Scale Effect on Runoff from Filed Plots under Natural Rainfall

Transcription

1 Amerin-Eursin J. Agri. & Environ. Si., (9): 48-5, 0 ISSN IDOSI Pulitions, 0 DOI: 0.589/iosi.ejes Sle Effet on Runoff from File Plots uner Nturl Rinfll 3 F. Aszeh, M. Gorji, A. Vezi, R. Sokouti n M. Shorf Deprtment of Soil Siene, University of Tehrn, Irn Deprtment of Soil Siene, Fulty of Agriulture, Znjn University, Znjn, Irn 3 West Azerijn Agriulturl n Nturl Reserh Center, Urmi, Irn Astrt: Plot sle stuies re wiely use to etermine runoff n soil erosion moel s si t. In orer to stuy the effet of plot size on runoff volume per unit re, plots with seven sizes iffering in length (, 5, 0, 5,., 5 n 30 m) n with (,.,.6,.8, n.4 m) were onstrute in Polsht, northwestern Irn. The experiment ws onute in ompletely rnomize lok esign using four replitions. Plots were estlishe on uniform slopes of 9% with.4m sping. Plots were instlle on fllow n were mintine in re onition in the stuy perio from Septemer, 00 until June, 0. The entire runoff volume ollete in tnks t the lower prt of plots ws mesure fter eh event. Runoff from these plots ws otine for eleven nturl storm events uring the stuy perio. Our results onfirme tht the unit re runoff ereses in ll events with power funtion (0.8 R 0.95), s plots re inreses. The egree of plot sle effet on unit re runoff is onsiere to hnge with the event hrteristis, ng low for little runoff-prouing events n high for lrger runoff-prouing events. Sttistil nlysis of unit re runoff verifie tht there were no signifint ifferenes mong the results of 5m n longer plots ut in plots with 0m or lower in length, the results were signifintly ifferent. It n e onlue tht the 5m is the minimum optiml length for urtely estimting runoff in plots. Key wors: Runoff plot Sle Plot size Nturl Rinfll Unit re runoff Polsht INTRODUCTION Nturl experimentl plots hve eome one of the most importnt methos of t gthering in surfe runoff n soil erosion stuies. Bsi t for eveloping most empiril moels suh s USLE, MUSLE n RUSLE were originte from nturl plots n lirtion of these moels t eh region mostly is one using t otine from these plots [-]. As result, reserh efforts re neee to investigte ftors ffeting plots t qulity. Sptil sle or size of plots is one of these ftors whih iretly ffet mesuring surfe runoff y mens of fiel plots. The effet of plot size on mesure runoff or soil loss from nturl plots is known s plot sle effet [6]. A quik review of the literture shows tht, plots with wie rnge of sptil sles hve een use y reserhers for estimting surfe runoff n in most ses there isn t ny rtionlity for seleting eh size or sptil sle of the plots [--6]. Le Bissonnis et l. [4] onfirme tht the effet of sle on runoff genertion is highly epenent on the surfe onition n sptil vriility of soil properties. Joel et l. [3] oserve erese in the runoff oeffiient with inresing plot size from 0.5 to 50 m ; they lso reporte the vliity of this tren even uring ontinuous runoff. Vn e Giessen et l. [] onsiere the importne of rinfll-runoff temporl ynmis on the sle effet of plots n emonstrte tht the sle effet vries enormously oring to the temporl pttern of runoff prouing rinfll event. Literture review shows tht there is not single sle effet for ll onitions n it is reporte to e site spfi n epennt on the size of the monitore plots or thments esies there is very limite tse on nturl plots t in Irn so tht, the min ojetive of this stuy ws to etermine n quntify the sle effets of runoff plots in rnge of plot sizes generlly use y ifferent reserhers. Corresponing Author: Frrokh Aszeh, Deprtment of Soil Siene, University of Tehrn, Irn. Tel/Fx:

