RELIABILITY OF THE RESERVOIRS AT THE REGION OF THE FORMER LAKE KARLA IN IN MEETING CROP WATER REQUIREMENTS

S. Kotsopoulosr,I.Alexiou2, P. Lokkasl,D. Kalfountzos',G. Gravanisrand S. Magalios3 ) TEI Larissa, STA,Dept CIW, 41I 10 Larissa, hals<:prtult.t{

Abstract: For the time being, twelve surface reseryoirsoperate in the area of the former lake Karla in order to supply the sufficient water quantitiesfor inigation of the nearby cultivated areasmainly during the period June- August when the irrigation water requirementsare high while the availablewater from other resoutcesis negligible. In the present study, monthly climatic data for a period of 43 years (1953-199'7),from the meteorologicalstation of the National Meteorological Service(N.M.S.) in Larissaare utilised for the estimationof reservoirevaporation and the crop water requirementsin order to evaluatethe efficiency of reservoirsin meeting crop water requirementswith referenceto their technicalcharacteristics and the size ofthe irrigated areas.The analysisexemplifies that the reliability amongthe various reservoirsofthe sfudy areais not the same.Reservoirs usually do not cover the total crop water requirements ofthe areasthey serve.On average,they cover only part ofthem (48 - 83%), dependingon their characteristicsand the cropping patternofthe sub-areathey serve.

Key words: Evaporation,evapotranspiration, FAO 56 Penman-Monteith,reliability, reservoir.

l.INTRODUCTION

The Thessalyplain, dominatedby the Pinios river watershed,is the largestagricultural area in .Under the presentwater managementregime, the availablewater provides only 40-70%oof the crop water needsover much of the arca andextensive droughts occur during critical periodsof the growing season(July-August) with adverseeffects on crop yield and quality. In order to alleviatethese effects a number of irrigation related structureshave beenplanned and constructed. For that pu{pose,twelve surfacereservoirs operate in the areaof the former lake Karla in order to supplythe sufficient water quantitiesfor irrigation of the nearbycultivated areas. In the frame of the researchprogramme "Archimedes - EPEAEK II", co-fundedby the European SocialFund & NationalResources and realised by the Dept.of Civil Engineeringof TEI of Larissa, Greece,under the title "spatialmapping and estimationof hydrologicalrisk, emphasisingon floods and draughtsin urban and rural areasof Thessalyand their environmentalimpacts", the above regionhas been selected as sfudy area. The researchaims at estimatingthe reliability of the above structures,i.e. water reservoirs,in coveringthe essentialwater quantitiesfor irrigation. In the study areathere are twelve (12) reservoirs(Land Reclamation 2005; Goumas2006) in total that supply irrigation water into nine sub-areas,as shown in Figure 1. Thesereservoirs are filled up with water, through pumping, early in the spring from Pinios river. This water is then used to irrigate the local cultivationsduring the dry period (mainly Juneand July). In the study area,sprinkler and trickle irrigation is applied on 70o/oof the cultivationswhile the rcst30oh,mainly serials,are rain fed. From thoseirrigated areascotton coversabout 85olo, while the rest is cultivatedby maize,alfalfa and processedtomatoes. Given the size of reservoirsalong with the coffespondingirrigated area and the distribution of crops, it is consideredmore than necessaryto evaluatethe reliability of eachreservoir in meeting

O EWRASeventh International Conference WaterResources Conservancy and Risk Reduction Under Climatic Unceftainty Limassol,Cyprus, 25-27 June2009 the irrigation water needs,taking into accountthe variability of climatic conditions from year to year. Methodologiesfor validating irrigation networkshave been proposed in the past for specificcrop species(Kotsopoulos 1989; Kotsopoulosand Svehlik 1995).This work necessitatesmainly the estimationof both the evaporationof reservoirsand the evapotranspirationof crops on a monthly basis. These estimationsare then utilised to calculatethe water balanceof each sub-regionfor a certainnumber of years.

E RESERVOIRS

= IRRIGATEDAREAS

KALAMAKI

Figure l: Resewoirs and irrigated by them areas in the region of former Lake Karla

This project considers monthly climate data taken from the meteorological station of the NationalMeteorological Service (N.M.S.) of Larissaalong with soil data(Kalfountzos et al. 1999) and crop speciesdata of the study area,with the aim at estimatingthe water balanceof eachsub- region which is irrigated from a certainreservoir. These estimations are then utilised to evaluatethe reliability of reservoirsin orderto cover sufficiently the local irrigation water needs.

