1、1Physical HydrologyS.Lawrence DingmanS.Lawrence Dingman2Who am I?Zhang XiangZhang Xiang 68772303-601(o)68772303-601(o)1397140609713971406097 Office:0101609Office:0101609 3Textbook and references TextbookTextbook Physical HydrologyPhysical Hydrology ReferencesReferences Hydrology for Engineers by R.K
2、.LinsleyHydrology for Engineers by R.K.Linsley Hydrology:principles,analysis and designHydrology:principles,analysis and design by H.M.Raghunath by H.M.Raghunath Hydrology:an introduction to hydrologic scienceHydrology:an introduction to hydrologic science by R.L.Brasby R.L.Bras 水文学原理水文学原理(一一)胡方荣胡方荣
3、 候宇光候宇光 水文学原理水文学原理(二二)于维忠于维忠 水文学原理水文学原理 芮孝芳芮孝芳4Time Arrange Lecture:36 class hours part 1 and 2:4 class hours part 4:8 class hours part 6:8 class hours part 7:6 class hours part 8:6 class hours part 9:4 class hours Lab:6 class hours for computer5The Finals Assignments(30%)Checking on attendance(20%)
4、Examination(50%)6Attention!Prepare your course beforehand words,sentences,phases No 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 71 Introduction to Hydrologic ScienceDEFINITION AND SCOPE OF HYDROLOGYDEVELOP
5、MENT OF SCENTIFIC HYDROLOGYAPPROACH AND SCOPE OF THIS BOOK81.1 DEFFINTION AND SCOPE OF HYDROLOGY9Hydrology is broadly defined as the geoscience that des-cribe and predicts the occurrence,circulation,and distri-bution of the water of the earth and its atmosphere.The global hydrologic cycle The land p
6、hase of the hydrologic cycle10Water Cycle11121314InterdisciplinaryScienceTo manage water resources and water related hazardsEngineering hydrology,economics and related social science for water-resources management151.2 DEVELOPMENT OF SCIENTIFIC HYDROLOGY 5000-6000 B.P.Pakistan,China,Egypt：Canals,lev
7、ees,dam,well 3800 B.P.Egyptians:monitoring of river flow 2400B.P India:rainfall measurement16 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;unto the place from whence
8、 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 about 1750.17Treatises on various
9、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 many aspect of hydrology and,with the formation of the Section of Scie
10、ntific 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.18 There are,in fact great opportunities for progress in physical hy-drology in many areas,
11、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 hydrology regimes to past and future climates and the interaction of hydrology processes and land-form developmen
12、t(Eagleson et al.1991).191.The ability to understand and model hydrologic processes at continental and global scale is be-come increasing impor-tant because of the need to predict the effects of large-scale changes in land and in climate.From point to larger2.In the land phase of the hydrologic cycl
13、e,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 and others.The temporal and spatial variability of natural conditions202 Basic Hydrologic Concepts2.1 PHYSICAL QUANTITIES AND LAWS2.1
14、 PHYSICAL QUANTITIES AND LAWS2.2 HYDROLOGIC SYSTEMS2.2 HYDROLOGIC SYSTEMS2.3 THE CONSERVATION EQUATIONS2.3 THE CONSERVATION EQUATIONS2.4 THE WATERSHED(DRAINAGE BASIN)2.4 THE WATERSHED(DRAINAGE BASIN)2.5 THE REGIONAL WATER BALANCE2.5 THE REGIONAL WATER BALANCE2.6 SPATIAL VARIABILITY2.6 SPATIAL VARIAB
15、ILITY2.7 TEMPORAL VARIABILITY2.7 TEMPORAL VARIABILITY2.8 STORAGE,STORAGE EFFECTS,AND RESIDENCE TIME 2.8 STORAGE,STORAGE EFFECTS,AND RESIDENCE TIME 212.1 PHYSICAL QUNTITES AND LAWS2.1 PHYSICAL QUNTITES AND LAWSHydrology is a quantity geophysical science,In principle,these numerical values of hydrolog
16、ic values are determined by either 1.counting,in which case the quantity takes 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 magnitud
17、e of a standard unit of measurement.22The basic relations of physical hydrology are derived form fundamental laws of classic physics,particularly those listed in Table 2-1.232.2 HYHDROLOGIC SYSTEM2.2 HYHDROLOGIC SYSTEMSeveral basic hydrologic concepts are related to the simple model of a system show
18、n in Figure 2-1.The outer dashed line 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.24252.3 THE CONSERVATION EQUATIONSTHE CONSERVATION EQUATIONSThe amount of a conservative quantity entering a contr
19、ol volume 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.26SQI(2-2)tstQtI(2-3)Amount In Amount out =Change In storage(2-1),27tImltQmQtSmmQl(2-4)(2-5)(2
20、-6),28 Another version of the conservation equation can be developed by defining the instantaneous rates of inflow,i i,and outflow,q q,astIil0limtQql0limdtdsqi(2-7)(2-8)(2-9),29Equations(2-2),(2-6),and(2-9),are called water-balance equa-tion when applied to the mass of water moving through various p
21、ortions 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 302.4 THE WATERSHED(DRAINAGE BASIN)THE WATERSHED(DRAINAGE BASIN)Watershed(also called
22、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 definition3132Thus the watershed can be viewed as a natural landscape unit,int
23、egrated 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 land-use planning agencies recognize that effective management of water quality and quality require a watershed perspective.The l
24、ocation of the stream cross section that defines the water-shed is determined by the purpose of the analysis.33The conventional manual method of watershed de-lineation requires a topographic map(or stereo-scopically viewed aerial photographs).Increasingly,topographic information is becoming availabl
25、e in the form of digital elevation models(DEMs).This automated approach to watershed delineation allows the concomitant rapid extraction of much hydrologically useful information on watershed characteristics(such as the distri-bution of elevation and slop)that previously could be obtained only by ve
26、ry tedious manual methods.2.4.2 Delineation 342.5 THE REGIONAL WATER BALANCE2.5 THE REGIONAL WATER BALANCEThe regional water balance is the application of the water-balance equation to a watershed(or to any land area,such as a state or continent).352.5.1 The Water-Balance Equation36SGETQGpoutin)(,(2
27、-10)If we average these quantities over a reasonably long time period(say,many years)in which there 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 wat
28、er balance as 0GoutETQGinp(2-11),37 run off,RO;hydrologic production;GoutQRO(2-12)ETpGinGoutQ(2-13),38ETGinpRO,(2-14)When we assume that inGis negligible and write the water-balanceequation asETpGoutQRo,(2-15)39Both precipitation and evaportranspiration can be considered to be externally imposed cli
29、matic boundary conditions.This,from Equation(2-15),runoff is a 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
30、-transpiration via the water-balance equation.40It is usually assumed that ground-water flows either are negligible or cancel out and that is negligible,so that equation(2-15)becomes SQpETmmm(2-16),Model error,which refers to the omission of potentially signifi-cant term form the equation,and measur
31、ement in the quantities and ,which is unavoidable.pmQm41 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.42
32、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.43 Measurement Error Accuracy of Regional Precipitation Values individual gag
33、es 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.44 Accuracy of Streamflow Values Winter(1981)estimated that the measurement un-certainly for long-term average values of streamflow at
34、 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 greater.%5Q45Potential measurement errors are usually assumed to be distri-buted sym
35、metrically 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 true value(i.e.,the larger is the error),the small is probability that it will occur(Figure 2-4).The spread,or var
36、iation,of the potential measured values about the true value is expressed as the standard deviation of the potential errors.46The standard deviations of the errors due to measurement of the quantities are related as222QpET,(2-17)“I am 100.p%sure that the true value of precipitation is within of the
37、measured value.”(2-18a)ppmu 47 is the estimate of average precipitation and is the relative uncertainty in the estimate(e.g,if the measurement uncertainty is stated to be 10%,=0.1).The absolute uncer-tainty in is .pupmpmppmu pmumionprecipitattruemumpppppppr)()(2-18b),pu48Given that potential measure
38、ment 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 that an observation will be within 1.96 standard deviations of the central(true)value.95.0)96.1()96.1(pppprSmionprecipitattrueSmP(2-19),49pppsmu96.1(
39、2-20),96.1pppmus(2-21a),2pppmus,(2-21b)502QQQmusQpQQppETETETmmmumumsu2122222(2-22),(2-23)Assume the relative measurement errors for precipitation and streamflow are =0.1 and =0.05.puQu512.6SPATIAL VARIABILITYSPATIAL VARIABILITY However,precipitation gages are usually unevenly distributed over any gi
40、ven 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 such as precipitation,basic statistical concepts have been incorporated into special technique for characterizin
41、g and accounting for spatial variability.522.7TEMPORAL VARIABILITYTEMPORAL VARIABILITYThe inputs,storages and outputs in Figure are all time-distributed variablesquantities that can vary with time.In particular,the streamflow rate at a given location is highly variable in time.From the human viewpoi
42、nt,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 therefore a measure of the ultimate water resources of a watershed or region.Qu53Streamflow variability is directly related to the
43、 seasonal and interannual variability of runoff(and hence of the climate of precipitation and evapo-transpiration)and inversely to the amount 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 attem
44、pt 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 for constructing and analyzing sample of tine-distributed variables.puETu54Each value of which is associated with a particular time in a sequence times,.Such a sequ
45、ence is called a time series.Some time-series variables are obtained by countingfor example,the number of days with 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 Series5556
46、 EXAMPLE 2-2Table 2-2 lists,and Figure 2-6 plots,three 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,Ho
47、wever,the discretization of the continuous record 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
48、 each year.(These data are also in the spreadsheet file table 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 natu
49、re of the series.t13TL5758Time series are usually treated as more or less representative sample of the long-term behavior of the variable and described and compared on the basis of their statistical attributes.For example,the temporal variability of a time series can be charac-terized in absolute te
50、rms by its interquartile range or by its standard deviation,and in relative terms by the ration of its interquartile rang to its median or by its coefficient of variation.59It is important to note that time series developed from a single continuous time trace by choosing different discretizing schem
