PhysicalHydrology水文学的原理（英文版）

1、Physical Hydrology水文学的原理（英文版）1PhysicalHydrology水文学的原理（英文版）Attention!Prepare your course beforehand words, sentences, phasesNo absence is allowed Dont be late for class Read as much as possible, write as much as possible, use the Internet for help as much as possible 2PhysicalHydrology水文学的原理（英文版）1 In

2、troduction to Hydrologic ScienceDEFINITION AND SCOPE OF HYDROLOGYDEVELOPMENT OF SCENTIFIC HYDROLOGYAPPROACH AND SCOPE OF THIS BOOK3PhysicalHydrology水文学的原理（英文版）1.1 DEFFINTION AND SCOPE OF HYDROLOGY4PhysicalHydrology水文学的原理（英文版）Hydrology is broadly defined as the geoscience that des-cribe and predicts

3、the occurrence,circulation, and distri-bution of the water of the earth and its atmosphere.The global hydrologic cycle The land phase of the hydrologic cycle5PhysicalHydrology水文学的原理（英文版）Water Cycle6PhysicalHydrology水文学的原理（英文版）7PhysicalHydrology水文学的原理（英文版）8PhysicalHydrology水文学的原理（英文版）9PhysicalHydrolo

4、gy水文学的原理（英文版）InterdisciplinaryScienceTo manage water resources and water related hazardsEngineering hydrology, economics and related social science for water-resources management10PhysicalHydrology水文学的原理（英文版）1.2 DEVELOPMENT OF SCIENTIFIC HYDROLOGY5000-6000 B.P. Pakistan, China, Egypt： Canals,levees,

5、dam,well3800 B.P. Egyptians: monitoring of river flow2400B.P India: rainfall measurement11PhysicalHydrology水文学的原理（英文版） The concept of a global hydrology cycle dates from at least 3000 P.B (Nace 1974),when Solomon wrote in Ecclesiastes 1:7 that All the rivers run into the sea ;yet the sea is not full

6、; unto the place from whence the rivers come ,thither they return again. The 18th century saw considerable advance in applications of mathematics to fluid mechanics and hydraulics by Pitot, Beroulli Chezy,Euler,and others in Europe. Use of term “hydrology” in approximately its current meaning began

7、about 1750. 12PhysicalHydrology水文学的原理（英文版）Treatises on various aspects of hydrology, beginning with the Englishman Nathaniel Beard-mores Manual of Hydrology in 1862 ,appeared with increasing frequ- ency in the last half of the 19th century. The half of the twentieth century saw great progress in man

8、y aspect of hydrology and ,with the formation of the Section of Scientific Hydrology in the International Union of Geodesy and Geophysics (IUGG,1992) and Hydrology Section of the American Geophysical Union (1930) , the first form recognition of the scientific status of hydrology. 13PhysicalHydrology

9、水文学的原理（英文版） There are,in fact great opportunities for progress in physical hy-drology in many areas, including the determination of regional evapotranspiration rate, the movement of ground water in rock fracture, the relation between hydrology behavior at different scales, the re- lation of hydrolog

10、y regimes to past and future climates and the interaction of hydrology processes and land-form development (Eagleson et al.1991). 14PhysicalHydrology水文学的原理（英文版）The ability to understand and model hydrologic processes at continental and global scale is be- come increasing impor-tant because of the ne

11、ed to predict the effects of large-scale changes in land and in climate.From point to largerIn the land phase of the hydrologic cycle, it is interesting that detailed field studies to understand the mechanisms by which water enters streams began to proliferate only in the 1960s, pioneered by T.Dunne

12、 and others. The temporal and spatial variability of natural conditions15PhysicalHydrology水文学的原理（英文版）2 Basic Hydrologic Concepts2.1 PHYSICAL QUANTITIES AND LAWS2.2 HYDROLOGIC SYSTEMS2.3 THE CONSERVATION EQUATIONS2.4 THE WATERSHED (DRAINAGE BASIN)2.5 THE REGIONAL WATER BALANCE2.6 SPATIAL VARIABILITY2

13、.7 TEMPORAL VARIABILITY2.8 STORAGE,STORAGE EFFECTS, AND RESIDENCE TIME 16PhysicalHydrology水文学的原理（英文版）2.1 PHYSICAL QUNTITES AND LAWSHydrology is a quantity geophysical science, In principle,these numerical values of hydrologic values are determined by either 1. counting, in which case the quantity ta

14、kes on a value that is a positive integer or zero ;or 2. Measuring ,in which case the quantity takes on a value corresponding to a point on the real number scale that is the ratio of the magnitude of the quantity to the magnitude of a standard unit of measurement.17PhysicalHydrology水文学的原理（英文版）The ba

