Water-conserving Potential for Agriculture in the Tarim Basin

清华大学学报/990116清华大学学报R资源系统TSINGHUA SCIENCE AND数字化期刊WANFANG DATA ( CHINAINFO)TECHNOLOGYDIGITIZED PE RIODICAL1999年第1期No.1 1999Water - conserving Potential for Agriculture in the Tarim BasinYU Suhua(于素花) , ZHAO Xiusheng(赵秀生), DAIJian(戴健)'Instituteof Nuclear Energy T echnology, T singhua University, Beijing 100084;Xinjiang Academy of Agricultural Science, Urumqi 830000Abstract To satisfly the water demand for T arim Basin's economic development in theyear2000, about 33.4x 108 m3 water needs to be further tapped. Acco rding to the analysis of thecurrent status of water utilization, it is pointed out th at, to achieve such economic objectives, thepolicy of emphasizing both water ex ploitation and water conservation with the preference givento conservation meas ures must be followed. For this end, the potentials of exploring newadditional sources and strengthening water conservation have been well analyzed, along with thecalculation and tech-economic - assessment of some related parameters like the canaltransmission efficiency in water delivery systems and the water irrigation effi ciency in the field.T he results indicate the potentials ofwater resource expan sion and conservation are34x 108m3 and 57x 108 m3, respectiely. Bas ed on such rese arch outputs, awater conservationprogram has been developed for the T arim Basi n, to provide important references and policyrecommendations for the decision- makers in Xinjiang agricultural department to implementwater utilization measur es.Key words water conservation potential; source expansion potential ; water deli very system;field irrigationIntroductionThe surface water resource in the T arim Basin amounts to 379.80x 108 m3, of which340.51x 108 m3 is availablefor use[ 1] . In 1995, theactual channeled water w as 218.49x 108m3, accounting for 64. 17% of the total available amount. C 0 nsider ing the water demand for theecological environment within the basin, the surfac e water for agricultural production can besupplied as much as 70% of the usable quantity, while the rest 30% must be consumed for theecological purpose. There fore, the only alternative left for local economic expansion fromthesurfacewa ter is none other than water- saving technology.The proven reserve of ground water in the T arim Basin is 112.85>中国煤化工nountof36.38x 108 m- +3 available for exploitation. In 1995, 2.34x 108 m-JYHCNMHGaccounting for only 6.4% of the total usable un derground water resources. Thereis still aboutfl// 7布散据。/qk/qhdxxb- e/qhdx99/qhdx9901/990116.htm (第1/ 6页) 2010-3-23 5:26:46清华大学学报/99011634.04x 108m3 ground water Ieft for further expl oitation, and thisis supposed to beoneof themost important sources of expandingwate r supply in theT arim Basin.1 Analysis of Water C onservation Potential in theT arim BasinIn this section, the potential for water utilization in the T arim Basin will be analyzed fromtwo aspects: new additional water source expansion potential an d possible water conservationpotential[1,2] .Here, we have two concepts: (a) theoretical maximum potential, which means the biggestpotential obtained from theoretical estimating that is difficult if not impossible to be reachedunder real conditionsin the foreseeable future; (b) exploitable potential, which implies bothsourceexpansion and conservation pot entials of thewater resources that can be reached throughthe development and u se of certain technologies.Our intensive techno- economic analysis on water utilization and the presen twater- savingstatus in the T arim Basin turns out that huge potentials of wate r utilization in the T arim Basinremain to be further tapped by increasing the ad ditional supply of surfacewater and exploitingthe largeintact reserves of gro und water. Asa matter of fact, the abundant ground water withapotential amoun ting to about34x 108 m3 will be the major option for future exploitation.As for thewater conservation potential, the water delivery system and fie ld irrigatingpractice are identified as the critical parts that should be overh auled or improved to raise boththe canal transmission and the field irrigation efficiencies.1.1 W ater conservation potential in water delivery systemsThe current irigation canal efficiency is only 40% on the average. The en tirewaterconservation potential is calculated to come up to 231.5x 108 m3 if the transmission efficiencyis assumed to be the upper limit of 100% althoug h impossible under real conditions. Based onthe empirical estimation and scient ific C alculation of the historical data collected in theT arimBasin, the surfacewate r delivery system efficiency will be 34% if the canal is totally soil- based with out any anti- seepage linings. By 1995, it rose to 40% with the ratio of the ant i-seepage lininglength to the total canal length becoming 14.5%. So it is poss ib leto come to such a conclusionthat one