2. MATERIALS AND METHODS

Each region of cultivation is characterisedby a numberof parameters,such as water evaporation from reservoirs, crop water needs, rainfalls and reduction of soil moisture, which have to be consider.All thesefeatures have to be taken into accountin order to estimatethe water shortase 621

during eachyear and consequentlythe risk of failure in water supply for irrigation. The studyarea is closeto the city of Larissa,where a meteorologicalstation of the N.M.S. is alreadyin operation.The greaterLarissa area is sufferingby warm and dry summers.This period is crucial for crop gtowth, demandingfor irrigation great quantitiesof water. At the plain part of the county and especiallyat the region of the former Lake Karla, the prevailingtemperatures along with other climatic parameterswhich determinethe level of evaporationand evapotranspirationof crop species(solar radiation, sunshine duration, relative humidity, wind speed)are practically considered to be the sameto thoserecorded bv the N.M.S. of Larissa.

2.1 Calculation of evaporationand evapotranspiration

Nowadays,the most reliable method for the calculationof evaporationand evapotranspirationis consideredthe modified Penman-Monteithequation, as describedin FAO-56 (Allen et al. 1998; Kotsopouloset al. 2003). The method is applied in two stages.Initially the evapotranspirationof the referencecrop is calculatedand then crop evapotranspirationis estimatedusing the conespondingcrop coefficientas shownin the followins relation:

ET"=I{"'g7o (2.r)

whereET, is the daily evapotranspiration(mm/d), K" the crop coefficientwhich is dependanton the crop developmentstage (Allen et al. 1998), andETo the evapotranspirationof the referencecrop (mm/d). Evaporationcan be calculatedin a similar way throughthe equation:

E = Kr'ETo (2.2)

where E is the daily evaporation(mm/d) andK" the surfacecoefficient, which, for shallow water surfacestakes the valueof 1.05 (Allen et al. 1998). The evapotranspirationof referencecrop is determinedthrough the modified Penman-Monteith methodas describedin FAO-56 (Allen et al. 1998;Kotsopoulos 2006) and is expressedthrough the equation:

0.4084(R,- q * y - eo) #hu2(e, uto - (2.3) L+ y.(1+0.34.u2) where ETo referenceevapotranspiration (mm/d), R, net radiation at the crop surface(MJm-'d-'),G soil heat flux density ltUJm-2d-t)which here can be considerednegligible_ (G = 0), T mean air temperatureat2m height (oQ, u, averagewind speedat the sameheight (ms-'), e" saturationvapour pressure.(kPa),e, actualvapour pressure(kPa), / slopeof safurationvapour curve at temperatureZ oC-') (kPa and 7 psychrometricconstant (kPaoc-'). For the evaluationof R,, the estimationof extra terrestrialradiation (R,) is essentialalong with the maximum sunshineduration (.V) which can be realisedthrough periodic functions (Kotsopoulos and Babajimopoulos 1997). Through equations (2.I) and (2.3) along with the monthly rates of climatic parameters (temperature,sunshine duration, relative humidity and wind speed)for the years 1955-1997taken from the N.M.S. of Larissa,the monthly ratesof evapotranspirationfor the aboveperiod of 43 years is calculated.These results are presented in Figure2 for theperiod 1990-94.

2.2 Cslculation of water balance The validation of reseryoirs'reliability of the study areanecessitates the water balanceof each sub-areainigated by a certainreservoir system.

7.0

6.0

. 5.0

€ 4.0

F .? 3.0 F rYl 2.0

1.0

0.0 1990 r99l 1992 1993 r994

Figure 2: Calculatedvaluesof referencecrop evapotranspiration(mm/d) at Larissafor theyears 1990-94

The water balanceis estimatedper year and takes into accountthe technical charccteristicsof reseryoirs(capacity, water surface)along with the evaporationrate (Kotsopouloset al. 2006), the size of inigation areasthe cropping pattern and the crop water requirements,the rainfalls and the reductionof soil moisture. The data used for the calculations are presentedon Table 1 and refer to the technical characteristicsof reservoirs(Goumas 2006) along with the characteristicsof their irrieated sub- areas(Kotsopoulos et al. 2007).