15、sic relations of physical hydrology are derived form fundamental laws of classic physics, particularly those listed in Table 2-1.18PhysicalHydrology水文学的原理（英文版）2.2 HYHDROLOGIC SYSTEMSeveral basic hydrologic concepts are related to the simple model of a system shown in Figure 2-1.The outer dashed line

16、 in Figure 2-1 indicates that any group of linked systems can be aggregated into a larger system; the smaller systems could then be called subsystems.19PhysicalHydrology水文学的原理（英文版）20PhysicalHydrology水文学的原理（英文版）2.3 THE CONSERVATION EQUATIONSThe amount of a conservative quantity entering a control vol

17、ume during a defined time period, minus the amount of the quantity leaving the volume during the time period, equals the change in the amount of the quantity stored in the volume during the time period. 21PhysicalHydrology水文学的原理（英文版）(2-2)(2-3)Amount In Amount out =Change In storage(2-1),22PhysicalHy

18、drology水文学的原理（英文版）(2-4)(2-5)(2-6),23PhysicalHydrology水文学的原理（英文版） Another version of the conservation equation can be developed by defining the instantaneous rates of inflow, i,and outflow, q, as(2-7)(2-8)(2-9),24PhysicalHydrology水文学的原理（英文版）Equations(2-2),(2-6),and (2-9),are called water-balance equa

19、-tion when applied to the mass of water moving through various portions of the hydrologic cycle; control volumes in these appli-cations range in size from infinitesimal to annual or longer (Figure 1-3).evaporation and snowmeltenergy-balance the conservation of momentumfluid flow 25PhysicalHydrology水

20、文学的原理（英文版） THE WATERSHED (DRAINAGE BASIN)Watershed (also called drainage basin, river basin, or catch-ment),defined as the area that appears on the basis of topography to contribute all the water that pass-es through a given cross section of a stream(Figure 2-2).dividedrainage area2.4.1 definition26

21、PhysicalHydrology水文学的原理（英文版）27PhysicalHydrology水文学的原理（英文版）Thus the watershed can be viewed as a natural landscape unit, integrated by water flowing through the land phase of the hydr- ologic cycle and, although political boundaries do not generally follow watershed boundaries, water-resource and lan

22、d-use planning agencies recognize that effective management of water quality and quality require a watershed perspective.The location of the stream cross section that defines the water- shed is determined by the purpose of the analysis.28PhysicalHydrology水文学的原理（英文版）The conventional manual method of

23、watershed de-lineation requires a topographic map (or stereo-scopically viewed aerial photographs).Increasingly,topographic information is becoming available in the form of digital elevation models (DEMs).This automated approach to watershed delineation allows the concomitant rapid extraction of muc

24、h hydrologically useful information on watershed characteristics (such as the distri-bution of elevation and slop) that previously could be obtained only by very tedious manual methods.2.4.2 Delineation 29PhysicalHydrology水文学的原理（英文版）2.5 THE REGIONAL WATER BALANCEThe regional water balance is the app

25、lication of the water-balance equation to a watershed (or to any land area, such as a state or continent).30PhysicalHydrology水文学的原理（英文版）2.5.1 The Water-Balance Equation31PhysicalHydrology水文学的原理（英文版）,(2-10)If we average these quantities over a reasonably long time period(say,many years) in which ther

26、e are no significant climatic trendsor geological changes and no anthropogenic inputs, or storage modifications,we can usually assume that net change in storage will be effectively zero and write the water balance as (2-11),32PhysicalHydrology水文学的原理（英文版）run off,RO;hydrologic production;(2-12)(2-13),

27、33PhysicalHydrology水文学的原理（英文版）,(2-14)When we assume that is negligible and write the water-balanceequation as,(2-15)34PhysicalHydrology水文学的原理（英文版）Both precipitation and evaportranspiration can be considered to be externally imposed climatic boundary conditions.This, from Equation (2-15),runoff is a

28、residual or difference between two climatically-determined quantities.2.5.2 Estimation of Regional EvaportranspirationPerhaps the most common form of hydrologic analysis is the estimation of the long-term average value of regional evapor-transpiration via the water-balance equation.35PhysicalHydrolo

29、gy水文学的原理（英文版）It is usually assumed that ground-water flows either are negligible or cancel out and that is negligible, so that equation (2-15) becomes (2-16),Model error, which refers to the omission of potentially signifi-cant term form the equation, and measurement in the quantities and ,which is

30、unavoidable .36PhysicalHydrology水文学的原理（英文版）Ground-water FlowsStreams draining larger watersheds tend to receive the subsur- face outflows of their smaller constituent watershed, so the importance of ground-water out-flow generally decrease as one considers larger and larger watershed. 37PhysicalHydr

31、ology水文学的原理（英文版）Storage ChangeHydrologists attempt to minimize its value by (1) us-ing long measurement periods and a (2) selecting the time of beginning and end of the measurement period such that storage values are likely to be nearly equal. 38PhysicalHydrology水文学的原理（英文版）Measurement ErrorAccuracy