percentage increase of this ratio would produce an increase of 0.41% of thewaterdelivery system eficienc y. T aking the year 1995 for example, the total non-lined canal lengthaccountedfo r 85.5%. If this section was overhauled to be seepage- resistant, then the over allcanal transmission efficiency might be expected to become up to 75%.Of course, thewater conservation potential in thewater delivery systemv aries dependingon the type of water- saving technologies applied which would re sult in differing degreesofefficiency improvement.In fact, the canal efficiency objective in the basin should be targetpd2n thr bhcinofthe中国煤化工future technological and economic developments aswell as the possibj YHCNMHaybythe agricultural sector. In our project, it has been set at the level of 70%./qk/qhdxxb- e/qhdx99/qhdx9901/990116.htm (第2/ 6页) 2010-3- 235:26:46清华大学学报/9901161.2W ater conservation potential in field irigationThewater conservation potential in the field irrigation depends mainly on the water- savingtechnology and planting structures [3] . D fferent crops and cro pping systems requiredifferentirrigating methods and technologies to be applie d, which have different water-saving rate.According to Xinjiang: S" Ninth FiveY ear Plan" and the Long- T er m DevelopmentProject to theyear 2010 for local economy, by the year 2000, the cultivated farmland in the basinwill have reached 150.8x 104 hm2, of whic h cott on areawill be 71.5x 104 hm2, wheat area willbe 55.9x 104 hm2, beet areawill be3.4x 104 hm, other crops areas, including oil-bearingcrops,beans, mel ons and vegetables, etc. will become 20x 104 hm2, and the multiple grain areaswill be1 6.4x 104 hm2. This is the underlying cropping structurewhich the calculati on and analysisofthe water conservation potential for field irrigation are based upo n.In the T arim Basin, all the cotton and the multiple corn fields are iriga ted with theuse ofpored plastic film on the soil, and wheat, beet, oil-bearin g crops and vegetable fields are irrigatedin the border- like basin square, with the field irrigation efficiencies for these two basictechnologies measured as 70% and 40%, respectively.Given the cropping structure and the technological parameters above, thew ater useefficiency in the field can be calculated to be 58.4% from the followi ng formula.7=之(s/Sr)x.n; (i = 1,2, .....whereS; isthe growing area for the i-th type of crop, Sτ is the total growing area and η i istheeficiency for i-th type of irigatio n technology. .1. 3 Analysis of water conservation potentialThe above analysis generates two realizable target water utilization effic iencies in both thedelivery system and the field irrigation. T he equation for t he comprehensive efficiency isη =η 1X η 2, whereη 1representsthe canal system del ivery eficiency, and η 2 indicatesthefield irigation eficiency. Nowsupposethecurrent overall water eficiencyisη ' =η'1X η'2, and the targetwater efici encyisη”=η”1X η”2 which can be achieved throughcertain water - saving technology in thewater - distributing system and field irrigation systemwithin the basin. Therefore, thewater conservation potential of the basin can be expressed asO Q=Q*η"-η' )=Q*η" 1x η”2η’1X η'2中国煤化工MHCNMHGwhereO Q indicates the water-saving potential in the basin, Q mea ns the availab le waterresources in the basin. W ith the parameters given above, Q=261.96x 108m3,η ’=0.4,η 'fl//E/ 0高数据.e/qhdx9/qhdx9901990116.htm (第3/ 6页) 2010-3-23 5:26:46清华大学学报/9901162=0.48,η”1=0.75,η ”2=0.584.0 Q=57x 108m3 .Ifη”1=0.85, then the potential equals80x 108 m3.Additionally, through the analysis on the possible expansion of newwater sources, it can beunderstood that there is still 34x 108 m3 of n ewwa ter resource for use in the T arim Basin. Sotheresult of the water-increasing potential in the basin is shown in Fig.1.120r10080。4020。extonsioncovervationtotalpotential■naximun potential■exploi table potentialFig.1The water - increasing potential in th eT arim BasinFrom Fig.1, it can be seen that there istill 114x 108 m3 potential to the limit under thecurrent situation of water utilization in the basin, however, th is potential can be only tapped bythe application of plastic - based and concr ete - lined anti - seepage technology. And theexploitalble potential means the goal that could be achieved on the condition of wholecanal -lining with the conventiona | water - saving technology.In general, two aspectsmust be taken into account for thewater- eficient irigationtechnologies. how to reduce the loss in water transmission and distri bution; and how to cutdown the leakage in fields.2 W aterConservation Plan and Forecast for W ater C onservation RequirementAccording to the agricultural plan, for the period from 1995 to 2000, 4 9.47x 10-+4 hm-+2of irrigation areawill be increased in the T arim Basin, incI uding33-^3x 10-+4 hm-+ 2 of arableland and 16.1x 104 hm2 for other purposes there is 3.3x 104 hm2 of shelter belt. If a unitamount of 6750 m3/hm2 is consumed, additional quantity of 33.4x 108 m3water will berequired for the agricultural prod uctio n in the T arim Basin. This requirement will bemetthrough both water conservati on and additional new source expansion.