?percolation

percolation發(fā)音

英：[?p?:k?'le??n]　　美：[?p?:k?'le??n]

英：　　美：

percolation中文意思翻譯

n. 過濾, 浸透

percolation詞形變化

動(dòng)詞現(xiàn)在分詞: percolating | 名詞: percolation | 動(dòng)詞過去分詞: percolated | 動(dòng)詞第三人稱單數(shù): percolates | 動(dòng)詞過去式: percolated |

percolation常見例句

1 、Reservoirs in the upper member of Guantao formation had been identified and divided into 5 types of flow u-nits according to their percolation capacity by using flow zone indicator method ( FZI).───應(yīng)用流動(dòng)分層指標(biāo)法對(duì)孤東油田七區(qū)館上段進(jìn)行了流體流動(dòng)單元的識(shí)別與劃分,將孤東油田館上段儲(chǔ)層按其滲流能力劃分為5種流動(dòng)單元類型。

2 、Although using the CT pit percolation, we need analyze and ascertain the exception effluent reasons joining mine cranny develop rules.───我們利用CT坑透，結(jié)合礦井裂隙發(fā)育規(guī)律，分析判明了異常出水的原因。

3 、Percolation Theory can explain the formation of conductive passages under the dependence of the conductivity and graphite content in ECAC.───導(dǎo)電瀝青混凝土中導(dǎo)電率與石墨摻量依賴性可用滲流理論解釋其導(dǎo)電通路的形成。

4 、In addition, pressure change of volatile oil well with time and distance during degassing percolation is presented.───描述了揮發(fā)性油井在脫氣滲流過程中壓力隨時(shí)間和距離的變化規(guī)律;

5 、fractional percolation equation───分?jǐn)?shù)階滲透方程

6 、Baaed on the law of permeability changing with pressure, a mathematical model is established for unsteady percolation in dual-porosity reservoirs with arbitrary shape of stress sensitivity.───摘要基于滲透率隨壓力呈指數(shù)變化規(guī)律，建立了任意形狀應(yīng)力敏感性雙重介質(zhì)油藏不穩(wěn)定滲流的數(shù)學(xué)模型。

7 、On microscopic and microstructural level, the relations between high Tc supercoduc-tivity and percolation have been discussed.───在微觀及亞微觀(顯微結(jié)構(gòu))層次上,討論了高溫超導(dǎo)與滲流的關(guān)系問題。

8 、Taipei Water Source Percolation Plant-at the left side of the picture is the Pumping Room.───臺(tái)北水源地慢濾場(chǎng),照片左方有當(dāng)年的唧筒室,您發(fā)現(xiàn)了嗎。

9 、On the basis of the predecessors' research work, a mathematical model of non-linear percolation in gas reservoir is developed, and a case is given in this paper.───基于前人的研究成果，建立了一個(gè)考慮啟動(dòng)壓力梯度和介質(zhì)變形的氣藏非線性滲流的數(shù)學(xué)模型，最后給出了計(jì)算實(shí)例。

10 、Keywords Suspension;Bridge;Flocculate;Percolation;Viscoelasticity;───懸浮液;架橋;絮凝;逾滲;粘彈性;

11 、Also the morphology and electrical properties of the PU/GN conductive foam plastics are studied.The percolation threshold effect appears when the content of the GN is 14%.───并觀察了其微觀結(jié)構(gòu)，分析了其導(dǎo)電性能，在納米石墨微片的質(zhì)量分?jǐn)?shù)為14%時(shí)出現(xiàn)了滲濾效應(yīng)。

12 、Though stricter proces sing method has been adopted, the pseudo-pressure deliverability equation of sin gle-phase gas is not suitable to multiphase percolation.───盡管單相氣體擬壓力產(chǎn)能方程采用了更嚴(yán)格的處理方法,但也不再適用于油、氣、水多相滲流。

13 、On the base of geological property and percolation features of Shanliudong super - heavy crude reservoir of Shanjiasi oilfield, a subcritical steam generator is developed.───在單家寺油田單6東超稠油油藏地質(zhì)特征和滲流特點(diǎn)研究的基礎(chǔ)上,成功研制了亞臨界濕蒸汽發(fā)生器。

14 、It's your job to find me work while things percolate on the followup.─── 未來情況不明朗之時(shí) 該是你負(fù)責(zé)給我找工作啊

15 、There are critical points to distinguish different percolation mechanism on Klinkenberg regression line.───在克氏回歸曲線上，存在著界定不同滲流機(jī)理影響的臨界點(diǎn)。

16 、Application of Underground Percolation Technique in Railway System───地下滲濾工藝在鐵路系統(tǒng)中的應(yīng)用