32、of Regional Precipitation Valuesindividual gages areal averagesIn regions of the high relief or with few or poorly distributed gages, or for shorter measurement peri-ods, the uncertainly can be considerably larger.39PhysicalHydrology水文学的原理（英文版）Accuracy of Streamflow Values Winter (1981) estimated th

33、at the measurement un- certainly for long-term average values of streamflow at a gaging station is on the order of . (The ac- curacy of such measurements is discussed further in Section F.2.4 ) where is estimated for locations other carefully maintained gaging stations, the uncertainty can be much g

34、reater.40PhysicalHydrology水文学的原理（英文版）Potential measurement errors are usually assumed to be distri-buted symmetrically about the true value (equal chance of under-or over-estimation) and to follow the bell-shaped normal distribution describe in Appendix C: the future a measured value is from the tru

35、e value (i.e.,the larger is the error), the small is probability that it will occur (Figure 2-4). The spread, or variation, of the potential measured values about the true value is expressed as the standard deviation of the potential errors.41PhysicalHydrology水文学的原理（英文版）The standard deviations of th

36、e errors due to measurement of the quantities are related as,(2-17)“I am 100.p% sure that the true value of precipitation is within of the measured value.” (2-18a) 42PhysicalHydrology水文学的原理（英文版） is the estimate of average precipitation and is the relative uncertainty in the estimate (e.g,if the meas

37、urement uncertainty is stated to be 10%, =0.1). The absolute uncer-tainty in is . (2-18b),43PhysicalHydrology水文学的原理（英文版）Given that potential measurement errors follow the normal distribution, we can find from the properties of that distribution, summarized in Table C-5,that there is a 95%probability

38、 that an observation will be within 1.96 standard deviations of the central (true) value. (2-19),44PhysicalHydrology水文学的原理（英文版）(2-20),(2-21a),(2-21b)45PhysicalHydrology水文学的原理（英文版）(2-22),(2-23)Assume the relative measurement errors for precipitation and streamflow are =0.1 and =0.05.46PhysicalHydrolo

39、gy水文学的原理（英文版）2.6SPATIAL VARIABILITY However, precipitation gages are usually unevenly distributed over any given region, and the point values are therefore an un- representative sample of the true precipitation field,Because of this, and because of the importance of accurately quantifying variables

40、such as precipitation ,basic statistical concepts have been incorporated into special technique for characterizing and accounting for spatial variability.47PhysicalHydrology水文学的原理（英文版）2.7TEMPORAL VARIABILITYThe inputs, storages and outputs in Figure are all time-distributed variablesquantities that

41、can vary with time.In particular ,the streamflow rate at a given location is highly variable in time. From the human viewpoint, the long-term average streamflow rate , , is highly significant: it represents the maximum rate at which water is potentially available for human use and management, and is

42、 therefore a measure of the ultimate water resources of a watershed or region.48PhysicalHydrology水文学的原理（英文版）Streamflow variability is directly related to the seasonal and interannual variability of runoff (and hence of the climate of precipitation and evapo-transpiration ) and inversely to the amoun

43、t of sto-rage in the watershed.Human can increase water availability by building storage reservoirs, as dis-cussed in Section 2.8 and 10.2.5 .Human can also attempt to increase through “rain-making”(Sec-tion 4.4.5) and to decrease by modifying vegeta-tion (Section7.6.4 and 10.2.5).The basic approach

44、 for constructing and analyzing sample of tine-distributed variables.49PhysicalHydrology水文学的原理（英文版）Each value of which is associated with a particular time in a sequence times,.Such a sequence is called a time series.Some time-series variables are obtained by countingfor example,the number of days w

45、ith more than 1mm rain in each year at a particular location.Such variables are inherently discrete.Continuous time trace: they take on values at every instant in time. 2.7.1 Time Series50PhysicalHydrology水文学的原理（英文版）51PhysicalHydrology水文学的原理（英文版）EXAMPLE 2-2Table 2-2 lists, and Figure 2-6 plots, thre

46、e time series developed from the continuous streamflow record obtain at the streamgaging station operated by the U.S.Geological Survey on the Oyster River in Durham, NH. In all three plots, = 1 yr, and the ordinate is a streamflow rate, or dis-charge , ,However,the discretization of the continuous r

47、ecord was done differently for each series: Se-ries a is the average streamflow for the year, series b is the high-est instantaneous flow rates for the year,series c is the lowest of the flow rates found by averaging over seven-consecutive-day periods within each year .(These data are also in the sp

48、readsheet 2-2,xls on the disk accompanying this text.) Note that the lines connecting the time-series values in each graph do not represent a time trace they serve only to connect the point value to provide a visual to provide impression of the nature of the series.52PhysicalHydrology水文学的原理（英文版）53PhysicalHydrology水文学的原理（英文版）Time series ar