydrology and therefore the water resources of other regions.
完整的水循环在自然界中是全球性的。

世界水问题需要在区域，国家，国际，洲际和全球范围的研究。

地球上可利用的淡水总量与海洋中的咸水相比是有限的，并且非常少，这个重要的显示尚未得到人们足够关注。

因此，在一个国家流动的水源并不能同时在世界的其他区域被利用。

现代水文学应该着力解决显著数量级的差异在不同尺度上的定义问题。

此外，发展控制天气的技术必须得到密切关注，因为一个地区的气候变化能够深刻地影响到其他地区的水文循环进而影响到其水资源。

Because the total quantity of water available to the earth is finite and indestructible, the global hydrologic system may be looked upon as closed. Open hydrologic system may be looked upon as closed. Open hydrologic subsystems are abundant, however, and these are usually the type analyzed. For any system, a water budget can be developed to account for the hydrologic components.
因为地球上可利用的水量是有限且不可避免的，所以全球的水文循环系统可以被看成是闭合的。

开放性的水文循环系统可以被看成是闭合的。

开放的水文子系统内容丰富，然而这些系统也是经常被分析到的。

对于任何系统，水预算都能够转变到对水文组成的计算。

Figures 1 and 2 show a hydrologic budget for the coterminous United States. These figures illustrate the components of the water cycle with which a hydrologist is concerned. In a practical sense, some hydrologic region is dealt with and a budget for that region is established. Such regions may be topographically defined (watersheds and river basins are examples),
politically specified(e.g. country or city limits), or chosen on some other grounds. Watersheds or drainage basins are the easiest to deal with since they sharply define surface water boundaries. These topographically determined areas are drained by a river/stream or system of connecting rivers/streams such that all outflow is discharged through a single outlet. Unfortunately, it is often necessary to deal with regions that are not well suited for tracking hydrologic components. For these areas, the hydrologist will find hydrologic budgeting somewhat of a challenge.
图1和图2展示了美国毗连地区的水文循环。

这些图展示了考虑水文的水循环的过程。

从实际意义上讲，一些水文区域被处理并且建立了预算。

这些区域可以是在地形上确定（如流域和河流盆地）、在政治上确定（如根据国家或者城市限制），或以其他因素确定。

流域或者排水流域是最容易确定的，因为它们明显地限定了地表水的边界。

这些地形上确定的区域由一条河流/溪流或者相连的河流/溪流排水，因此所有的出流都从某个单一的出口排出。

不幸的是，我们经常会处理到不适合通过跟踪水文组成部分的区域。

对于这些区域，水文学家会在不同程度上挑战地进行水文预算。

The primary input in a hydrologic budget is precipitation. Some of the precipitation(e.g. rain, snow, hail) may be intercepted by trees, grass, other vegetation, and structural objects and will eventually return to the atmosphere by evaporation. Once precipitation reaches the ground, some of it may fill depressions (become depression storage), part may penetrate the ground (infiltrate) to replenish soil moisture and groundwater reservoirs, and some may become surface runoff, that is, flow over the earth’s surface to a defined channel such as a stream.
在水文预算中首要的输入是降水。

部分降水（如雨、雪、冰雹）会被树木、草地、其它植被以及建筑物截留，并最终会通过蒸发返回大气。

若降水到达地面，其中一些会在洼地储存（成为洼地存水），部分会入渗到地下（渗透）补充含水层和地下储水，一些会成为地
表径流，即流过地表进入到已有的通道中，比如溪流。

Water entering the ground may take several paths. Some may be directly evaporated if adequate transfer from the soil to the surface is maintained. This can easily occur where a high groundwater table (free water surface) is within the limits of capillary transport to the ground surface. Vegetation using soil moisture or ground water directly can also transmit infiltrated water to the atmosphere by a process known as transpiration. Infiltrated water may likewise replenish soil moisture deficiencies and enter storage provided in groundwater reservoirs, which in turn maintain dry weather stream flow. Important bodies of groundwater are usually flowing so that infiltrated water reaching the saturated zone may be transported for considerable distances before it is discharged. Groundwater movement is subject, of course, to physical and geological constraints.
水进入地表后可能有几个途径（被利用）。

如果土壤水到地表的转移能够得到保证，一些可能被直接蒸发。

这种现象很容易发生在毛细现象运输到达地表限制水位内的高地下水位情况下。

植被直接利用的土壤水或地下水可通过所谓的“蒸腾”过程把如深水转换到大气中去。

入渗水同样可以补充不足的土壤水且接入到地下水库提供的容量中，这些水反过来会在干燥天气保持水流运动。

重要的地下水体一般都在流动，因此到达饱和区域的入渗水可能会在被运输了相当远的距离后才被排出。

地下水的运动自然地会受到物理和地质条件的限制。

Water stored in depressions will eventually evaporate or infiltrate the ground surface. Surface runoff ultimately reaches minor channels (gullies, rivulets, and the like), flows to major streams and finally reaches an ocean. Along the course of a stream, evaporation and infiltration can also occur.
储存在洼地的水会最终蒸发或入渗到地表。

地表径流最终到达小的通道（沟渠，溪流等），流向大的溪流，最后到达海洋。

在水流动的过程中，蒸发和渗流也同时发生着。

2. Unit Hydrographs
2. 单位线
Ways to predict flood peak discharges and discharge hydrographs from rainfall events have been studied intensively since the early 1930s. One approach receiving considerable use is called the unit hydrograph method. It derives from a method of unit graphs employed by Sherman, in 1932. The unit graph is defined as follows: if a given X-hour rainfall produces a 10cm depth of runoff over the given drainage area, the hydrograph showing the rates at which the runoff occurred can be considered a unit graph for that watershed.
自20世纪30年代早期就已经深入研究了降雨事件中预测洪峰流量和流量过程线的方法。

一个应用广泛的方法被称为单位线法。

它源于谢尔曼在1932年使用的单位曲线的方法。

该单位曲线定义如下：如果在给定的X小时内，给定的流域上产生了10cm深的径流，则在该流域出口断面形成的地面径流过程线即为单位线。

It is incorrect to describe a unit hydrograph without specifying the duration, X of the storm that produced it. An X-hour unit hydrograph is defined as a direct runoff hydrograph having a 10cm. Volume and resulting from an X-hour storm having a steady intensity of 10/X cm/hr. A 2-hr unit hydrograph would be that produced by a 2-hr storm during which 10cm of excess runoff was uniformly generated over the basin. A 1-day unit hydrograph would be produced by a storm having 10cm of excess rain uniformly produced during a 24-hr period. The value X is often a fraction of 1 hr.
如果不指明单位线的降雨历时X，那么描述单位线是不正确的。

X小时的单位线被定义为具有10厘米的直接径流的过程线。

一个X小时的暴雨有着稳定的10/X厘米/小时的体量和结果。

一个2小时的单位线将由在流域内均匀产生10厘米过量径流的2小时暴雨所产生。

一个1日单位线将由在24小时期间内均匀产生的具有10厘米过量降雨的暴雨所产生的。

X值通常是1小时的几分之一。

Application an X-hour unit graph to design rainfall excess amounts other than 10cm is accomplished simply by multiplying the rainfall excess amount by the unit graph ordinates, since the runoff ordinates for a given duration are assumed to be directly proportional to rainfall excess. A 3-hr storm producing 20 cm of net rain would have runoff rates 2 times the values of the 3-hr unit hydrograph. 5cm in 3 hr would produce flows half the magnitude of the 3-hr unit hydrograph. This assumption of proportional flows applies only to equal duration storms.
采用X小时的单位线来计算并非等于10厘米的径流过程，可简单地用净雨深乘以单位线的纵标，因为对一个给定时段，单位线假定径流与净雨直接成正比。

一个产生20厘米净雨的3小时暴雨的径流速率值将是3小时单位线的2倍。

3小时内5厘米将会产生3小时单位线一半的量。

该成比例径流假设仅适用于相同历时的暴雨。

If the duration of another storm is an integer multiple of X, the storm is treated as a series of end to end X-hour storms. First, the hydrographs from each X increment of rain are determined from the X-hour unit hydrograph. The ordinates are then added at corresponding times to determine the total hydrograph.
如果另一个暴雨的历时是X的整数倍，那么该暴雨就被视作一系列首尾相连的X小时暴雨系列。

首先，每个X降雨增量的过程线由X小时单位线确定。

然后在相应的时间叠加到纵轴，以确定总的过程线。

Implicit in deriving the unit hydrograph is the assumption that rainfall is distributed in the same temporal and spatial pattern for all storms. This is generally not true; consequently, variations in ordinates for different storm of equal duration can be expected.
在推导单位线隐含的假设是所有暴雨中降雨都按照相同的时间和空间类型而分布。

这通常并不是真实的；因此，可以预期对于相同历时的不同暴雨中的纵坐标的变化。

The construction of unit hydrographs for other than integer multiples of
the derived duration is facilitated by a method known as the S-hydrograph. The procedure employs a unit hydrograph to form an S-hydrograph resulting from a continuous applied rainfall. The unit hydrograph theory can be applied ungauged watersheds by relating unit hydrograph features to watershed characteristics. As a result of the attempted synthesis of data, these approaches are referred to as synthetic unit hydrograph methods. The need to alter duration of a unit hydrograph encouraged studies to define the shortest possible storm duration, that is, an instantaneous unit rainfall. The concept of instantaneous unit hydrograph (IUH) can be used in construction unit hydrographs for other than the derived duration.
对于历时不是整数倍的单位线的建立，引入了一个被称为“S曲线”的方法。

该过程引入了一个单位线以组成一个自所引用连续降雨产生的S曲线。

单位线理论可以通过将单位线特征与流域特性相关联而应用到无水文资料流域。

作为数据的尝试合成的结果，这些方法被称为“综合单位线法”。

改变单位线历时的需要鼓励研究确定最短的风暴历时，即，瞬时单位的降雨量。

“瞬时单位线”（IUH）的概念可以被用于构建非引用历时的单位线。

Methods of deriving unit hydrographs vary and are subject to engineering judgment. The level of sophistication employed to unravel the problem depends largely on the kind of issue in question. Several methods useful in the determination of unit hydrographs will be discussed. They are subdivided into starting with unit hydrographs obtained from field data and manipulating them by S-hydrograph methods and constructing synthetic unit hydrographs.
获得单位线的方法各异且受工程师判断的影响。

用来解开问题的复杂程度在很大程度上取决于所讨论的那种问题。

在确定单位线的过程中将讨论很多有用的方法。

它们细分为开始从现场数据获得单位线，然后用S曲线方法操作它们并构建综合单位线。

Data collection preparatory to deriving a unit hydrograph for a gauged watershed can be extremely time consuming. To develop a unit hydrograph, it
is desirable to acquire as many rainfall records as possible within the study area to ensure that the amount and distribution of rainfall over the watershed is accurately known. Preliminary selection of storms to use in deriving a unit hydrograph for a watershed should be restricted to the following：
1) Storms occurring individually, that is, simple storm structure.
2) Storms having uniform distribution of rainfall throughout the period of rainfall excess.
3) Storms having uniform spatial distribution over the entire watershed.
获得一个有水文资料流域的单位线的数据收集准备会相当地费时。