17 、microscopic percolation mechanism───微觀滲流機(jī)理

18 、Abstract Micromechanics and Percolation theory were employed to predict the asphalt mixtures’ viscoelasticity.───摘要 利用微觀力學(xué)和逾滲理論預(yù)測(cè)了瀝青混合料的粘彈性能。

19 、The results show that the composite exhibits percolation threshold effect,positive temperature effect and nonlinear volt ampere characteristics.───實(shí)驗(yàn)結(jié)果表明,材料具有明顯的滲濾效應(yīng)、正溫度系數(shù)效應(yīng)和非線性伏安特性。

20 、Below the critical points, capillary resistance affects gas percolation, appearing the gas effective permeability increases as the net pressure increases.───在臨界點(diǎn)以下，氣體滲流受毛細(xì)管阻力影響，表現(xiàn)為氣體有效滲透率隨凈壓力增大而遞增；

21 、The High Energy Gas Fracturing (HEGF)technique adopting oil well pressure fracture has been widely used in oid field, It can produce many radial fracture and improve reservoir percolation capability.───利用油井壓裂彈產(chǎn)生高能氣體壓裂是近幾年在油田廣泛應(yīng)用的油井增產(chǎn)技術(shù)。它可以在油層形成多條徑向裂縫,改善油層滲流能力,提高采收率。

22 、soil and stone dam percolation───土石壩滲流

23 、If flow is too slow,excessive percolation will occur near the ditch,and too little water will reach the lower end of the field.───如果流率太慢，溝渠又發(fā)生過度浸透，那么，將會(huì)有很少的少會(huì)到達(dá)田地最低處。

24 、Application and progress of percolation theory in the process of study for conduction mechanism of conductive composites were introduced.───介紹了近年來滲流理論在導(dǎo)電復(fù)合材料機(jī)理研究中的應(yīng)用和最新進(jìn)展;

25 、The percolation process also washes out components present on the surface of the coffee grounds, including aroma-filled oil and bits of the cellular structure.───在濾滴的過程中，位于咖啡粉末表面的成分也會(huì)被沖刷下來；其中包括香濃的油滴以及細(xì)胞構(gòu)造的碎片。

26 、Conventional gas reservoir simulation technique is based on Darcy's Law, and cannot accurately describe the percolation with start-up pressure gradient and rock deformation.───常規(guī)氣藏?cái)?shù)值模擬技術(shù)基于線性的達(dá)西定律，無法對(duì)啟動(dòng)壓力梯度和介質(zhì)變形的情況予以準(zhǔn)確描述。

27 、Development of the sewerage collection and treatment system will be basically accomplished and sewerage percolation pits in the protection zone of ground drinking water sources will all been eliminated.───基本完成城市污水排除與處理系統(tǒng)建設(shè)，取消地下水飲用水源地防護(hù)區(qū)范圍內(nèi)的污水滲井、滲坑。

28 、Cyclic water injection increases swept volume through oil-water percolation effect and capillary pressure effect to improve water drive recovery factor.───周期注水技術(shù)主要是通過油水交滲效應(yīng)、毛管壓力作用,增加注水波及體積,從而提高水驅(qū)采收率的技術(shù)。

29 、Full-automatic function,switch on electricity the percolation,enter the water and boil the water,heat preservation whole process from the familiar water the absolute separating.───全自動(dòng)功能、從開始通電到過濾、進(jìn)水、煮水、保溫全過程全自動(dòng)、無須人工看管。

30 、preferential percolation path───優(yōu)勢(shì)通道

31 、The damage evolution process is similar to percolation, and the unusual behavior of some properties at fracture or fragmentation is often related to certain scaling relations.───損傷演化過程與逾滲現(xiàn)象極為相似,臨近斷裂和破碎時(shí),某些物理量所表現(xiàn)出來的異常行為往往滿足一定的標(biāo)度關(guān)系。

32 、Of all components of water balance in farmlands, evapotranspiration, capillary rise from a water table and deep percolation are difficult to determine.───在農(nóng)田水分平衡中,較難測(cè)定的要素有農(nóng)田蒸騰蒸發(fā)量、地下水毛細(xì)上升量和土壤水滲漏量。

33 、Several new logging techniques (including FMI, ARI and DSI) are adopted to determine kinds of reservoir space, quantitative characters of fissure and cavity, reservoir effectiveness and connected percolation.───應(yīng)用測(cè)井新技術(shù),包括井壁成象(FMI)、方位電阻率測(cè)井(ARI)和偶極聲波測(cè)井(DSI)確定儲(chǔ)集空間類型、縫洞定量特征、儲(chǔ)集層有效性和連通滲濾性;