2 MATERIALS AND METHODS Am-Eurs. J. Agri. & Environ. Si., (9): 48-5, 0 Stuy Are: Plots use in this stuy were onstrute t the experimentl wtershe in Polsht region of the West Azerijn provine whih ws lote in the Northwestern of Irn. The wtershe enompsses n re of 300 km etween 39 00'-39 5' N n 44 45'-45 0' E. Aoring to Domrton lssifition, the limte of the region is ri with the men nnul prpittion of 3 mm n men nnul temperture of 3 C. The soils hve generlly sny ly lom texture n hve out 0.58% n 6% orgni mtter n CCO 3, respetively [9]. Plots Constrution: In orer to etermine the sle effet of plots on surfe runoff seven plots, iffering in with n length, were onstrute in uniform slope of 9% t three replitions thus totl plots were instlle in ompletely rnomize lok esign for runoff mesurements. Tle shows the etils of plots length n with. Plots were instlle on fllows n mintine in re onition uring the stuy perio y mens of heriie tretment [7]. Plots were ploughe in slope iretion in Septemer 00. The plots were surroune using soil stk with hght of 30m to iret generte surfe runoff to the lower prt of plots where runoff olletion systems ompose of gutters, pipes n tnks were instlle []. Fig. shows the geogrphil lotion n pln of onstruting plots t the stuy region. Hyrologil Mesurements: From Septemer 00 to June 0, surfe runoff ws monitore on the onstrute plots. Runoff ollete from the plots ws mnully mesure fter eh runoff prouing rinfll event. Prpittion mounts n hrteristis were iretly mesure y n utomti reoring tippinguket rin guge lote out 00 m from the experimentl plots. Tle : With n length of the plots Plot Nme (Tretment) With(m) length(m) Plot Are(m ) P P. 5 5 P3.6 0 P P P P Fig. : Lotion of experimentl wtershe n pln of onstrute plots for one of the Bloks Sttistil Anlysis: This experiment ws rrie out with ompletely rnomize lok esign with three replitions for eh size of plots s tretments (Tle ). To ssess the sle effet of plots, totl runoff volume of eh plot ws ivie y the re of plot to otin unit re runoff (lit/m equl to mm). Unit re runoff (UAR) of ll plots for eh rinfll event ws nlyze seprtely y nlysis of vrine using of the sttistil nlysis system (SAS version 9.). Men seprtion ws one y Dunn rnge test. RESULTS AND DISCUSSION Rinfll Events: During the stuy perio runoff prouing rinfll events ws ourring. Chrteristis of these events re presente in tle. Prpittion regime within the stuy perio, showe high sesonl vriility n ll of the runoff prouing events ws ourre uring April, My n erly June. Men Intensity of runoff prouing events were etween 0.6 n 3.3 mmh. Plot Size Effet: There ws teneny towr inrese mounts of runoff with eresing the plot size. On verge, the men mounts of runoff per unit re in smll plots (P) ws.75 to 3.98 times greter thn the lrge plots (P7) t ifferent rinfll events. Regression nlysis of the plot size effet ginst unit re runoff showe tht the following power reltionship signifintly esries vritions of UAR ginst plot size of eh single event. UAR = A Where, UAR represents the men unit re runoff (lit/m, equl to mm) for event; A is the plot size (m ); n 49

3 Am-Eurs. J. Agri. & Environ. Si., (9): 48-5, 0 Tle : Chrteristis of runoff prouing events uring the stuy perio Event Event te Rinfll mount(mm) Men Intensity(mm h ) I 30(mm h ) Kineti Energy*(MJ h ) E 05 April E 3 April E3 7 April E4 0 My E5 06 My E6 08 My E7 3 My E8 0 My E9 30 My E0 04 June E 09 June * Kineti energy ws lulte using: E= log(I) [3] Tle 3: results of regression nlysis of UAR (mm) ginst plot re (m ) for eh event e i UARe = i e A i Coeffiient of Event etermintion (r )* e E * E * E * E * E * E * E * E * E * E * E * *P vlue for ll reltions <0.0 re empiril oeffiients whih re prtiulr for eh event (). Results of UAR n plot size reltionship for eh event were presente in tle 3. It n e onlue from the negtive mounts of in tle 3, tht the mount of unit re runoff ereses s plots re inrese in ll reore events. As generl pttern for ll events, the reltionship etween unit re runoff n plot re ws shown in figure se on the ove eqution. Results showe tht the smll plots ten to proue high mounts of runoff in omprison with lrge plots. Men unit re runoff for P plot s the smllest plot ws etween 0.8mm n 6.66mm for E5 n E0 events respetively, wheres these mounts for P7 s lrgest plot were 0.4mm n.89mm for ove mentione events. The erese in unit re runoff with inresing the ontriuting re shows tht the most of the runoff generte throughout the lrge plots is infiltrte own Fig. : Reltionship etween UAR n plot size for the E event slope n oesn t reh to the plots outlet. Similr results were reporte y Myor et l. [5], Vn e Giessen et l. [] n Joel et l. [3] with the ifferent rnge of plot sizes n rinfll regimes. Vn e Giessen et l. [] verifie tht the m plots proue only 40% of mesure runoff in.5 m plots. Joel et l. [3] lso oserve shrp erese in the runoff oeffiients from smll plots (0.5 m ) to lrge plots (50 m ). It seems tht the inrese time of hyrologil response in lrge plots ffets the pttern of the runoff reistriution over the plot surfe n provies high infiltrtion opportunity in those plots []. Contrry to our oservtions, Thomz n Vesten [0] foun tht there is no signifint ifferene etween the mount of runoff in n 0 m plots. These uthors worke on sutropil region with n verge nnul prpittion of 94.9 mm n frequeny of one storm every four ys. Therefore, these onitions resulte in high nteeent soil moisture whih erese the effets of infiltrtion proesses in plots n susequently eliminte the effets of sle on plots. 50