为了建立一个单位线，最好是获得尽可能多的研究区域内的降水记录，以确保准确知晓流域内降雨的数量和分布。

要用于流域获得单位线的降雨初步选择应该严格遵循如下：
1）暴雨独立地发生，即，单独的暴雨结构。

2）在整个过量降雨期间，暴雨具有均匀的降雨分布。

3）降雨在整个流域内具有均匀的空间分布。

These restrictions place both upper and lower limits on size of the watershed to be employed. An upper limit of watershed size of approximately 2000km2is overcautious, although general storms over such areas are not unrealistic and some studies of areas up to 3000 km2have used the unit hydrograph technique. The lower limit of watershed extent depends on numerous other factors and cannot be precisely defined. A general rule of thumb is to assume about 10 km2. Fortunately, other hydrologic techniques help resolve unit hydrographs for watersheds outside this range.
这些约束限制了要应用流域大小的上限和下限。

2000平方公里左右的流域大小的上限是过于谨慎的，尽管在这些区域的通常暴雨并非不切实际并且一些面积达到3000平方公里地区的研究也应用了单位线技术。

流域范围的下限取决于众多的其他因素，并不能被准确定义。

一般的经验是假设约10平方公里。

幸运的是，其它过程线技术可以帮助解决在这个范
围外的流域单位线。

The preliminary screening of suitable storms for unit hydrograph formation must meet more restrictive criteria before further analysis:
1) Duration of rainfall event should be approximately 10%-30% of the drainage area lag time.
2) Direct runoff for the selected storm should be greater than 5 cm.
3) A suitable number of storms should be analyzed to obtain an average of the ordinates for a selected unit hydrograph duration. Modifications may be made to adjust unit hydrograph durations by means of S-hydrographs of IUH procedures.
4) Direct runoff ordinates for each storm should be reduced so that each event represents 10 cm of direct runoff.
5) The final unit hydrograph of a specific duration for the watershed is obtained by averaging ordinates of selected events and adjusting the result to obtain 10cm of direct runoff.
在进一步分析之前，单位线形成的合适暴雨的初步筛选必须满足以下更加严格的标准：1）降雨事件的历时应该大约是流域面积延迟时间的10%-30%。

2）所选择的暴雨的直接径流应该大于5厘米。

3）应该分析合适数量的暴雨以获得一个所选单位线历时的平均纵标。

可以通过IUH 过程的S曲线法来调整修改单位线历时。

4）每场暴雨的直接径流纵标应该被减少，所以每场降雨代表10厘米的直接径流。

5）流域特定历时的最终单位线是通过平均所选择降雨事件的纵标和调整结果以获得10厘米的直接径流而得到的。

Construction the unit hydrograph in this way produces the integrated effect of runoff resulting from a representative set of equal duration storms. Extreme rainfall intensity is not reflected in the determination. If intense storms are needed, a study of records should be made to ascertain their
influence upon the discharge hydrograph and actual hydrographs from intense storms.
用这种方式构建单位线产生了径流的综合效应，这来自一个代表系列的相同历时的暴雨。

极端暴雨强度不会再决定中反映出来。

如果需要强暴雨，就要研究记录以判明它们对流量过程线的影响以及强暴雨的实际过程线。

Essential steps in developing a unit hydrograph for an isolated storm follow:
1) Analyze the stream flow hydrograph to permit separation of surface runoff from groundwater flow.
2) Measure the total volume of surface runoff (direct runoff) from the storm producing the original hydrograph equal to the area under the hydrograph after groundwater base flow has been removed.
3) Divide the ordinates of direct runoff hydrograph by total direct runoff volume in inches and plot these results versus time as unit graph for the basin.
4) Finally, the effective duration of the runoff-producing rain for this unit graph must be found from the hyetograph (time history of rainfall intensity) of the storm used.
建立一个独立暴雨单位线的基本过程如下：
1）分析径流过程线以允许将地表径流和地下径流分离。

2）在移除地下水基流后，测量暴雨产生的地表径流（直接径流）的总量，该暴雨产生了与过程线下该地区相等的原始过程线。

3）以英尺为单位划分直接径流总量的直接径流过程线纵标，并将这些结果和时间绘制成一个流域的单位线。

4）最后，必须从所用暴雨的雨量计图来建立产流降雨的有效历时。

Procedures other than those listed are required for complex storms or in developing synthetic unit graphs when few data are available. Unit
hydrographs can also be transposed from one basin to another under certain circumstances.
更复杂的暴雨或者当有很少可用资料情况下建立综合单位线时会需要除上述列出以外的步骤。