34 、The percolation process of WSPS is taken as a unit, and a simplified contamination percolation process combined functional model is put forward, in which includes four layers as bottom sludge layer, substrate layer.───把穩(wěn)定塘中污染質(zhì)的下滲過程看作一種單元系統(tǒng)，提出了概化的穩(wěn)定塘中污染質(zhì)下滲單元耦合功能模型，對(duì)各功能層的功能進(jìn)行了描述。

35 、In the case of continuous producting oil reservoir,for complex percolation change,oil/gas phase state transition and the variation of densities and viscosities in oil reservoir are yielded.───在油層不斷開采的情況下 ,由于復(fù)雜的滲流變化 ,伴隨產(chǎn)生了油氣相態(tài)轉(zhuǎn)變和油層中各項(xiàng)密度和粘度的變化。

36 、The uniformity of conductive function was better once the percolation phe nomena occurred.───形成滲濾效應(yīng)之后，導(dǎo)電功能的均勻性較好。

37 、It is pointed out that the turnaround tech is a new repeat fracture wa tor percolation and high containing water reservoir.───提出了轉(zhuǎn)向壓裂技術(shù)是江蘇油田低滲透油藏高含水期一種新的重復(fù)壓裂技術(shù)。

38 、A site with plenty of green spaces among the paved areas will have less runoff, and percolation through the soil will remove many of the contaminants swept from the asphalt and concrete.───因?yàn)槁访娓浇写笃G地的地點(diǎn)，逕流量將會(huì)減少，而滲透土壤的過程，也會(huì)清除來自柏油地面和混凝土地面的許多污染物。

39 、In the waste filling,it is extremely important that the earth fill retards the percolation of the leaching solution of waste.───在生活垃圾的衛(wèi)生填埋中，填土層對(duì)垃圾淋濾液滲透的阻滯作用具有重要意義。

40 、The critical pressure reflects the influence of the two different mechanisms caused by capillary resistance and slippage effect of gas molecule on gas percolation with low speed.───臨界壓力的高低反映了毛細(xì)管阻力和氣體分子滑脫效應(yīng)作用力這兩種不同作用機(jī)理對(duì)氣體低速滲流的影響程度。

41 、The experimental results are explained in the view of the swelling of the polymer chain and percolation theory.───回應(yīng)的重復(fù)穩(wěn)定性受炭黑粒子分散行為的影響，從聚合物溶脹行為及逾滲導(dǎo)電理論解釋了實(shí)驗(yàn)結(jié)果。

42 、From the shape of semi-logarithm and dual-logarithm derivative curves of transient testing data,it is comprehensively determined dual percolation system of reservoir.───從不穩(wěn)定試井資料單對(duì)數(shù)與雙對(duì)數(shù)導(dǎo)數(shù)曲線形態(tài)特征入手,可以綜合確定油藏儲(chǔ)集層的雙滲流動(dòng)系統(tǒng)。

43 、Pilot test of bacterial percolation leaching at Fuzhou Uranium Mine───撫州鈾礦石細(xì)菌滲濾浸出擴(kuò)大試驗(yàn)

44 、The secondary pores and fractures constitute the major storage space and percolation path in muddy gravels in Kulongshan oilfield, Jiuquan Basin.───摘要酒泉盆地青西油田泥礫巖儲(chǔ)層中發(fā)育的次生孔隙和裂縫系統(tǒng)構(gòu)成了油藏主要儲(chǔ)集空間和滲流通道。

45 、Fracture acidizing has become a necessary measure for improving effectively reservoir percolation flow condition and enhancing individual-well oil/gas producting rate in Sichuan.───四川地區(qū)壓裂酸化已成為有效改善儲(chǔ)層滲流條件、提高單井油氣產(chǎn)量的必要手段。

46 、The percolation results from conjunct effects of dispersion, interface polarization and nano-effect of MWNTs.The percolation threshold of the Ag-filled MWNTs/epoxy composite is about 1.01 wt%.───Ag填充碳納米管/環(huán)氧樹脂有明顯的介電逾滲現(xiàn)象，這是填料的分散狀態(tài)、界面極化與納米填料表面效應(yīng)共同作用的結(jié)果，體系的逾滲閾值為1.01 wt%。

47 、The 3D percolation mechanism in porous media,the characteristics of percolation cluster by numerical simulation method,and the theory of renormalization are studied.───利用重正化群原理,通過數(shù)值模擬的方法研究孔隙介質(zhì)三維逾滲機(jī)制和逾滲團(tuán)特性,提出有效表面積率概念。