Table L' Technical characteristics ofreservoirs and their irrigated sub-areas

Technical characteristics of reservoirs Characteristicsof the irrigated sub-areas

R- r 3'l- s Ec' o:c s 9E * s'r ?,E Reservoir :€ (}! Li N J !c '-!<= . a^ Q =

Eleftherio I. II r.70 600 4000 85 t5 2 Glafki 2.10 550 5415 85 t0

J Kalamaki I. II 8.00 2750 20000 85 l5

4 Dimitra 1.00 400 2600 6) l5 5 PlatikamposII 1.45 500 4560 85 10 5 6 PlatikamposI 0.50 250 1500 85 10 5 7 NamataI. II 2.90 983 10000 80 10 5 5 8 Omorfochori t.25 350 5000 80 20 9 Kastri l .10 350 4900 85 15

3. Resultsand discussion 623

Results refer to the averagereliability of reservoirs,R,n, its standarddeviation, SDn and the variation coefficient, CVn. Thesevalues come from a simulationperiod of 43 years.As reliability of a reservoiris defined,the ratio of its capacityover the total crop water requirementsof the sub- areait serves.The value 1.0 for reliability (maximum value) meansthat water requirementsof all cropsirrigated in a certainsub-area are completelysatisfied. These results are shownin Table 2.

Table2: Reliability parametersof reservoirsfor the study area

Standard Deviation, Variation Reservoir Average rate, R^ SDn Coefficient, CVR Vo

Eleftherio I, II 0.832 0.113 r3.6

2 Glafki 0.816 0.115 t4.l

J Kalamaki I. II 0.800 0.il 1 r3.9

4 Dimitra 0.758 0.116 15.3

5 PlatikamposII 0.667 0.105 15.8

6 PlatikamposI 0.660 0.109 r6.5

7 NamataI, II 0.610 0.099 16.3

8 Omorfochori 0.s43 0.091 t6.'7

o Kastri 0.483 0.082 17.0

For the cropping pattem assumedunder the existing agricultural conditions (Table 2), the averagereliability, R. and its standarddeviation, SDa, var/ significantly from areato area.Average reliability, R., maybe as low as -48o/o(Kastri) while its maximum value slightly exceeds83% (Eleftherio).On the confiary,the variation coefficientsof reliability, CVp, vary slightly from areato areaand are in the rangeof 13.5-17.UYo. Taking into accountthe valuesof the aboveparameters and the assumptionsof the CentralLimit Theorem(Haan 1977;Kite 1985;Yevjevich 1982;Chatfield 1983), a generalclassification of those reservoirsis feasibleaccording to theirreliability under specific conditions. The validation is typically realisedwith respectto the averagereliability of reservoirsfor various planningperiods and risk levels.These reliability results are presented in Table3.

Table 3: Estimatedreliability of reservoirsfor the study area

Mean -R. for a period Mean -R. for a period Mean .R,,for a period Reservoir ofl0years andal0%o ofl0years anda5o/o of5 yearsanda5Yo risk level risk level risk level

Eleftherio I, II 0.78'7 0.766 0.'749

2 Glafki 0.'769 0.'749 0.'732

J Kalamaki I. II 0.755 0.735 0.718

I Dimitra 0.71I 0.690 0.673

5 PlatikamposII 0.625 0.606 0.590

o PlatikamposI 0.616 0.597 0.580 'l NamataI, II 0.570 0.552 0.53',7

8 Omorfochori 0.506 0.490 0.4'76

9 Kastri 0.449 0.435 0.422

In general, the most reliable reservoirsare thoseof Eleftherio I & II followed by Glafki, Kalamakil&il,Dimitra, PlatikamposII, Platikampos[. Namata.Omorfochori and Kastri. More specifically, for a planning period of 10 years and a 10% risk level, the reseryorrsare classifiedaccording to their averagereliability as follows: Eleftherion I & II (78.7%) followed by Glafki (76.9%),Kalamaki I & II (75.5%),Dimitra (71J%), Platikamposll (62.5%),Platikampos I (6L6%), Namata(57 .0%), Omorfochori(50.6%) and Kastri (44.9%).These results are depictedin Figure3.

.-r LEGEND ' Im nesenvotns r:1 60-tu "h t ) 70-6Q To n 60-50 % o .o-1 n

'--''' , - ,. ..;r.