在某些情况下，也可以将一个流域的单位线移用到另外一个流域。

3. Flood Routing
3.洪水演算
Flood forecasting, reservoir design, watershed simulation, and comprehensive water resources planning generally utilize some form of routing technique. Routing is used to predict the temporal and spatial variations of a flood wave as it traverses a river reach or reservoir, or it can be employed to predict the outflow hydrograph from a watershed subjected to a known amount of precipitation. Routing techniques may be classified into two categories-hydrologic routing and hydraulic routing.
洪水预测、水库设计、流域仿真和水资源综合规划通常应用某种形式的演算技术。

演算被用来预测一个洪峰在通过一个河段或水库时的时间和空间变化，或者它可以被用于预测受到一个已知量降水的流域的出流过程线。

演算技术可以分为两类：水文演算和水力演算。

Hydrologic routing employs the equation of continuity with either an analytic or an assumed relation between storage and discharge within the system. Hydraulic routing, on the other hand, uses both the equation of continuity and the equation of motion, customarily the momentum equation. This particular form utilizes the partial differential equations for unsteady flow in open channels. It more adequately describes the dynamics of flow than does the hydrologic routing technique.
水文演算应用了连续性方程，表达系统内储蓄和排放之间的一个分析或假设的关系。

另一方面，水力演算既应用连续性方程，也应用运动方程，习惯上是动量方程。

这种特殊的形式使用偏微分方程来表达明渠的非恒定流。

它比水文演算技术更充分地描述水流动力情
况。

Applications of hydrologic routing techniques to problems of flood prediction, evaluations of flood control measures, and assessments the effects of urbanization are numerous. Most flood warning systems incorporate this technique to predict flood stages in advance of a severe storm. It is the method most frequently used to size spillways for small, intermediate, and large dams. Additionally, the synthesis of runoff hydrographs from gauged and ungauged watersheds is possible by the use of this approach.
水文演算技术在洪水预测问题、防洪措施评估以及城镇化影响评价中有很多应用。

大多数洪水预警系统引入了该项技术以在一场剧烈暴雨之前预测洪水过程。

它是确定小型、中型和大型大坝溢洪道尺寸的最常用方法。

此外，在可测量和无测量资料的流域中径流水文过程的综合可能使用这种方法。

Hydrologic river routing techniques are all founded upon the equation of continuity
(1) where I is the inflow rate to the reach, O is the outflow rate from the reach, d S/d t is the rate of change of storage within the reach.
水文河流演算技术都建立在连续性方程的基础上
（1）其中I是到达该河段的入流速率，O是河段的出流速率，d S/d t是河段内蓄水的变化速率。

Storage in a stable river reach can be expected to depend primarily on the discharge into and out of a reach and on hydraulic characteristics of the channel section. The storage within the reach at a given time can be expressed as
(2) Constants a and n reflect the stage discharge characteristics of control
sections at each end of the reach, and b and m mirror the stage-volume characteristics of the section. The factor X defines the relative weights given to inflow and outflow for the reach.
稳定河段中的蓄水量主要取决于该河段的入流和出流，以及河流断面的水力特征值。

在给定时间点的河段内蓄水量可以被表示为
（2）常数a和n反映每个河段两端的阶段排放特性，且b和m反映了河段的阶段体积特性。

因素X确定了河段入流和出流的相对权重。

The Muskingum method assumes that m/n =1 and lets b/a=K, resulting in
(3) where K is the storage time constant for the reach, X is a weighting factor that varies between 0 and 0.5.
马斯京根法假设m/n =1 且令b/a=K，得到
（3）其中K是河段存储时间常数，X是在0-0.5之间的权重因数。