48 、The thesis will introduce the water percolation of external walls and common quality faults of climbing water of tier buildings along with the measures for prevention.───介紹多層住宅外墻滲水及爬水質(zhì)量通病及其防治若干措施,實(shí)踐證明,其施工方法是行之有效的,值得借鑒。

49 、The perturbation technique and Laplace transform method are employed in the calculation of the model to study the features of percolation in stress-sensitive gas reservoirs and the infl.───應(yīng)用攝動(dòng)技術(shù)和拉普拉斯變換方法求解數(shù)學(xué)模型,據(jù)此研究應(yīng)力敏感性氣藏的滲流特征以及開關(guān)井不同程度應(yīng)力敏感效應(yīng)對(duì)井底壓力動(dòng)態(tài)的影響。

50 、A concrete analysis is carried out on piezometers and percolation gages measured data.───對(duì)測(cè)壓管和滲壓計(jì)的觀測(cè)成果進(jìn)行了具體分析；

51 、In scientific terms, the process is no longer percolation, but extraction.───在科學(xué)計(jì)算,過程不再是滲流,但提取。

52 、The percolation threshold of composite is 20% by weight.Their critical resistivity-exponent is 9.2.PTC intensities of all prepared composite is larger than four orders of magnitude.───復(fù)合材料的滲流閾值為20%,臨界電阻率指數(shù)為9.2,PTC強(qiáng)度都大于4個(gè)數(shù)量級(jí)。

53 、The factors affecting electrical properties and percolation threshold are discussed.───對(duì)影響復(fù)合材料導(dǎo)電性能及滲濾閾值的因素進(jìn)行了討論。

54 、Starting with the mechanism of CBM production,this paper analyzes the factors that affect the processes of coalbed methane desorption,diffusion and percolation from coal seams.───從煤層甲烷產(chǎn)出機(jī)理入手,分析了影響煤層甲烷解吸、**和滲流過程的因素。

55 、Wang F Q.The fault fractal dimensions and the fractal percolation of the rift system [J].Journal of Sichuan Teachers College, 1994,15 (4): 308-309.───[9]汪富泉.斷層分維與裂縫系統(tǒng)的分形滲流研究[J].四川師范學(xué)院學(xué)報(bào),1994,15(4):308-309.

56 、And percolate on it over the weekend like your little coffee machine.─── 這個(gè)周末好好考慮[過濾]一下 就像你的小咖啡機(jī)一樣

57 、Nevertheless, the model accounts for water percolation towards the deeper subsoil layers even though it does not contribute to the discharge.───盡管如此，雖然它對(duì)出流量沒有太大的影響，模型仍然考慮了水向深層土壤層的滲透。

58 、That was just an idea that percolated down from one of your ideas.─── 那就是個(gè) 依附于你的點(diǎn)子的點(diǎn)子

59 、You can learn a lot from percolators.─── 你可以從咖啡滲濾壺身上學(xué)到很多

60 、In accordance with the characteristics of reservoir and percolation body with constant volume, the principles of water-flooding and replacing oil technology are developed to .───因此可利用定容性儲(chǔ)滲體易恢復(fù)地層能量和油水易重新分布的滲流特征,在定容性儲(chǔ)滲體實(shí)施注水替油技術(shù)。

61 、The results showed that the intensity distribution had relation with the velocity of percolation,time,coefficient of convection and diffusion.───發(fā)現(xiàn)污染物在土壤中的質(zhì)量濃度分布與滲流速度、作用時(shí)間、**系數(shù)等有關(guān)。

62 、I'm gonna stick this guy and start percolating some platelets.─── 我會(huì)給他扎針然后開始 過濾一些血小板

63 、Long gestating plans have been percolating and coming into fruition all at once.─── 一個(gè)長期孕育的計(jì)劃正在被逐步滲透 將會(huì)一下子開花結(jié)果

64 、Using tech of oil extraction and test with intermission and constant production to low percolation reservoir can prevent energy near borehole from crocking up quickly.───對(duì)于低滲透儲(chǔ)層采用間歇定產(chǎn)試采,可以防止井筒附近能量衰竭過快。

65 、Therefore, the function of generalized pseudo-pressure is hold up, and corresponding deliverability equ ation for multiphase percolation is ...───為此,提出了廣義的擬壓力函數(shù),從而導(dǎo)出適用于氣井多相滲流的產(chǎn)能方程。通過實(shí)例計(jì)算證明該方法是正確、可行的。

66 、Fat fractal percolation model of porous media and its scaling rule───多孔介質(zhì)的胖分形滲流模型及其分形維數(shù)

67 、The foundation of Xixiayuan powerhouse belongs to Tertiary soft rock.In order to prevent destruction by percolation, it builds a suspended impervious curtain in the foundation.───摘要西霞院電站廠房地基為第三系軟巖，為防止電站壩段的滲透破壞，廠房地基設(shè)懸掛式防滲帷幕；