' .:11 -'

Figure 3 : Average reliability of reservoirs in ihe region of Karla for a decade and a I 0(%risk level

4. Conclusions

From the calculatedvalues of water shortagerelated to crop water requirementsand the reservoir capacityfor eachpart of the studyarea (broader area of the former lake Karla) that take into account the stochasticityof climatic conditionsfor a period of 43 years,the size of reservoirsalong with the size of the irrigated areasand the currentdistribution of crop species,the following conclusionscan be drawn: a) The reliability of the reservoirswithin the study area as it is related to irrigation water requirementsvary significantly from place to place. Reservoirsusually do not cover the total crop water requirementsof the areasthey serye.On average,they cover only part of them (48 - 83%), dependingon their characteristicsand the cropping pattern of the sub-areathey serve.The most 625

reliable reservoirs,according to the characteristicspresented above, are thoseofEleftherio I & II, Glafki, and Kalamaki I & il while the leastis the one of Kastri. b) Reliability valuesfor the cultivatedareas served by the samereservoir vary from year to year, due to the discrepanciesof the climatic conditions.This variability, expressedthrough the variation coefficient,fluctuates between -13.5 - I7%. The abovereliability analysisfor the structuresused to storewater for irrigation, may be a useful tool for evaluatingthe efficiency of the existing reservoirsand planning the constructionof new ones,so that, they meetthe local inigation waterrequirements.

REFERENCES

Allen, R. G., Pereira, L. S., Raes, D. and Smith, M. 1998. Crop Evapotranspiration:Guidelines for computing crop water requirements,FAO Inigation and DrainagePaper No 56, FAO, Rome. Chatfield, C. 1983.Statistics for Technology.Chapman and Hall, London. Goumas, K. 2006. The irrigations on Thessalyplain; consequenceson the ground and surface waters.In Proc. of EYE meeting: WaterResources and Agriculture, Thessalonica,2006, pp.39-53 (in Greek). Haan, C. T. 1977. StatisticalMethods in Hydrology. The Iowa StateUniversity Press,Ames, Iowa. Kite, G. W. 1985.Frequency and Risk Analysesin Hydrology. Water ResourcesPublications, Colorado. Kotsopoulos,S. I. 1989.On the evaluationof risk of failure in irrigation water delivery Ph.D. Thesis,Southampton University, UK. Kotsopoulos,S. and Svehlik, Z. 1995. Risk of failure in irrigation systems:Its estimation.In Proc. of the EWM 95 Symposiumon WaterResources under Drought or WaterShortage Conditions, Nicosia, Cyprus, 1995,pp. 243-250. Kotsopoulos,S. and Babajimopoulos,C., 199"1. Analytical estimationof modified Penmanequation parameters, J. Irrig. and Drain. Engng.,ASCE, 123(4):253-256. Kalfountzos, D., Alexiou, J., Magalios, S., Vyrlas, P. and Tsitsipa,G. 1999. An expert systemforthe integratedmanagement of irrigation water. Special application on the region of LOLR Pinios. 1n Proc. of 4'' National Conferenceon the Water resources managementfordrought prone regions ofGreece. 1999,pp.20-27 (in Greek). Kotsopoulos,S., Kalfountzos,D., Alexiou, l.,Zewa, G., Karamaligas,C. and Vyrlas, P.,2003. Actual evapotranspirationand soil moisture studiesin irrigated cotton fields, EuropeanWater (e-bulletin of EWRA), lssue 3 I 4:22-28. Kotsopoulos,S. 2006. Hydrology. Ion Publications,, Greece (in Greek). Kotsopoulos,S., Alexiou, J., Lokkas, P., Gravanis,G. and Magalios, S. 2006. Estimationof evaporationlosses from the reservoirsof Larissacount. In Proc.ofthe lOthNational Conference ofEYE, 2006,Xanthi, Greece, pp. 103-1l0 (in Greek). Kotsopoulos,S., Alexiou, J., Lokkas, P., Gravanis,G. and Magalios, S. 2007. Reliability of reservoirsof Pinios L.O.L.R in meeting crop water requirements.In Proc. of the 7'nNational Conferenceof EGME, 2007, Larissa,Greece, pp.320-327 (in Greek). Land ReclamationDirectory of LarissaPrefecture, 2005. Land ReclamationWorks Actions - Aims, Larissa,2005 (in Greek). Yevjevich, V. 1982.Probability and Statisticsin Hydrology. Water ResourcesPublications, Colorado.