Application of this equation has shown that K is usually reasonably close to the wave travel time through the reach and X averages about 0.2.
该方程的应用已经表明K通常合理地接近于水流通过河段流动的时间，且X平均值约0.2。

Behavior of the flood wave due to changes in the value of weighting factor X is readily apparent. The resulting downstream flood wave is commonly described by the amount of translation, that is , the time lag and by the amount of attenuation or reduction in peak discharge. The value X=0.5 results in a pure translation of the flood wave.
权重因数X的值的变化很明显地影响着洪峰的表现。

所得的下游洪峰通常被描述为移动量，即，时间滞后和衰减量或洪峰流量的减少。

X=0.5时导致了洪峰的单纯的平移。

Application of Eqs. (1) and (3) to a river reach is a straightforward procedure if K and X are known. The routing procedure begins by dividing time into a number of equal increments, Δt, and expressing Eq. (1) in finite difference form, using subscripts 1 and 2 to denote the beginning and ending times forΔt. This gives
-=(4)如果K和X已知，那么方程（1）和（3）在河段中的应用就是非常简单的流程。

演算过程开始于将时间分成一定数量的相同增量，Δt，并将方程（1）表达为有限差分的形式，使用下标1和2表示Δt的开始和结束时间。

由此得出
-=（4）The routing time intervalΔt is normally assigned any convenient value between the limits of K/3 and K.
演算时间间隔Δt通常被指定为K /3和K的界限之间的任何方便的值。

The storage change in the river reach during the routing interval from Eq.(3) is
(5) and substituting this into Eq.(4) results in the Muskingum routing equation
(6) In which
Note that K andΔt must have the same time units and also that the three coefficients sum to 1.0.
方程（3）中演算间隔中河段内的蓄水变化为马斯京根方程
（5）将此式带入方程（4）中得到
（6）其中
注意K和Δt必须有相同的单位且三个系数和为1.0。

Theoretical stability of the numerical method is accomplished ifΔt falls between the limits 2KX and 2K(1-X). The theoretical value of K is the time required for an elemental (kinematic) wave to traverse the reach. It is approximately the time interval between inflow and outflow peaks, if data are available. If not, the wave velocity can be estimated for various channel shapes as a function of average velocity V for any representative flow rate Q. Velocity for steady uniform flow can be estimated by either the Manning or Chezy equation.
如果Δt在2KX和2K（1-X）之间，那么数值计算方法就满足理论稳定性。

K的理论值是一个元素（运动）峰穿过河段所需的时间。

如果可以获得数据，那么它大约是流入及流出峰值之间的时间间隔。

如果不是，波速可以对不同的渠道形状作为代表性流量Q的平均速率的函数来估算。

稳定均匀流的速度可以通过曼宁或谢才公式来估算
Since, I1and I2are known for every time increment, routing is accomplished by solving Eq. (6) successive time increments using each O2 as O1 for the next time increment.
因此，I1和I2是已知的每个时间增值，并通过将O2作为下个时间增量的O1来解决方程（6）的连续的时间增量，从而完成演算。

4. Water Quality Models
4.水质模型
Because water quality is inextricably linked to water quantity, it is important for the hydrologist to understand the significance of developing modeling techniques that can accommodate both features.
由于水质与水量密不可分，因此了解开发能够适用于两个特性的建模技术对水文学家来说是很重要的。

A water quality model is a mathematical statement or set of statements that equate water quality at a point of interest to causative factors. In general, water quality models are designed to (1) accept as input, constituent concentration versus time at points of entry to the system, (2) simulate the mixing and reaction kinetics of the system, and (3) synthesize a time-distributed output at the system outlet.
水质模型是一个或一系列的数学表达，描述了所关注点的诱发因素的水质。