中国煤化工21 Potential additional supply from newwater sourceMHCNM HGIn theT arim Basin, large potential remains only in underground water explo itation. Itis/qk/qhdxxb e/qhdx9/qhdx9901990116.htm (第4/ 6页) 20103-23 5:26:46清华大学学报/990116predicted that, in theyear 2000 about4x 108 m3 of addition al un derground water still needstobe extracted to meet the growing agricultural pro duction, and then the total amount ofunderground water uilizationwill reach 6.24x 108 m3.2.2 Potential supply from eficiency gainsAt present, thewater use efficiency for irrigation agriculture in theT ari m Basin is ratherlow, hence, a huge potential increase through efficiency impro vement can be expected. To meetthenet demand of 33.4x 108 m3 water in theyear 2000, the total eficiency should be enhancedby 12%. To reach this goal, the canal efficiency should be raised from 40% in 1995 to 57% in2000, and the field efficiency from 48% to 54%.To satisfy the new increment of under ground water resourcesof 4x 108 m3, itwill need todig 670- 700wells. According to the condition of the ground W ater resource in the T arim Basin,the averagewater output per well is 200 m3/ h with 3000 operation hours in oneyear, then theannual water output per well is 60x 104 m3. H owever, as different wells have different wateroutputs, the n umber of wells needed also varies to satisfy the water requirement of4x 108 m3.The efficiency of the canal system has to be improved from the present 40% to 57% in orderto save 30x 108 m3 of water. In other words, the utilizatio n rat eof the canal system should beraised by 17%. If0.41% is to be incre as ed for the canal utilization rate each time, the canal anti-seepage lining len g th should beincreased by 1% as mentioned above. Then in theyear 2000, theanti-seepage length percentagewill go up from the present 14.5% to 55.5 % in the basin. In 1995,therewere 133 891 km - long unlined canalsin thef our subsystems, so 54 895 km watertransmission canal needs to be lined against seepage, about 10 979 km on the annual average.Before theyear 2000, all the main canals and branch canals have to be lined against seepage.3 C onclusionsThrough the analysis in our project, the current situation and prospects for water use andconservation in the T arim Basin can be summarized as follows:(1) New additional water source extension should be combined withwater con servationeffortswith the latter prevailing. Thewater- increasing potential of the basin is91x 108 m3including 34x 108 m3 from newwater source expan sion, acco unting for 37%, and 57x 108 m3from thewater conservation, making up 63% of the total.(2) Thewater conservation potential is rather huge. According to our study, the quantity ofnet 57x 108 m3 water conservation equals the gross supply of ab out 163x 108 m3 from thewater sources, which is equivalent to 62% of the total actual water use for agriculture in 1995. If7500 m3 water is used for farm land irrigation per hm2, therewill be an expansion of farmland of76x 104 hm2.In the process of increasing water supply and improving thefici中国煤化工| fieldirrigation, recent benefit should be combined with long term b enefit,MHCNMHentofthe reservoir capacity in order to guarantee the balance of the demand and supply of spring water.By theend of this century, main canals and branch canals will be lined aga inst seepageinfl//E/ 0高数据./qk/qhdxxb- e/qhdx99/qhdx9901/990116.htm (第5/ 6页) 2010-3-23 5:26.46清华大学学报/990116most regions in theTarim Basin. In the mean time, the lining Co nstruction for lateral canals andfield ditches should be well strengthened. Pla stic film for soil and plastic flm plus concrete antic-seepage technologies sh ould be broadly spread. As for irrigation technology, the waterconservation S hould be extended from the current traditional technologies such as pored pla sticflm, furrow rrigation and border irrigation to some advanced technologies like sprinkler, drip,pipe and micro- sprinkler technologies with the economic development.References[1] 新疆水利厅.新疆灌溉.乌鲁木齐:新疆人民出版社, 1993Xinjiang W ater C onservancy Administration. Xinjiang Irrigation. Xinjiang People sPublishingHouse，Urumqi, 1993[2]邹广荣,董冠群.农田灌溉与排水.北京:农业出版社,1993Zou Guangrong Dong Guanqun. Farmland Irrigation and Drainage.Agri cultural PublishingHouse, Bejjing, 1993[3] DinarA ，Zilberman D. Effects of input quality and environmental cond itions onselection of irigation technologies. In: Dinar A, Zillberman D, ed S. The Economics andManagement of W ater and Drainage in Agriculture. K luwer Academic Publishers, Norwell,Mass, 1991Manuscript received : 1998-06-04中国煤化工MHCNM HGl//=/0/7据/qk/qhdxxb- .e/qhdx99/qhdx99199116.htm (第6/ 6页) 2010-3235:26:46