4 Am-Eurs. J. Agri. & Environ. Si., (9): 48-5, 0 Tle 4: Comprison of plot size effet on UAR (mm) for eh rinfll event Men UAR (mm) for eh event Plot Size (Tretment) E E E3 E4 E5 E6 E7 E8 E9 E0 E P P P P P P P Men seprtion y Dunn rnge test (P = 0.05) In support of the hieve generl tren tht use s key pproh to introue 5m s n minimum onfirms the eresing of unit re runoff with inresing optiml length for runoff mesuring with the im of plot size, in the next step men unit re runoff of eh lirting ULSE fmily moels suh s MUSLE or USLEplot size ws sttistilly nlyze using ompletely M in fiel plots. rnomize lok esign n unit re runoff men seprtion ws one y mens of Dunn test. REFERENCES Results of vrine nlysis (Tle 4) for eh event onfirm tht the runoff genertion ehvior of plots. Bgrello, V. n V. Ferro, 00. Anlysis of iffering in size is signifintly ifferent for ll events soil loss t from plots of iffering length exept E8, whih hve the lowest kineti energy n I30 for the Spri experimentl re, Siily, Itly. mong ll events. Comprison of men unit re runoff of Biosystems Engineering, 05: 4-4. plots verifie tht there were no signifint ifferenes. Boix-Fyos, C., M. Mrtínez-Men, mong the results of 5m n longer plots ut in plots E. Arnu-Roslen, A. Clvo-Cses, V. Cstillo n with 0m or lower in length, the results were signifintly J. Allejo, 006. Mesuring soil erosion y fiel ifferent. These results re onsistent with the finings of plots: Unerstning the soures of vrition. Seghi et l, [8] who showe tht in steep slopes plots Erth Si. Rev, 78: with 0 to 5 m in length n e use to estimte the smll 3. Joel, A., I. Messing, O. Seguel n M. Csnov, wtershe runoff t event temporl sle. 00. Mesurement of surfe wter runoff from plots of two ifferent sizes. Hyrol. Proesses, CONCLUSION 6: Le Bissonnis, Y., H. Benkhr, V. Chplot, D. Fox, Plot size effets were empirilly etermine in D. King n J. Droussin, 998. Crusting, runoff n semi-ri region in north western of Irn, y using runoff sheet erosion on silty lomy soils t vrious sles volume mesure t event temporl sle with plots n up sling from m to smll thments. vrying in lengths from to 30m. Importnt ifferenes in Soil Tillge Res., 46: the mount of unit re runoff were oserve for the 5. Myor, A.G., S. Butist n J. Bellot, 0. ifferent plot sizes n lrge plots ten to hve lower Sle-epenent vrition in runoff n seiment runoff ompre to smll plots, esplly uring the yiel in semiri Meiterrnen thment. events with high mounts of kineti energy n mximum Journl of Hyrology., 397: minute intensity. An inverse power reltion ws 6. Prsons, A.J., R.E. Brzier, J. Winwright n otine etween unit re runoff n plot re t event D.M. Powell, 006. Sle reltionships in hillslope temporl sle. Comprison of the men unit re runoff runoff n erosion. Erth Surf. Proesses Lnforms, in ifferent plots inite tht there ws signifint 3: ifferene. Aoring to the sttistil nlysis it n e 7. Rejmn, J., R. Turski n J. Pluszek, 998. Sptil onlue tht the ifferenes of UAR in plots lrger thn n temporl vritions in eroiility of loess soil. 4m (longer thn 5) is lwys insignifint, whih n e Soil Tillge Res., 46:

5 Am-Eurs. J. Agri. & Environ. Si., (9): 48-5, 0 8. Seghi, S.H.R., M.B. Seghleh n A.S. Rngvr,. Vezi, A.R., S.H.R. Seghi, H.A. Bhrmi n 0. Plot sizes epeneny of runoff n seiment M.H. Mhin, 008. Moeling the USLE K-ftor for yiel estimtes from smll wtershe. Cten, lreous soils in northwestern Irn. oi:0.06/j.ten Geomorphology, 97: Sokoti Oskoui, R. n M.H. Mhin, 009. Stuy on. Vn e Giessen, N.C., T.J. Stomph n N. De Rier, seimenttion in floo spreing networks of 000. Sle effets of Hortonin overln flow n Polsht quifer, West Azrijn. Wtershe rinfll runoff ynmis in West Afrin ten Mngement Reserhes (Pjouhesh n Sznegi), lnspe. Hyrol. Proesses, 4: : Wishmer, W.H. n D.D. Smith, Thomz, E.L. n L.R. Vesten, 0. Preiting Rinfll Erosion Losses: A Guie to Mesurements of runoff n soil loss from two Conservtion Plnning. Vol. 537, U.S. Deprtment of ifferently size plots in sutropil environment Agriulture, Wshington DC., pp: 8-3. (Brzil). Erth Surfe Proesses on Lnforms, 37: