Experimental Investigation of Pressure Flushing Technique in Reservoir Storages

Transcription

1 Experimental Invetigation of Preure Fluhing Technique in Reervoir Storage M. E. MESKATI SAMIRZADI 1, A. A. DEGANI 1, T. SUMI, A. MOSAEDI 1 and M. MEFTA. 1 1 Dept. of Water Engineering, Gorgan Univerity of Agriculture Science and Natural Reource, Gorgan, Iran mehkati@gau.ac.ir, a.dehghani@gau.ac.ir, moaedi@gau.ac.ir,meftah@gau.ac.ir Water Reource Reearch Center, Diater Prevention Reearch Intitute, Kyoto Univerity, Goka-ho, Uji-hi, , Japan, umi@mbox.kudpc.kyoto-u.ac.jp Abtract: - One of the mot effective technique for removing the depoited ediment from reervoir i preure fluhing hich ha le local effect. It i often ued a a clearing proce to remove ediment around the entrance of intake. In thi tudy, the effect of bottom outlet cro ection on the dimenion of fluhing cone a invetigated experimentally. The experiment a carried out ith different bottom outlet diameter, different dicharge and different ater depth above the bottom outlet. The reult indicate that the volume and dimenion of fluhing cone are trongly affected by the bottom outlet diameter. Finally, by uing regreion analyi, a dimenionle equation a preented for calculating the volume of ediment releaed from a dam during the preure fluhing. Key-Word: - Preure Fluhing, Fluhing Cone, Bottom, Cro Section, Sediment, Reervoir. 1 Introduction The lo of torage capacity ith reervoir edimentation i one of the mot eriou problem of dam. Sutaining the torage capacity of exiting reervoir ha become an important iue rather than building ne reervoir hich i difficult due to trict environmental regulation, high cot of contruction, and lack of uitable dam ite [1]. Several method have been propoed to control edimentation proce. Thee may include catchment management, fluhing, luicing, denity current venting and dredging. Fluhing i ued to erode previouly depoited ediment, luicing i ued to route incoming ediment through the reervoir by draing don the ater level, and denity current venting i ued to route incoming ediment through the reervoir ithout draing on the ater level []. One of the mot effective technique i fluhing through hich the depoited ediment i hydraulically removed by the flo. ydraulic fluhing i not a ne technique. The oldet knon method of fluhing, practiced in Spain in the 16th century, a referred to by D Rohan [3]. The exce in hear force of accelerated flo created by udden opening of the bottom outlet of dam looen and re-upend the ediment. The flo ill then ah them up from the ytem. If fluhing take place under a preurized condition and the ater level in reervoir i kept approximately contant, thi fluhing i called preure fluhing and ha only local effect around the outlet. In preurized fluhing, the ediment in the vicinity of the outlet opening i coured and a funnel haped crater i created. Fig. 1 illutrate the longitudinal and plan vie of fluhing cone in the vicinity of bottom. Thi i only an option in reervoir ith mall reervoir capacity to ater inflo, and large capacity of luice [4]. Preurized fluhing ha been tudied extenively in the literature. White and Bette [5] tudied ho far releae affect the ediment depoit. They provided a diagram indicating the interrelationhip beteen the limit ditance of cour in tatic ater, reervoir depth and outlet dicharge. Alo their reult hoed that by decreaing ater height in the reervoir, the rate of developing of couring cone increae toard uptream for a given dicharge. ISSN: ISBN:

2 Sediment Sediment Water Level Fluhing Cone Fluhing Cone Dam all Bottom Figure 1 - longitudinal and plan vie of fluhing cone in the vicinity of bottom Dicharge Fang and Cao [6], uing phyical model, hoed that large amount of ediment are releaed in the beginning of fluhing. Their tudy indicated that in equilibrium condition the clear ater i releaed through bottom intake and funnel-haped crater i developed ith an angle of repoe of the ediment. They alo pointed out that although the effect of the funnel cour i retricted to the zone cloe to the intake, it ha a very important role in preventing coare ediment to enter poer tation. Fig. illutrated the high concentration of ediment releae from Jiroft dam Iran, at the beginning of the preure fluhing operation [7]. For preure fluhing condition, Shen and et al. [8] preented a dimenionle regreion relation for determining the maximum couring depth of a luhing cone in non-coheive ediment. Lai and Shen [1] invetigated the fluhing procee during dradon fluhing, including outflo ediment dicharge, characteritic of the fluhing channel and fluhing effectivene. Scheuerlein et al.[9] indicated that in the preurized fluhing the flo pattern in the vicinity of the fluhing outlet i three dimenional and alo due to many parameter involved in the phenomena, analytical treatment i difficult if not impoible. They alo claimed that fluhing action are retricted to very limited efficiency and for ucceful continuation of the fluhing action dradon of ater level i required. Experimental tudie by Emamgholizadeh et al. [10] hoed that, by increaing the dicharge from outlet and decreaing of reervoir' ater depth, the amount of fluhed ediment increae. And under ame condition the fluhed ediment increae hen the ize of the ediment change from coure to fine. In pite of advance in the invetigation of preure fluhing technique at reervoir torage hon above, tudie about the effect of bottom outlet diameter on fluhing cone development are limited and more information about thi phenomenon i needed. Etimation of ediment volume removed or volume of fluhing cone in thi technique i important for deigning bottom outlet gate, in hich the optimum and the bet bottom outlet can be deigned ith repect to the cro ection. Reearche for undertanding the geometric variation of couring cone ith the cro ection change of the bottom outlet are neceary in order to make a rational deign for the bottom outlet. Deigning the bottom outlet mut be through an optimization beteen ome important rule tipulation uch a: gate cot veru economical value of the increaed reervoir volume after fluhing. Dimenion of fluhing cone are alo effective on recue of poer plant intake. Moreover, in the planning of dam operation, it can be vital to ae ho much of the ediment can be removed, and ho much fluhing ater i required. Thi paper deal experimentally ith preure fluhing phenomena and invetigation about the effect of bottom outlet cro ection on volume and dimenion of fluhing cone. Figure - Preure Fluhing operation in Jiroft dam, Iran. Material and Method. 1 Experimental etup The experiment ere conducted at the hydraulic laboratory of Gorgan Univerity of Agricultural Science and Natural Reource in Iran [11].Thi experimental model conit of three main part including, ater upply ytem, main reervoir and ettling bain reervoir. ISSN: ISBN:

3 Water upply ytem It conit of an underground tank and a pump to recirculate a deired teady flo. The ytem i alo upported by an adjuting valve, a digital flometer, and an 11-meter flume uptream of main reervoir.. 1. Main reervoir Main reervoir a hexahedral hape hoe overall dimenion conit of 3 meter length, meter ide and 1.5 meter height. Uing to reticulate heet at the reervoir entrance, a mooth flo i created. The outlet of main reervoir include a gate valve of diameter of.54 cm. Sediment depoit at the main reervoir. The ediment conit of ilica particle ith uniform ize ditribution ith a median diameter of d =1 mm and geometric tandard deviation of σ= ettling bain reervoir During the operation of bottom outlet, the mixing flo of ater and ediment a trapped in ettling bain reervoir. The bain i a rectangular flume of 3.6 meter long, 1 meter ide, and 0.76 meter height. At the end of ettling reervoir there a a V-notch eir ith angle of 90 o to meaure of outflo dicharge.. Dimenion analyi The volume of fluhing cone V may be ritten a a function of the folloing variable: V = φ Q, A,,, B, d50, ρ, ρ, g, υ 1 here, U i velocity of flo at the entrance of bottom outlet, A outlet i the cro ection of bottom outlet, i the height of ater above the center of bottom outlet, i the height of ediment depoited above the center of outlet, B i the idth of reervoir, d 50 i the median ize of ediment particle, ρ i the denity of ediment, ρ i ater denity, and g i the acceleration due to gravity. By uing Buckingham theorem, and chooing the ρ,, and U a repeating variable, the folloing dimenionle parameter ere obtained: V A S B π1= 3 π= π 3 = π =,, π = d ,,, ρ π = ρ π = g υ 6 π 7 8 =, U, U here the parameter, B, d 50, ρ, ρ and g are contant. ence, the aforementioned dimenionle parameter can be ummarized to four parameter. Conequently, the folloing functional relationhip decribe dimenionle fluhing volume: Fr outlet V A U =ϕ,, 3 g Uing the ame procedure, the dimenion of fluhing cone uch a length L and idth W of fluhing cone can be expreed a: L A =ϕ,, Fr 3 W A =ϕ,, Fr 4 The notation of fluhing cone dimenion at the vicinity of bottom outlet and alo a threedimenional vie of the fluhing cone after the experiment ith a dicharge of lit/, ater depth of 36 cm above the center of the outlet and 5.08 cm diameter of the outlet are illutrated in Fig. 3 and Fig. 4 repectively.. 3 Experiment Deigning For conidering the effect of bottom outlet cro ection on dimenion of fluhing cone, the experiment ere conducted ith 3 different outlet diameter 1, and 3 Inch, three ater depth above the center of bottom outlet i.e. 36, 66, 96 cm and ix different dicharge. Table 1 and ho the range of variable conducted in thi tudy for meaured experimental data and non-dimenional parameter for dimenional analyi.. Figure 4 A three-dimenional vie of the fluhing cone, for dicharge of lit/, ater depth of 36 cm and 5.08 cm diameter of the outlet. ISSN: ISBN:

4 Width of cone Bottom Length of cone very fat, and the proce finihed in le than one minute to ten minute in the experimental model. In thi tudy, the time for running the experiment a et to 45 minute. At the end of each experiment, the fluhing outlet a cloed and ater a carefully and loly drained from the main reervoir and the meaurement of bed configuration a done in a grid ytem around the bottom outlet. After the run of each experiment, the bed level of couring a meaured uing digital point gage, and the volume of fluhing cone a calculated by Surfer 0.8 oftare. Figure 5 Fluhing cone at the vicinity of bottom outlet Table 1 Range of variable in thi reearch Parameter Variation Dicharge releae Q Litr ec - 1 Depth of ater 36, 66, 96 Bottom outlet A 1, and 3 Inch Table Range of non-dimenional parameter in thi reearch Parameter Variation 3 V / 3.74 E Fr / A / Experimental Procedure For running the experiment, the depoited ediment ere flattened and leveled firtly to a pecific level above the bottom outlet 30 cm, and the model a loly filled ith ater until the ater urface elevation reached to a deired level. Then, the bottom outlet a manually opened until the outflo dicharge, become equal to the inflo dicharge. Conequently, the ediment a releaed from main reervoir. At the beginning of the experiment hen the dontream outlet opened, ediment a dicharged ith high concentration, but the concentration of ediment fluhing decreae ith time. Experiment ere continued until the fluhing cone reached to an equilibrium condition in hich the ediment concentration a negligible at the end of the experiment. The time required for the formation of the fluhing cone depend on hydraulic condition. The development of fluhing cone a 3 Reult and Dicuion A previouly mentioned, a funnel hape of couring i created at the vicinity of outlet gate in the preure fluhing operation. The maximum cour depth of thi cone i found very cloe to the dam all. Surface development of couring cone i ame in both idth and length, but the plan hape of the fluhing cone over the depoited ediment i cloe to half a circumference. The cone lope of both longitudinal and ide are approximately equal, and alo thee are imilar to the repoe angle of the ubmerged ediment. Fig. 5 ho the variation of Q againt V for each bottom outlet hen depth of ater above the center of outlet i 36 cm. It can be found that in a pecific dicharge by increaing of outlet cro ection, the cour volume increae. Fig. 6 and 7 alo preent the variation of Q againt V for 66 and 96 cm depth of ater, repectively. The figure ho the ame trend for volume releae of ediment ith outlet dicharge. The comparion of reult ho that the effect of bottom outlet diameter on couring volume i much higher at the greater value of ater depth. According to the dimenional analyi and functional relationhip given by equation 5 to 7, folloing equation are obtained for volume, idth and length of fluhing cone, repectively by uing regreion analyi: V W L 3 = 0.04 Fr = Fr = Fr A A A ISSN: ISBN:

5 Vcouring ccm Inch Inch 3 Inch Qoutlet litr/ec Figure 5 The variation of Q againt V for =0.36m. Etimate of Vcouring/^ y = 0.991x R = Oberved of Vcouring/^3 Fig 8 Comparion beteen meaured and computed relative fluhing volume cone. Vcouring ccm Inch Inch 3 Inch Etimate of Vcouring/^ y = x R = Qoutlet Litr/ec Figure 6 The variation of Q againt V for =0.66m Oberved of Vcouring/^3 Figure 9 Comparion beteen meaured and computed relative fluhing idth cone. 1. Vcouringccm inch Inch 3 Inch Etimate of Vcouring/^ y = x R = Qoutlet Litr/ec Figure 7 The variation of Q againt V for =0.96m Oberved of Vcouring/^3 Figure 10 Comparion beteen meaured and computed relative fluhing length cone. ISSN: ISBN:

6 Fig. 8 to 10 ho the comparion beteen the calculated fluhing cone parameter uing above equation and oberved value. For the verification of reult, the tatitical parameter uch a root mean quare error RMSE,mean abolute percentage error MAPE and R- quared value ere calculated for the above equation and preented in Table 3. Table 3 Statitical verification for preented equation Number of Equation 4 Concluion RMSE MAPE R Eq Eq Eq Thi tudy ho that A i the main parameter in correlating the fluhing cone dimenion. The reult indicate that ith increae of diameter of bottom outlet, the ne hydraulically condition etablihed on fluhing mechanim. And thi mechanim i common beteen all of couring dimenion. Baed upon experimental data, under clear ater flo, dimenionle equation for prediction of fluhing cone parameter are preented. The preent equation have high correlation coefficient and in pite of their correlation there applicability hould be teted uing other experimental and field data. Further experiment are neceary by uing different ize, hape and graduation of bed material, under different hydraulic condition to conform the reult obtained from thi tudy. Reference: [1] Shen,.W. and Lai, J. S., Sutain reervoir ueful life by fluhing ediment, International Journal of Sediment Reearch. Vol. 113: 10-17, [] Brandt, S. A., A revie of reervoir deolation, International Journal of Sediment Reearch.Vol. 15, No.. pp , 000. [3] Bron, C.B., The Control of Reervoir Silting, United State Department of Agriculture, Micellaneou Publication No. 51, Wahington, D.C. p. 166, [4] Qian, N., Reervoir edimentation and lope tability; technical and environmental effect, Fourteenth International Congre on Large Dam, Tranaction, Rio de Janeiro, Brazil, 3-7 May, Vol. III. pp , 198. [5] White, W.R. and Bette, R., The feaibility of fluhing ediment through reervoir, Challenge in African ydrology and Water Reource, Proceeding of arare Sympoium, July, D.E. Walling, S.S.D. Foter, P. Wurzel, ed, IAS Publication No, [6] Fang, D. and Cao, S., An experimental tudy on cour funnel in front of a ediment fluhing outlet of a reervoir, Proceeding of the 6th Federal Interagency Sedimentation Conference, La Vega, March , pp. I.78-I.84, [7] Emamgholizadeh, S., Samadi,. and Bina, M., The fluhing of the ediment near the poer intake in the Dez Reervoir, River Bain Management. Italy, 005. [8] Shen,.W., Lai, J.S. and Zhao, D., ydraulic deiltation for noncoheive ediment, Proceeding of the 1993 Annual ASCE ydraulic Engineering Conference, San Francico,.W Shen, S.T. Su, and F. Wen, ed, pp , [9] Scheuerlein,., Tritthart, M. and Nunez Gonzalez, F., Numerical and phyical modeling concerning the removal of ediment depoit from reervoir, Conference proceeding of ydraulic of Dam and River Structure, Tehran, Iran, 004. [10] Emamgholizadeh, S., Bina, M., Fathimoghadam, M. and Gomeyhi, M., Invetigation and Evaluation of the Preure Fluhing Through Storage Reervoir, ARPN Journal of Engineering and Applied Science. Vol. 1, No. 4, 006. [11] Mehkati Shahmirzadi, M. E, Experimental invetigation of preure fluhing operation in reervoir torage, M Sc thei, Gorgan Univerity of Agriculture Science and Natural Reource, 009. ISSN: ISBN: