教程水文学原理cycle

1、Principles of Hydrology水文学原理资源环境学院张卫华 博士 副教授 Email: Tel: 68250281(H) (M)教材及参考资料Textbooks & ReferencesPrinciples of Hydrology (4th Ed). R.C. Ward etc 水文学原理 芮孝芳著Main references:Introduction to hydrology(5th Ed) Warren&LewisPrinciples of hydrology (UNESCO-IHE) Handbook of hydrology Edited by David Maid

2、ment工程水文学 王燕生著工程水文学 詹道江著现代水文学 左其亭编著河流水文学 芮孝芳等著地下水水文学 张元禧等著环境水文学 梁瑞驹编著工程水文学题库及题解 宋星原等编著Student responsibilities & policiesConsistent class attendance is expected.Students are expected to do the homework & to do the reading, and to do it On TimeStudents are expected to raise & answer QEvaluation: Home

3、work + attendance 15% Mid term exam 10% Experiment + Fieldtrip 15% Final exam 60%Learning Objectives Students will e familiar with some of the current issues in hydrology and water resources.Students will acquire a working knowledge of the hydrologic cycle. A “working knowledge” will pass a basic un

4、derstanding of processes, awareness of how measurements are made, and the ability to use observations and hydrologic concepts to address a variety of problems.Students will e sufficiently familiar with hydrologic vocabulary and concepts that they will be capable of reading and interpreting professio

5、nal level reports.Assignments are intended to help students develop and polish skills that are expected of working professionals. These skills include:Accessing and interpreting information (both standard data sets and the scientific literature)Quantitative analysisWriting, both formal & informalLas

6、t but not least, EnjoyCh1 Introduction1.1 Facts & Figures1.2 The changing nature of Hydrology1.3 The hydrological cycle and system1.4 The nature of hydrological processes1.1 Facts & FiguresHydrology水文学Hydrology is the branch of Science that asksWhat happens to rain after it falls?DefinitionHydrology

7、 is the science dealing with the waters to the earth, their occurrence, dis-tribution & circulation, their chemical and physical properties & their interaction with the environment.Water, the subject of hydrology both Commonplace & UniqueCommonplace: is found everywhere in the earths ecosystem & tak

8、en for granted in much of the developed world.Unique: the only naturally occurring inorganic liquid & the only chemical compound that occurs in normal conditions as a solid, a liquid & a gas.Its distribution over the globe is amazingly uneven.Water plays a fundamental part in the distribu-tion of ch

9、emicals through its central role in many chemical reactionsTransport of dissolved chemicalsErosion & deposition of sediments.Water vapour, the principal greenhouse gas in the earths atmosphere, the second is ? CO2: the second most important greenhouse gasApproximately, about 97% of water occurs as s

10、aline water in seas & oceans only 3% as freshwater half of the 3% is locked up & another substantial volume as immobile deep GWThe real mobile freshwater: rainfall, evaporationStream-flow, represents only 0.3%Volume (km)Share of world reservesShare of total water(%)Share of fresh water(%)Atmospheric

11、 water12,9000.0010.01Glaciers end permanent snow cover24,064,0001.7468.7Ground ice in zones of permafrost strata300,0000.0220.86Water in rivers2,1200.00020.006Water in lakes (fresh, 91,000 km)176,4000.0130.26Water in marshes11,4700.00080.03Soil moisture16,5000.0010.05Active groundwater (in aquifers)

12、, including brackish and fossil10,530,0000.7630.1Inactive groundwater (in lithosphere)23,400,0001.7World ocean1,338,000,00096.5ReservoirAverage Residence TimeGlaciers20 to 100 yearsSeasonal Snow Cover2 to 6 monthsSoil Moisture1 to 2 monthsGroundwater: Shallow100 to 200 yearsGroundwater: Deep10,000 y

13、earsLakes50 to 100 yearsRivers2 to 6 monthsWhy do I give you so much figures (data)?These estimates must be treated with caution because of the difficulties of Monitoring & （监测） Quantification （量化） at the Macroscale (宏观尺度）Therefore, a broad range of estimate of the global water storage depending on

14、the data used and assumptions Hydrologists 水文学家 usually focusing on a small amount of fresh water rivers lakes soil water shallow groundwater (GW) vegetation cover atmosphereOcean plays an important role in global water & energy budgete.g. Hydrological system disturbed by sea surface temperature fro

15、m El NinoThe freshwater itself distributed unevenly both in time & spaceWetland, prairie (大牧场), forest, desert etc differs in patterns of Precipitation, Evaporation & streamflow challenges for Hydrologists & WM1.2 The changing nature of HydrologyHydrology water esp atmospheric & terrestrialHowever,

16、its emphases have changed from time to time from one person to another Changes of historical pattern from physical to engineering, then to WRHowever, evidence shown they are simultaneously & interdependentlyE.g. ancient search for Spring (泉), GW Stream-flow etc based on guess, religion, mythology In

17、terdisciplinary (交叉学科) issueThe challenge of modeling the global atmospheric & hydro-spheric circulationThe ever increasing demand of water quadruple(四倍的) from 19401990 10% worlds people is affected currently likely one third in the year 2025Much clearer understanding of the PhysicalEconomicSocialPo

18、litical Ecological needed to reduce the impact of large-scale water resource project & major irrigation & flood-defense schemes1.3 The hydrological cycle and systemHydrological cycle (水文循环) the interdependence & continuous movement of all phases of water, i.e. liquid, solid, gaseousThe quantity of w

19、ater kept unchanged but the quality may be changedDefinitionCirculation of water vapor from sea and land surface, its transport through the atmosphere to the land & its return to the sea via surface, subsurface & atmospheric routes.Main components P precipitationE evaporationT transpirationI infiltr

20、ationR runoffG ground water flowIc interceptionAlso including percolation, capillary rise etcPrecipitation (降水)Water vapor in the atmosphere condenses(凝结) & may give rise to precipitation.For the terrestrial(陆地的) portion, the P is:not directly to the ground surface because ofVegetation coverSurfaces

21、 of buildings will be evaporated from here to atmosphere to the ground surfaceBe stored in water body (rivers, pools, etc) evaporated quickly back to atmos.Be stored as snow or ice melting or sublimation(升华) but many years Flow to rivers or lakes evaporated or seepage(渗流) to GWInfiltration to soils

22、evaporated or vegetation cover, percolation(浸透)3 水汽输送1蒸发4 降水1蒸发4 降水1 植物蒸腾湖6 地表径流6 地下径流海洋5 蒸发2 降水Human interference to hydro cycleHuman interference to hydro cycle1、advantages：reservoirsDiversion for irrigationInter-basin diversion2、 disadvantages：deforestationLakes & marshes drying upOver-withdrawn

23、GWWater balance or hydrological budgetThe hydrological budgetAn accounting of the inflow, outflow & storage of water in a designated hydrological system.Continuity equation or Law of conservation of MassI(t) - O(t)=S/tI: inflow (L3/T)O: outflow (L3/T)S/t: the rate of change in storage over a finite

24、time step in (L3/T) of the considered control volumeNote: the equation holds for a specific of time and may be applied to any given system provided that the boundaries are well defined.111385Several types of water balancethe earth surfacea drainage basinthe water diversion cycleA local area, e.g. a

25、city, a forest etcThe water balance of the earth surfaceThe water balance of a drainage basinWater balance is Very often used in a river basinA river basin (watershed, catchment, drainage basin) is the area contributing to the discharge at a particular river cross-sectionThe size of the catchment in

26、creases if the point selected as outlet moves downstream.If no water moves across the boundary, then the input =precipitation P the output =E+ river discharge Q at outlet Water balance (P E)A-Q= S/tNote: all terms must be expressed in the same unitP & E : mm/d Q: m3/sA: m2In order to convert the uni

27、t, A must be knownUnit conversione.g. from m3/s to mm/d with the catchment area A=200Mm2Conversion of seconds to days: 1 m3/s = 86400 m3/dConversion of m3 to mm 1 m3/(200Mm2)=1/(200*106)*103mmResulting in: 86400m3/d/2*108m2*103mm/m=0.432mm/dS/t: the rate of change, difficult to measure.However, If t

28、: long enough, S varies within a certain range. S/t es less important.For computing annual periods (年周期), the beginning of the balance period is preferably chosen at a time that the amount of water in store is expected not to vary much for each successive year. this annual periods, known as hydrolog

29、ical year or water year (水文年)水文年：按总体蓄量变化最小的原则所选的连续十二个月，据此，跨年度的水量可减至最低限度。水文年一般指由当年枯季末至次年枯季末所经历的时间，包括了一年中河流水情的各个阶段。水文年的划分还有其他方法，如把河流从以地下水补给为主转变到地面水补给增多的时候作为水文年开始；按这种方法一些河流一般取春季开始作为水文年的开始。而苏联对其欧洲部分的河流，则取秋季作为水文年的开始。另一种分法是把降水稀少或流域内开始积雪、地面径流基本停止时作为水文年的开始。按这种分法，水文年的开始可选择流域内日平均温度低于零度的月份，相当于冬季开始之时。中国北方河流采用这种

30、分法。 Figure shows that topographic divide applies to surface but may not necessarily coincide with the boundary for GWWhat will happen if we choose A as the watershed boundary?Leakage of GW to a neighbouring catchment 补充内容：河流与流域 一、概述 流动的水体与容纳流水的河槽是构成河流的两个要素。河槽亦称河床，枯水期水流所占部位为基本河床，或称主槽；洪水泛滥及部位为洪水河床，或称滩

31、地。河床主槽滩地枯水位洪水位 一条河流可分为河源、上游、中游、下游及河口五段。 长度最长或水量最大者作为干流，汇入干流的为一级支流，汇入一级支流的称二级支流，其余类推。 河口是河流注入海洋、湖泊的地段。有些河流最终消失在沙漠中，就没有河口，称内陆河。 河流某断面的集水区域称为该断面的流域。流域的周界称为分水线。如果地面分水线与地下分水线重合，这样的流域称为闭合流域。地面分水线与地下分水线不一致的流域称为不闭合流域。 流域各条河流构成脉 络相通的系统，称为水系，河系或河网。干流分水线流 域(catchment)出口断面集水面积支流水系二、河道及流域的主要特征 河流长度 L（km）： 自河源沿河道

32、至河口的长度称为河流长度，或称河长，可在地形图上量出。河口河源落差：河段两端的河底高程差河道纵比降 J ：当河流纵断面近于直线时当河流纵断面呈折线时:h0h1h2h3h4h5l1l2l3l4l5L图11 河道纵比降计算示意图121 = 2 流域面积 F（km2）: 流域面积是流域的主要几何特征。通常先在适当比便例尺的地形图上定出流域分水线，然后量出它所包围的面积。分水线流域面积河流河网密度: 单位面积内的河流总长度称为河网密度。它表示一个地区河网的疏密度。河网 流域长度 L（km）：流域的轴长。流域轴线（1）以河口为圆心绘制同心圆（2）作同心圆弧割线交于流域周线（3）通过割线中点作流域轴线，其

33、长度为流域长度流域河口流域平均宽度B（km）：流域面积与流域长度的比值 B F / L流域形状系数：流域平均宽度与流域长度的比值 r B / L F / L 2 流域平均高度H（m）与平均坡度J：将流域划分成100以上的正方格，定出每个方格交叉点上的高程及坡度，这些格点的高程和坡度的平均值为流域平均高度和平均坡度。 流域平均高度直接影响流域的气温与降水，流域平均坡度对径流的产流、汇流、下渗、土壤流失等有很大的影响。 流域的自然地理特征：流域的地理位置、气候、地形、植物被覆、土壤特性，地质构造，沼泽及湖泊情况等，都是与流域水文特性密切有关的自然地理特征。两个重要系数径流系数 0 R / P蒸发系

34、数 0 E / P多年平均情况下 0 0 1流域面积万km2PmmRmmEmm径流系数辽河21.9472.664.6408.013.7松花江55.7526.8136.8390.026.0海河26.3558.786.5472.215.5黄河75.2474.687.5387.118.4淮河26.9888.7231.0657.726.0长江180.91070.5526.0544.549.1珠江44.21469.3751.3718.051.1雅鲁藏布江24.1949.4687.8261.672.4中国主要河流流域水量平衡Water balance for some other great rivers

35、riversizePER0Nile280.32201903014Mississippi392.480065414618Parana97.5100062538238Orinoco85.0133042093570Mekong64.61500100038234Amur173.045026518842Lena243.035014021260Yenisei244.045022023051Ob295.045032513129Rhine20.085050035041E.g. 1 the drainage area of the James River at Scottsville, is 11839 km2

36、. if the mean annual runoff is determined to be 144.4m3/s and the average annual rainfall is 1.08m, estimate the ET losses for the area? How does this compare with the lake evaporation of 1m/year measured at Richmond, Virginia?To simplify: A=11839km2 R=144.4m3/s P=1.08m ET=? ET (, ,=)1m/year?Solutio

37、n:Assuming that S=0, using equation P E R = S/t2) Runoff is converted from m3 to m/yr as follows:R=(144.4*86400*365)/(11839*106) =0.38m3) ET = P R = 1.08 0.38 = 0.7m4) The ET losses are less than themeasured lake ET E.g.2 the average annual discharge at the outlet of a catchment is 0.5m3/s. The catc

38、hment is situated in a desert area (no vegetation) and the size is 800 Mm2. The average annual precipitation is 200 mm/year. 1) compute the average annual evaporation from the catchment in mm/y?In the catchment area an irrigation project covering 10 Mm2 is developed. After some years the average dis

39、charge at the outlet of the catchment appears to be 0.175 m3/s.2) Compute the evapotranspiration from the irrigated area in mm/y, assuming no change in the evaporation from the rest of the catchment.To simplify 1): A=800Mm2 R=0.5m3/s P=200mm E=?Solution:Assuming that S=0, using equation P E R = S/tb

40、) Runoff is converted from m3/s to mm/yr as follows:R=(0.5*86400*365)*103/(800*106) =19.7mm/yc) E = P R = 200 19.7 =180.3mmTo simplify 2): A1 =790Mm2(desert) A2 =10Mm2(vegetated) R*=0.175m3/s P=200mm E unchanged for desert ET=? for irrigated areaSolution:Assuming that S=0, using equation P Ed-Ei R*

41、= S/tb) P & Ed is converted from mm/yr to m3/s to calculate as follows:E.g. 3 A catchment has a size of 100Mm2. In its original condition, the average annual total runoff from the catchment is 1.1 m3/s. the average annual rainfall is 800 mm/y. In an average year, 50% of the rainfall infiltrates and

42、12.5% of the rainfall reaches the groundwater. Tests have turned out that the average annual evapotranspiration from the unsaturated zone (being the sum of the transpiration and the bare soil evaporation) amounts to 340 mm/y. In all water balance computations over the year, one may assume the storag

43、e effects are small. (dS/dt=0)How much water, in mm/y, reaches the root zone through capillary rise in an average year? How much water, in mm/y, seeps out from the groundwater to the surface water in an average year?How much water, in mm/y, evaporates directly from interception in an average year?Ho

44、w much water, in mm/y, is the total evapotranspiration in the catchment in an average year?To simplify：A=100Mm2=100106m2 Q=1.1m3/S=(1.1365864001000)/(100106) =347mm/aP=800mm/a, I=80050%=400mm/aPerc=12.5%800=100mm/aET=340mm/aAccording to water balanceI + Cap Perc - ET=0Cap = Perc + ET I =100 =40mm/aU

45、nsaturated zoneIETCapPercb) According to water balancePerc- Qb - Cap=0Qb = Perc Cap =100 40 = 60mm/a c) According to water balanceTake the whole system as the control volumeP ET Ei Q=0Ei=P ET Q = 800 340 347 = 113mm/ad) According to water balanceTake the whole system as the control volumeP E Q=0 E =

46、 P Q = 800 347 = 453mm/aA well field is planned to withdraw 0.16 m3/s from the catchment for drinking water consumption elsewhere. As a result, the GW level is expected to go down and capillary rise into the root zone will no longer be possible. The percolation, however, is expected to remain the sa

47、me.e. What will be the effect of the withdrawal on the different components of the hydrological cycle: the groundwater seepage, the total runoff, the evapotranspiration from the unsaturated zone and the total evapotranspiration? Please quantify in mm/y.Ex1: The storage in a reach of river is 20,000m

48、3 at a given time. Determine the storage 1hr later if the average rates of inflow & outflow during the hour are 20 & 18 m3/s?Ex2: If the mean annual runoff of a drainage basin of 10,000 km2 is 140 m3, and the average annual precipitation is 105 cm, estimate the ET losses for the area in 1 year. What

49、 are your assumptions? How reliable do you think this estimate is? Calculate the mean annual runoff coefficient and evaporation coefficient?Ex 3For a watershed with a size of 120 Mm2, the following data on precipitation P, evaporation E and runoff Q are given in mm.At the end of which month is the amount of water stored in the basin largest & when is the smallest amount of water present in the catchment? The difference?JanFebMarAprMayJunJulAugSepOctNovDecP250205165505005105565190E525305080100150706020105Q150110805000001015120Water balance as a result of human