68 、The results shown that emough attention to the percolation phenomenon of p nitrophenylamine salt in the organic membrane should be paid.───實(shí)際工業(yè)廢水經(jīng)**液膜萃取可達(dá)到國家排放標(biāo)準(zhǔn)。

69 、However, studies have shown that flow in low permeability media does not follow Darcy's law, and that a starting pressure gradient (SPG) occurs in the percolation.───建立了低滲非達(dá)西滲流相對(duì)滲透率計(jì)算方法,導(dǎo)出了計(jì)算公式,并進(jìn)行了非穩(wěn)態(tài)流動(dòng)實(shí)驗(yàn)。結(jié)果表明:在低滲油藏相對(duì)滲透率曲線中,束縛水和殘余油飽和度較高,兩相滲流區(qū)范圍較窄;

70 、The composites exhibited a significant piezoresistance, when CB mass fraction to was located in the vicinity of the percolation threshold w(subscript c).───當(dāng)CB含量低于滲流閾值時(shí)，PVC/CB復(fù)合材料呈現(xiàn)PPC效應(yīng)；

71 、Calculating the relative permeability from displacement experiments based on percolation theory.───應(yīng)用逾滲理論計(jì)算非穩(wěn)態(tài)法油水相滲曲線。

72 、It is pointed out that,further research of BDT percolation theory is of obviously scientific and technological significance.───并指出對(duì)BDT逾滲模型的進(jìn)一步研究具有很明顯的科學(xué)意義和實(shí)際意義.

73 、The most sinister neurochemistry in the field cannot help percolating in your presence.─── 神經(jīng)化學(xué)領(lǐng)域最兇險(xiǎn)的病人 都不由得向你吐露心聲

74 、The percolation threshold of surface resistivity of PVC/CB composite appears when the addition of CB reaches 4phr.───當(dāng)炭黑添加量僅為4份時(shí),PVC/CB即有逾滲現(xiàn)象發(fā)生,表面電阻大幅度降低。

75 、APPLICATION OF LOW-VELOCITY NON-DARCY PERCOLATION MODEL IN DST───低速非達(dá)西滲流理論方法在DST試井中的應(yīng)用

76 、A New Percolation Model Used for Low Permeability Porous Medium───低滲透多孔介質(zhì)中新型滲流模型

77 、Treatment of the Percolation Water on Landfill Sites───垃圾填埋場(chǎng)滲濾液處理

78 、The stady on the laws of phase behavior and percolation of gas condensate system in porous media is a theme which is of difficulty, but of practical and theoretical values.───多孔介質(zhì)中凝析油氣體系相平衡規(guī)律和滲流規(guī)律的研究是一個(gè)具有相當(dāng)難度和較高理論及應(yīng)用價(jià)值的研究課題。

79 、Critical flow pressure reflects the impact of capillary pressure and boundary effect and gas percolation, and causes non-Darcy gas flaw.───臨界流動(dòng)壓力反映了毛細(xì)管力與邊界層作用對(duì)氣體滲流的影響，并使氣體表現(xiàn)出非達(dá)西滲流特征。

80 、Thermofor continuous percolation process───塞摩福流動(dòng)床連續(xù)滲濾過程

81 、I was lead to believe films about him were um, percolating you know, there were a couple of them to my recollection that people were gonna make.─── 我相信關(guān)于他的** 可以說是 逐漸流傳開 你知道 在我的記憶中 人們會(huì)那樣

82 、According to bethe network percolation, the reaction between SO2 and.───并應(yīng)用bethe網(wǎng)格逾滲模型，模擬干性條件下SO_2和多孔CaO顆粒反應(yīng)；

83 、Low velocity non-Darcy percolation───低速非達(dá)西滲流

84 、I detect the pheromones percolating out of your pores.─── 我感受到渾身散發(fā)出來的費(fèi)洛蒙

85 、And combining R/S analysis with the model GM (1, 1) is the effective way to predict the production-changing law of unstable percolation of coal-bed gas.───R/S分析方法和GM(1,1)模型相結(jié)合是預(yù)測(cè)煤層氣不穩(wěn)定滲流產(chǎn)量變化的有效方法；

86 、By percolation is made the comparison between the EMT, EMTDD and BW theories so as to find that under the condition of low water/oil ratio the work system in this paper is in comformity with the EMT theory.───從滲濾作用來比較EMT、EMTDD和BW三種理論,發(fā)現(xiàn)在水油比較低的情況下,本體系符合EMT理論.