通常来讲，水质模型被设计于（1）作为输入条件，在系统入口处浓度与时间的关系，（2）模拟混合及系统的动力学反应，以及（3）综合为一个系统出口处随时间分布的输出。

Either stochastic (containing probabilistic elements) or deterministic approaches may be taken in developing methods for predicting pollutional loads. The former technique is based on determining the likelihood(frequency) of a particular output quality response by statistical means. This is similar to frequency analysis of floods or low flows. Water quality records should be available for at least 5 years (and preferably much longer) if estimates of return periods for infrequent events are to be reliable.
随机（包含概率元素）或确定性方法都可能被用于开发预测污染负荷的方法。

前者技术基于通过统计方法确定的一个特定的输出质量响应的可能性（频率）。

这类似于洪水或低流量的频率分析。

如果要求可靠的偶发事件重现期的估计，那么就要至少获得5年（最好
更长）的水质记录。

The deterministic approach (output explicitly determined for a given input) requires that a model be developed to relate water quality loading to a known or assumed hydrologic input. Such a model can range from an empirical concentration discharge relation to a physical equation representing the hydrochemical cycle. The ultimate modeling technique is that which best defines the actual mechanism triggering the water quality response. The cause of a given state of pollution can then be specifically identified.
确定性方法（对于给定的输入明确地确定输出）要求一个模型被开发于将水质负荷与一个已知的或假设的水文输入关联起来。

这样的一个模型可以从一个浓度流量的经验关系到一个物理方程，描述水化学循环。

最终的建模技术最好地定义了触发水质响应的实际机制。

随后即可具体确定给定污染状态的起因。

Water quality models vary in their complexity. Their nature depends on the application to be made of the model, the availability of data, and the level of understanding of the hydrochemical and hydrobiological processes involved. Unfortunately, the complexities of these processes, which are great, make the difficulties associated with hydrological modeling seem small in comparison.
水质模型的复杂性各有不同。

其本质取决于作为模型的应用、数据的可获得性以及对于所涉及的水化学和水生物学过程的理解程度。

可惜，这些过程巨大的复杂性使得与水文模拟相关联的复杂性看起来相对较小。

In general, water quality models should permit acceptance of inputs in terms of pollutant (constituent) concentration versus time at points of entry into the system, description of the mixing and reaction kinetics in the stream element or groundwater element of concern, and synthesis of a time-distributed output indicating pollutant concentration at the outlet of
the element (segment) being modeled. An analogy may be drawn to the stream flow routing, which is performed in a downstream sequence from one stream channel segment to another. In the case of water quality modeling, the common representation is the calculation of change in constituent concentration as it passes through successive states of the water body being modeled.
通常来讲，水质模型应该允许在系统进口处的污染物（组分）浓度相对时间的输入形式，所关注的水流元素或地下水元素混合和反应动力学的描述，以及综合成一个随时间分布输出，该输出描述所模拟的出口元素（分段）的污染物浓度。

可以对水流演算打个比喻，这发生在向下游的从一个向另一个的水流通道段中。

在水质模拟的情况下，通常的表达是对在通过被模拟连续水体时组分浓度变化的计算。

As in the case of other water resources modeling processes, the approach may be deterministic or stochastic. In the case of water quality models, the stochastic approach is often ruled out because actual records of water quality parameters are unavailable for long enough periods to permit frequency methods to be used. Of course, generated sequences can be used for this purpose if adequate mathematical statements representing the kinetics of the system can be developed and their parameters determined.
对于其它水资源模拟过程，其方法可以是确定性或随机性的。

对于水质模型，随机方法往往被排出在外，因为不能获得足够长时段内的水质参数的实际记录，所以不允许应用概率方法。

当然，如果可以开发表示该系统的动力学适当的数学命题，且它们的参数可以确定，那么所产生的序列可以被用于此目的。

The deterministic approach to water quality modeling requires that relations between water quality loading and the flow or hydraulic features of the system be established and that the appropriate chemical and/or biological reactions be tractable for solutions. Where theory-based relations cannot be employed, empirical relations are often used. The optimum model to use。