87 、The basic theory of porous mediums in 2D condition is introduced and the theory of Renormalization method is applied to research the percolation.───摘要詳細(xì)介紹了在二維情況下孔隙介質(zhì)逾滲流的基本理論、重正化群方法的原理及其在逾滲研究中的應(yīng)用。

88 、In fact, knowledgeable scientists of the time accepted land irrigation and percolation into the porous underground formations as methods of waste treatment.───事實(shí)上，當(dāng)代有見識(shí)的科學(xué)家，已經(jīng)接受了土地清洗以及過濾可滲透地底層這兩種可作為處理廢棄物治理的方法。

89 、Meteoric water, artificial exploitation and percolation for irrigation canals are the main influence factor of dynamic variation of groundwater.───地下水位頻繁的升降一是改變了上覆土體的狀態(tài)和強(qiáng)度，促進(jìn)土體崩落；

More Yield with Less Water-Techniques to Achieve A Higher Efficiency in Irrigation

Dieter Prinz and A.H.Malik

Institute of Water Resources Management,Hydraulic and Rural Engineering,University of Karlsruhe,D-76128 Karlsruhe,Germany

1　Introduction

In the Developing World,agriculture counts for about 80% of total water withdrawal（Prinz,2000）.Agriculture is under enormous pressure by the other sectors of the economy,as the economic value created per unit water is lowest in agriculture.At the same time,growing populations make it necessary to produce more food and fibre and to ensure that crop yields per unit land continue to rise.Therefore,developing countries will have to find ways of growing more food with less water.But there is not only the problem of water quantity but additionally the one of deteriorating quality of water.

There are many modern and traditional or combined technologies available to improve water conservation development（Agarwal,2001,Rijsberman,2001）.

There is the need①to define the aim（under given frame work conditions）；②to analyze the losses（conveyance,distribution,application a.o.losses）；③to identify the most promising water conservation methods and techniques,and,eventually；④to integrate the various elements within a（soil and）water conservation strategy（Emerson,1998,UNEP,1998）.

2　Measures applied in irrigated agriculture

Irrigation water,if in ample supply,reduces considerable the risk of agricultural production and allows yields double as high as the yields which can be obtained from rain-fed agriculture（FAO,2001）.Roughly 40% of the food is produced on irrigated land,on 17% of the total cultivated land.The water needed for crops amounts to 1000～3000 m**er ton of cereal harvested.With other words,it takes one to three tones of water to grow 1kg of rice.

As mentioned before,the losses of water have to be covered as well as the measures to increase the efficiency of water use in irrigation.

We have to distinguish between recoverable water losses and unrecoverable water losses;the latter ones are those quantities of water lost to the atmosphere,to saline aquifers or to the sea.

Recoverable losses include:seepage,surface runoff,operational losses and losses due to deep percolation.

Fig.1　Water losses within a surface irrigation system in a semi-arid region

The water losses could be（Fig.1）

conveyance losses.

distribution losses（e.g.canal evaporation,percolation and operation losses）or

field-ditch losses,

field-application losses which depend on soil,irrigation method and management,

Reduction of conveyance and distribution losses

33%～50% of water diverted for irrigation is lost‘en route’：The conveyance and distribution losses are enormous.By lining the canal system or by conveying the water in pipes,these losses can be significantly reduced.It should be kept in mind,that at least the seepage losses are in most cases recoverable losses;the water might be lifted up from the groundwater layer downstream.

Seepage losses occur in unlined main canals,in the canal distribution system and in field ditches.Most of the water is lost in unlined main canals.The questions which arise here are the following:

What quantities of water are lost?

Are these losses easy to recover?

What feasible lining methods could be used?

How high are the costs of lining and of maintenance?

What are the benefits of the saved water?

Could the unlined canal be used in the rainy season to recharge an aquifer?

Reduction of application losses

Application losses are either surface runoff losses or percolation losses,often summarised as“operational losses”.The water applied,should be sufficient to wet the volume of root penetration,but should not go beyond.Numerous technical means are available to apply exactly the amount of water needed,but financial and labour problems,in large irrigation schemes also management problems,hinder this.

Operational losses depend on：①the chosen distribution system；②the available regulating and mechanical facilities；③the skill and discipline of the operator.

3　Crop root zone depth

The active root zone of the crop（if water is not a constraint）depends on：①crop type；②its stage of maturity；③soil conditions（Fig.2）.

Fig.2　The water applied should be sufficient to wet the volume of root penetration（but not more）

Use of efficient irrigation methods

The large differences in water efficiency between the various irrigation methods are quite well known:Traditional surface irrigation generally achieves only around 40%　efficiency,sprinkler irrigation can be 70%～80% efficient and drip irrigation might reach over 90% efficiency（Wolf and Stein,1998,Fig.3）.Modern irrigation technology could in theory save about half of the water presently consumed in irrigation,but technical,economic and socio-cultural factors hinder the transformation of theory into practice.

These methods are arranged according to their average efficiency.

The surface irrigation techniques are：①basin irrigation，②furrow irrigation and③border irrigation.

Fig.3　The five basic methods of applying water to the soil

These techniques have one drawback in common:the uneven water application over the irrigated area.Water infiltration is much greater at the top end of the field than the bottom because of the longer opportunity time at the top end and this results in high deep percolation.

Surge irrigation（Fig.4）has been shown to markedly improve the efficiency of water application.It is the practice of intermittently stopping and starting water flows across a field.

Fig.4　Water percolation in surge and continuous flow

Another method is the sprinkler irrigation.Low Energy Precision Application（LEPA）center pivots are one of the most efficient irrigation methods available today because they offer both high water application efficiency and low operating pressure.The water is applied near the ground surface below canopy.

Drip/trickle irrigation is characterised by the following:

low flow rate,long duration irrigation,frequent irrigation,water applied near or into the plant's root zone,and low-pressure delivery system shigh investment costs and maintenance demand.

In drip irrigation some techniques were developed which are not as efficient as the more costly ones,but which allow even small farmers a very high efficiency e.g.in vegetable cropping:the drip bucket irrigation is such a low cost and relatively efficient technique,applied already on thousands of farms in East Africa（Prinz and Malik,2001）.

3.1　Case study:Growing More Rice with Less Water（China）

Water Efficient Irrigation Techniques

One method to save water in irrigated rice cultivation is the intermittent（submerged）irrigation.This example shows real water saving and increase of production.Production levels remained stable over the time period in spite of this massive shift of water（see Fig.5,Table 1）out of agriculture.Growing more rice with less water improves also the productivity of water.This was made possible through pol-icy,management,and technological changes（Rijsberman,2001）.

Fig.5　Water quantities used for domestic,industrial and hydropower purposes increased 10 times during the period 1976 and 1996,with subsequent reduction of water quantities for irrigation

Table 1 Changes in land and land productivity in Zhanghe Irrigation District,China（1966～1998）

Source:Rijsberman 2001.

3.2　Subsurface Irrigation Techniques

3.2.1　Pitcher irrigation

Pitcher irrigation or“Pot Irrigation”is a traditional,extreme efficient form of irrigation.The technique is particularly suitable to the irrigation of vegetables（like legumes,beans,water-melons,etc.）in home ardens（Fig.6）.

The clay pots can either be installed independently,i.e.the water supply is done by the farmers manually,one by one,or interconnected:the water supply is done by using a water reservoir,which can be a tank,a well,etc.

3.2.2　Surface trickle irrigation

Fig.6　Clay pots used for

pitcher irrigation

To reduce deep percolation losses in subsurface irrigation,a trench is dug and a layer of plastic sheets is positioned below the trickler pipe（Fig.7）.

3.2.3　Vertical Pipe Method

A very simple but effective method for ree cultivation is the vertical pipe method:Provided sufficient water storage capacity in the root one is given,a larger quantity of water is applied through the vertical pipe to supply the tree with water for 2～4 weeks（Fig.8）.

Fig.7　Subsurface trickle irrigation with reduced percolation losses

Fig.8　Vertical pipe method

The water efficiency depends not only on the method

Wolf and Stein（1998）cite a study made in Israel by Hagan（1994）,who found surface irrigation to be 70% water efficient but drip irrigation only 42%～56%.

This deviation from generally believed figures is due to differences in the available underlying conditions.For the farms using surface irrigation,water was in very short supply and therefore it had to be used as efficiently as possible.Drip irrigation on the other hand has been used under conditions of sufficient water to grow crops of high market value.Low cost of water and high market prices did not give any incentive to the farmers to use water efficiently.

3.3　More rational use of irrigation water

3.3.1　Supplemental irrigation（SI）

It is the application of small quantities of irrigation water to essentially rain-fed crops in times when the demand can not be covered by rainfall（Oweis,1997）.SI is usually practiced usually in the wetter part of the dry areas with 300 to 600 mm annual rainfall in order to improve and stabilise yields（Oweis et al.,2001）.Supplemental irrigation might be taken from groundwater or from excess water stored during the rainy season.

3.3.2　Deficit irrigation

Another technique which allows a very high water use efficiency under fully irrigated conditions is deficit irrigation.The deficit irrigation is the distribution of limited amounts of irrigation water to satisfy essential water needs of plants.The water supply is reduced in less critical periods of water demand by the crop and supply of full amount of water during stress-sensitive periods.A similar technique is the“intermittent submerged irrigation technique”for rice（ISI）.This technique has been promoted in China but it is now applied in many rice growing areas world wide.Up to 20% of the irrigation water can be saved,if the paddy crop is not grown under submerged conditions through out the main growing season,but only intermittently.The phases where submerged conditions are recommended are those“sensitive”stages mentioned earlier.

Precondition for deficit irrigation management is the knowledge of the sensitive periods of the crop/the variety in question.

3.3.3　Aquaculture

Paddy croppingcan be combined with fish raising if certain preconditions are given（Fig.9）.This allows a multiple use of water and hence water saving per unit produce.

Fig.9　Combining paddy cropping with fish raising

Case study:Drip Irrigation Systems（DIS）in India

Drip Irrigation Systems in India are being praticised since 1970,being used on a limited scale in Tamil Nadu,Karnataka,Kerala and Maharashtra States,mainly for high value,horticultural crops like coconut,coffee,grape and vegetable production without the benefit of any subsidies from the governments.At Rahuri,in Maharashtra State,the use of drip irrigation of pomegranates,grown in gravely soils,resulted in a savings of about 44%（as compared to conventional check basin irrigation systems）with a further water savings of about 14% when compared to un-mulched plots.

The capital costs involved are high compared to conventional irrigation systems,but the labor and operational costs are low in India.The net result is that the benefit-cost ratio for DIS is very favourable compared to conventional systems since the payback period for investment very short.The cost of using drip irrigation system is summarized in the Table 1.

With DIS in India,there was an improvement in crop yields and savings in water use of between 18% and 40%.Consequently,there was a substantial improvement in the water use efficiency that ranged up to three times that of conventional surface irrigation methods,even with the use of poor quality irrigation water.See Table 2 for water savings and increased yields achieved using drip irrigation in Indian case.

Table 2　Drip irrigation cost;water savings v.increased yield achieved in India

Source:Saksena 2000.

4　Improving water availability

As mentioned earlier,aquifer depletion is a common problem in many dry areas of the world.Many techniques have been developed to artificially recharge aquifers to sustain the water table and to allow further control of pumping water to cover the water needs of humans and crops.One interesting example of combined basin irrigation with groundwater recharge is reported from Uttar Pradesh Province in India（IWMI,2002）.In the monsoon season,surface water is diverted through an unlined canal system to provide farmers with irrigation water for rice crops.Around 60% of the irrigation water applied is used by the plants,most of the remaining 40%filters through the soil to recharge the groundwater.Combined with seepage from unlined canals those“l(fā)osses”provide farmers with groundwater to irrigate dry season crops.The research showed,that the water table in the study area,which had been progressively declining,has been raised from an average of 12m below ground level to an average of6.5m.

5　Summary

We need information on crop water requirements.Losses have to be avoided in conveyance,distribution and application of irrigation water.In larger irrigation schemes the conveyance losses alone sum up 30%～50% of the total water demand.

Farmers can apply more efficient irrigation methods like trickle irrigation,subsurface irrigation or pitcher irrigation.

Improved application techniques like surge irrigation have also shown a great potential to increase water productivity in irrigation.

Further-on,an increase in efficiency in irrigation water can be accomplished by a more rational use of water e.g.in“supplemental irrigation”or“deficit irrigation”.

Aside of increasing the efficiency of irrigation water use,there are some other important water conservation methods,e.g.

selecting best suited crops and cropping methods reducing the losses of stored water and improving water availability.

“More yield with less water”can be achieved to a very large extent by applying appropriate methods and techniques in irrigation management.

References

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[15]Prinz D.and Malik A.H.Water Conservation in Agriculture,FAO Training Course,Draft Version on CD ROM,FAO,Rom.2001.

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[17]Rijsberman F.R.Balancing water uses,water for food and water for nature.Thematic Background Paper,International Conference on Freshwater-Bonn 2001.International Water Management Institute IWMI,Colombo,Sri Lanka.2001.

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滲流閥值是什么概念最常用在哪方面學(xué)科

percolation threshold 逾滲閾[值]

導(dǎo)電粒子填充的聚合物中,當(dāng)填充粒子達(dá)到一定的濃度時(shí),體系的電導(dǎo)率發(fā)生突變,稱為逾滲現(xiàn)象〔8〕。這和貫穿于體系的導(dǎo)電網(wǎng)絡(luò)形成直接相關(guān)，并依賴于基體的自身特性、加工條件等因素。解釋逾滲現(xiàn)象的理論模型主要有基于幾何學(xué)的唯象理論和基于熱力學(xué)的理論模型。